Mercurial > sdl-ios-xcode
view include/SDL_config_nds.h @ 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> |
|---|---|
| date | Fri, 28 Dec 2007 22:05:17 +0000 |
| parents | 8582c6a5ca16 |
| children | a1b03ba2fcd0 |
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/* SDL - Simple DirectMedia Layer Copyright (C) 1997-2006 Sam Lantinga This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA Sam Lantinga slouken@libsdl.org */ #ifndef _SDL_config_nds_h #define _SDL_config_nds_h #include "SDL_platform.h" /* This is a set of defines to configure the SDL features */ /* General platform specific identifiers */ #include "SDL_platform.h" /* C datatypes */ #define SDL_HAS_64BIT_TYPE 1 /* Endianness */ #define SDL_BYTEORDER 1234 /* Useful headers */ #define HAVE_ALLOCA_H 1 #define HAVE_SYS_TYPES_H 1 #define HAVE_STDIO_H 1 #define STDC_HEADERS 1 #define HAVE_STDLIB_H 1 #define HAVE_STDARG_H 1 #define HAVE_MALLOC_H 1 #define HAVE_STRING_H 1 #define HAVE_INTTYPES_H 1 #define HAVE_STDINT_H 1 #define HAVE_CTYPE_H 1 #define HAVE_MATH_H 1 #define HAVE_ICONV_H 1 #define HAVE_SIGNAL_H 1 /* C library functions */ #define HAVE_MALLOC 1 #define HAVE_CALLOC 1 #define HAVE_REALLOC 1 #define HAVE_FREE 1 #define HAVE_ALLOCA 1 #define HAVE_GETENV 1 #define HAVE_PUTENV 1 #define HAVE_UNSETENV 1 #define HAVE_QSORT 1 #define HAVE_ABS 1 #define HAVE_BCOPY 1 #define HAVE_MEMSET 1 #define HAVE_MEMCPY 1 #define HAVE_MEMMOVE 1 #define HAVE_STRLEN 1 #define HAVE_STRLCPY 1 #define HAVE_STRLCAT 1 #define HAVE_STRDUP 1 #define HAVE_STRCHR 1 #define HAVE_STRRCHR 1 #define HAVE_STRSTR 1 #define HAVE_STRTOL 1 #define HAVE_STRTOUL 1 #define HAVE_STRTOLL 1 #define HAVE_STRTOULL 1 #define HAVE_ATOI 1 #define HAVE_ATOF 1 #define HAVE_STRCMP 1 #define HAVE_STRNCMP 1 #define HAVE_STRCASECMP 1 #define HAVE_STRNCASECMP 1 #define HAVE_SSCANF 1 #define HAVE_SNPRINTF 1 #define HAVE_VSNPRINTF 1 #define HAVE_SETJMP 1 /* Enable various audio drivers */ #define SDL_AUDIO_DRIVER_NDS 1 #define SDL_AUDIO_DRIVER_DUMMY 1 /* Enable the stub cdrom driver (src/cdrom/dummy/\*.c) */ #define SDL_CDROM_DISABLED 1 /* Enable various input drivers */ #define SDL_JOYSTICK_NDS 1 /* Enable the stub shared object loader (src/loadso/dummy/\*.c) */ #define SDL_LOADSO_DISABLED 1 /* Enable the stub thread support (src/thread/generic/\*.c) */ #define SDL_THREADS_DISABLED 1 /* Enable various timer systems */ #define SDL_TIMER_NDS 1 /* Enable various video drivers */ #define SDL_VIDEO_DRIVER_NDS 1 #define SDL_VIDEO_DRIVER_DUMMY 1 #endif /* _SDL_config_nds_h */