osproc: use clone with CLONE_VM on Linux for faster process spawning

2 files changed, 147 insertions, 73 deletions

diff --git a/lib/posix/linux.nim b/lib/posix/linux.nim
new file mode 100644
index 000000000..1ed1af3b6
--- /dev/null
+++ b/lib/posix/linux.nim
@@ -0,0 +1,25 @@
+import posix
+
+const
+  CSIGNAL* = 0x000000FF
+  CLONE_VM* = 0x00000100
+  CLONE_FS* = 0x00000200
+  CLONE_FILES* = 0x00000400
+  CLONE_SIGHAND* = 0x00000800
+  CLONE_PTRACE* = 0x00002000
+  CLONE_VFORK* = 0x00004000
+  CLONE_PARENT* = 0x00008000
+  CLONE_THREAD* = 0x00010000
+  CLONE_NEWNS* = 0x00020000
+  CLONE_SYSVSEM* = 0x00040000
+  CLONE_SETTLS* = 0x00080000
+  CLONE_PARENT_SETTID* = 0x00100000
+  CLONE_CHILD_CLEARTID* = 0x00200000
+  CLONE_DETACHED* = 0x00400000
+  CLONE_UNTRACED* = 0x00800000
+  CLONE_CHILD_SETTID* = 0x01000000
+  CLONE_STOPPED* = 0x02000000
+
+# fn should be of type proc (a2: pointer): void {.cdecl.}
+proc clone*(fn: pointer; child_stack: pointer; flags: cint;
+            arg: pointer; ptid: ptr TPid; tls: pointer; ctid: ptr TPid): cint {.importc, header: "<sched.h>".}
diff --git a/lib/pure/osproc.nim b/lib/pure/osproc.nim
index c0c7f46d7..40877f638 100644
--- a/lib/pure/osproc.nim
+++ b/lib/pure/osproc.nim
@@ -20,6 +20,11 @@ when defined(windows):
 else:
   import posix
 
+when defined(linux):
+  import linux
+  when not defined(useFork):
+    const useClone = true
+
 type
   TProcess = object of TObject
     when defined(windows):
@@ -590,6 +595,19 @@ elif not defined(useNimRtl):
       copyMem(result[i], addr(x[0]), x.len+1)
       inc(i)
 
+  type TStartProcessData = object
+    sysCommand: cstring
+    sysArgs: cstringArray
+    sysEnv: cstringArray
+    workingDir: cstring
+    pStdin, pStdout, pStderr: array[0..1, cint]
+    optionPoUsePath: bool
+    optionPoParentStreams: bool
+    optionPoStdErrToStdOut: bool
+
+  proc startProcessAuxSpawn(data: TStartProcessData): TPid {.tags: [FExecIO, FReadEnv].}
+  proc startProcessAfterFork(data: ptr TStartProcessData) {.tags: [FExecIO, FReadEnv], cdecl.}
+
   proc startProcess(command: string,
                  workingDir: string = "",
                  args: openArray[string] = [],
@@ -616,88 +634,48 @@ elif not defined(useNimRtl):
       for arg in args.items:
         sysArgsRaw.add arg
 
+    var pid: TPid
+
     var sysArgs = allocCStringArray(sysArgsRaw)
     finally: deallocCStringArray(sysArgs)
 
