Mercurial > sdl-ios-xcode
view include/SDL_config_dreamcast.h @ 3069:caefe2344f65
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 | Tue, 17 Feb 2009 05:39:18 +0000 |
| parents | 99210400e8b9 |
| children | b7a48f533966 |
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/* SDL - Simple DirectMedia Layer Copyright (C) 1997-2009 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_dreamcast_h #define _SDL_config_dreamcast_h #include "SDL_platform.h" /* This is a set of defines to configure the SDL features */ typedef signed char int8_t; typedef unsigned char uint8_t; typedef signed short int16_t; typedef unsigned short uint16_t; typedef signed int int32_t; typedef unsigned int uint32_t; typedef signed long long int64_t; typedef unsigned long long uint64_t; typedef unsigned long uintptr_t; #define SDL_HAS_64BIT_TYPE 1 /* Useful headers */ #define HAVE_SYS_TYPES_H 1 #define HAVE_STDIO_H 1 #define STDC_HEADERS 1 #define HAVE_STRING_H 1 #define HAVE_CTYPE_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_QSORT 1 #define HAVE_ABS 1 #define HAVE_BCOPY 1 #define HAVE_MEMSET 1 #define HAVE_MEMCPY 1 #define HAVE_MEMMOVE 1 #define HAVE_MEMCMP 1 #define HAVE_STRLEN 1 #define HAVE_STRDUP 1 #define HAVE_INDEX 1 #define HAVE_RINDEX 1 #define HAVE_STRCHR 1 #define HAVE_STRRCHR 1 #define HAVE_STRSTR 1 #define HAVE_STRTOL 1 #define HAVE_STRTOD 1 #define HAVE_ATOI 1 #define HAVE_ATOF 1 #define HAVE_STRCMP 1 #define HAVE_STRNCMP 1 #define HAVE_STRICMP 1 #define HAVE_STRCASECMP 1 #define HAVE_SSCANF 1 #define HAVE_SNPRINTF 1 #define HAVE_VSNPRINTF 1 /* Enable various audio drivers */ #define SDL_AUDIO_DRIVER_DC 1 #define SDL_AUDIO_DRIVER_DISK 1 #define SDL_AUDIO_DRIVER_DUMMY 1 /* Enable various cdrom drivers */ #define SDL_CDROM_DC 1 /* Enable various input drivers */ #define SDL_JOYSTICK_DC 1 #define SDL_HAPTIC_DUMMY 1 /* Enable various shared object loading systems */ #define SDL_LOADSO_DUMMY 1 /* Enable various threading systems */ #define SDL_THREAD_DC 1 /* Enable various timer systems */ #define SDL_TIMER_DC 1 /* Enable various video drivers */ #define SDL_VIDEO_DRIVER_DC 1 #define SDL_VIDEO_DRIVER_DUMMY 1 #endif /* _SDL_config_dreamcast_h */