Merge pull request #6796 from nim-lang/async-improvements

Async improvements

12 files changed, 109 insertions, 1668 deletions

diff --git a/lib/pure/asyncdispatch.nim b/lib/pure/asyncdispatch.nim
index 42ffa236c..598b0195b 100644
--- a/lib/pure/asyncdispatch.nim
+++ b/lib/pure/asyncdispatch.nim
@@ -265,9 +265,15 @@ when defined(windows) or defined(nimdoc):
       setGlobalDispatcher(newDispatcher())
     result = gDisp
 
+  proc getIoHandler*(disp: PDispatcher): Handle =
+    ## Returns the underlying IO Completion Port handle (Windows) or selector
+    ## (Unix) for the specified dispatcher.
+    return disp.ioPort
+
   proc register*(fd: AsyncFD) =
     ## Registers ``fd`` with the dispatcher.
     let p = getGlobalDispatcher()
+
     if createIoCompletionPort(fd.Handle, p.ioPort,
                               cast[CompletionKey](fd), 1) == 0:
       raiseOSError(osLastError())
@@ -757,6 +763,9 @@ when defined(windows) or defined(nimdoc):
     ## Unregisters ``fd``.
     getGlobalDispatcher().handles.excl(fd)
 
+  proc contains*(disp: PDispatcher, fd: AsyncFD): bool =
+    return fd in disp.handles
+
   {.push stackTrace:off.}
   proc waitableCallback(param: pointer,
                         timerOrWaitFired: WINBOOL): void {.stdcall.} =
@@ -977,7 +986,7 @@ when defined(windows) or defined(nimdoc):
   proc newAsyncEvent*(): AsyncEvent =
     ## Creates a new thread-safe ``AsyncEvent`` object.
     ##
-    ## New ``AsyncEvent`` object is not automatically registered with             # TODO: Why? -- DP
+    ## New ``AsyncEvent`` object is not automatically registered with
     ## dispatcher like ``AsyncSocket``.
     var sa = SECURITY_ATTRIBUTES(
       nLength: sizeof(SECURITY_ATTRIBUTES).cint,
@@ -1095,6 +1104,9 @@ else:
       setGlobalDispatcher(newDispatcher())
     result = gDisp
 
+  proc getIoHandler*(disp: PDispatcher): Selector[AsyncData] =
+    return disp.selector
+
   proc register*(fd: AsyncFD) =
     let p = getGlobalDispatcher()
     var data = newAsyncData()
@@ -1110,6 +1122,9 @@ else:
 
   proc unregister*(ev: AsyncEvent) =
     getGlobalDispatcher().selector.unregister(SelectEvent(ev))
+  
+  proc contains*(disp: PDispatcher, fd: AsyncFd): bool =
+    return fd.SocketHandle in disp.selector
 
   proc addRead*(fd: AsyncFD, cb: Callback) =
     let p = getGlobalDispatcher()
diff --git a/lib/pure/asyncfile.nim b/lib/pure/asyncfile.nim
index 9f4da16a3..6ce9e8f75 100644
--- a/lib/pure/asyncfile.nim
+++ b/lib/pure/asyncfile.nim
@@ -85,7 +85,7 @@ proc newAsyncFile*(fd: AsyncFd): AsyncFile =
   ## Creates `AsyncFile` with a previously opened file descriptor `fd`.
   new result
   result.fd = fd
-  register(result.fd)
+  register(fd)
 
 proc openAsync*(filename: string, mode = fmRead): AsyncFile =
   ## Opens a file specified by the path in ``filename`` using
@@ -97,16 +97,16 @@ proc openAsync*(filename: string, mode = fmRead): AsyncFile =
     when useWinUnicode:
       let fd = createFileW(newWideCString(filename), desiredAccess,
           FILE_SHARE_READ,
-          nil, creationDisposition, flags, 0).AsyncFd
+          nil, creationDisposition, flags, 0)
     else:
       let fd = createFileA(filename, desiredAccess,
           FILE_SHARE_READ,
-          nil, creationDisposition, flags, 0).AsyncFd
+          nil, creationDisposition, flags, 0)
 
-    if fd.Handle == INVALID_HANDLE_VALUE:
+    if fd == INVALID_HANDLE_VALUE:
       raiseOSError(osLastError())
 
-    result = newAsyncFile(fd)
+    result = newAsyncFile(fd.AsyncFd)
 
     if mode == fmAppend:
       result.offset = getFileSize(result)
@@ -115,11 +115,11 @@ proc openAsync*(filename: string, mode = fmRead): AsyncFile =
     let flags = getPosixFlags(mode)
     # RW (Owner), RW (Group), R (Other)
     let perm = S_IRUSR or S_IWUSR or S_IRGRP or S_IWGRP or S_IROTH
-    let fd = open(filename, flags, perm).AsyncFD
-    if fd.cint == -1:
+    let fd = open(filename, flags, perm)
+    if fd == -1:
       raiseOSError(osLastError())
 
-    result = newAsyncFile(fd)
+    result = newAsyncFile(fd.AsyncFd)
 
 proc readBuffer*(f: AsyncFile, buf: pointer, size: int): Future[int] =
   ## Read ``size`` bytes from the specified file asynchronously starting at
diff --git a/lib/pure/asyncfutures.nim b/lib/pure/asyncfutures.nim
index 11461d994..6df6527d5 100644
--- a/lib/pure/asyncfutures.nim
+++ b/lib/pure/asyncfutures.nim
@@ -342,6 +342,7 @@ proc asyncCheck*[T](future: Future[T]) =
   ## finished with an error.
   ##
   ## This should be used instead of ``discard`` to discard void futures.
+  assert(not future.isNil, "Future is nil")
   future.callback =
     proc () =
       if future.failed:
diff --git a/lib/pure/asyncnet.nim b/lib/pure/asyncnet.nim
index 93399bb40..bdbf47004 100644
--- a/lib/pure/asyncnet.nim
+++ b/lib/pure/asyncnet.nim
@@ -140,9 +140,16 @@ proc newAsyncSocket*(fd: AsyncFD, domain: Domain = AF_INET,
     sockType: SockType = SOCK_STREAM,
     protocol: Protocol = IPPROTO_TCP, buffered = true): AsyncSocket =
   ## Creates a new ``AsyncSocket`` based on the supplied params.
+  ##
+  ## The supplied ``fd``'s non-blocking state will be enabled implicitly.
+  ##
+  ## **Note**: This procedure will **NOT** register ``fd`` with the global
+  ## async dispatcher. You need to do this manually. If you have used
+  ## ``newAsyncNativeSocket`` to create ``fd`` then it's already registered.
   assert fd != osInvalidSocket.AsyncFD
   new(result)
   result.fd = fd.SocketHandle
+  fd.SocketHandle.setBlocking(false)
   result.isBuffered = buffered
   result.domain = domain
   result.sockType = sockType
diff --git a/lib/pure/ioselects/ioselectors_epoll.nim b/lib/pure/ioselects/ioselectors_epoll.nim
index 8827f239f..98b8a2b2b 100644
--- a/lib/pure/ioselects/ioselectors_epoll.nim
+++ b/lib/pure/ioselects/ioselectors_epoll.nim
@@ -141,7 +141,7 @@ template checkFd(s, f) =
   if f >= s.maxFD:
     raiseIOSelectorsError("Maximum number of descriptors is exhausted!")
 
-proc registerHandle*[T](s: Selector[T], fd: SocketHandle,
+proc registerHandle*[T](s: Selector[T], fd: int | SocketHandle,
                         events: set[Event], data: T) =
   let fdi = int(fd)
   s.checkFd(fdi)
@@ -156,7 +156,7 @@ proc registerHandle*[T](s: Selector[T], fd: SocketHandle,
       raiseIOSelectorsError(osLastError())
     inc(s.count)
 
-proc updateHandle*[T](s: Selector[T], fd: SocketHandle, events: set[Event]) =
+proc updateHandle*[T](s: Selector[T], fd: int | SocketHandle, events: set[Event]) =
   let maskEvents = {Event.Timer, Event.Signal, Event.Process, Event.Vnode,
                     Event.User, Event.Oneshot, Event.Error}
   let fdi = int(fd)
@@ -392,9 +392,19 @@ proc selectInto*[T](s: Selector[T], timeout: int,
       let pevents = resTable[i].events
       var pkey = addr(s.fds[fdi])
       doAssert(pkey.ident != 0)
-      var rkey = ReadyKey(fd: int(fdi), events: {})
+      var rkey = ReadyKey(fd: fdi, events: {})
 
       if (pevents and EPOLLERR) != 0 or (pevents and EPOLLHUP) != 0:
+        if (pevents and EPOLLHUP) != 0:
+          rkey.errorCode = ECONNRESET.OSErrorCode
+        else:
+          # Try reading SO_ERROR from fd.
+          var error: cint
+          var size = sizeof(error).SockLen
+          if getsockopt(fdi.SocketHandle, SOL_SOCKET, SO_ERROR, addr(error),
+                        addr(size)) == 0'i32:
+            rkey.errorCode = error.OSErrorCode
+
         rkey.events.incl(Event.Error)
       if (pevents and EPOLLOUT) != 0:
         rkey.events.incl(Event.Write)
@@ -482,7 +492,7 @@ template isEmpty*[T](s: Selector[T]): bool =
   (s.count == 0)
 
 proc contains*[T](s: Selector[T], fd: SocketHandle|int): bool {.inline.} =
-  return s.fds[fd].ident != 0
+  return s.fds[fd.int].ident != 0
 
 proc getData*[T](s: Selector[T], fd: SocketHandle|int): var T =
   let fdi = int(fd)
@@ -516,3 +526,6 @@ template withData*[T](s: Selector[T], fd: SocketHandle|int, value, body1,
     body1
   else:
     body2
+
+proc getFd*[T](s: Selector[T]): int =
+  return s.epollFd.int
\ No newline at end of file
diff --git a/lib/pure/ioselects/ioselectors_kqueue.nim b/lib/pure/ioselects/ioselectors_kqueue.nim
index af5aa15df..10e23c072 100644
--- a/lib/pure/ioselects/ioselectors_kqueue.nim
+++ b/lib/pure/ioselects/ioselectors_kqueue.nim
@@ -217,7 +217,7 @@ else:
           raiseIOSelectorsError(osLastError())
         s.changes.setLen(0)
 
-proc registerHandle*[T](s: Selector[T], fd: SocketHandle,
+proc registerHandle*[T](s: Selector[T], fd: int | SocketHandle,
                         events: set[Event], data: T) =
   let fdi = int(fd)
   s.checkFd(fdi)
@@ -235,7 +235,7 @@ proc registerHandle*[T](s: Selector[T], fd: SocketHandle,
     when not declared(CACHE_EVENTS):
       flushKQueue(s)
 
-proc updateHandle*[T](s: Selector[T], fd: SocketHandle,
+proc updateHandle*[T](s: Selector[T], fd: int | SocketHandle,
                       events: set[Event]) =
   let maskEvents = {Event.Timer, Event.Signal, Event.Process, Event.Vnode,
                     Event.User, Event.Oneshot, Event.Error}
@@ -503,6 +503,7 @@ proc selectInto*[T](s: Selector[T], timeout: int,
 
       if (kevent.flags and EV_ERROR) != 0:
         rkey.events = {Event.Error}
+        rkey.errorCode = kevent.data.OSErrorCode
 
       case kevent.filter:
       of EVFILT_READ:
@@ -569,6 +570,13 @@ proc selectInto*[T](s: Selector[T], timeout: int,
         doAssert(true, "Unsupported kqueue filter in the queue!")
 
