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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html> <head> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> <title>Mu - 075channel.mu</title> <meta name="Generator" content="Vim/7.4"> <meta name="plugin-version" content="vim7.4_v2"> <meta name="syntax" content="none"> <meta name="settings" content="use_css,pre_wrap,no_foldcolumn,expand_tabs,prevent_copy="> <meta name="colorscheme" content="minimal"> <style type="text/css">  </style> <script type='text/javascript'>  </script> </head> <body> <pre id='vimCodeElement'> # Mu synchronizes between routines using channels rather than locks, like # Erlang and Go. # # Key properties of channels: # # a) Writing to a full channel or reading from an empty one will put the # current routine in 'waiting' state until the operation can be completed. # # b) Writing to a channel implicitly performs a deep copy. This prevents # addresses from being shared between routines, and therefore eliminates all # possibility of race conditions. scenario channel [ run [ local-scope source:address:source:number, sink:address:sink:number <- new-channel 3/capacity sink <- write sink, 34 10:number/raw, 11:boolean/raw, source <- read source ] memory-should-contain [ 10 <- 34 11 <- 0 # read was successful ] ] container channel:_elem [ lock:boolean # inefficient but simple: serialize all reads as well as writes first-full:number # for write first-free:number # for read # A circular buffer contains values from index first-full up to (but not # including) index first-empty. The reader always modifies it at first-full, # while the writer always modifies it at first-empty. data:address:array:_elem ] # Since channels have two ends, and since it's an error to use either end from # multiple routines, let's distinguish the ends. container source:_elem [ chan:address:channel:_elem ] container sink:_elem [ chan:address:channel:_elem ] def new-channel capacity:number -> in:address:source:_elem, out:address:sink:_elem [ local-scope load-ingredients result:address:channel:_elem <- new {(channel _elem): type} *result <- put *result, first-full:offset, 0 *result <- put *result, first-free:offset, 0 capacity <- add capacity, 1 # unused slot for 'full?' below data:address:array:_elem <- new _elem:type, capacity *result <- put *result, data:offset, data in <- new {(source _elem): type} *in <- put *in, chan:offset, result out <- new {(sink _elem): type} *out <- put *out, chan:offset, result ] def write out:address:sink:_elem, val:_elem -> out:address:sink:_elem [ local-scope load-ingredients assert out, [write to null channel] chan:address:channel:_elem <- get *out, chan:offset <channel-write-initial> # block until lock is acquired AND queue has room lock:location <- get-location *chan, lock:offset #? $print [write], 10/newline { #? $print [trying to acquire lock for writing], 10/newline wait-for-reset-then-set lock #? $print [lock acquired for writing], 10/newline full?:boolean <- channel-full? chan break-unless full? #? $print [but channel is full; relinquishing lock], 10/newline # channel is full; relinquish lock and give a reader the opportunity to # create room on it reset lock current-routine-is-blocked switch # avoid spinlocking loop } current-routine-is-unblocked #? $print [performing write], 10/newline # store a deep copy of val circular-buffer:address:array:_elem <- get *chan, data:offset free:number <- get *chan, first-free:offset val-copy:_elem <- deep-copy val # on this instruction rests all Mu's concurrency-safety *circular-buffer <- put-index *circular-buffer, free, val-copy # mark its slot as filled free <- add free, 1 { # wrap free around to 0 if necessary len:number <- length *circular-buffer at-end?:boolean <- greater-or-equal free, len break-unless at-end? free <- copy 0 } # write back *chan <- put *chan, first-free:offset, free #? $print [relinquishing lock after writing], 10/newline reset lock ] def read in:address:source:_elem -> result:_elem, eof?:boolean, in:address:source:_elem [ local-scope load-ingredients assert in, [read on null channel] eof? <- copy 0/false # default result chan:address:channel:_elem <- get *in, chan:offset # block until lock is acquired AND queue has data lock:location <- get-location *chan, lock:offset #? $print [read], 10/newline { #? $print [trying to acquire lock for reading], 10/newline wait-for-reset-then-set lock #? $print [lock acquired for reading], 10/newline empty?:boolean <- channel-empty? chan break-unless empty? #? $print [but channel is empty; relinquishing lock], 10/newline # channel is empty; relinquish lock and give a writer the opportunity to # add to it reset lock current-routine-is-blocked <channel-read-empty> switch # avoid spinlocking loop } current-routine-is-unblocked # pull result off full:number <- get *chan, first-full:offset