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Bug 668

Summary: Windows implementation of SDL Semaphores does not use atomic increment/decrement operations
Product: SDL Reporter: John Bartholomew <john.waffles>
Component: threadAssignee: Ryan C. Gordon <icculus>
Status: RESOLVED FIXED QA Contact: Sam Lantinga <slouken>
Severity: major    
Priority: P2    
Version: HG 2.0   
Hardware: x86   
OS: Windows (All)   

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.