-    var pid: TPid
-    when defined(posix_spawn) and not defined(useFork):
-      var attr: Tposix_spawnattr
-      var fops: Tposix_spawn_file_actions
-
-      template chck(e: expr) =
-        if e != 0'i32: osError(osLastError())
-
-      chck posix_spawn_file_actions_init(fops)
-      chck posix_spawnattr_init(attr)
-
-      var mask: Tsigset
-      chck sigemptyset(mask)
-      chck posix_spawnattr_setsigmask(attr, mask)
-      chck posix_spawnattr_setpgroup(attr, 0'i32)
-
-      chck posix_spawnattr_setflags(attr, POSIX_SPAWN_USEVFORK or
-                                          POSIX_SPAWN_SETSIGMASK or
-                                          POSIX_SPAWN_SETPGROUP)
-
-      if poParentStreams notin options:
-        chck posix_spawn_file_actions_addclose(fops, pStdin[writeIdx])
-        chck posix_spawn_file_actions_adddup2(fops, pStdin[readIdx], readIdx)
-        chck posix_spawn_file_actions_addclose(fops, pStdout[readIdx])
-        chck posix_spawn_file_actions_adddup2(fops, pStdout[writeIdx], writeIdx)
-        chck posix_spawn_file_actions_addclose(fops, pStderr[readIdx])
-        if poStdErrToStdOut in options:
-          chck posix_spawn_file_actions_adddup2(fops, pStdout[writeIdx], 2)
-        else:
-          chck posix_spawn_file_actions_adddup2(fops, p_stderr[writeIdx], 2)
-
-      var sysEnv = if env == nil: envToCStringArray() else: envToCStringArray(env)
-      var res: cint
-      # FIXME: chdir is global to process
-      if workingDir.len > 0: os.setCurrentDir(workingDir)
-      if poUsePath in options:
-        res = posix_spawnp(pid, sysCommand, fops, attr, sysArgs, sysEnv)
+    var sysEnv = if env == nil:
+        envToCStringArray()
       else:
-        res = posix_spawn(pid, sysCommand, fops, attr, sysArgs, sysEnv)
-      deallocCStringArray(sysEnv)
-      discard posix_spawn_file_actions_destroy(fops)
-      discard posix_spawnattr_destroy(attr)
-      chck res
+        envToCStringArray(env)
+
+    finally: deallocCStringArray(sysEnv)
+
+    var data: TStartProcessData
+    data.sysCommand = sysCommand
+    data.sysArgs = sysArgs
+    data.sysEnv = sysEnv
+    data.pStdin = pStdin
+    data.pStdout = pStdout
+    data.pStderr = pStderr
+    data.optionPoParentStreams = poParentStreams in options
+    data.optionPoUsePath = poUsePath in options
+    data.optionPoStdErrToStdOut = poStdErrToStdOut in options
+    data.workingDir = workingDir
+
+    when defined(useClone):
+      const stackSize = 8096
+      let stackEnd = cast[clong](alloc(stackSize))
+      let stack = cast[pointer](stackEnd + stackSize)
+      let fn: pointer = startProcessAfterFork
+      pid = clone(fn, stack,
+                  cint(CLONE_VM or CLONE_VFORK or SIGCHLD),
+                  pointer(addr data), nil, nil, nil)
 
+      if pid < 0: osError(osLastError())
+    elif defined(posix_spawn) and not defined(useFork):
+      pid = startProcessAuxSpawn(data)
     else:
       pid = fork()
       if pid < 0: osError(osLastError())
       if pid == 0:
-        ## child process:
-
-        if poParentStreams notin options:
-          discard close(p_stdin[writeIdx])
-          if dup2(p_stdin[readIdx], readIdx) < 0: osError(osLastError())
-          discard close(p_stdout[readIdx])
-          if dup2(p_stdout[writeIdx], writeIdx) < 0: osError(osLastError())
-          discard close(p_stderr[readIdx])
-          if poStdErrToStdOut in options:
-            if dup2(p_stdout[writeIdx], 2) < 0: osError(osLastError())
-          else:
-            if dup2(p_stderr[writeIdx], 2) < 0: osError(osLastError())
-
-        # Create a new process group
-        if setpgid(0, 0) == -1: quit("setpgid call failed: " & $strerror(errno))
-
-        if workingDir.len > 0: os.setCurrentDir(workingDir)
-
-        if env == nil:
-          if poUsePath in options:
-            discard execvp(sysCommand, sysArgs)
-          else:
-            discard execv(sysCommand, sysArgs)
-        else:
-          var cEnv = envToCStringArray(env)
-          if poUsePath in options:
-            discard execvpe(sysCommand, sysArgs, cEnv)
-          else:
-            discard execve(sysCommand, sysArgs, cEnv)
-        # too risky to raise an exception here:
-        quit("execve call failed: " & $strerror(errno))
+        startProcessAfterFork(addr(data))
+
     # Parent process. Copy process information.
     if poEchoCmd in options:
       echo(command, " ", join(args, " "))
@@ -723,6 +701,77 @@ elif not defined(useNimRtl):
       discard close(pStdin[readIdx])
       discard close(pStdout[writeIdx])
 
