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Bug 668 - Windows implementation of SDL Semaphores does not use atomic increment/decrement operations
Summary: Windows implementation of SDL Semaphores does not use atomic increment/decrem...
Status: RESOLVED FIXED
Alias: None
Product: SDL
Classification: Unclassified
Component: thread (show other bugs)
Version: HG 2.0
Hardware: x86 Windows (All)
: P2 major
Assignee: Ryan C. Gordon
QA Contact: Sam Lantinga
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2009-01-04 10:15 UTC by John Bartholomew
Modified: 2009-02-16 21:39 UTC (History)
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Description John Bartholomew 2009-01-04 10:15:52 UTC 
The Windows semaphore implementation maintains its own count on top of the use of the normal Windows semaphore primitive.  This count is maintained in a non-threadsafe manner, being incremented and decremented with naked ops.
Fix by using InterlockedIncrement and InterlockedDecrement.  Can cause deadlocks (in, e.g., audio code)

NB: Already fixed in the 1.2 branch, just needs to be merged back to HEAD.  Relevant revision is r3470.

For history, see SDL mailing list archives:
http://lists.libsdl.org/pipermail/sdl-libsdl.org/2007-December/thread.html#63669
Thread "[SDL] SDL Semaphore implementation broken on Windows?"
Comment 1 Sam Lantinga 2009-02-16 21:39:52 UTC 
Thanks, this is fixed in revision 4435.