Difference between revisions of "Concurrency demos/Haskell-Javascript concurrency"

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(Note about simpler form of delimit)
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This piece of code is intended for compilation to Javascript via [[Yhc/Javascript|Yhc Javascript Backend]] and loading into a web browser.
  
This piece of code is intended for compilation to Javascript via [[Yhc/Javascript|Yhc Javascript Backend]] and loading into a web browser.
   
−
The program is written in monadic style, but it is based on the [[Continuation|Continuation Monad]].
 +
The program is written based on the [[Continuation|plain CPS notation]].
   
−
When started, the <hask>main</hask> function forks out three pseudo-threads, and exits. Each thread outputs some lines of text and terminates. Each line printed contains absolute timestamp obtined via Javascript function <code>newDate.getTime()</code>. Explicit delays are used to yield control to other threads.
 +
When started, the <hask>main</hask> function forks out three pseudo-threads, and exits. Each thread outputs some lines of text and terminates. Each line printed contains absolute timestamp obtined via Javascript function <code>newDate.getTime()</code>. Explicit delays are used to yield control to other threads. This test also demonstrates the use of message boxes that may be used for Javascript threads to interact with each other.
   
 
==Program==
  
==Program==
 
<haskell>
  
<haskell>
−
-- Test of Control.Monad.Cont in Javascript
 +
-- Test of plain CPS based concurrency in Javascript
   
 
module ContTest where
  
module ContTest where
   
  +
import CPS
 
import UnsafeJS
  
import UnsafeJS
−
import Control.Monad
 +
import Data.JSRef
−
import Control.Monad.Cont
 +
import Control.Concurrent.JSThreads
 
import CDOM.Level2.DomUtils
  
import CDOM.Level2.DomUtils
 
import DOM.Level2.Dom
  
import DOM.Level2.Dom
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import Debug.Profiling
  
import Debug.Profiling
   
  +
putLineTm = putLine0 True
−
-- Output a line of text into browser's window.
  
−
-- tmf: boolean value instructing to output timestamp when True
  
−
-- cls: stylesheet class name
  
−
-- txt: text to output
  
−
-- doc: reference to the owner document
  
−
-- par: parent element where text will be output
  
   
  +
putLine = putLine0 False
−
putLineTm = putLine True
  
   
−
putLine tmf cls txt doc par = do
 +
putLine0 tmf cls txt doc par =
  +
getTimeStamp $ \tm ->
−
tm <- getTimeStamp 0
  
−
t <- mkText doc $ (if tmf then (show tm ++ ": ") else "") ++ txt
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mkText doc ((if tmf then (show tm ++ ": ") else "") ++ txt) $ \t ->
−
d <- mkDiv doc >>= set'className cls
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mkDiv doc (set'className cls) $ \d ->
−
addChild t d
 +
addChild t d $ \_ ->
 
addChild d par
  
addChild d par
   
  +
main = getHTMLDocument $ \doc ->
−
-- Main function. References to the document and document body will be passed
  
  +
documentBody doc $ \body ->
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-- to every thread for simplicity. All output goes into the document's body.
  
  +
putLine "title" "Simple Concurrency Test with Plain CPS" doc body $ \_ ->
−
-- In our example all computations have type Cont Bool x. This makes sense
  
  +
forkThread (step1 doc body) $
−
-- because Javascript event handlers are expected to return a boolean value.
  
  +
forkThread (step3 doc body) $
  +
msgBox $ \mb ->
  +
forkThread (thr1 doc body mb) $
  +
forkThread (thr2 doc body mb) $
  +
True
   
−
main = (`runCont` id) $ do
  
−
doc <- getHTMLDocument
  
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body <- documentBody doc
  
−
putLine False "title" "Simple Concurrency Test with Control.Monad.Cont" doc body
  
   
  +
step1 doc body =
−
-- Fork three pseudo-threads.
  
  +
putLineTm "" "Line 1-5" doc body |>>|
  +
putLineTm "" "Line 1-6" doc body |>>|
  +
getTimeStamp $ \t1 ->
  +
yieldMs 1000 $
  +
getTimeDiff t1 $ \tmm ->
  +
putLineTm "" ("Actual timeout was " ++ show tmm ++ "ms") doc body |>>|
  +
putLineTm "" "Line 1-7" doc body |>>|
  +
putLineTm "" "Line 1-8" doc body |>>|
  +
True
   
−
forkCont $ step0 doc body
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step3 doc body =
−
forkCont $ step1 doc body
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putLineTm "" "Line 3-9" doc body |>>|
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forkCont $ step3 doc body
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putLineTm "" "Line 3-A" doc body |>>|
  +
yieldMs 500 $
−
return True
  
  +
putLineTm "" "Line 3-B" doc body |>>|
  +
putLineTm "" "Line 3-C" doc body |>>|
  +
True
   
−
-- Home-grown continuation delimiter function. Passes remainder of the
 
−
-- whole computation to a given function and forces the whole computation
  
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-- to complete by returning a final value. Something similar to returning
 
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-- a final value in plain CPS instead of invoking the continuation.
  
