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[GHC] #6061: threadDelay broken on Windows

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[GHC] #6061: threadDelay broken on Windows

#6061: threadDelay broken on Windows
---------------------------------+------------------------------------------
Reporter: simonmar | Owner:
Type: bug | Status: new
Priority: highest | Milestone: 7.6.1
Component: Compiler | Version: 7.4.1
Keywords: | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: None/Unknown
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
---------------------------------+------------------------------------------
There seems to be new breakage in `threadDelay` on Windows. I noticed
`conc070` failing in a validate:

{{{
=====> conc070(ghci) 191 of 3265 [0, 0, 0]

cd ./concurrent/should_run && 'c:/simonmar/ghc-
validate/bindisttest/install dir/bin/ghc.exe' -fforce-recomp -dcore-lint
-dcmm-lint -dno-debug-output -no-user-package-conf -rtsopts -fno-ghci-
history conc070.hs --interactive -v0 -ignore-dot-ghci +RTS -I0.1 -RTS
<conc070.genscript 1>conc070.interp.stdout 2>conc070.interp.stderr

Actual stdout output differs from expected:

--- ./concurrent/should_run/conc070.stdout 2011-08-02 14:43:53 +0100
+++ ./concurrent/should_run/conc070.run.stdout 2012-04-27 10:54:04 +0100
@@ -1 +1 @@
-[ThreadBlocked BlockedOnMVar,ThreadBlocked
BlockedOnMVar,ThreadRunning,ThreadFinished]
+[ThreadFinished,ThreadBlocked BlockedOnMVar,ThreadRunning,ThreadFinished]

*** unexpected failure for conc070(ghci)
}}}

and strangely if you try `threadDelay 1000000` in GHCi it returns
immediately.

This test is also failing:

{{{
=====> ThreadDelay001(threaded1) 7 of 7 [0, 0, 0]
cd . && 'c:/simonmar/ghc-validate/inplace/bin/ghc-stage2.exe' -fforce-
recomp -dcore-lint -dcmm-lint -dno-debug-output -no-user-package-conf
-rtsopts -fno-ghci-history -o ThreadDelay001 ThreadDelay001.hs -threaded
-debug >ThreadDelay001.comp.stderr 2>&1
cd . && ./ThreadDelay001 </dev/null >ThreadDelay001.run.stdout
2>ThreadDelay001.run.stderr
Actual stdout output differs from expected:
--- /dev/null 2012-04-30 11:17:41 +0100
+++ ./ThreadDelay001.run.stdout 2012-04-30 11:17:41 +0100
@@ -0,0 +1,2 @@
+(Mon Apr 30 11:17:29 GMT Daylight Time 2012,Mon Apr 30 11:17:29 GMT
Daylight Time 2012,1000000,0,-1000000,-1.0e-6)
+(Mon Apr 30 11:17:29 GMT Daylight Time 2012,Mon Apr 30 11:17:29 GMT
Daylight Time 2012,5000000,0,-5000000,-5.0e-6)
*** unexpected failure for ThreadDelay001(threaded1)
}}}

Possibly related to the fix for #5865

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6061>
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Re: [GHC] #6061: threadDelay broken on Windows

#6061: threadDelay broken on Windows
---------------------------------+------------------------------------------
Reporter: simonmar | Owner: pcapriotti
Type: bug | Status: new
Priority: highest | Milestone: 7.6.1
Component: Compiler | Version: 7.4.1
Keywords: | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: None/Unknown
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
---------------------------------+------------------------------------------
Changes (by pcapriotti):

* owner: => pcapriotti

Comment:

I can't reproduce the first two failures.

The `ThreadDelay001` test is failing because `threadDelay` sometimes
sleeps for slightly less time than requested. I'm looking into that.

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6061#comment:1>
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Re: [GHC] #6061: threadDelay broken on Windows

In reply to this post by GHC

#6061: threadDelay broken on Windows
---------------------------------+------------------------------------------
Reporter: simonmar | Owner: pcapriotti
Type: bug | Status: new
Priority: highest | Milestone: 7.6.1
Component: Compiler | Version: 7.4.1
Keywords: | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: None/Unknown
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
---------------------------------+------------------------------------------

Comment(by pcapriotti):

I think this is due to clock skew among different CPUs when using QPC. The
skew itself shouldn't be very large (up to 5 μs on my system), so it's not
a concern for the purpose of `threadDelay`, but it does break the
invariant that the actual delay time is greater or equal to the requested
time. Maybe we could just change the test and add a few μs tolerance.

