Mercurial > sdl-ios-xcode
annotate BUGS @ 4105:84882a89ca50 SDL-1.2
Date: Thu, 27 Dec 2007 07:38:25 +0000
From: John Bartholomew
Subject: [SDL] SDL Semaphore implementation broken on Windows?
Hi,
Over the past couple of days, I've been battling with SDL, SDL_Mixer and SMPEG to try to find an audio hang bug. I believe I've found the problem, which I think is a race condition inside SDL's semaphore implementation (at least the Windows implementation). The semaphore code uses Windows' built in semaphore functions, but it also maintains a separate count value. This count value is updated with bare increment and decrement operations in SemPost and SemWaitTimeout - no locking primitives to protect them.
In tracking down the apparent audio bug, I found that at some point a semaphore's count value was being decremented to -1, which is clearly not a valid value for it to take.
I'm still not certain exactly what sequence of operations is occuring for this to happen, but I believe that overall it's a race condition between a thread calling SemPost (which increments the count) and the thread on the other end calling SemWait (which decrements it).
I will try to make a test case to verify this, but I'm not sure if I'll be able to (threading errors being difficult to reproduce even in the best circumstances).
However, assuming this is the cause of my problems, there is a very
simple fix:
Windows provides InterlockedIncrement() and InterlockedDecrement()
functions to perform increments and decrements which are guaranteed to be atomic. So the fix is in thread/win32/SDL_syssem.c: replace occurrences of --sem->count with InterlockedDecrement(&sem->count); and replace occurrences of ++sem->count with InterlockedIncrement(&sem->count);
This is using SDL v1.2.12, built with VC++ 2008 Express, running on a
Core 2 duo processor.
author | Sam Lantinga <slouken@libsdl.org> |
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date | Fri, 28 Dec 2007 22:05:17 +0000 |
parents | 89b0f3d12fe2 |
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3915
89b0f3d12fe2
Removed the contents of the BUGS file, as most (all?) of the issues were
Ryan C. Gordon <icculus@icculus.org>
parents:
3888
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2 Bugs are now managed in the SDL bug tracker, here: |
0 | 3 |
3915
89b0f3d12fe2
Removed the contents of the BUGS file, as most (all?) of the issues were
Ryan C. Gordon <icculus@icculus.org>
parents:
3888
diff
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4 http://bugzilla.libsdl.org/ |
0 | 5 |
3915
89b0f3d12fe2
Removed the contents of the BUGS file, as most (all?) of the issues were
Ryan C. Gordon <icculus@icculus.org>
parents:
3888
diff
changeset
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6 You may report bugs there, and search to see if a given issue has already |
89b0f3d12fe2
Removed the contents of the BUGS file, as most (all?) of the issues were
Ryan C. Gordon <icculus@icculus.org>
parents:
3888
diff
changeset
|
7 been reported, discussed, and maybe even fixed. |
0 | 8 |
9 | |
27
a7e598a8d8be
The keyboard modifiers are not set to the correct state on X11 startup.
Sam Lantinga <slouken@lokigames.com>
parents:
21
diff
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10 |
3915
89b0f3d12fe2
Removed the contents of the BUGS file, as most (all?) of the issues were
Ryan C. Gordon <icculus@icculus.org>
parents:
3888
diff
changeset
|
11 You may also find help at the SDL mailing list. Subscription information: |
0 | 12 |
3915
89b0f3d12fe2
Removed the contents of the BUGS file, as most (all?) of the issues were
Ryan C. Gordon <icculus@icculus.org>
parents:
3888
diff
changeset
|
13 http://lists.libsdl.org/listinfo.cgi/sdl-libsdl.org |
250
74a8f672f2f8
Added support for building SDL for EPOC/SymbianOS 6.0 (thanks Hannu!)
Sam Lantinga <slouken@libsdl.org>
parents:
172
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14 |
3915
89b0f3d12fe2
Removed the contents of the BUGS file, as most (all?) of the issues were
Ryan C. Gordon <icculus@icculus.org>
parents:
3888
diff
changeset
|
15 Bug reports are welcome here, but we really appreciate if you use Bugzilla, as |
89b0f3d12fe2
Removed the contents of the BUGS file, as most (all?) of the issues were
Ryan C. Gordon <icculus@icculus.org>
parents:
3888
diff
changeset
|
16 bugs discussed on the mailing list may be forgotten or missed. |
0 | 17 |
27
a7e598a8d8be
The keyboard modifiers are not set to the correct state on X11 startup.
Sam Lantinga <slouken@lokigames.com>
parents:
21
diff
changeset
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18 |