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-- f: function which the remainder of the program will be passed to.
  
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-- Remainder will not be evaluated.
  
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-- r: final value of the whole computation that the latter will be
 
−
-- terminated with.
  
   
−
delimit f r = Cont $ \c -> runCont (return 0) $ \a -> f (runCont (return a) c) r
  
   
  +
showresp r doc body = case r of
−
-- Derek Elkins suggested much simpler from for this function:
  
  +
Nothing -> putLine "" "Failed" doc body
−
-- http://haskell.org/pipermail/haskell-cafe/2007-November/035144.html
  
−
-- delimit f r = Cont $ \c -> f (c 0) r
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Just m -> putLine "" ("Success") doc body
   
  +
showmsg t m doc body =
−
-- A primitive to fork out a thread. See the Yhc/Javascript Programmers Guide
  
  +
case m of
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-- for the implementation of forkAfter; briefly, it saves the continuation
  
  +
Nothing -> putLine "" (t ++ " " ++ "No message") doc body
−
-- in a global Javascript object, and calls window.setTimeout to execute
  
  +
Just m' -> putLine "" (t ++ " " ++ "Message: " ++ show m') doc body
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-- the saved continuation after the timeout expires. Thus effects like
  
−
-- forking parallel thread and cooperative concurrency may be achieved.
  
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-- As follows from the function source below, it yields execution to whatever
  
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-- given as `x' (which must return a final value of the same type as
 
−
-- the "parent" thread), while the remainder of the parent will be started
  
−
-- after a minimal timeout. The "child" thread is expected to be courteous
  
−
-- to its parent and yield execution shortly.
  
   
  +
thr1 doc body mb =
−
forkCont x = delimit (forkAfter 0) (runCont x id)
  
  +
putLine "" "Thread 1 started" doc body |>>|
  +
putLine "" "Thread 1 waiting" doc body |>>|
  +
recvMsg mb $ \m ->
  +
showmsg "T1:" m doc body |>>|
  +
putLine "" "Thread 1 resumed" doc body |>>|
  +
putLine "" "Thread 1 sending" doc body |>>|
  +
sendMsg mb "123" $ \x ->
  +
showresp x doc body |>>|
  +
putLine "" "Thread 1 finishing" doc body |>>|
  +
True
   
  +
thr2 doc body mb =
−
-- A primitive to yield execution for a given interval (in milliseconds).
  
  +
putLine "" "Thread 2 started" doc body |>>|
−
-- It just sets the timeout desired (0 is OK, but it of course will be longer)
  
  +
putLine "" "Thread 2 sending" doc body |>>|
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-- and terminates the whole computation with final value of True.
  
  +
sendMsg mb "abc" $ \x ->
−  
  +
showresp x doc body |>>|
−
yield n = delimit (forkAfter n) True
  
  +
putLine "" "Thread 2 has sent message" doc body |>>|
−  
  +
putLine "" "Thread 2 waiting" doc body |>>|
−
-- Thread 0. It also features callCC to make sure it is compatible with
  
  +
recvMsg mb $ \m ->
−
-- our home-grown delimiter. Within callCC's nested computation, actual
  
  +
showmsg "T2:" m doc body |>>|
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-- timeout is measured as pair of timestamps before and after yield. Output
  
  +
putLine "" "Thread 2 finishing" doc body |>>|
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-- continues then, and finally the timeput value is passed back to callCC.
  
  +
True
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-- As output shows, line 0-3 is printed after the thread is resumed, so
  
−
-- the delimiter works from any depth.
  
−  
−
step0 doc body = do
  
−
putLineTm "" "Line 0-1" doc body
  
−
tmm <- callCC $ \tdiff -> do
  
−
putLineTm "" "Line 0-2" doc body
  
−
t1 <- getTimeStamp 0
  
−
yield 1000
  
−
t2 <- getTimeStamp t1
  
−
putLineTm "" "Line 0-3" doc body
  
−
tdiff t2
  
−
putLineTm "" "Line 0-4" doc body
  
−
putLineTm "" ("Actual timeout was " ++ show tmm ++ "ms") doc body
  
−
return True
  
−  
−
-- Two other threads are nothing spectacular, only they have different
  
−
-- timeout lengths, so thread 3 will wake up first.
  
