#40858 [Asn]: Thread safety issue in GD

ID: 40858 Updated by: nlopess@php.net Reported By: scottmacvicar at ntlworld dot com Status: Assigned Bug Type: GD related Operating System: RHEL 4 PHP Version: 5.2.1 Assigned To: pajoye New Comment: yep, having a statically declared mutex would fix the problems we are having. I've a patch identical to yours (http://mega.ist.utl.pt/~ncpl/libgd_mutexes.txt) for a while, but we are still waiting for a win32 implementation to merge the patches (there is another open bug report in the gd bugs db about a similar issue) to definitely fix those nasty TS issues. Previous Comments: ------------------------------------------------------------------------ [2007-03-21 01:37:18] scottmacvicar at ntlworld dot com Patch is available at http://public.vbulletin.com/bugs/php/gd-mutex-patch.txt Quick explanation: * The mutex is created at module startup and destroyed at module shutdown courtesy of two new helper functions within the libGD code base. * The mutex is no longer destroyed at request shutdown. * Locking is performed prior to checking fontCache to prevent the race condition we're seeing. This can't be merged back into libGD at the moment since it breaks backwards compatibility by assuming a mutex has been allocated, the way to fix this for pthread is fairly easy. #define gdMutexDeclare(x) pthread_mutex_t x #define gdMutexDeclare(x) pthread_mutex_t x becomes #define gdMutexDeclare(x) static pthread_mutex_t x = PTHREAD_MUTEX_INITIALIZER #define gdMutexSetup(x) That would just leave the win32 implementation to deal with via DLLMain, a quick patch to add that would only take a few minutes though I don't have VC6 installed yet. ------------------------------------------------------------------------ [2007-03-21 00:48:56] pajoye@php.net "Moving the code to PHP_MINIT fixes the problem for PHP but the threading options of GD doesn't extend itself to this setup since the function to create the mutex can be called more than once in a short period of time." Do you mean for libGD itself used a library in a random project? If yes, a solution is very similar to this one. We have to do it at load time (like DLLMain on windows). Many other libraries (and many related to FT2, with ft2 cache or their own) rely on this solution. We can give it a try, at least. "I've got a patch that implements the PHP solution running on our boxes, I can provide it if interested." You can always post it, I still did not get the time to do it, so any help is welcome. ------------------------------------------------------------------------ [2007-03-21 00:40:40] scottmacvicar at ntlworld dot com Moving the code to PHP_MINIT fixes the problem for PHP but the threading options of GD doesn't extend itself to this setup since the function to create the mutex can be called more than once in a short period of time. This small race condition could be fixed by using pthread_once to ensure the mutexes are allocated only once but I'm unsure of the Win32 equivalent. I've got a patch that implements the PHP solution running on our boxes, I can provide it if interested. ------------------------------------------------------------------------ [2007-03-19 19:27:31] pajoye@php.net Did we not put it inside in the latest version of the last patch? I do not have the code at hand but as far as I remember Nuno updated it. I will check again tonight. ------------------------------------------------------------------------ [2007-03-19 19:24:54] tony2001@php.net >The first problem looks weird. It defeats the whole purpose of the mutex. The !=NULL check is out of the mutex protected block. ------------------------------------------------------------------------ The remainder of the comments for this report are too long. To view the rest of the comments, please view the bug report online at http://bugs.php.net/40858 -- Edit this bug report at http://bugs.php.net/?id=40858&edit=1