Mercurial > sdl-ios-xcode
view src/SDL.c @ 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 | 972a69e47cd9 |
children | 5db962a9a991 |
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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 */ #include "SDL_config.h" /* Initialization code for SDL */ #include "SDL.h" #include "SDL_fatal.h" #if !SDL_VIDEO_DISABLED #include "video/SDL_leaks.h" #endif #if SDL_THREAD_PTH #include <pth.h> #endif /* Initialization/Cleanup routines */ #if !SDL_JOYSTICK_DISABLED extern int SDL_JoystickInit(void); extern void SDL_JoystickQuit(void); #endif #if !SDL_HAPTIC_DISABLED extern int SDL_HapticInit(void); extern int SDL_HapticQuit(void); #endif #if !SDL_CDROM_DISABLED extern int SDL_CDROMInit(void); extern void SDL_CDROMQuit(void); #endif #if !SDL_TIMERS_DISABLED extern void SDL_StartTicks(void); extern int SDL_TimerInit(void); extern void SDL_TimerQuit(void); #endif #if defined(__WIN32__) extern int SDL_HelperWindowCreate(void); extern int SDL_HelperWindowDestroy(void); #endif /* The initialized subsystems */ static Uint32 SDL_initialized = 0; static Uint32 ticks_started = 0; #ifdef CHECK_LEAKS int surfaces_allocated = 0; #endif int SDL_InitSubSystem(Uint32 flags) { #if !SDL_VIDEO_DISABLED /* Initialize the video/event subsystem */ if ((flags & SDL_INIT_VIDEO) && !(SDL_initialized & SDL_INIT_VIDEO)) { if (SDL_VideoInit(NULL, (flags & SDL_INIT_EVENTTHREAD)) < 0) { return (-1); } SDL_initialized |= SDL_INIT_VIDEO; } #else if (flags & SDL_INIT_VIDEO) { SDL_SetError("SDL not built with video support"); return (-1); } #endif #if !SDL_AUDIO_DISABLED /* Initialize the audio subsystem */ if ((flags & SDL_INIT_AUDIO) && !(SDL_initialized & SDL_INIT_AUDIO)) { if (SDL_AudioInit(NULL) < 0) { return (-1); } SDL_initialized |= SDL_INIT_AUDIO; } #else if (flags & SDL_INIT_AUDIO) { SDL_SetError("SDL not built with audio support"); return (-1); } #endif #if !SDL_TIMERS_DISABLED /* Initialize the timer subsystem */ if (!ticks_started) { SDL_StartTicks(); ticks_started = 1; } if ((flags & SDL_INIT_TIMER) && !(SDL_initialized & SDL_INIT_TIMER)) { if (SDL_TimerInit() < 0) { return (-1); } SDL_initialized |= SDL_INIT_TIMER; } #else if (flags & SDL_INIT_TIMER) { SDL_SetError("SDL not built with timer support"); return (-1); } #endif #if !SDL_JOYSTICK_DISABLED /* Initialize the joystick subsystem */ if ((flags & SDL_INIT_JOYSTICK) && !(SDL_initialized & SDL_INIT_JOYSTICK)) { if (SDL_JoystickInit() < 0) { return (-1); } SDL_initialized |= SDL_INIT_JOYSTICK; } #else if (flags & SDL_INIT_JOYSTICK) { SDL_SetError("SDL not built with joystick support"); return (-1); } #endif #if !SDL_HAPTIC_DISABLED /* Initialize the haptic subsystem */ if ((flags & SDL_INIT_HAPTIC) && !(SDL_initialized & SDL_INIT_HAPTIC)) { if (SDL_HapticInit() < 0) { return (-1); } SDL_initialized |= SDL_INIT_HAPTIC; } #else if (flags & SDL_INIT_HAPTIC) { SDL_SetError("SDL not built with haptic (force feedback) support"); return (-1); } #endif #if !SDL_CDROM_DISABLED /* Initialize the CD-ROM subsystem */ if ((flags & SDL_INIT_CDROM) && !(SDL_initialized & SDL_INIT_CDROM)) { if (SDL_CDROMInit() < 0) { return (-1); } SDL_initialized |= SDL_INIT_CDROM; } #else if (flags & SDL_INIT_CDROM) { SDL_SetError("SDL not built with cdrom support"); return (-1); } #endif return (0); } int SDL_Init(Uint32 flags) { #if !SDL_THREADS_DISABLED && SDL_THREAD_PTH if (!pth_init()) { return -1; } #endif /* Clear the error message */ SDL_ClearError(); #if defined(__WIN32__) if (SDL_HelperWindowCreate() < 0) { return -1; } #endif /* Initialize the desired subsystems */ if (SDL_InitSubSystem(flags) < 0) { return (-1); } /* Everything is initialized */ if (!