       if (kevent.flags and EV_EOF) != 0:
+        if kevent.fflags != 0:
+          rkey.errorCode = kevent.fflags.OSErrorCode
+        else:
+          # This assumes we are dealing with sockets.
+          # TODO: For future-proofing it might be a good idea to give the
+          #       user access to the raw `kevent`.
+          rkey.errorCode = ECONNRESET.OSErrorCode
         rkey.events.incl(Event.Error)
 
       results[k] = rkey
@@ -585,7 +593,7 @@ template isEmpty*[T](s: Selector[T]): bool =
   (s.count == 0)
 
 proc contains*[T](s: Selector[T], fd: SocketHandle|int): bool {.inline.} =
-  return s.fds[fd].ident != 0
+  return s.fds[fd.int].ident != 0
 
 proc getData*[T](s: Selector[T], fd: SocketHandle|int): var T =
   let fdi = int(fd)
@@ -619,3 +627,7 @@ template withData*[T](s: Selector[T], fd: SocketHandle|int, value, body1,
     body1
   else:
     body2
+
+
+proc getFd*[T](s: Selector[T]): int =
+  return s.kqFD.int
\ No newline at end of file
diff --git a/lib/pure/ioselects/ioselectors_poll.nim b/lib/pure/ioselects/ioselectors_poll.nim
index cc06aa592..66d52b352 100644
--- a/lib/pure/ioselects/ioselectors_poll.nim
+++ b/lib/pure/ioselects/ioselectors_poll.nim
@@ -141,7 +141,7 @@ template checkFd(s, f) =
   if f >= s.maxFD:
     raiseIOSelectorsError("Maximum number of descriptors is exhausted!")
 
-proc registerHandle*[T](s: Selector[T], fd: SocketHandle,
+proc registerHandle*[T](s: Selector[T], fd: int | SocketHandle,
                         events: set[Event], data: T) =
   var fdi = int(fd)
   s.checkFd(fdi)
@@ -149,7 +149,7 @@ proc registerHandle*[T](s: Selector[T], fd: SocketHandle,
   setKey(s, fdi, events, 0, data)
   if events != {}: s.pollAdd(fdi.cint, events)
 
-proc updateHandle*[T](s: Selector[T], fd: SocketHandle,
+proc updateHandle*[T](s: Selector[T], fd: int | SocketHandle,
                       events: set[Event]) =
   let maskEvents = {Event.Timer, Event.Signal, Event.Process, Event.Vnode,
                     Event.User, Event.Oneshot, Event.Error}
@@ -280,7 +280,7 @@ template isEmpty*[T](s: Selector[T]): bool =
   (s.count == 0)
 
 proc contains*[T](s: Selector[T], fd: SocketHandle|int): bool {.inline.} =
-  return s.fds[fd].ident != 0
+  return s.fds[fd.int].ident != 0
 
 proc getData*[T](s: Selector[T], fd: SocketHandle|int): var T =
   let fdi = int(fd)
@@ -314,3 +314,7 @@ template withData*[T](s: Selector[T], fd: SocketHandle|int, value, body1,
     body1
   else:
     body2
+
+
+proc getFd*[T](s: Selector[T]): int =
+  return -1
\ No newline at end of file
diff --git a/lib/pure/ioselects/ioselectors_select.nim b/lib/pure/ioselects/ioselectors_select.nim
index c787f0070..7ed250307 100644
--- a/lib/pure/ioselects/ioselectors_select.nim
+++ b/lib/pure/ioselects/ioselectors_select.nim
@@ -229,7 +229,7 @@ proc delKey[T](s: Selector[T], fd: SocketHandle) =
   doAssert(i < FD_SETSIZE,
            "Descriptor [" & $int(fd) & "] is not registered in the queue!")
 
-proc registerHandle*[T](s: Selector[T], fd: SocketHandle,
+proc registerHandle*[T](s: Selector[T], fd: int | SocketHandle,
                         events: set[Event], data: T) =
   when not defined(windows):
     let fdi = int(fd)
@@ -255,7 +255,7 @@ proc registerEvent*[T](s: Selector[T], ev: SelectEvent, data: T) =
     IOFD_SET(ev.rsock, addr s.rSet)
     inc(s.count)
 
-proc updateHandle*[T](s: Selector[T], fd: SocketHandle,
+proc updateHandle*[T](s: Selector[T], fd: int | SocketHandle,
                       events: set[Event]) =
   let maskEvents = {Event.Timer, Event.Signal, Event.Process, Event.Vnode,
                     Event.User, Event.Oneshot, Event.Error}
@@ -453,3 +453,6 @@ template withData*[T](s: Selector[T], fd: SocketHandle|int, value,
       else:
         body2
 
+
+proc getFd*[T](s: Selector[T]): int =
+  return -1
\ No newline at end of file
diff --git a/lib/pure/nativesockets.nim b/lib/pure/nativesockets.nim
index 6c8701843..790ad627d 100644
--- a/lib/pure/nativesockets.nim
+++ b/lib/pure/nativesockets.nim
@@ -187,12 +187,12 @@ proc toSockType*(protocol: Protocol): SockType =
 proc newNativeSocket*(domain: Domain = AF_INET,
                       sockType: SockType = SOCK_STREAM,
                       protocol: Protocol = IPPROTO_TCP): SocketHandle =
-  ## Creates a new socket; returns `InvalidSocket` if an error occurs.
+  ## Creates a new socket; returns `osInvalidSocket` if an error occurs.
   socket(toInt(domain), toInt(sockType), toInt(protocol))
 
 proc newNativeSocket*(domain: cint, sockType: cint,
                       protocol: cint): SocketHandle =
-  ## Creates a new socket; returns `InvalidSocket` if an error occurs.
+  ## Creates a new socket; returns `osInvalidSocket` if an error occurs.
   ##
   ## Use this overload if one of the enums specified above does
   ## not contain what you need.
@@ -666,6 +666,19 @@ proc selectWrite*(writefds: var seq[SocketHandle],
 
   pruneSocketSet(writefds, (wr))
 
+proc accept*(fd: SocketHandle): (SocketHandle, string) =
+  ## Accepts a new client connection.
+  ##
+  ## Returns (osInvalidSocket, "") if an error occurred.
+  var sockAddress: Sockaddr_in
+  var addrLen = sizeof(sockAddress).SockLen
+  var sock = accept(fd, cast[ptr SockAddr](addr(sockAddress)),
+                    addr(addrLen))
+  if sock == osInvalidSocket:
+    return (osInvalidSocket, "")
+  else:
+    return (sock, $inet_ntoa(sockAddress.sin_addr))
+
 when defined(Windows):
   var wsa: WSAData
   if wsaStartup(0x0101'i16, addr wsa) != 0: raiseOSError(osLastError())
diff --git a/lib/pure/net.nim b/lib/pure/net.nim
index f348b7c51..e63f7ad55 100644
--- a/lib/pure/net.nim
+++ b/lib/pure/net.nim
@@ -753,10 +753,8 @@ proc acceptAddr*(server: Socket, client: var Socket, address: var string,
   ## flag is specified then this error will not be raised and instead
   ## accept will be called again.
   assert(client != nil)
-  var sockAddress: Sockaddr_in
-  var addrLen = sizeof(sockAddress).SockLen
-  var sock = accept(server.fd, cast[ptr SockAddr](addr(sockAddress)),
-                    addr(addrLen))
+  let ret = accept(server.fd)
+  let sock = ret[0]
 
   if sock == osInvalidSocket:
     let err = osLastError()
@@ -764,6 +762,7 @@ proc acceptAddr*(server: Socket, client: var Socket, address: var string,
       acceptAddr(server, client, address, flags)
     raiseOSError(err)
   else:
+    address = ret[1]
     client.fd = sock
     client.isBuffered = server.isBuffered
 
@@ -776,9 +775,6 @@ proc acceptAddr*(server: Socket, client: var Socket, address: var string,
         let ret = SSLAccept(client.sslHandle)
         socketError(client, ret, false)
 
-    # Client socket is set above.
-    address = $inet_ntoa(sockAddress.sin_addr)
-
 when false: #defineSsl:
   proc acceptAddrSSL*(server: Socket, client: var Socket,
                       address: var string): SSLAcceptResult {.
diff --git a/lib/pure/selectors.nim b/lib/pure/selectors.nim
index 518cc4bd5..ea90972fe 100644
--- a/lib/pure/selectors.nim
+++ b/lib/pure/selectors.nim
@@ -54,9 +54,9 @@ when defined(nimdoc):
       Timer,       ## Timer descriptor is completed
       Signal,      ## Signal is raised
       Process,     ## Process is finished
-      Vnode,       ## BSD specific file change happens
+      Vnode,       ## BSD specific file change
       User,        ## User event is raised
-      Error,       ## Error happens while waiting, for descriptor
+      Error,       ## Error occurred while waiting for descriptor
       VnodeWrite,  ## NOTE_WRITE (BSD specific, write to file occurred)
       VnodeDelete, ## NOTE_DELETE (BSD specific, unlink of file occurred)
       VnodeExtend, ## NOTE_EXTEND (BSD specific, file extended)
@@ -69,6 +69,8 @@ when defined(nimdoc):
       ## An object which holds result for descriptor
       fd* : int ## file/socket descriptor
       events*: set[Event] ## set of events
+      errorCode*: OSErrorCode ## additional error code information for
+                              ## Error events
 
     SelectEvent* = object
       ## An object which holds user defined event
@@ -79,13 +81,14 @@ when defined(nimdoc):
   proc close*[T](s: Selector[T]) =
     ## Closes the selector.
 
-  proc registerHandle*[T](s: Selector[T], fd: SocketHandle, events: set[Event],
-                          data: T) =
+  proc registerHandle*[T](s: Selector[T], fd: int | SocketHandle,
+                          events: set[Event], data: T) =
     ## Registers file/socket descriptor ``fd`` to selector ``s``
     ## with events set in ``events``. The ``data`` is application-defined
     ## data, which will be passed when an event is triggered.
 
-  proc updateHandle*[T](s: Selector[T], fd: SocketHandle, events: set[Event]) =
+  proc updateHandle*[T](s: Selector[T], fd: int | SocketHandle,
+                        events: set[Event]) =
     ## Update file/socket descriptor ``fd``, registered in selector
     ## ``s`` with new events set ``event``.
 
@@ -221,11 +224,15 @@ when defined(nimdoc):
   proc contains*[T](s: Selector[T], fd: SocketHandle|int): bool {.inline.} =
     ## Determines whether selector contains a file descriptor.
 