−  
−
step1 doc body = do
  
−
putLineTm "" "Line 1-5" doc body
  
−
putLineTm "" "Line 1-6" doc body
  
−
yield 1000
  
−
putLineTm "" "Line 1-7" doc body
  
−
putLineTm "" "Line 1-8" doc body
  
−
return True
  
−  
−
step3 doc body = do
  
−
putLineTm "" "Line 3-9" doc body
  
−
putLineTm "" "Line 3-A" doc body
  
−
yield 500
  
−
putLineTm "" "Line 3-B" doc body
  
−
putLineTm "" "Line 3-C" doc body
  
−
return True
  
 
</haskell>
  
</haskell>
   
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http://darcs.haskell.org/yhc/web/jsdemos/ContTest.html
  
http://darcs.haskell.org/yhc/web/jsdemos/ContTest.html
  +
  +
[[Category:Pages with broken file links]]

Latest revision as of 04:59, 26 April 2021

Introduction

This piece of code is intended for compilation to Javascript via Yhc Javascript Backend and loading into a web browser.

The program is written based on the plain CPS notation.

When started, the main function forks out three pseudo-threads, and exits. Each thread outputs some lines of text and terminates. Each line printed contains absolute timestamp obtined via Javascript function newDate.getTime(). Explicit delays are used to yield control to other threads. This test also demonstrates the use of message boxes that may be used for Javascript threads to interact with each other.

Program

-- Test of plain CPS based concurrency in Javascript

module ContTest where

import CPS
import UnsafeJS
import Data.JSRef
import Control.Concurrent.JSThreads
import CDOM.Level2.DomUtils
import DOM.Level2.Dom
import DOM.Level2.Html2
import DOM.Level2.HTMLElement
import DOM.Level2.HTMLDivElement
import Debug.Profiling

putLineTm = putLine0 True

putLine = putLine0 False

putLine0 tmf cls txt doc par =
  getTimeStamp $ \tm ->
  mkText doc ((if tmf then (show tm ++ ": ") else "") ++ txt) $ \t ->
  mkDiv doc (set'className cls) $ \d ->
  addChild t d $ \_ ->
  addChild d par

main = getHTMLDocument $ \doc ->
       documentBody doc $ \body ->
       putLine "title" "Simple Concurrency Test with Plain CPS" doc body $ \_ ->
       forkThread (step1 doc body) $
       forkThread (step3 doc body) $
       msgBox $ \mb ->
       forkThread (thr1 doc body mb) $
       forkThread (thr2 doc body mb) $
       True


step1 doc body =
  putLineTm "" "Line 1-5" doc body |>>|
  putLineTm "" "Line 1-6" doc body |>>|
  getTimeStamp $ \t1 ->
  yieldMs 1000 $
  getTimeDiff t1 $ \tmm ->
  putLineTm "" ("Actual timeout was " ++ show tmm ++ "ms") doc body |>>|
  putLineTm "" "Line 1-7" doc body |>>|
  putLineTm "" "Line 1-8" doc body |>>|
  True

step3 doc body =
  putLineTm "" "Line 3-9" doc body |>>|
  putLineTm "" "Line 3-A" doc body |>>|
  yieldMs 500 $
  putLineTm "" "Line 3-B" doc body |>>|
  putLineTm "" "Line 3-C" doc body |>>|
  True



showresp r doc body =  case r of
    Nothing -> putLine "" "Failed" doc body
    Just m -> putLine "" ("Success") doc body

showmsg t m doc body =
  case m of
    Nothing -> putLine "" (t ++ " " ++ "No message") doc body
    Just m' -> putLine "" (t ++ " " ++ "Message: " ++ show m') doc body

thr1 doc body mb =
  putLine "" "Thread 1 started" doc body |>>|
  putLine "" "Thread 1 waiting" doc body |>>|
  recvMsg mb $ \m ->
  showmsg "T1:" m doc body |>>|
  putLine "" "Thread 1 resumed" doc body |>>|
  putLine "" "Thread 1 sending" doc body |>>|
  sendMsg mb "123" $ \x ->
  showresp x doc body |>>|
  putLine "" "Thread 1 finishing" doc body |>>|
  True

thr2 doc body mb =
  putLine "" "Thread 2 started" doc body |>>|
  putLine "" "Thread 2 sending" doc body |>>|
  sendMsg mb "abc" $ \x ->
  showresp x doc body |>>|
  putLine "" "Thread 2 has sent message" doc body |>>|
  putLine "" "Thread 2 waiting" doc body |>>|
  recvMsg mb $ \m ->
  showmsg "T2:" m doc body |>>|
  putLine "" "Thread 2 finishing" doc body |>>|
  True

Output

The figure below shows contents of the web browser window after running the test program above. Actual timeout value is of course different in each run of the program.


ContTest.jpg

Fig. 1: Web browser window showing output of the test program

Try it out

The compiled HTML page of this demo program is accessible at:

http://darcs.haskell.org/yhc/web/jsdemos/ContTest.html

Retrieved from "https://wiki.haskell.org/index.php?title=Concurrency_demos/Haskell-Javascript_concurrency&oldid=64378"