circular-buffer:address:array:_elem <- get *chan, data:offset result <- index *circular-buffer, full # clear the slot empty:address:_elem <- new _elem:type *circular-buffer <- put-index *circular-buffer, full, *empty # mark its slot as empty full <- add full, 1 { # wrap full around to 0 if necessary len:number <- length *circular-buffer at-end?:boolean <- greater-or-equal full, len break-unless at-end? full <- copy 0 } # write back *chan <- put *chan, first-full:offset, full #? $print [relinquishing lock after reading], 10/newline reset lock ] def clear in:address:source:_elem -> in:address:source:_elem [ local-scope load-ingredients chan:address:channel:_elem <- get *in, chan:offset { empty?:boolean <- channel-empty? chan break-if empty? _, _, in <- read in } ] scenario channel-initialization [ run [ local-scope source:address:source:number <- new-channel 3/capacity chan:address:channel:number <- get *source, chan:offset 10:number/raw <- get *chan, first-full:offset 11:number/raw <- get *chan, first-free:offset ] memory-should-contain [ 10 <- 0 # first-full 11 <- 0 # first-free ] ] scenario channel-write-increments-free [ run [ local-scope _, sink:address:sink:number <- new-channel 3/capacity sink <- write sink, 34 chan:address:channel:number <- get *sink, chan:offset 10:number/raw <- get *chan, first-full:offset 11:number/raw <- get *chan, first-free:offset ] memory-should-contain [ 10 <- 0 # first-full 11 <- 1 # first-free ] ] scenario channel-read-increments-full [ run [ local-scope source:address:source:number, sink:address:sink:number <- new-channel 3/capacity sink <- write sink, 34 _, _, source <- read source chan:address:channel:number <- get *source, chan:offset 10:number/raw <- get *chan, first-full:offset 11:number/raw <- get *chan, first-free:offset ] memory-should-contain [ 10 <- 1 # first-full 11 <- 1 # first-free ] ] scenario channel-wrap [ run [ local-scope # channel with just 1 slot source:address:source:number, sink:address:sink:number <- new-channel 1/capacity chan:address:channel:number <- get *source, chan:offset # write and read a value sink <- write sink, 34 _, _, source <- read source # first-free will now be 1 10:number/raw <- get *chan, first-free:offset 11:number/raw <- get *chan, first-free:offset # write second value, verify that first-free wraps sink <- write sink, 34 20:number/raw <- get *chan, first-free:offset # read second value, verify that first-full wraps _, _, source <- read source 30:number/raw <- get *chan, first-full:offset ] memory-should-contain [ 10 <- 1 # first-free after first write 11 <- 1 # first-full after first read 20 <- 0 # first-free after second write, wrapped 30 <- 0 # first-full after second read, wrapped ] ] scenario channel-new-empty-not-full [ run [ local-scope source:address:source:number <- new-channel 3/capacity chan:address:channel:number <- get *source, chan:offset 10:boolean/raw <- channel-empty? chan 11:boolean/raw <- channel-full? chan ] memory-should-contain [ 10 <- 1 # empty? 11 <- 0 # full? ] ] scenario channel-write-not-empty [ run [ source:address:source:number, sink:address:sink:number <- new-channel 3/capacity chan:address:channel:number <- get *source, chan:offset sink <- write sink, 34 10:boolean/raw <- channel-empty? chan 11:boolean/raw <- channel-full? chan ] memory-should-contain [ 10 <- 0 # empty? 11 <- 0 # full? ] ] scenario channel-write-full [ run [ local-scope source:address:source:number, sink:address:sink:number <- new-channel 1/capacity chan:address:channel:number <- get *source, chan:offset sink <- write sink, 34 10:boolean/raw <- channel-empty? chan 11:boolean/raw <- channel-full? chan ] memory-should-contain [ 10 <- 0 # empty? 11 <- 1 # full? ] ] scenario channel-read-not-full [ run [ local-scope source:address:source:number, sink:address:sink:number <- new-channel 1/capacity chan:address:channel:number <- get *source, chan:offset sink <- write sink, 34 _, _, source <- read source 10:boolean/raw <- channel-empty? chan 11:boolean/raw <- channel-full? chan ] memory-should-contain [ 10 <- 1 # empty? 11 <- 0 # full? ] ] ## cancelling channels # every channel comes with a boolean signifying if it's been closed # initially this boolean is false container channel:_elem [ closed?:boolean ] # a channel can be closed from either the source or the sink # both routines can modify the 'closed?' bit, but they can only ever set it, so this is a benign race def close x:address:source:_elem -> x:address:source:_elem [ local-scope load-ingredients chan:address:channel:_elem <- get *x, chan:offset *chan <- put *chan, closed?:offset, 1/true ] def close x:address:sink:_elem -> x:address:sink:_elem [ local-scope load-ingredients chan:address:channel:_elem <- get *x, chan:offset *chan <- put *chan, closed?:offset, 1/true ] # once a channel is closed from one side, no further