+  proc getFd*[T](s: Selector[T]): int =
+    ## Retrieves the underlying selector's file descriptor.
+    ##
+    ## For *poll* and *select* selectors ``-1`` is returned.
+
 else:
   when hasThreadSupport:
     import locks
 
-
     type
       SharedArray[T] = UncheckedArray[T]
 
@@ -234,7 +241,6 @@ else:
 
     proc deallocSharedArray[T](sa: ptr SharedArray[T]) =
       deallocShared(cast[pointer](sa))
-
   type
     Event* {.pure.} = enum
       Read, Write, Timer, Signal, Process, Vnode, User, Error, Oneshot,
@@ -247,6 +253,7 @@ else:
     ReadyKey* = object
       fd* : int
       events*: set[Event]
+      errorCode*: OSErrorCode
 
     SelectorKey[T] = object
       ident: int
@@ -264,7 +271,7 @@ else:
       msg.add("Internal Error\n")
     var err = newException(IOSelectorsException, msg)
     raise err
-
+  
   proc setNonBlocking(fd: cint) {.inline.} =
     setBlocking(fd.SocketHandle, false)
 
diff --git a/lib/upcoming/asyncdispatch.nim b/lib/upcoming/asyncdispatch.nim
deleted file mode 100644
index 4e3b06173..000000000
--- a/lib/upcoming/asyncdispatch.nim
+++ /dev/null
@@ -1,1630 +0,0 @@
-#
-#
-#            Nim's Runtime Library
-#        (c) Copyright 2015 Dominik Picheta
-#
-#    See the file "copying.txt", included in this
-#    distribution, for details about the copyright.
-#
-
-include "system/inclrtl"
-
-import os, tables, strutils, times, heapqueue, lists, options, asyncstreams
-import asyncfutures except callSoon
-
-import nativesockets, net, deques
-
-export Port, SocketFlag
-export asyncfutures, asyncstreams
-
-#{.injectStmt: newGcInvariant().}
-
-## AsyncDispatch
-## *************
-##
-## This module implements asynchronous IO. This includes a dispatcher,
-## a ``Future`` type implementation, and an ``async`` macro which allows
-## asynchronous code to be written in a synchronous style with the ``await``
-## keyword.
-##
-## The dispatcher acts as a kind of event loop. You must call ``poll`` on it
-## (or a function which does so for you such as ``waitFor`` or ``runForever``)
-## in order to poll for any outstanding events. The underlying implementation
-## is based on epoll on Linux, IO Completion Ports on Windows and select on
-## other operating systems.
-##
-## The ``poll`` function will not, on its own, return any events. Instead
-## an appropriate ``Future`` object will be completed. A ``Future`` is a
-## type which holds a value which is not yet available, but which *may* be
-## available in the future. You can check whether a future is finished
-## by using the ``finished`` function. When a future is finished it means that
-## either the value that it holds is now available or it holds an error instead.
-## The latter situation occurs when the operation to complete a future fails
-## with an exception. You can distinguish between the two situations with the
-## ``failed`` function.
-##
-## Future objects can also store a callback procedure which will be called
-## automatically once the future completes.
-##
-## Futures therefore can be thought of as an implementation of the proactor
-## pattern. In this
-## pattern you make a request for an action, and once that action is fulfilled
-## a future is completed with the result of that action. Requests can be
-## made by calling the appropriate functions. For example: calling the ``recv``
-## function will create a request for some data to be read from a socket. The
-## future which the ``recv`` function returns will then complete once the
-## requested amount of data is read **or** an exception occurs.
-##
-## Code to read some data from a socket may look something like this:
-##
-##   .. code-block::nim
-##      var future = socket.recv(100)
-##      future.callback =
-##        proc () =
-##          echo(future.read)
-##
-## All asynchronous functions returning a ``Future`` will not block. They
-## will not however return immediately. An asynchronous function will have
-## code which will be executed before an asynchronous request is made, in most
-## cases this code sets up the request.
-##
-## In the above example, the ``recv`` function will return a brand new
-## ``Future`` instance once the request for data to be read from the socket
-## is made. This ``Future`` instance will complete once the requested amount
-## of data is read, in this case it is 100 bytes. The second line sets a
-## callback on this future which will be called once the future completes.
-## All the callback does is write the data stored in the future to ``stdout``.
-## The ``read`` function is used for this and it checks whether the future
-## completes with an error for you (if it did it will simply raise the
-## error), if there is no error however it returns the value of the future.
-##
-## Asynchronous procedures
-## -----------------------
-##
-## Asynchronous procedures remove the pain of working with callbacks. They do
-## this by allowing you to write asynchronous code the same way as you would
-## write synchronous code.
-##
-## An asynchronous procedure is marked using the ``{.async.}`` pragma.
-## When marking a procedure with the ``{.async.}`` pragma it must have a
-## ``Future[T]`` return type or no return type at all. If you do not specify
-## a return type then ``Future[void]`` is assumed.
-##
-## Inside asynchronous procedures ``await`` can be used to call any
-## procedures which return a
-## ``Future``; this includes asynchronous procedures. When a procedure is
-## "awaited", the asynchronous procedure it is awaited in will
-## suspend its execution
-## until the awaited procedure's Future completes. At which point the
-## asynchronous procedure will resume its execution. During the period
-## when an asynchronous procedure is suspended other asynchronous procedures
-## will be run by the dispatcher.
-##
-## The ``await`` call may be used in many contexts. It can be used on the right
-## hand side of a variable declaration: ``var data = await socket.recv(100)``,
-## in which case the variable will be set to the value of the future
-## automatically. It can be used to await a ``Future`` object, and it can
-## be used to await a procedure returning a ``Future[void]``:
-## ``await socket.send("foobar")``.
-##
-## Discarding futures
-## ------------------
-##
-## Futures should **never** be discarded. This is because they may contain
-## errors. If you do not care for the result of a Future then you should
-## use the ``asyncCheck`` procedure instead of the ``discard`` keyword.
-##
-## Examples
-## --------
-##
-## For examples take a look at the documentation for the modules implementing
-## asynchronous IO. A good place to start is the
-## `asyncnet module <asyncnet.html>`_.
-##
-## Limitations/Bugs
-## ----------------
-##
-## * The effect system (``raises: []``) does not work with async procedures.
-## * Can't await in a ``except`` body
-## * Forward declarations for async procs are broken,
-##   link includes workaround: https://github.com/nim-lang/Nim/issues/3182.
-## * FutureVar[T] needs to be completed manually.
-
-# TODO: Check if yielded future is nil and throw a more meaningful exception
-
-type
-  PDispatcherBase = ref object of RootRef
-    timers: HeapQueue[tuple[finishAt: float, fut: Future[void]]]
-    callbacks: Deque[proc ()]
-
-proc processTimers(p: PDispatcherBase) {.inline.} =
-  #Process just part if timers at a step
-  var count = p.timers.len
-  let t = epochTime()
-  while count > 0 and t >= p.timers[0].finishAt:
-    p.timers.pop().fut.complete()
-    dec count
-
-proc processPendingCallbacks(p: PDispatcherBase) =
-  while p.callbacks.len > 0:
-    var cb = p.callbacks.popFirst()
-    cb()
-
-proc adjustedTimeout(p: PDispatcherBase, timeout: int): int {.inline.} =
-  # If dispatcher has active timers this proc returns the timeout
-  # of the nearest timer. Returns `timeout` otherwise.
-  result = timeout
-  if p.timers.len > 0:
-    let timerTimeout = p.timers[0].finishAt
-    let curTime = epochTime()
-    if timeout == -1 or (curTime + (timeout / 1000)) > timerTimeout:
-      result = int((timerTimeout - curTime) * 1000)
-      if result < 0: result = 0
-
-proc callSoon(cbproc: proc ()) {.gcsafe.}
-
-proc initCallSoonProc =
-  if asyncfutures.getCallSoonProc().isNil:
-    asyncfutures.setCallSoonProc(callSoon)
-
-when defined(windows) or defined(nimdoc):
-  import winlean, sets, hashes
-  type
-    CompletionKey = ULONG_PTR
-
-    CompletionData* = object
-      fd*: AsyncFD # TODO: Rename this.
-      cb*: proc (fd: AsyncFD, bytesTransferred: Dword,
-                errcode: OSErrorCode) {.closure,gcsafe.}
-      cell*: ForeignCell # we need this `cell` to protect our `cb` environment,
-                         # when using RegisterWaitForSingleObject, because
-                         # waiting is done in different thread.
-
-    PDispatcher* = ref object of PDispatcherBase
-      ioPort: Handle
-      handles: HashSet[AsyncFD]
-
-    CustomOverlapped = object of OVERLAPPED
-      data*: CompletionData
-
-    PCustomOverlapped* = ref CustomOverlapped
-
-    AsyncFD* = distinct int
-
-    PostCallbackData = object
-      ioPort: Handle
-      handleFd: AsyncFD
-      waitFd: Handle
-      ovl: PCustomOverlapped
-    PostCallbackDataPtr = ptr PostCallbackData
-
-    AsyncEventImpl = object
-      hEvent: Handle
-      hWaiter: Handle
-      pcd: PostCallbackDataPtr
-    AsyncEvent* = ptr AsyncEventImpl
-
-    Callback = proc (fd: AsyncFD): bool {.closure,gcsafe.}
-  {.deprecated: [TCompletionKey: CompletionKey, TAsyncFD: AsyncFD,
-                TCustomOverlapped: CustomOverlapped, TCompletionData: CompletionData].}
-
-  proc hash(x: AsyncFD): Hash {.borrow.}
-  proc `==`*(x: AsyncFD, y: AsyncFD): bool {.borrow.}
-
-  proc newDispatcher*(): PDispatcher =
-    ## Creates a new Dispatcher instance.
-    new result
-    result.ioPort = createIoCompletionPort(INVALID_HANDLE_VALUE, 0, 0, 1)
-    result.handles = initSet[AsyncFD]()
-    result.timers.newHeapQueue()
-    result.callbacks = initDeque[proc ()](64)
-
-  var gDisp{.threadvar.}: PDispatcher ## Global dispatcher
-
-  proc setGlobalDispatcher*(disp: PDispatcher) =
-    if not gDisp.isNil:
-      assert gDisp.callbacks.len == 0
-    gDisp = disp
-    initCallSoonProc()
-
-  proc getGlobalDispatcher*(): PDispatcher =
-    if gDisp.isNil:
-      setGlobalDispatcher(newDispatcher())
-    result = gDisp
-
-  proc register*(fd: AsyncFD) =
-    ## Registers ``fd`` with the dispatcher.
-    let p = getGlobalDispatcher()
-    if createIoCompletionPort(fd.Handle, p.ioPort,
-                              cast[CompletionKey](fd), 1) == 0:
-      raiseOSError(osLastError())
-    p.handles.incl(fd)
-
-  proc verifyPresence(fd: AsyncFD) =
-    ## Ensures that file descriptor has been registered with the dispatcher.