+  proc startProcessAuxSpawn(data: TStartProcessData): TPid =
+    var attr: Tposix_spawnattr
+    var fops: Tposix_spawn_file_actions
+
+    template chck(e: expr) =
+      if e != 0'i32: osError(osLastError())
+
+    chck posix_spawn_file_actions_init(fops)
+    chck posix_spawnattr_init(attr)
+
+    var mask: Tsigset
+    chck sigemptyset(mask)
+    chck posix_spawnattr_setsigmask(attr, mask)
+    chck posix_spawnattr_setpgroup(attr, 0'i32)
+
+    chck posix_spawnattr_setflags(attr, POSIX_SPAWN_USEVFORK or
+                                        POSIX_SPAWN_SETSIGMASK or
+                                        POSIX_SPAWN_SETPGROUP)
+
+    if not data.optionPoParentStreams:
+      chck posix_spawn_file_actions_addclose(fops, data.pStdin[writeIdx])
+      chck posix_spawn_file_actions_adddup2(fops, data.pStdin[readIdx], readIdx)
+      chck posix_spawn_file_actions_addclose(fops, data.pStdout[readIdx])
+      chck posix_spawn_file_actions_adddup2(fops, data.pStdout[writeIdx], writeIdx)
+      chck posix_spawn_file_actions_addclose(fops, data.pStderr[readIdx])
+      if data.optionPoStdErrToStdOut:
+        chck posix_spawn_file_actions_adddup2(fops, data.pStdout[writeIdx], 2)
+      else:
+        chck posix_spawn_file_actions_adddup2(fops, data.pStderr[writeIdx], 2)
+
+    var res: cint
+    # FIXME: chdir is global to process
+    if data.workingDir.len > 0:
+      setCurrentDir($data.workingDir)
+    var pid: TPid
+
+    if data.optionPoUsePath:
+      res = posix_spawnp(pid, data.sysCommand, fops, attr, data.sysArgs, data.sysEnv)
+    else:
+      res = posix_spawn(pid, data.sysCommand, fops, attr, data.sysArgs, data.sysEnv)
+
+    discard posix_spawn_file_actions_destroy(fops)
+    discard posix_spawnattr_destroy(attr)
+    chck res
+    return pid
+
+  proc startProcessAfterFork(data: ptr TStartProcessData) =
+    # Warning: no GC here!
+    if not data.optionPoParentStreams:
+      discard close(data.pStdin[writeIdx])
+      if dup2(data.pStdin[readIdx], readIdx) < 0: osError(osLastError())
+      discard close(data.pStdout[readIdx])
+      if dup2(data.pStdout[writeIdx], writeIdx) < 0: osError(osLastError())
+      discard close(data.pStderr[readIdx])
+      if data.optionPoStdErrToStdOut:
+        if dup2(data.pStdout[writeIdx], 2) < 0: osError(osLastError())
+      else:
+        if dup2(data.pStderr[writeIdx], 2) < 0: osError(osLastError())
+
+    if data.workingDir.len > 0:
+      if chdir(data.workingDir) < 0:
+        quit("chdir failed")
+
+    if data.optionPoUsePath:
+      discard execvpe(data.sysCommand, data.sysArgs, data.sysEnv)
+    else:
+      discard execve(data.sysCommand, data.sysArgs, data.sysEnv)
+
+    # too risky to raise an exception here:
+    quit("execve call failed: " & $strerror(errno))
+
   proc close(p: PProcess) =
     if p.inStream != nil: close(p.inStream)
     if p.outStream != nil: close(p.outStream)