operations are expected from that side # if a channel is closed for reading, # no further writes will be let through # if a channel is closed for writing, # future reads continue until the channel empties, # then the channel is also closed for reading after <channel-write-initial> [ closed?:boolean <- get *chan, closed?:offset return-if closed? ] after <channel-read-empty> [ closed?:boolean <- get *chan, closed?:offset { break-unless closed? empty-result:address:_elem <- new _elem:type current-routine-is-unblocked return *empty-result, 1/true } ] ## helpers # An empty channel has first-empty and first-full both at the same value. def channel-empty? chan:address:channel:_elem -> result:boolean [ local-scope load-ingredients # return chan.first-full == chan.first-free full:number <- get *chan, first-full:offset free:number <- get *chan, first-free:offset result <- equal full, free ] # A full channel has first-empty just before first-full, wasting one slot. # (Other alternatives: <a href="https://en.wikipedia.org/wiki/Circular_buffer#Full_.2F_Empty_Buffer_Distinction)">https://en.wikipedia.org/wiki/Circular_buffer#Full_.2F_Empty_Buffer_Distinction)</a> def channel-full? chan:address:channel:_elem -> result:boolean [ local-scope load-ingredients # tmp = chan.first-free + 1 tmp:number <- get *chan, first-free:offset tmp <- add tmp, 1 { # if tmp == chan.capacity, tmp = 0 len:number <- capacity chan at-end?:boolean <- greater-or-equal tmp, len break-unless at-end? tmp <- copy 0 } # return chan.first-full == tmp full:number <- get *chan, first-full:offset result <- equal full, tmp ] def capacity chan:address:channel:_elem -> result:number [ local-scope load-ingredients q:address:array:_elem <- get *chan, data:offset result <- length *q ] # helper for channels of characters in particular def buffer-lines in:address:source:character, buffered-out:address:sink:character -> buffered-out:address:sink:character, in:address:source:character [ local-scope load-ingredients # repeat forever eof?:boolean <- copy 0/false { line:address:buffer <- new-buffer 30 # read characters from 'in' until newline, copy into line { +next-character c:character, eof?:boolean, in <- read in break-if eof? # drop a character on backspace { # special-case: if it's a backspace backspace?:boolean <- equal c, 8 break-unless backspace? # drop previous character { buffer-length:number <- get *line, length:offset buffer-empty?:boolean <- equal buffer-length, 0 break-if buffer-empty? buffer-length <- subtract buffer-length, 1 *line <- put *line, length:offset, buffer-length } # and don't append this one loop +next-character:label } # append anything else line <- append line, c line-done?:boolean <- equal c, 10/newline break-if line-done? loop } # copy line into 'buffered-out' i:number <- copy 0 line-contents:text <- get *line, data:offset max:number <- get *line, length:offset { done?:boolean <- greater-or-equal i, max break-if done? c:character <- index *line-contents, i buffered-out <- write buffered-out, c i <- add i, 1 loop } { break-unless eof? buffered-out <- close buffered-out return } loop } ] scenario buffer-lines-blocks-until-newline [ run [ local-scope source:address:source:character, sink:address:sink:character <- new-channel 10/capacity _, buffered-stdin:address:sink:character/buffered-stdin <- new-channel 10/capacity buffered-chan:address:channel:character <- get *buffered-stdin, chan:offset empty?:boolean <- channel-empty? buffered-chan assert empty?, [ F buffer-lines-blocks-until-newline: channel should be empty after init] # buffer stdin into buffered-stdin, try to read from buffered-stdin buffer-routine:number <- start-running buffer-lines, source, buffered-stdin wait-for-routine-to-block buffer-routine empty? <- channel-empty? buffered-chan assert empty?:boolean, [ F buffer-lines-blocks-until-newline: channel should be empty after buffer-lines bring-up] # write 'a' sink <- write sink, 97/a restart buffer-routine wait-for-routine-to-block buffer-routine empty? <- channel-empty? buffered-chan assert empty?:boolean, [ F buffer-lines-blocks-until-newline: channel should be empty after writing 'a'] # write 'b' sink <- write sink, 98/b restart buffer-routine wait-for-routine-to-block buffer-routine empty? <- channel-empty? buffered-chan assert empty?:boolean, [ F buffer-lines-blocks-until-newline: channel should be empty after writing 'b'] # write newline sink <- write sink, 10/newline restart buffer-routine wait-for-routine-to-block buffer-routine empty? <- channel-empty? buffered-chan data-emitted?:boolean <- not empty? assert data-emitted?, [ F buffer-lines-blocks-until-newline: channel should contain data after writing newline] trace 1, [test], [reached end] ] trace-should-contain [ test: reached end ] ] </pre> </body> </html>


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