-    let p = getGlobalDispatcher()
-    if fd notin p.handles:
-      raise newException(ValueError,
-        "Operation performed on a socket which has not been registered with" &
-        " the dispatcher yet.")
-
-  proc hasPendingOperations*(): bool =
-    ## Returns `true` if the global dispatcher has pending operations.
-    let p = getGlobalDispatcher()
-    p.handles.len != 0 or p.timers.len != 0 or p.callbacks.len != 0
-
-  proc poll*(timeout = 500) =
-    ## Waits for completion events and processes them. Raises ``ValueError``
-    ## if there are no pending operations.
-    let p = getGlobalDispatcher()
-    if p.handles.len == 0 and p.timers.len == 0 and p.callbacks.len == 0:
-      raise newException(ValueError,
-        "No handles or timers registered in dispatcher.")
-
-    let at = p.adjustedTimeout(timeout)
-    var llTimeout =
-      if at == -1: winlean.INFINITE
-      else: at.int32
-
-    if p.handles.len != 0:
-      var lpNumberOfBytesTransferred: Dword
-      var lpCompletionKey: ULONG_PTR
-      var customOverlapped: PCustomOverlapped
-      let res = getQueuedCompletionStatus(p.ioPort,
-          addr lpNumberOfBytesTransferred, addr lpCompletionKey,
-          cast[ptr POVERLAPPED](addr customOverlapped), llTimeout).bool
-
-      # http://stackoverflow.com/a/12277264/492186
-      # TODO: http://www.serverframework.com/handling-multiple-pending-socket-read-and-write-operations.html
-      if res:
-        # This is useful for ensuring the reliability of the overlapped struct.
-        assert customOverlapped.data.fd == lpCompletionKey.AsyncFD
-
-        customOverlapped.data.cb(customOverlapped.data.fd,
-            lpNumberOfBytesTransferred, OSErrorCode(-1))
-
-        # If cell.data != nil, then system.protect(rawEnv(cb)) was called,
-        # so we need to dispose our `cb` environment, because it is not needed
-        # anymore.
-        if customOverlapped.data.cell.data != nil:
-          system.dispose(customOverlapped.data.cell)
-
-        GC_unref(customOverlapped)
-      else:
-        let errCode = osLastError()
-        if customOverlapped != nil:
-          assert customOverlapped.data.fd == lpCompletionKey.AsyncFD
-          customOverlapped.data.cb(customOverlapped.data.fd,
-              lpNumberOfBytesTransferred, errCode)
-          if customOverlapped.data.cell.data != nil:
-            system.dispose(customOverlapped.data.cell)
-          GC_unref(customOverlapped)
-        else:
-          if errCode.int32 == WAIT_TIMEOUT:
-            # Timed out
-            discard
-          else: raiseOSError(errCode)
-
-    # Timer processing.
-    processTimers(p)
-    # Callback queue processing
-    processPendingCallbacks(p)
-
-  var acceptEx*: WSAPROC_ACCEPTEX
-  var connectEx*: WSAPROC_CONNECTEX
-  var getAcceptExSockAddrs*: WSAPROC_GETACCEPTEXSOCKADDRS
-
-  proc initPointer(s: SocketHandle, fun: var pointer, guid: var GUID): bool =
-    # Ref: https://github.com/powdahound/twisted/blob/master/twisted/internet/iocpreactor/iocpsupport/winsock_pointers.c
-    var bytesRet: Dword
-    fun = nil
-    result = WSAIoctl(s, SIO_GET_EXTENSION_FUNCTION_POINTER, addr guid,
-                      sizeof(GUID).Dword, addr fun, sizeof(pointer).Dword,
-                      addr bytesRet, nil, nil) == 0
-
-  proc initAll() =
-    let dummySock = newNativeSocket()
-    if dummySock == INVALID_SOCKET:
-      raiseOSError(osLastError())
-    var fun: pointer = nil
-    if not initPointer(dummySock, fun, WSAID_CONNECTEX):
-      raiseOSError(osLastError())
-    connectEx = cast[WSAPROC_CONNECTEX](fun)
-    if not initPointer(dummySock, fun, WSAID_ACCEPTEX):
-      raiseOSError(osLastError())
-    acceptEx = cast[WSAPROC_ACCEPTEX](fun)
-    if not initPointer(dummySock, fun, WSAID_GETACCEPTEXSOCKADDRS):
-      raiseOSError(osLastError())
-    getAcceptExSockAddrs = cast[WSAPROC_GETACCEPTEXSOCKADDRS](fun)
-    close(dummySock)
-
-  proc recv*(socket: AsyncFD, size: int,
-             flags = {SocketFlag.SafeDisconn}): Future[string] =
-    ## Reads **up to** ``size`` bytes from ``socket``. Returned future will
-    ## complete once all the data requested is read, a part of the data has been
-    ## read, or the socket has disconnected in which case the future will
-    ## complete with a value of ``""``.
-    ##
-    ## **Warning**: The ``Peek`` socket flag is not supported on Windows.
-
-
-    # Things to note:
-    #   * When WSARecv completes immediately then ``bytesReceived`` is very
-    #     unreliable.
-    #   * Still need to implement message-oriented socket disconnection,
-    #     '\0' in the message currently signifies a socket disconnect. Who
-    #     knows what will happen when someone sends that to our socket.
-    verifyPresence(socket)
-    assert SocketFlag.Peek notin flags, "Peek not supported on Windows."
-
-    var retFuture = newFuture[string]("recv")
-    var dataBuf: TWSABuf
-    dataBuf.buf = cast[cstring](alloc0(size))
-    dataBuf.len = size.ULONG
-
-    var bytesReceived: Dword
-    var flagsio = flags.toOSFlags().Dword
-    var ol = PCustomOverlapped()
-    GC_ref(ol)
-    ol.data = CompletionData(fd: socket, cb:
-      proc (fd: AsyncFD, bytesCount: Dword, errcode: OSErrorCode) =
-        if not retFuture.finished:
-          if errcode == OSErrorCode(-1):
-            if bytesCount == 0 and dataBuf.buf[0] == '\0':
-              retFuture.complete("")
-            else:
-              var data = newString(bytesCount)
-              assert bytesCount <= size
-              copyMem(addr data[0], addr dataBuf.buf[0], bytesCount)
-              retFuture.complete($data)
-          else:
-            if flags.isDisconnectionError(errcode):
-              retFuture.complete("")
-            else:
-              retFuture.fail(newException(OSError, osErrorMsg(errcode)))
-        if dataBuf.buf != nil:
-          dealloc dataBuf.buf
-          dataBuf.buf = nil
-    )
-
-    let ret = WSARecv(socket.SocketHandle, addr dataBuf, 1, addr bytesReceived,
-                      addr flagsio, cast[POVERLAPPED](ol), nil)
-    if ret == -1:
-      let err = osLastError()
-      if err.int32 != ERROR_IO_PENDING:
-        if dataBuf.buf != nil:
-          dealloc dataBuf.buf
-          dataBuf.buf = nil
-        GC_unref(ol)
-        if flags.isDisconnectionError(err):
-          retFuture.complete("")
-        else:
-          retFuture.fail(newException(OSError, osErrorMsg(err)))
-    elif ret == 0:
-      # Request completed immediately.
-      if bytesReceived != 0:
-        var data = newString(bytesReceived)
-        assert bytesReceived <= size
-        copyMem(addr data[0], addr dataBuf.buf[0], bytesReceived)
-        retFuture.complete($data)
-      else:
-        if hasOverlappedIoCompleted(cast[POVERLAPPED](ol)):
-          retFuture.complete("")
-    return retFuture
-
-  proc recvInto*(socket: AsyncFD, buf: pointer, size: int,
-                flags = {SocketFlag.SafeDisconn}): Future[int] =
-    ## Reads **up to** ``size`` bytes from ``socket`` into ``buf``, which must
-    ## at least be of that size. Returned future will complete once all the
-    ## data requested is read, a part of the data has been read, or the socket
-    ## has disconnected in which case the future will complete with a value of
-    ## ``0``.
-    ##
-    ## **Warning**: The ``Peek`` socket flag is not supported on Windows.
-
-
-    # Things to note:
-    #   * When WSARecv completes immediately then ``bytesReceived`` is very
-    #     unreliable.
-    #   * Still need to implement message-oriented socket disconnection,
-    #     '\0' in the message currently signifies a socket disconnect. Who
-    #     knows what will happen when someone sends that to our socket.
-    verifyPresence(socket)
-    assert SocketFlag.Peek notin flags, "Peek not supported on Windows."
-
-    var retFuture = newFuture[int]("recvInto")
-
-    #buf[] = '\0'
-    var dataBuf: TWSABuf
-    dataBuf.buf = cast[cstring](buf)
-    dataBuf.len = size.ULONG
-
-    var bytesReceived: Dword
-    var flagsio = flags.toOSFlags().Dword
-    var ol = PCustomOverlapped()
-    GC_ref(ol)
-    ol.data = CompletionData(fd: socket, cb:
-      proc (fd: AsyncFD, bytesCount: Dword, errcode: OSErrorCode) =
-        if not retFuture.finished:
-          if errcode == OSErrorCode(-1):
-            retFuture.complete(bytesCount)
-          else:
-            if flags.isDisconnectionError(errcode):
-              retFuture.complete(0)
-            else:
-              retFuture.fail(newException(OSError, osErrorMsg(errcode)))
-        if dataBuf.buf != nil:
-          dataBuf.buf = nil
-    )
-
-    let ret = WSARecv(socket.SocketHandle, addr dataBuf, 1, addr bytesReceived,
-                      addr flagsio, cast[POVERLAPPED](ol), nil)
-    if ret == -1:
-      let err = osLastError()
-      if err.int32 != ERROR_IO_PENDING:
-        if dataBuf.buf != nil:
-          dataBuf.buf = nil
-        GC_unref(ol)
-        if flags.isDisconnectionError(err):
-          retFuture.complete(0)
-        else:
-          retFuture.fail(newException(OSError, osErrorMsg(err)))
-    elif ret == 0:
-      # Request completed immediately.
-      if bytesReceived != 0:
-        assert bytesReceived <= size
-        retFuture.complete(bytesReceived)
-      else:
-        if hasOverlappedIoCompleted(cast[POVERLAPPED](ol)):
-          retFuture.complete(bytesReceived)
-    return retFuture
-
-  proc send*(socket: AsyncFD, buf: pointer, size: int,
-             flags = {SocketFlag.SafeDisconn}): Future[void] =
-    ## Sends ``size`` bytes from ``buf`` to ``socket``. The returned future
-    ## will complete once all data has been sent.
-    ## **WARNING**: Use it with caution. If ``buf`` refers to GC'ed object,
-    ## you must use GC_ref/GC_unref calls to avoid early freeing of the buffer.
-    verifyPresence(socket)
-    var retFuture = newFuture[void]("send")
-
-    var dataBuf: TWSABuf
-    dataBuf.buf = cast[cstring](buf)
-    dataBuf.len = size.ULONG
-
-    var bytesReceived, lowFlags: Dword
-    var ol = PCustomOverlapped()
-    GC_ref(ol)
-    ol.data = CompletionData(fd: socket, cb:
-      proc (fd: AsyncFD, bytesCount: Dword, errcode: OSErrorCode) =
-        if not retFuture.finished:
-          if errcode == OSErrorCode(-1):
-            retFuture.complete()
-          else:
-            if flags.isDisconnectionError(errcode):
-              retFuture.complete()
-            else:
-              retFuture.fail(newException(OSError, osErrorMsg(errcode)))
-    )
-
-    let ret = WSASend(socket.SocketHandle, addr dataBuf, 1, addr bytesReceived,
-                      lowFlags, cast[POVERLAPPED](ol), nil)
