mu - Soul of a tiny new machine. More thorough tests → More comprehensible and rewrite-friendly software → More resilient society.

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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>~/Desktop/s/mu/061channel.mu.html</title> <meta name="Generator" content="Vim/7.4"> <meta name="plugin-version" content="vim7.4_v1"> <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 using channels rather than locks, like Erlang and Go. # # The two ends of a channel will usually belong to different routines, but # each end should only be used by a single one. Don't try to read from or # write to it from multiple routines at once. # # The key property of channels is that 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. scenario channel [ run [ 1:address:channel <- init-channel 3:literal/capacity 1:address:channel <- write 1:address:channel, 34:literal 2:integer, 1:address:channel <- read 1:address:channel ] memory-should-contain [ 2 <- 34 ] ] container channel [ # To avoid locking, writer and reader will never write to the same location. # So channels will include fields in pairs, one for the writer and one for the # reader. first-full:integer # for write first-free:integer # 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:location ] # result:address:channel <- init-channel capacity:integer recipe init-channel [ default-space:address:array:location <- new location:type, 30:literal # result = new channel result:address:channel <- new channel:type # result.first-full = 0 full:address:integer <- get-address result:address:channel/deref, first-full:offset full:address:integer/deref <- copy 0:literal # result.first-free = 0 free:address:integer <- get-address result:address:channel/deref, first-free:offset free:address:integer/deref <- copy 0:literal # result.data = new location[ingredient+1] capacity:integer <- next-ingredient capacity:integer <- add capacity:integer, 1:literal # unused slot for 'full?' below dest:address:address:array:location <- get-address result:address:channel/deref, data:offset dest:address:address:array:location/deref <- new location:type, capacity:integer reply result:address:channel ] # chan:address:channel <- write chan:address:channel, val:location recipe write [ default-space:address:array:location <- new location:type, 30:literal chan:address:channel <- next-ingredient val:location <- next-ingredient { # block if chan is full full:boolean <- channel-full? chan:address:channel break-unless full:boolean full-address:address:integer <- get-address chan:address:channel/deref, first-full:offset wait-for-location full-address:address:integer/deref } # store val circular-buffer:address:array:location <- get chan:address:channel/deref, data:offset free:address:integer <- get-address chan:address:channel/deref, first-free:offset dest:address:location <- index-address circular-buffer:address:array:location/deref, free:address:integer/deref dest:address:location/deref <- copy val:location # increment free free:address:integer/deref <- add free:address:integer/deref, 1:literal { # wrap free around to 0 if necessary len:integer <- length circular-buffer:address:array:location/deref at-end?:boolean <- greater-or-equal free:address:integer/deref, len:integer break-unless at-end?:boolean free:address:integer/deref <- copy 0:literal } reply chan:address:channel/same-as-ingredient:0 ] # result:location, chan:address:channel <- read chan:address:channel recipe read [ default-space:address:array:location <- new location:type, 30:literal chan:address:channel <- next-ingredient { # block if chan is empty empty:boolean <- channel-empty? chan:address:channel break-unless empty:boolean free-address:address:integer <- get-address chan:address:channel/deref, first-free:offset wait-for-location free-address:address:integer/deref } # read result full:address:integer <- get-address chan:address:channel/deref, first-full:offset circular-buffer:address:array:location <- get chan:address:channel/deref, data:offset result:location <- index circular-buffer:address:array:location/deref, full:address:integer/deref # increment full full:address:integer/deref <- add full:address:integer/deref, 1:literal { # wrap full around to 0 if necessary len:integer <- length circular-buffer:address:array:location/deref at-end?:boolean <- greater-or-equal full:address:integer/deref, len:integer break-unless at-end?:boolean full:address:integer/deref <- copy 0:literal } reply result:location, chan:address:channel/same-as-ingredient:0 ] scenario channel-initialization [ run [ 1:address:channel <- init-channel 3:literal/capacity 