Mercurial > sdl-ios-xcode
view README.NanoX @ 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 | 26dafefeebb2 |
children |
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================================================================= Patch version 0.9 of SDL(Simple DirectMedia Layer) for Nano-X API ================================================================= Authors: Hsieh-Fu Tsai, clare@setabox.com Greg Haerr, greg@censoft.com This patch is against SDL version 1.2.4. It enhances previous patch 0.8 by providing direct framebuffer access as well as dynamic hardware pixel type support, not requiring a compile-time option setting for different framebuffer modes. Tested against Microwindows version 0.89pre9. Older Microwindows versions =========================== If running on a version older than Microwindows 0.89pre9, the following items might need to be patched in Microwindows. 1. Patch src/nanox/client.c::GrClose() It fixes the client side GrClose(). In the original version, GrOpen() can only be called once. When the GrOpen() is called at the second time, the program will terminate. In order to prevent this situation, we need to insert "nxSocket = -1" after "close(nxSocket)" in GrClose(). If you do not have this problem, you may skip this step. 2. Patch src/nanox/clientfb.c to return absolute x,y coordinates when using GrGetWindowFBInfo(). Copy the version 0.89pre9 of src/nanox/clientfb.c to your system, or configure using --disable-nanox-direct-fb. ============= Quick Install ============= 1. ./configure --disable-video-x11 --disable-video-fbcon \ --enable-video-nanox \ --with-nanox-pixel-type=[rgb/0888/888/565/555/332/pal] 2. make clean 3. make 4. make install (as root) ============ Nitty-gritty ============ --enable-nanox-direct-fb Use direct framebuffer access --enable-nanox-debug Show debug messages --enable-nanox-share-memory Use shared-memory to speed up When running multi-threaded applications using SDL, such as SMPEG, set THREADSAFE=Y in Microwindows' config file, to enable GrXXX() system call critical section support. ============================================= Some programs can be used to test this patch. ============================================= 1. http://www.cs.berkeley.edu/~weimer/atris (a tetris-like game) 2. http://www.libsdl.org/projects/newvox/ 3. http://www.libsdl.org/projects/xflame/ 4. http://www.libsdl.org/projects/optimum/ 5. http://www.gnugeneration.com/software/loop/ 6: http://www.lokigames.com/development/smpeg.php3 (SMPEG version 0.4.4) ========= Todo List ========= 1. Create hardware surface 2. Create YUVOverlay on hardware 3. Use OpenGL 4. Gamma correction 5. Hide/Change mouse pointer 6. Better window movement control with direct fb access 7. Palette handling in 8bpp could be improved ===================== Supporting Institutes ===================== Many thanks to go to Setabox Co., Ltd. and CML (Communication and Multimedia Laboratory, http://www.cmlab.csie.ntu.edu.tw/) in the Department of Computer Science and Information Engineering of National Taiwan University for supporting this porting project. Century Embedded Technologies (http://embedded.censoft.com) for this patch. =================== Contact Information =================== Welcome to give me any suggestion and to report bugs. My e-mail address : clare@setabox.com or niky@cmlab.csie.ntu.edu.tw or greg@censoft.com