-    if ret == -1:
-      let err = osLastError()
-      if err.int32 != ERROR_IO_PENDING:
-        GC_unref(ol)
-        if flags.isDisconnectionError(err):
-          retFuture.complete()
-        else:
-          retFuture.fail(newException(OSError, osErrorMsg(err)))
-    else:
-      retFuture.complete()
-      # We don't deallocate ``ol`` here because even though this completed
-      # immediately poll will still be notified about its completion and it will
-      # free ``ol``.
-    return retFuture
-
-  proc send*(socket: AsyncFD, data: string,
-             flags = {SocketFlag.SafeDisconn}): Future[void] =
-    ## Sends ``data`` to ``socket``. The returned future will complete once all
-    ## data has been sent.
-    verifyPresence(socket)
-    var retFuture = newFuture[void]("send")
-
-    var dataBuf: TWSABuf
-    dataBuf.buf = data
-    GC_ref(data) # we need to protect data until send operation is completed
-                 # or failed.
-    dataBuf.len = data.len.ULONG
-
-    var bytesReceived, lowFlags: Dword
-    var ol = PCustomOverlapped()
-    GC_ref(ol)
-    ol.data = CompletionData(fd: socket, cb:
-      proc (fd: AsyncFD, bytesCount: Dword, errcode: OSErrorCode) =
-        GC_unref(data) # if operation completed `data` must be released.
-        if not retFuture.finished:
-          if errcode == OSErrorCode(-1):
-            retFuture.complete()
-          else:
-            if flags.isDisconnectionError(errcode):
-              retFuture.complete()
-            else:
-              retFuture.fail(newException(OSError, osErrorMsg(errcode)))
-    )
-
-    let ret = WSASend(socket.SocketHandle, addr dataBuf, 1, addr bytesReceived,
-                      lowFlags, cast[POVERLAPPED](ol), nil)
-    if ret == -1:
-      let err = osLastError()
-      if err.int32 != ERROR_IO_PENDING:
-        GC_unref(ol)
-        GC_unref(data) # if operation failed `data` must be released, because
-                       # completion routine will not be called.
-        if flags.isDisconnectionError(err):
-          retFuture.complete()
-        else:
-          retFuture.fail(newException(OSError, osErrorMsg(err)))
-    else:
-      retFuture.complete()
-      # We don't deallocate ``ol`` here because even though this completed
-      # immediately poll will still be notified about its completion and it will
-      # free ``ol``.
-    return retFuture
-
-  proc sendTo*(socket: AsyncFD, data: pointer, size: int, saddr: ptr SockAddr,
-               saddrLen: Socklen,
-               flags = {SocketFlag.SafeDisconn}): Future[void] =
-    ## Sends ``data`` to specified destination ``saddr``, using
-    ## socket ``socket``. The returned future will complete once all data
-    ## has been sent.
-    verifyPresence(socket)
-    var retFuture = newFuture[void]("sendTo")
-    var dataBuf: TWSABuf
-    dataBuf.buf = cast[cstring](data)
-    dataBuf.len = size.ULONG
-    var bytesSent = 0.Dword
-    var lowFlags = 0.Dword
-
-    # we will preserve address in our stack
-    var staddr: array[128, char] # SOCKADDR_STORAGE size is 128 bytes
-    var stalen: cint = cint(saddrLen)
-    zeroMem(addr(staddr[0]), 128)
-    copyMem(addr(staddr[0]), saddr, saddrLen)
-
-    var ol = PCustomOverlapped()
-    GC_ref(ol)
-    ol.data = CompletionData(fd: socket, cb:
-      proc (fd: AsyncFD, bytesCount: Dword, errcode: OSErrorCode) =
-        if not retFuture.finished:
-          if errcode == OSErrorCode(-1):
-            retFuture.complete()
-          else:
-            retFuture.fail(newException(OSError, osErrorMsg(errcode)))
-    )
-
-    let ret = WSASendTo(socket.SocketHandle, addr dataBuf, 1, addr bytesSent,
-                        lowFlags, cast[ptr SockAddr](addr(staddr[0])),
-                        stalen, cast[POVERLAPPED](ol), nil)
-    if ret == -1:
-      let err = osLastError()
-      if err.int32 != ERROR_IO_PENDING:
-        GC_unref(ol)
-        retFuture.fail(newException(OSError, osErrorMsg(err)))
-    else:
-      retFuture.complete()
-      # We don't deallocate ``ol`` here because even though this completed
-      # immediately poll will still be notified about its completion and it will
-      # free ``ol``.
-    return retFuture
-
-  proc recvFromInto*(socket: AsyncFD, data: pointer, size: int,
-                     saddr: ptr SockAddr, saddrLen: ptr SockLen,
-                     flags = {SocketFlag.SafeDisconn}): Future[int] =
-    ## Receives a datagram data from ``socket`` into ``buf``, which must
-    ## be at least of size ``size``, address of datagram's sender will be
-    ## stored into ``saddr`` and ``saddrLen``. Returned future will complete
-    ## once one datagram has been received, and will return size of packet
-    ## received.
-    verifyPresence(socket)
-    var retFuture = newFuture[int]("recvFromInto")
-
-    var dataBuf = TWSABuf(buf: cast[cstring](data), len: size.ULONG)
-
-    var bytesReceived = 0.Dword
-    var lowFlags = 0.Dword
-
-    var ol = PCustomOverlapped()
-    GC_ref(ol)
-    ol.data = CompletionData(fd: socket, cb:
-      proc (fd: AsyncFD, bytesCount: Dword, errcode: OSErrorCode) =
-        if not retFuture.finished:
-          if errcode == OSErrorCode(-1):
-            assert bytesCount <= size
-            retFuture.complete(bytesCount)
-          else:
-            # datagram sockets don't have disconnection,
-            # so we can just raise an exception
-            retFuture.fail(newException(OSError, osErrorMsg(errcode)))
-    )
-
-    let res = WSARecvFrom(socket.SocketHandle, addr dataBuf, 1,
-                          addr bytesReceived, addr lowFlags,
-                          saddr, cast[ptr cint](saddrLen),
-                          cast[POVERLAPPED](ol), nil)
-    if res == -1:
-      let err = osLastError()
-      if err.int32 != ERROR_IO_PENDING:
-        GC_unref(ol)
-        retFuture.fail(newException(OSError, osErrorMsg(err)))
-    else:
-      # Request completed immediately.
-      if bytesReceived != 0:
-        assert bytesReceived <= size
-        retFuture.complete(bytesReceived)
-      else:
-        if hasOverlappedIoCompleted(cast[POVERLAPPED](ol)):
-          retFuture.complete(bytesReceived)
-    return retFuture
-
-  proc acceptAddr*(socket: AsyncFD, flags = {SocketFlag.SafeDisconn}):
-      Future[tuple[address: string, client: AsyncFD]] =
-    ## Accepts a new connection. Returns a future containing the client socket
-    ## corresponding to that connection and the remote address of the client.
-    ## The future will complete when the connection is successfully accepted.
-    ##
-    ## The resulting client socket is automatically registered to the
-    ## dispatcher.
-    ##
-    ## The ``accept`` call may result in an error if the connecting socket
-    ## disconnects during the duration of the ``accept``. If the ``SafeDisconn``
-    ## flag is specified then this error will not be raised and instead
-    ## accept will be called again.
-    verifyPresence(socket)
-    var retFuture = newFuture[tuple[address: string, client: AsyncFD]]("acceptAddr")
-
-    var clientSock = newNativeSocket()
-    if clientSock == osInvalidSocket: raiseOSError(osLastError())
-
-    const lpOutputLen = 1024
-    var lpOutputBuf = newString(lpOutputLen)
-    var dwBytesReceived: Dword
-    let dwReceiveDataLength = 0.Dword # We don't want any data to be read.
-    let dwLocalAddressLength = Dword(sizeof(Sockaddr_in6) + 16)
-    let dwRemoteAddressLength = Dword(sizeof(Sockaddr_in6) + 16)
-
-    template failAccept(errcode) =
-      if flags.isDisconnectionError(errcode):
-        var newAcceptFut = acceptAddr(socket, flags)
-        newAcceptFut.callback =
-          proc () =
-            if newAcceptFut.failed:
-              retFuture.fail(newAcceptFut.readError)
-            else:
-              retFuture.complete(newAcceptFut.read)
-      else:
-        retFuture.fail(newException(OSError, osErrorMsg(errcode)))
-
-    template completeAccept() {.dirty.} =
-      var listenSock = socket
-      let setoptRet = setsockopt(clientSock, SOL_SOCKET,
-          SO_UPDATE_ACCEPT_CONTEXT, addr listenSock,
-          sizeof(listenSock).SockLen)
-      if setoptRet != 0:
-        let errcode = osLastError()
-        discard clientSock.closeSocket()
-        failAccept(errcode)
-      else:
-        var localSockaddr, remoteSockaddr: ptr SockAddr
-        var localLen, remoteLen: int32
-        getAcceptExSockaddrs(addr lpOutputBuf[0], dwReceiveDataLength,
-                             dwLocalAddressLength, dwRemoteAddressLength,
-                             addr localSockaddr, addr localLen,
-                             addr remoteSockaddr, addr remoteLen)
-        try:
-          let address = getAddrString(remoteSockAddr)
-          register(clientSock.AsyncFD)
-          retFuture.complete((address: address, client: clientSock.AsyncFD))
-        except:
-          # getAddrString may raise
-          clientSock.close()
-          retFuture.fail(getCurrentException())
-
-    var ol = PCustomOverlapped()
-    GC_ref(ol)
-    ol.data = CompletionData(fd: socket, cb:
-      proc (fd: AsyncFD, bytesCount: Dword, errcode: OSErrorCode) =
-        if not retFuture.finished:
-          if errcode == OSErrorCode(-1):
-            completeAccept()
-          else:
-            failAccept(errcode)
-    )
-
-    # http://msdn.microsoft.com/en-us/library/windows/desktop/ms737524%28v=vs.85%29.aspx
-    let ret = acceptEx(socket.SocketHandle, clientSock, addr lpOutputBuf[0],
-                       dwReceiveDataLength,
-                       dwLocalAddressLength,
-                       dwRemoteAddressLength,
-                       addr dwBytesReceived, cast[POVERLAPPED](ol))
-
-    if not ret:
-      let err = osLastError()
-      if err.int32 != ERROR_IO_PENDING:
-        failAccept(err)
-        GC_unref(ol)
-    else:
-      completeAccept()
-      # We don't deallocate ``ol`` here because even though this completed
-      # immediately poll will still be notified about its completion and it will
-      # free ``ol``.
-
-    return retFuture
-
-  proc closeSocket*(socket: AsyncFD) =
-    ## Closes a socket and ensures that it is unregistered.
-    socket.SocketHandle.close()
-    getGlobalDispatcher().handles.excl(socket)
-
-  proc unregister*(fd: AsyncFD) =
-    ## Unregisters ``fd``.
-    getGlobalDispatcher().handles.excl(fd)
-
-  {.push stackTrace:off.}
-  proc waitableCallback(param: pointer,
-                        timerOrWaitFired: WINBOOL): void {.stdcall.} =
-    var p = cast[PostCallbackDataPtr](param)
-    discard postQueuedCompletionStatus(p.ioPort, timerOrWaitFired.Dword,
-                                       ULONG_PTR(p.handleFd),