2:integer <- get 1:address:channel/deref, first-full:offset 3:integer <- get 1:address:channel/deref, first-free:offset ] memory-should-contain [ 2 <- 0 # first-full 3 <- 0 # first-free ] ] scenario channel-write-increments-free [ run [ 1:address:channel <- init-channel 3:literal/capacity 1:address:channel <- write 1:address:channel, 34:literal 2:integer <- get 1:address:channel/deref, first-full:offset 3:integer <- get 1:address:channel/deref, first-free:offset ] memory-should-contain [ 2 <- 0 # first-full 3 <- 1 # first-free ] ] scenario channel-read-increments-full [ run [ 1:address:channel <- init-channel 3:literal/capacity 1:address:channel <- write 1:address:channel, 34:literal _, 1:address:channel <- read 1:address:channel 2:integer <- get 1:address:channel/deref, first-full:offset 3:integer <- get 1:address:channel/deref, first-free:offset ] memory-should-contain [ 2 <- 1 # first-full 3 <- 1 # first-free ] ] scenario channel-wrap [ run [ # channel with just 1 slot 1:address:channel <- init-channel 1:literal/capacity # write and read a value 1:address:channel <- write 1:address:channel, 34:literal _, 1:address:channel <- read 1:address:channel # first-free will now be 1 2:integer <- get 1:address:channel/deref, first-free:offset 3:integer <- get 1:address:channel/deref, first-free:offset # write second value, verify that first-free wraps 1:address:channel <- write 1:address:channel, 34:literal 4:integer <- get 1:address:channel/deref, first-free:offset # read second value, verify that first-full wraps _, 1:address:channel <- read 1:address:channel 5:integer <- get 1:address:channel/deref, first-full:offset ] memory-should-contain [ 2 <- 1 # first-free after first write 3 <- 1 # first-full after first read 4 <- 0 # first-free after second write, wrapped 5 <- 0 # first-full after second read, wrapped ] ] ## helpers # An empty channel has first-empty and first-full both at the same value. recipe channel-empty? [ default-space:address:array:location <- new location:type, 30:literal chan:address:channel <- next-ingredient # return chan.first-full == chan.first-free full:integer <- get chan:address:channel/deref, first-full:offset free:integer <- get chan:address:channel/deref, first-free:offset result:boolean <- equal full:integer, free:integer reply result:boolean ] # 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> recipe channel-full? [ default-space:address:array:location <- new location:type, 30:literal chan:address:channel <- next-ingredient # tmp = chan.first-free + 1 tmp:integer <- get chan:address:channel/deref, first-free:offset tmp:integer <- add tmp:integer, 1:literal { # if tmp == chan.capacity, tmp = 0 len:integer <- channel-capacity chan:address:channel at-end?:boolean <- greater-or-equal tmp:integer, len:integer break-unless at-end?:boolean tmp:integer <- copy 0:literal } # return chan.first-full == tmp full:integer <- get chan:address:channel/deref, first-full:offset result:boolean <- equal full:integer, tmp:integer reply result:boolean ] # result:integer <- channel-capacity chan:address:channel recipe channel-capacity [ default-space:address:array:location <- new location:type, 30:literal chan:address:channel <- next-ingredient q:address:array:location <- get chan:address:channel/deref, data:offset result:integer <- length q:address:array:location/deref reply result:integer ] scenario channel-new-empty-not-full [ run [ 1:address:channel <- init-channel 3:literal/capacity 2:integer <- channel-empty? 1:address:channel 3:integer <- channel-full? 1:address:channel ] memory-should-contain [ 2 <- 1 # empty? 3 <- 0 # full? ] ] scenario channel-write-not-empty [ run [ 1:address:channel <- init-channel 3:literal/capacity 1:address:channel <- write 1:address:channel, 34:literal 2:integer <- channel-empty? 1:address:channel 3:integer <- channel-full? 1:address:channel ] memory-should-contain [ 2 <- 0 # empty? 3 <- 0 # full? ] ] scenario channel-write-full [ run [ 1:address:channel <- init-channel 1:literal/capacity 1:address:channel <- write 1:address:channel, 34:literal 2:integer <- channel-empty? 1:address:channel 3:integer <- channel-full? 1:address:channel ] memory-should-contain [ 2 <- 0 # empty? 3 <- 1 # full? ] ] scenario channel-read-not-full [ run [ 1:address:channel <- init-channel 1:literal/capacity 1:address:channel <- write 1:address:channel, 34:literal _, 1:address:channel <- read 1:address:channel 2:integer <- channel-empty? 1:address:channel 3:integer <- channel-full? 1:address:channel ] memory-should-contain [ 2 <- 1 # empty? 3 <- 0 # full? ] ] </pre> </body> </html>


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