(flags & SDL_INIT_NOPARACHUTE)) { SDL_InstallParachute(); } return (0); } void SDL_QuitSubSystem(Uint32 flags) { /* Shut down requested initialized subsystems */ #if !SDL_CDROM_DISABLED if ((flags & SDL_initialized & SDL_INIT_CDROM)) { SDL_CDROMQuit(); SDL_initialized &= ~SDL_INIT_CDROM; } #endif #if !SDL_JOYSTICK_DISABLED if ((flags & SDL_initialized & SDL_INIT_JOYSTICK)) { SDL_JoystickQuit(); SDL_initialized &= ~SDL_INIT_JOYSTICK; } #endif #if !SDL_HAPTIC_DISABLED if ((flags & SDL_initialized & SDL_INIT_HAPTIC)) { SDL_HapticQuit(); SDL_initialized &= ~SDL_INIT_HAPTIC; } #endif #if !SDL_TIMERS_DISABLED if ((flags & SDL_initialized & SDL_INIT_TIMER)) { SDL_TimerQuit(); SDL_initialized &= ~SDL_INIT_TIMER; } #endif #if !SDL_AUDIO_DISABLED if ((flags & SDL_initialized & SDL_INIT_AUDIO)) { SDL_AudioQuit(); SDL_initialized &= ~SDL_INIT_AUDIO; } #endif #if !SDL_VIDEO_DISABLED if ((flags & SDL_initialized & SDL_INIT_VIDEO)) { SDL_VideoQuit(); SDL_initialized &= ~SDL_INIT_VIDEO; } #endif } Uint32 SDL_WasInit(Uint32 flags) { if (!flags) { flags = SDL_INIT_EVERYTHING; } return (SDL_initialized & flags); } void SDL_Quit(void) { /* Quit all subsystems */ #ifdef DEBUG_BUILD printf("[SDL_Quit] : Enter! Calling QuitSubSystem()\n"); fflush(stdout); #endif #if defined(__WIN32__) SDL_HelperWindowDestroy(); #endif SDL_QuitSubSystem(SDL_INIT_EVERYTHING); #ifdef CHECK_LEAKS #ifdef DEBUG_BUILD printf("[SDL_Quit] : CHECK_LEAKS\n"); fflush(stdout); #endif /* Print the number of surfaces not freed */ if (surfaces_allocated != 0) { fprintf(stderr, "SDL Warning: %d SDL surfaces extant\n", surfaces_allocated); } #endif #ifdef DEBUG_BUILD printf("[SDL_Quit] : SDL_UninstallParachute()\n"); fflush(stdout); #endif /* Uninstall any parachute signal handlers */ SDL_UninstallParachute(); #if !SDL_THREADS_DISABLED && SDL_THREAD_PTH pth_kill(); #endif #ifdef DEBUG_BUILD printf("[SDL_Quit] : Returning!\n"); fflush(stdout); #endif } /* Get the library version number */ void SDL_GetVersion(SDL_version * ver) { SDL_VERSION(ver); } /* Get the library source revision */ int SDL_GetRevision(void) { return SDL_REVISION; } #if defined(__OS2__) /* Building for OS/2 */ #ifdef __WATCOMC__ #define INCL_DOSERRORS #define INCL_DOSEXCEPTIONS #include <os2.h> /* Exception handler to prevent the Audio thread hanging, making a zombie process! */ ULONG _System SDL_Main_ExceptionHandler(PEXCEPTIONREPORTRECORD pERepRec, PEXCEPTIONREGISTRATIONRECORD pERegRec, PCONTEXTRECORD pCtxRec, PVOID p) { if (pERepRec->fHandlerFlags & EH_EXIT_UNWIND) return XCPT_CONTINUE_SEARCH; if (pERepRec->fHandlerFlags & EH_UNWINDING) return XCPT_CONTINUE_SEARCH; if (pERepRec->fHandlerFlags & EH_NESTED_CALL) return XCPT_CONTINUE_SEARCH; /* Do cleanup at every fatal exception! */ if (((pERepRec->ExceptionNum & XCPT_SEVERITY_CODE) == XCPT_FATAL_EXCEPTION) && (pERepRec->ExceptionNum != XCPT_BREAKPOINT) && (pERepRec->ExceptionNum != XCPT_SINGLE_STEP)) { if (SDL_initialized & SDL_INIT_AUDIO) { /* This removes the zombie audio thread in case of emergency. */ #ifdef DEBUG_BUILD printf ("[SDL_Main_ExceptionHandler] : Calling SDL_CloseAudio()!\n"); #endif SDL_CloseAudio(); } } return (XCPT_CONTINUE_SEARCH); } EXCEPTIONREGISTRATIONRECORD SDL_Main_xcpthand = { 0, SDL_Main_ExceptionHandler }; /* The main DLL entry for DLL Initialization and Uninitialization: */ unsigned _System LibMain(unsigned hmod, unsigned termination) { if (termination) { #ifdef DEBUG_BUILD /* printf("[SDL DLL Unintialization] : Removing exception handler\n"); */ #endif DosUnsetExceptionHandler(&SDL_Main_xcpthand); return 1; } else { #ifdef DEBUG_BUILD /* Make stdout and stderr unbuffered! */ setbuf(stdout, NULL); setbuf(stderr, NULL); #endif /* Fire up exception handler */ #ifdef DEBUG_BUILD /* printf("[SDL DLL Initialization] : Setting exception handler\n"); */ #endif /* Set exception handler */ DosSetExceptionHandler(&SDL_Main_xcpthand); return 1; } } #endif /* __WATCOMC__ */ #elif defined(__WIN32__) #if !defined(HAVE_LIBC) || (defined(__WATCOMC__) && defined(BUILD_DLL)) /* Need to include DllMain() on Watcom C for some reason.. */ #define WIN32_LEAN_AND_MEAN #include <windows.h> BOOL APIENTRY _DllMainCRTStartup(HANDLE hModule, DWORD ul_reason_for_call, LPVOID lpReserved) { switch (ul_reason_for_call) { case DLL_PROCESS_ATTACH: case DLL_THREAD_ATTACH: case DLL_THREAD_DETACH: case DLL_PROCESS_DETACH: break; } return TRUE; } #endif /* building DLL with Watcom C */ #endif /* OS/2 elif __WIN32__ */ /* vi: set ts=4 sw=4 expandtab: */