-                                       cast[pointer](p.ovl))
-  {.pop.}
-
-  proc registerWaitableEvent(fd: AsyncFD, cb: Callback; mask: Dword) =
-    let p = getGlobalDispatcher()
-    var flags = (WT_EXECUTEINWAITTHREAD or WT_EXECUTEONLYONCE).Dword
-    var hEvent = wsaCreateEvent()
-    if hEvent == 0:
-      raiseOSError(osLastError())
-    var pcd = cast[PostCallbackDataPtr](allocShared0(sizeof(PostCallbackData)))
-    pcd.ioPort = p.ioPort
-    pcd.handleFd = fd
-    var ol = PCustomOverlapped()
-    GC_ref(ol)
-
-    ol.data = CompletionData(fd: fd, cb:
-      proc(fd: AsyncFD, bytesCount: Dword, errcode: OSErrorCode) =
-        # we excluding our `fd` because cb(fd) can register own handler
-        # for this `fd`
-        p.handles.excl(fd)
-        # unregisterWait() is called before callback, because appropriate
-        # winsockets function can re-enable event.
-        # https://msdn.microsoft.com/en-us/library/windows/desktop/ms741576(v=vs.85).aspx
-        if unregisterWait(pcd.waitFd) == 0:
-          let err = osLastError()
-          if err.int32 != ERROR_IO_PENDING:
-            deallocShared(cast[pointer](pcd))
-            discard wsaCloseEvent(hEvent)
-            raiseOSError(err)
-        if cb(fd):
-          # callback returned `true`, so we free all allocated resources
-          deallocShared(cast[pointer](pcd))
-          if not wsaCloseEvent(hEvent):
-            raiseOSError(osLastError())
-          # pcd.ovl will be unrefed in poll().
-        else:
-          # callback returned `false` we need to continue
-          if p.handles.contains(fd):
-            # new callback was already registered with `fd`, so we free all
-            # allocated resources. This happens because in callback `cb`
-            # addRead/addWrite was called with same `fd`.
-            deallocShared(cast[pointer](pcd))
-            if not wsaCloseEvent(hEvent):
-              raiseOSError(osLastError())
-          else:
-            # we need to include `fd` again
-            p.handles.incl(fd)
-            # and register WaitForSingleObject again
-            if not registerWaitForSingleObject(addr(pcd.waitFd), hEvent,
-                                    cast[WAITORTIMERCALLBACK](waitableCallback),
-                                       cast[pointer](pcd), INFINITE, flags):
-              # pcd.ovl will be unrefed in poll()
-              let err = osLastError()
-              deallocShared(cast[pointer](pcd))
-              discard wsaCloseEvent(hEvent)
-              raiseOSError(err)
-            else:
-              # we incref `pcd.ovl` and `protect` callback one more time,
-              # because it will be unrefed and disposed in `poll()` after
-              # callback finishes.
-              GC_ref(pcd.ovl)
-              pcd.ovl.data.cell = system.protect(rawEnv(pcd.ovl.data.cb))
-    )
-    # We need to protect our callback environment value, so GC will not free it
-    # accidentally.
-    ol.data.cell = system.protect(rawEnv(ol.data.cb))
-
-    # This is main part of `hacky way` is using WSAEventSelect, so `hEvent`
-    # will be signaled when appropriate `mask` events will be triggered.
-    if wsaEventSelect(fd.SocketHandle, hEvent, mask) != 0:
-      let err = osLastError()
-      GC_unref(ol)
-      deallocShared(cast[pointer](pcd))
-      discard wsaCloseEvent(hEvent)
-      raiseOSError(err)
-
-    pcd.ovl = ol
-    if not registerWaitForSingleObject(addr(pcd.waitFd), hEvent,
-                                    cast[WAITORTIMERCALLBACK](waitableCallback),
-                                       cast[pointer](pcd), INFINITE, flags):
-      let err = osLastError()
-      GC_unref(ol)
-      deallocShared(cast[pointer](pcd))
-      discard wsaCloseEvent(hEvent)
-      raiseOSError(err)
-    p.handles.incl(fd)
-
-  proc addRead*(fd: AsyncFD, cb: Callback) =
-    ## Start watching the file descriptor for read availability and then call
-    ## the callback ``cb``.
-    ##
-    ## This is not ``pure`` mechanism for Windows Completion Ports (IOCP),
-    ## so if you can avoid it, please do it. Use `addRead` only if really
-    ## need it (main usecase is adaptation of `unix like` libraries to be
-    ## asynchronous on Windows).
-    ## If you use this function, you dont need to use asyncdispatch.recv()
-    ## or asyncdispatch.accept(), because they are using IOCP, please use
-    ## nativesockets.recv() and nativesockets.accept() instead.
-    ##
-    ## Be sure your callback ``cb`` returns ``true``, if you want to remove
-    ## watch of `read` notifications, and ``false``, if you want to continue
-    ## receiving notifies.
-    registerWaitableEvent(fd, cb, FD_READ or FD_ACCEPT or FD_OOB or FD_CLOSE)
-
-  proc addWrite*(fd: AsyncFD, cb: Callback) =
-    ## Start watching the file descriptor for write availability and then call
-    ## the callback ``cb``.
-    ##
-    ## This is not ``pure`` mechanism for Windows Completion Ports (IOCP),
-    ## so if you can avoid it, please do it. Use `addWrite` only if really
-    ## need it (main usecase is adaptation of `unix like` libraries to be
-    ## asynchronous on Windows).
-    ## If you use this function, you dont need to use asyncdispatch.send()
-    ## or asyncdispatch.connect(), because they are using IOCP, please use
-    ## nativesockets.send() and nativesockets.connect() instead.
-    ##
-    ## Be sure your callback ``cb`` returns ``true``, if you want to remove
-    ## watch of `write` notifications, and ``false``, if you want to continue
-    ## receiving notifies.
-    registerWaitableEvent(fd, cb, FD_WRITE or FD_CONNECT or FD_CLOSE)
-
-  template registerWaitableHandle(p, hEvent, flags, pcd, timeout,
-                                  handleCallback) =
-    let handleFD = AsyncFD(hEvent)
-    pcd.ioPort = p.ioPort
-    pcd.handleFd = handleFD
-    var ol = PCustomOverlapped()
-    GC_ref(ol)
-    ol.data.fd = handleFD
-    ol.data.cb = handleCallback
-    # We need to protect our callback environment value, so GC will not free it
-    # accidentally.
-    ol.data.cell = system.protect(rawEnv(ol.data.cb))
-
-    pcd.ovl = ol
-    if not registerWaitForSingleObject(addr(pcd.waitFd), hEvent,
-                                    cast[WAITORTIMERCALLBACK](waitableCallback),
-                                    cast[pointer](pcd), timeout.Dword, flags):
-      let err = osLastError()
-      GC_unref(ol)
-      deallocShared(cast[pointer](pcd))
-      discard closeHandle(hEvent)
-      raiseOSError(err)
-    p.handles.incl(handleFD)
-
-  template closeWaitable(handle: untyped) =
-    let waitFd = pcd.waitFd
-    deallocShared(cast[pointer](pcd))
-    p.handles.excl(fd)
-    if unregisterWait(waitFd) == 0:
-        let err = osLastError()
-        if err.int32 != ERROR_IO_PENDING:
-          discard closeHandle(handle)
-          raiseOSError(err)
-    if closeHandle(handle) == 0:
-      raiseOSError(osLastError())
-
-  proc addTimer*(timeout: int, oneshot: bool, cb: Callback) =
-    ## Registers callback ``cb`` to be called when timer expired.
-    ## ``timeout`` - timeout value in milliseconds.
-    ## ``oneshot`` - `true`, to generate only one timeout event, `false`, to
-    ## generate timeout events periodically.
-
-    doAssert(timeout > 0)
-    let p = getGlobalDispatcher()
-
-    var hEvent = createEvent(nil, 1, 0, nil)
-    if hEvent == INVALID_HANDLE_VALUE:
-      raiseOSError(osLastError())
-
-    var pcd = cast[PostCallbackDataPtr](allocShared0(sizeof(PostCallbackData)))
-    var flags = WT_EXECUTEINWAITTHREAD.Dword
-    if oneshot: flags = flags or WT_EXECUTEONLYONCE
-
-    proc timercb(fd: AsyncFD, bytesCount: Dword, errcode: OSErrorCode) =
-      let res = cb(fd)
-      if res or oneshot:
-        closeWaitable(hEvent)
-      else:
-        # if callback returned `false`, then it wants to be called again, so
-        # we need to ref and protect `pcd.ovl` again, because it will be
-        # unrefed and disposed in `poll()`.
-        GC_ref(pcd.ovl)
-        pcd.ovl.data.cell = system.protect(rawEnv(pcd.ovl.data.cb))
-
-    registerWaitableHandle(p, hEvent, flags, pcd, timeout, timercb)
-
-  proc addProcess*(pid: int, cb: Callback) =
-    ## Registers callback ``cb`` to be called when process with pid ``pid``
-    ## exited.
-    let p = getGlobalDispatcher()
-    let procFlags = SYNCHRONIZE
-    var hProcess = openProcess(procFlags, 0, pid.Dword)
-    if hProcess == INVALID_HANDLE_VALUE:
-      raiseOSError(osLastError())
-
-    var pcd = cast[PostCallbackDataPtr](allocShared0(sizeof(PostCallbackData)))
-    var flags = WT_EXECUTEINWAITTHREAD.Dword
-
-    proc proccb(fd: AsyncFD, bytesCount: Dword, errcode: OSErrorCode) =
-      closeWaitable(hProcess)
-      discard cb(fd)
-
-    registerWaitableHandle(p, hProcess, flags, pcd, INFINITE, proccb)
-
-  proc newAsyncEvent*(): AsyncEvent =
-    ## Creates new ``AsyncEvent`` object.
-    ## New ``AsyncEvent`` object is not automatically registered with
-    ## dispatcher like ``AsyncSocket``.
-    var sa = SECURITY_ATTRIBUTES(
-      nLength: sizeof(SECURITY_ATTRIBUTES).cint,
-      bInheritHandle: 1
-    )
-    var event = createEvent(addr(sa), 0'i32, 0'i32, nil)
-    if event == INVALID_HANDLE_VALUE:
-      raiseOSError(osLastError())
-    result = cast[AsyncEvent](allocShared0(sizeof(AsyncEventImpl)))
-    result.hEvent = event
-
-  proc setEvent*(ev: AsyncEvent) =
-    ## Set event ``ev`` to signaled state.
-    if setEvent(ev.hEvent) == 0:
-      raiseOSError(osLastError())
-
-  proc unregister*(ev: AsyncEvent) =
-    ## Unregisters event ``ev``.
-    doAssert(ev.hWaiter != 0, "Event is not registered in the queue!")
-    let p = getGlobalDispatcher()
-    p.handles.excl(AsyncFD(ev.hEvent))
-    if unregisterWait(ev.hWaiter) == 0:
-      let err = osLastError()
-      if err.int32 != ERROR_IO_PENDING:
-        raiseOSError(err)
-    ev.hWaiter = 0
-
-  proc close*(ev: AsyncEvent) =
-    ## Closes event ``ev``.
-    let res = closeHandle(ev.hEvent)
-    deallocShared(cast[pointer](ev))
-    if res == 0:
-      raiseOSError(osLastError())
-
-  proc addEvent*(ev: AsyncEvent, cb: Callback) =
-    ## Registers callback ``cb`` to be called when ``ev`` will be signaled
-    doAssert(ev.hWaiter == 0, "Event is already registered in the queue!")
-
-    let p = getGlobalDispatcher()
-    let hEvent = ev.hEvent
-
-    var pcd = cast[PostCallbackDataPtr](allocShared0(sizeof(PostCallbackData)))
-    var flags = WT_EXECUTEINWAITTHREAD.Dword
-
-    proc eventcb(fd: AsyncFD, bytesCount: Dword, errcode: OSErrorCode) =
-      if ev.hWaiter != 0:
-        if cb(fd):
-          # we need this check to avoid exception, if `unregister(event)` was
-          # called in callback.
-          deallocShared(cast[pointer](pcd))