I'm not sure why you saw `threadDelay 1000000` return immediately. I
haven't been able to reproduce that here. Maybe the clock skew can got
over 1 second somehow? That would mean we can't really rely on
`QueryPerformanceCounter`.

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6061#comment:2>
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Re: [GHC] #6061: threadDelay broken on Windows

In reply to this post by GHC

#6061: threadDelay broken on Windows
---------------------------------+------------------------------------------
Reporter: simonmar | Owner: pcapriotti
Type: bug | Status: patch
Priority: highest | Milestone: 7.6.1
Component: Compiler | Version: 7.4.1
Keywords: | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: None/Unknown
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
---------------------------------+------------------------------------------
Changes (by pcapriotti):

* status: new => patch

Comment:

I realized that we can actually work around the clock skew issue by
calculating the delay target directly in the IO manager thread, assuming
it always wakes up promptly enough to make the difference in timing
negligible.

The attached patch fixes the `ThreadDelay001` test for me.

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6061#comment:3>
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Re: [GHC] #6061: threadDelay broken on Windows

In reply to this post by GHC

#6061: threadDelay broken on Windows
---------------------------------+------------------------------------------
Reporter: simonmar | Owner: pcapriotti
Type: bug | Status: patch
Priority: highest | Milestone: 7.6.1
Component: Compiler | Version: 7.4.1
Keywords: | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: None/Unknown
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
---------------------------------+------------------------------------------

Comment(by pcapriotti):

As discussed with Simon, I moved `getMonotonicUSec` to the RTS (actually,
I made it into `getMonotonicNSec` to avoid an intermediate conversion).

For the moment, it's used only on Windows, but it could possibly be used
by the other platforms as well, to avoid duplication. That can be done
separately, in any case.

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6061#comment:4>
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Re: [GHC] #6061: threadDelay broken on Windows

In reply to this post by GHC

GHC

Re: [GHC] #6061: threadDelay broken on Windows

In reply to this post by GHC

#6061: threadDelay broken on Windows
---------------------------------+------------------------------------------
Reporter: simonmar | Owner: pcapriotti
Type: bug | Status: patch
Priority: highest | Milestone: 7.6.1
Component: Compiler | Version: 7.4.1
Keywords: | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: None/Unknown
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
---------------------------------+------------------------------------------

Comment(by simonmar):

BTW - I suggest not calculating the delay target on the IO manager thread,
because that could introduce an arbitrary extra delay if the IO manager is
not scheduled quickly. Instead we should allow some tolerance (maybe only
on Windows) for `ThreadDelay001`.

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6061#comment:6>
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Re: [GHC] #6061: threadDelay broken on Windows

In reply to this post by GHC

#6061: threadDelay broken on Windows
-------------------------------+--------------------------------------------
Reporter: simonmar | Owner: pcapriotti
Type: bug | Status: closed
Priority: highest | Milestone: 7.6.1
Component: Compiler | Version: 7.4.1
Resolution: fixed | Keywords:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
Failure: None/Unknown | Difficulty: Unknown
Testcase: | Blockedby:
Blocking: | Related:
-------------------------------+--------------------------------------------
Changes (by pcapriotti):

* status: patch => closed
* resolution: => fixed

Comment:

Pushed to GHC:

{{{
commit c04619769d5a09325d9e7f28b1382f52df6051b4
Author: Paolo Capriotti <[hidden email]>
Date: Tue May 8 13:05:14 2012 +0100

Move getMonotonicUSec from base to the RTS.
}}}

and base:

{{{
commit 29ef12e8b6b4fa38d1c70588e902e205b82e9d52
Author: Paolo Capriotti <[hidden email]>
Date: Tue May 8 13:06:12 2012 +0100

Use RTS version of getMonotonicNSec on Windows (#6061)
}}}

--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6061#comment:7>
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