Concurrency demos/Haskell-Javascript concurrency: Difference between revisions

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__TOC__
==Introduction==
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==
<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
Line 20: Line 25:
import Debug.Profiling
import Debug.Profiling


-- Output a line of text into browser's window.
putLineTm = putLine0 True
--  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


putLineTm = putLine True
putLine = putLine0 False


putLine tmf cls txt doc par = do
putLine0 tmf cls txt doc par =
   tm <- getTimeStamp 0
   getTimeStamp $ \tm ->
   t <- mkText doc $ (if tmf then (show tm ++ ": ") else "") ++ txt
   mkText doc ((if tmf then (show tm ++ ": ") else "") ++ txt) $ \t ->
   d <- mkDiv doc >>= set'className cls
   mkDiv doc (set'className cls) $ \d ->
   addChild t d
   addChild t d $ \_ ->
   addChild d par
   addChild d par


-- Main function. References to the cdocument and document body will be passed
main = getHTMLDocument $ \doc ->
-- to every thread for simplicity. All output goes into the document's body.
      documentBody doc $ \body ->
-- In our example all computations have type Cont Bool x. This makes sense
      putLine "title" "Simple Concurrency Test with Plain CPS" doc body $ \_ ->
-- because Javascript event handlers are expected to return a boolean value.
      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


main = (`runCont` id) $ do
step3 doc body =
   doc <- getHTMLDocument
   putLineTm "" "Line 3-9" doc body |>>|
   body <- documentBody doc
  putLineTm "" "Line 3-A" doc body |>>|
   putLine False "title" "Simple Concurrency Test with Control.Monad.Cont" doc body
   yieldMs 500 $
  putLineTm "" "Line 3-B" doc body |>>|
   putLineTm "" "Line 3-C" doc body |>>|
  True


-- Fork three pseudo-threads.


  forkCont $ step0 doc body
  forkCont $ step1 doc body
  forkCont $ step3 doc body
  return True


-- Home-grown continiation delimiter function. Passes remainder of the
showresp r doc body = case r of
-- whole computation to a given function and forces the whole computation
     Nothing -> putLine "" "Failed" doc body
-- to complete by returning a final value. Something similar to returning
    Just m -> putLine "" ("Success") doc body
-- a final value in plain CPS instead of invoking the continuation.
-- f: function which the remainder of the program will be passed to.
--     Remainder will not be evaluated.
-- 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
showmsg t m doc body =
  case m of
    Nothing -> putLine "" (t ++ " " ++ "No message") doc body
    Just m' -> putLine "" (t ++ " " ++ "Message: " ++ show m') doc body


-- A primitive to fork out a thread. See the Yhc/Javascript Programmers Guide
thr1 doc body mb =
-- for the implementation of forkAfter; briefly, it saves the continuation
  putLine "" "Thread 1 started" doc body |>>|
-- in a global Javascript object, and calls window.setTimeout to execute
  putLine "" "Thread 1 waiting" doc body |>>|
-- the saved continuation after the timeout expires. Thus effects like
  recvMsg mb $ \m ->
-- forking parallel thread and cooperative concurrency may be achieved.
  showmsg "T1:" m doc body |>>|
-- As follows from the function source below, it yields execution to whatever
  putLine "" "Thread 1 resumed" doc body |>>|
-- given as `x' (which must return a final value of the same type as
  putLine "" "Thread 1 sending" doc body |>>|
-- the "parent" thread), while the remained of the parent will be started
  sendMsg mb "123" $ \x ->
-- after a minimal timeout. The "child" thread is expected to be courteous
  showresp x doc body |>>|
-- to its parent and yield execution shortly.
  putLine "" "Thread 1 finishing" doc body |>>|
  True


forkCont x = delimit (forkAfter 0) (runCont x id)
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
</haskell>


-- A primitive to yield execution for a given interval (in milliseconds).
==Output==
-- It just sets the timeout desired (0 is OK, but it of course will be longer)
-- and terminates the whole computation with final value of True.


yield n = delimit (forkAfter n) True
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.


-- Thread 0. It also features callCC to make sure it is compatible with
-- our home-grown delimiter. Within callCC's nested computation, actual
-- timeout is measured as pair timestamps before and after yield. Output
-- continues then, and finally the timeput value is passed back to callCC.
-- As output shows, line 0-3 is printed after the thread is resumed, so
-- the delimiter works from any depth.


step0 doc body = do
<center>
  putLineTm "" "Line 0-1" doc body
[[Image:ContTest.jpg]]
  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
<small>'''Fig. 1:''' Web browser window showing output of the test program</small>
-- timeout lengths, so thread 3 will wake up first.
</center>


step1 doc body = do
==Try it out==
  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
The compiled HTML page of this demo program is accessible at:
  putLineTm "" "Line 3-9" doc body
 
  putLineTm "" "Line 3-A" doc body
http://darcs.haskell.org/yhc/web/jsdemos/ContTest.html
  yield 500
 
  putLineTm "" "Line 3-B" doc body
[[Category:Pages with broken file links]]
  putLineTm "" "Line 3-C" doc body
  return True
</haskell>

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.


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"