-          if ev.hWaiter != 0:
-            unregister(ev)
-        else:
-          # if callback returned `false`, then it wants to be called again, so
-          # we need to ref and protect `pcd.ovl` again, because it will be
-          # unrefed and disposed in `poll()`.
-          GC_ref(pcd.ovl)
-          pcd.ovl.data.cell = system.protect(rawEnv(pcd.ovl.data.cb))
-      else:
-        # if ev.hWaiter == 0, then event was unregistered before `poll()` call.
-        deallocShared(cast[pointer](pcd))
-
-    registerWaitableHandle(p, hEvent, flags, pcd, INFINITE, eventcb)
-    ev.hWaiter = pcd.waitFd
-
-  initAll()
-else:
-  import ioselectors
-  from posix import EINTR, EAGAIN, EINPROGRESS, EWOULDBLOCK, MSG_PEEK,
-                    MSG_NOSIGNAL
-  const
-    InitCallbackListSize = 4         # initial size of callbacks sequence,
-                                     # associated with file/socket descriptor.
-    InitDelayedCallbackListSize = 64 # initial size of delayed callbacks
-                                     # queue.
-  type
-    AsyncFD* = distinct cint
-    Callback = proc (fd: AsyncFD): bool {.closure,gcsafe.}
-
-    AsyncData = object
-      readList: seq[Callback]
-      writeList: seq[Callback]
-
-    AsyncEvent* = distinct SelectEvent
-
-    PDispatcher* = ref object of PDispatcherBase
-      selector: Selector[AsyncData]
-  {.deprecated: [TAsyncFD: AsyncFD, TCallback: Callback].}
-
-  proc `==`*(x, y: AsyncFD): bool {.borrow.}
-  proc `==`*(x, y: AsyncEvent): bool {.borrow.}
-
-  template newAsyncData(): AsyncData =
-    AsyncData(
-      readList: newSeqOfCap[Callback](InitCallbackListSize),
-      writeList: newSeqOfCap[Callback](InitCallbackListSize)
-    )
-
-  proc newDispatcher*(): PDispatcher =
-    new result
-    result.selector = newSelector[AsyncData]()
-    result.timers.newHeapQueue()
-    result.callbacks = initDeque[proc ()](InitDelayedCallbackListSize)
-
-  var gDisp{.threadvar.}: PDispatcher ## Global dispatcher
-
-  proc setGlobalDispatcher*(disp: PDispatcher) =
-    if not gDisp.isNil:
-      assert gDisp.callbacks.len == 0
-    gDisp = disp
-    initCallSoonProc()
-
-  proc getGlobalDispatcher*(): PDispatcher =
-    if gDisp.isNil:
-      setGlobalDispatcher(newDispatcher())
-    result = gDisp
-
-  proc register*(fd: AsyncFD) =
-    let p = getGlobalDispatcher()
-    var data = newAsyncData()
-    p.selector.registerHandle(fd.SocketHandle, {}, data)
-
-  proc closeSocket*(sock: AsyncFD) =
-    let disp = getGlobalDispatcher()
-    disp.selector.unregister(sock.SocketHandle)
-    sock.SocketHandle.close()
-
-  proc unregister*(fd: AsyncFD) =
-    getGlobalDispatcher().selector.unregister(fd.SocketHandle)
-
-  proc unregister*(ev: AsyncEvent) =
-    getGlobalDispatcher().selector.unregister(SelectEvent(ev))
-
-  proc addRead*(fd: AsyncFD, cb: Callback) =
-    let p = getGlobalDispatcher()
-    var newEvents = {Event.Read}
-    withData(p.selector, fd.SocketHandle, adata) do:
-      adata.readList.add(cb)
-      newEvents.incl(Event.Read)
-      if len(adata.writeList) != 0: newEvents.incl(Event.Write)
-    do:
-      raise newException(ValueError, "File descriptor not registered.")
-    p.selector.updateHandle(fd.SocketHandle, newEvents)
-
-  proc addWrite*(fd: AsyncFD, cb: Callback) =
-    let p = getGlobalDispatcher()
-    var newEvents = {Event.Write}
-    withData(p.selector, fd.SocketHandle, adata) do:
-      adata.writeList.add(cb)
-      newEvents.incl(Event.Write)
-      if len(adata.readList) != 0: newEvents.incl(Event.Read)
-    do:
-      raise newException(ValueError, "File descriptor not registered.")
-    p.selector.updateHandle(fd.SocketHandle, newEvents)
-
-  proc hasPendingOperations*(): bool =
-    let p = getGlobalDispatcher()
-    not p.selector.isEmpty() or p.timers.len != 0 or p.callbacks.len != 0
-
-  template processBasicCallbacks(ident, rwlist: untyped) =
-    # Process pending descriptor's and AsyncEvent callbacks.
-    # Invoke every callback stored in `rwlist`, until first one
-    # returned `false`, which means callback wants to stay
-    # alive. In such case all remaining callbacks will be added
-    # to `rwlist` again, in the order they have been inserted.
-    #
-    # `rwlist` associated with file descriptor MUST BE emptied before
-    # dispatching callback (See https://github.com/nim-lang/Nim/issues/5128),
-    # or it can be possible to fall into endless cycle.
-    var curList: seq[Callback]
-
-    withData(p.selector, ident, adata) do:
-      shallowCopy(curList, adata.rwlist)
-      adata.rwlist = newSeqOfCap[Callback](InitCallbackListSize)
-
-    let newLength = max(len(curList), InitCallbackListSize)
-    var newList = newSeqOfCap[Callback](newLength)
-
-    for cb in curList:
-      if len(newList) > 0:
-        newList.add(cb)
-      else:
-        if not cb(fd.AsyncFD):
-          newList.add(cb)
-
-    withData(p.selector, ident, adata) do:
-      # descriptor still present in queue.
-      adata.rwlist = newList & adata.rwlist
-      rLength = len(adata.readList)
-      wLength = len(adata.writeList)
-    do:
-      # descriptor was unregistered in callback via `unregister()`.
-      rLength = -1
-      wLength = -1
-
-  template processCustomCallbacks(ident: untyped) =
-    # Process pending custom event callbacks. Custom events are
-    # {Event.Timer, Event.Signal, Event.Process, Event.Vnode}.
-    # There can be only one callback registered with one descriptor,
-    # so there no need to iterate over list.
-    var curList: seq[Callback]
-
-    withData(p.selector, ident, adata) do:
-      shallowCopy(curList, adata.readList)
-      adata.readList = newSeqOfCap[Callback](InitCallbackListSize)
-
-    let newLength = len(curList)
-    var newList = newSeqOfCap[Callback](newLength)
-
-    var cb = curList[0]
-    if not cb(fd.AsyncFD):
-      newList.add(cb)
-
-    withData(p.selector, ident, adata) do:
-      # descriptor still present in queue.
-      adata.readList = newList & adata.readList
-      if len(adata.readList) == 0:
-        # if no callbacks registered with descriptor, unregister it.
-        p.selector.unregister(fd)
-    do:
-      # descriptor was unregistered in callback via `unregister()`.
-      discard
-
-  proc poll*(timeout = 500) =
-    var keys: array[64, ReadyKey]
-
-    let p = getGlobalDispatcher()
-    when ioselSupportedPlatform:
-      let customSet = {Event.Timer, Event.Signal, Event.Process,
-                       Event.Vnode}
-
-    if p.selector.isEmpty() and p.timers.len == 0 and p.callbacks.len == 0:
-      raise newException(ValueError,
-        "No handles or timers registered in dispatcher.")
-
-    if not p.selector.isEmpty():
-      var count = p.selector.selectInto(p.adjustedTimeout(timeout), keys)
-      var i = 0
-      while i < count:
-        var custom = false
-        let fd = keys[i].fd
-        let events = keys[i].events
-        var rLength = 0 # len(data.readList) after callback
-        var wLength = 0 # len(data.writeList) after callback
-
-        if Event.Read in events or events == {Event.Error}:
-          processBasicCallbacks(fd, readList)
-
-        if Event.Write in events or events == {Event.Error}:
-          processBasicCallbacks(fd, writeList)
-
-        if Event.User in events or events == {Event.Error}:
-          processBasicCallbacks(fd, readList)
-          custom = true
-          if rLength == 0:
-            p.selector.unregister(fd)
-
-        when ioselSupportedPlatform:
-          if (customSet * events) != {}:
-            custom = true
-            processCustomCallbacks(fd)
-
-        # because state `data` can be modified in callback we need to update
-        # descriptor events with currently registered callbacks.
-        if not custom:
-          var newEvents: set[Event] = {}
-          if rLength != -1 and wLength != -1:
-            if rLength > 0: incl(newEvents, Event.Read)
-            if wLength > 0: incl(newEvents, Event.Write)
-            p.selector.updateHandle(SocketHandle(fd), newEvents)
-        inc(i)
-
-    # Timer processing.
-    processTimers(p)
-    # Callback queue processing
-    processPendingCallbacks(p)
-
-  proc recv*(socket: AsyncFD, size: int,
-             flags = {SocketFlag.SafeDisconn}): Future[string] =
-    var retFuture = newFuture[string]("recv")
-
-    var readBuffer = newString(size)
-
-    proc cb(sock: AsyncFD): bool =
-      result = true
-      let res = recv(sock.SocketHandle, addr readBuffer[0], size.cint,
-                     flags.toOSFlags())
-      if res < 0:
-        let lastError = osLastError()
-        if lastError.int32 notin {EINTR, EWOULDBLOCK, EAGAIN}:
-          if flags.isDisconnectionError(lastError):
-            retFuture.complete("")
-          else:
-            retFuture.fail(newException(OSError, osErrorMsg(lastError)))
-        else:
-          result = false # We still want this callback to be called.
-      elif res == 0:
-        # Disconnected
-        retFuture.complete("")
-      else:
-        readBuffer.setLen(res)
-        retFuture.complete(readBuffer)
-    # TODO: The following causes a massive slowdown.
-    #if not cb(socket):
-    addRead(socket, cb)
-    return retFuture
-
-  proc recvInto*(socket: AsyncFD, buf: pointer, size: int,
-                 flags = {SocketFlag.SafeDisconn}): Future[int] =
-    var retFuture = newFuture[int]("recvInto")
-
-    proc cb(sock: AsyncFD): bool =
-      result = true
-      let res = recv(sock.SocketHandle, buf, size.cint,
-                     flags.toOSFlags())
-      if res < 0:
-        let lastError = osLastError()
-        if lastError.int32 notin {EINTR, EWOULDBLOCK, EAGAIN}:
-          if flags.isDisconnectionError(lastError):
-            retFuture.complete(0)
-          else:
-            retFuture.fail(newException(OSError, osErrorMsg(lastError)))
-        else:
-          result = false # We still want this callback to be called.
-      else:
-        retFuture.complete(res)
-    # TODO: The following causes a massive slowdown.
-    #if not cb(socket):
-    addRead(socket, cb)
-    return retFuture
-
-  proc send*(socket: AsyncFD, buf: pointer, size: int,
-             flags = {SocketFlag.SafeDisconn}): Future[void] =
-    var retFuture = newFuture[void]("send")
-
-    var written = 0
-
-    proc cb(sock: AsyncFD): bool =
-      result = true
-      let netSize = size-written
-      var d = cast[cstring](buf)
-      let res = send(sock.SocketHandle, addr d[written], netSize.cint,
-                     MSG_NOSIGNAL)
-      if res < 0:
-        let lastError = osLastError()
-        if lastError.int32 notin {EINTR, EWOULDBLOCK, EAGAIN}:
-          if flags.isDisconnectionError(lastError):
-            retFuture.complete()
-          else:
-            retFuture.fail(newException(OSError, osErrorMsg(lastError)))
-        else:
-          result = false # We still want this callback to be called.
-      else:
-        written.inc(res)
-        if res != netSize:
-          result = false # We still have data to send.
-        else:
-          retFuture.complete()
-    # TODO: The following causes crashes.
-    #if not cb(socket):
-    addWrite(socket, cb)
-    return retFuture
-
-  proc send*(socket: AsyncFD, data: string,
-             flags = {SocketFlag.SafeDisconn}): Future[void] =
-    var retFuture = newFuture[void]("send")
-
-    var written = 0
-
-    proc cb(sock: AsyncFD): bool =
-      result = true
-      let netSize = data.len-written
-      var d = data.cstring
-      let res = send(sock.SocketHandle, addr d[written], netSize.cint,
-                     MSG_NOSIGNAL)
-      if res < 0:
-        let lastError = osLastError()
-        if lastError.int32 notin {EINTR, EWOULDBLOCK, EAGAIN}:
-          if flags.isDisconnectionError(lastError):
-            retFuture.complete()
-          else:
-            retFuture.fail(newException(OSError, osErrorMsg(lastError)))
-        else:
-          result = false # We still want this callback to be called.
-      else:
-        written.inc(res)
-        if res != netSize:
-          result = false # We still have data to send.
-        else:
-          retFuture.complete()
-    # TODO: The following causes crashes.
-    #if not cb(socket):
-    addWrite(socket, cb)
-    return retFuture
-
-  proc sendTo*(socket: AsyncFD, data: pointer, size: int, saddr: ptr SockAddr,
-               saddrLen: SockLen,
-               flags = {SocketFlag.SafeDisconn}): Future[void] =
-    ## Sends ``data`` of size ``size`` in bytes to specified destination
-    ## (``saddr`` of size ``saddrLen`` in bytes, using socket ``socket``.
-    ## The returned future will complete once all data has been sent.
-    var retFuture = newFuture[void]("sendTo")
-
-    # we will preserve address in our stack
-    var staddr: array[128, char] # SOCKADDR_STORAGE size is 128 bytes
-    var stalen = saddrLen
-    zeroMem(addr(staddr[0]), 128)
-    copyMem(addr(staddr[0]), saddr, saddrLen)
-
-    proc cb(sock: AsyncFD): bool =
-      result = true
-      let res = sendto(sock.SocketHandle, data, size, MSG_NOSIGNAL,
-                       cast[ptr SockAddr](addr(staddr[0])), stalen)
-      if res < 0:
-        let lastError = osLastError()
-        if lastError.int32 notin {EINTR, EWOULDBLOCK, EAGAIN}:
-          retFuture.fail(newException(OSError, osErrorMsg(lastError)))
-        else:
-          result = false # We still want this callback to be called.
-      else:
-        retFuture.complete()
-
-    addWrite(socket, cb)
-    return retFuture
-
-  proc recvFromInto*(socket: AsyncFD, data: pointer, size: int,
-                     saddr: ptr SockAddr, saddrLen: ptr SockLen,
-                     flags = {SocketFlag.SafeDisconn}): Future[int] =
-    ## Receives a datagram data from ``socket`` into ``data``, which must
-    ## be at least of size ``size`` in bytes, address of datagram's sender
-    ## will be stored into ``saddr`` and ``saddrLen``. Returned future will
-    ## complete once one datagram has been received, and will return size
-    ## of packet received.
-    var retFuture = newFuture[int]("recvFromInto")
-    proc cb(sock: AsyncFD): bool =
-      result = true
-      let res = recvfrom(sock.SocketHandle, data, size.cint, flags.toOSFlags(),
-                         saddr, saddrLen)
-      if res < 0:
-        let lastError = osLastError()
-        if lastError.int32 notin {EINTR, EWOULDBLOCK, EAGAIN}:
-          retFuture.fail(newException(OSError, osErrorMsg(lastError)))
-        else:
-          result = false
-      else:
-        retFuture.complete(res)
-    addRead(socket, cb)
-    return retFuture
-
-  proc acceptAddr*(socket: AsyncFD, flags = {SocketFlag.SafeDisconn}):
-      Future[tuple[address: string, client: AsyncFD]] =
-    var retFuture = newFuture[tuple[address: string,
-        client: AsyncFD]]("acceptAddr")
-    proc cb(sock: AsyncFD): bool =
-      result = true
-      var sockAddress: Sockaddr_storage
-      var addrLen = sizeof(sockAddress).Socklen
-      var client = accept(sock.SocketHandle,
-                          cast[ptr SockAddr](addr(sockAddress)), addr(addrLen))
-      if client == osInvalidSocket:
-        let lastError = osLastError()
-        assert lastError.int32 notin {EWOULDBLOCK, EAGAIN}
-        if lastError.int32 == EINTR:
-          return false
-        else:
-          if flags.isDisconnectionError(lastError):
-            return false
-          else:
-            retFuture.fail(newException(OSError, osErrorMsg(lastError)))
-      else:
-        try:
-          let address = getAddrString(cast[ptr SockAddr](addr sockAddress))
-          register(client.AsyncFD)
-          retFuture.complete((address, client.AsyncFD))
-        except:
-          # getAddrString may raise
-          client.close()
-          retFuture.fail(getCurrentException())
-    addRead(socket, cb)
-    return retFuture
-
-  when ioselSupportedPlatform:
-
-    proc addTimer*(timeout: int, oneshot: bool, cb: Callback) =
-      ## Start watching for timeout expiration, and then call the
-      ## callback ``cb``.
-      ## ``timeout`` - time in milliseconds,
-      ## ``oneshot`` - if ``true`` only one event will be dispatched,
-      ## if ``false`` continuous events every ``timeout`` milliseconds.
-      let p = getGlobalDispatcher()
-      var data = newAsyncData()
-      data.readList.add(cb)
-      p.selector.registerTimer(timeout, oneshot, data)
-
-    proc addSignal*(signal: int, cb: Callback) =
-      ## Start watching signal ``signal``, and when signal appears, call the
-      ## callback ``cb``.
-      let p = getGlobalDispatcher()
-      var data = newAsyncData()
-      data.readList.add(cb)
-      p.selector.registerSignal(signal, data)
-
-    proc addProcess*(pid: int, cb: Callback) =
-      ## Start watching for process exit with pid ``pid``, and then call
-      ## the callback ``cb``.
-      let p = getGlobalDispatcher()
-      var data = newAsyncData()
-      data.readList.add(cb)
-      p.selector.registerProcess(pid, data)
-
-  proc newAsyncEvent*(): AsyncEvent =
-    ## Creates new ``AsyncEvent``.
-    result = AsyncEvent(newSelectEvent())
-
-  proc setEvent*(ev: AsyncEvent) =
-    ## Sets new ``AsyncEvent`` to signaled state.
-    setEvent(SelectEvent(ev))
-
-  proc close*(ev: AsyncEvent) =
-    ## Closes ``AsyncEvent``
-    close(SelectEvent(ev))
-
-  proc addEvent*(ev: AsyncEvent, cb: Callback) =
-    ## Start watching for event ``ev``, and call callback ``cb``, when
-    ## ev will be set to signaled state.
-    let p = getGlobalDispatcher()
-    var data = newAsyncData()
-    data.readList.add(cb)
-    p.selector.registerEvent(SelectEvent(ev), data)
-
-# Common procedures between current and upcoming asyncdispatch
-include includes.asynccommon
-
-proc sleepAsync*(ms: int): Future[void] =
-  ## Suspends the execution of the current async procedure for the next
-  ## ``ms`` milliseconds.
-  var retFuture = newFuture[void]("sleepAsync")
-  let p = getGlobalDispatcher()
-  p.timers.push((epochTime() + (ms / 1000), retFuture))
-  return retFuture
-
-proc withTimeout*[T](fut: Future[T], timeout: int): Future[bool] =
-  ## Returns a future which will complete once ``fut`` completes or after
-  ## ``timeout`` milliseconds has elapsed.
-  ##
-  ## If ``fut`` completes first the returned future will hold true,
-  ## otherwise, if ``timeout`` milliseconds has elapsed first, the returned
-  ## future will hold false.
-
-  var retFuture = newFuture[bool]("asyncdispatch.`withTimeout`")
-  var timeoutFuture = sleepAsync(timeout)
-  fut.callback =
-    proc () =
-      if not retFuture.finished: retFuture.complete(true)
-  timeoutFuture.callback =
-    proc () =
-      if not retFuture.finished: retFuture.complete(false)
-  return retFuture
-
-proc accept*(socket: AsyncFD,
-    flags = {SocketFlag.SafeDisconn}): Future[AsyncFD] =
-  ## Accepts a new connection. Returns a future containing the client socket
-  ## corresponding to that connection.
-  ## The future will complete when the connection is successfully accepted.
-  var retFut = newFuture[AsyncFD]("accept")
-  var fut = acceptAddr(socket, flags)
-  fut.callback =
-    proc (future: Future[tuple[address: string, client: AsyncFD]]) =
-      assert future.finished
-      if future.failed:
-        retFut.fail(future.error)
-      else:
-        retFut.complete(future.read.client)
-  return retFut
-
-# -- Await Macro
-include asyncmacro
-
-proc readAll*(future: FutureStream[string]): Future[string] {.async.} =
-  ## Returns a future that will complete when all the string data from the
-  ## specified future stream is retrieved.
-  result = ""
-  while true:
-    let (hasValue, value) = await future.read()
-    if hasValue:
-      result.add(value)
-    else:
-      break
-
-proc recvLine*(socket: AsyncFD): Future[string] {.async.} =
-  ## Reads a line of data from ``socket``. Returned future will complete once
-  ## a full line is read or an error occurs.
-  ##
-  ## If a full line is read ``\r\L`` is not
-  ## added to ``line``, however if solely ``\r\L`` is read then ``line``
-  ## will be set to it.
-  ##
-  ## If the socket is disconnected, ``line`` will be set to ``""``.
-  ##
-  ## If the socket is disconnected in the middle of a line (before ``\r\L``
-  ## is read) then line will be set to ``""``.
-  ## The partial line **will be lost**.
-  ##
-  ## **Warning**: This assumes that lines are delimited by ``\r\L``.
-  ##
-  ## **Note**: This procedure is mostly used for testing. You likely want to
-  ## use ``asyncnet.recvLine`` instead.
-
-  template addNLIfEmpty(): typed =
-    if result.len == 0:
-      result.add("\c\L")
-
-  result = ""
-  var c = ""
-  while true:
-    c = await recv(socket, 1)
-    if c.len == 0:
-      return ""
-    if c == "\r":
-      c = await recv(socket, 1)
-      assert c == "\l"
-      addNLIfEmpty()
-      return
-    elif c == "\L":
-      addNLIfEmpty()
-      return
-    add(result, c)
-
-proc callSoon(cbproc: proc ()) =
-  ## Schedule `cbproc` to be called as soon as possible.
-  ## The callback is called when control returns to the event loop.
-  getGlobalDispatcher().callbacks.addLast(cbproc)
-
-proc runForever*() =
-  ## Begins a never ending global dispatcher poll loop.
-  while true:
-    poll()
-
-proc waitFor*[T](fut: Future[T]): T =
-  ## **Blocks** the current thread until the specified future completes.
-  while not fut.finished:
-    poll()
-
-  fut.read