Unsafe locking of critical sections

[GoogleCodeExporter]

the following code sequence is not safe:

   while (context->event_stack_lock) sceKernelDelayThread(1000);
   context->event_stack_lock = 1;
   ...do something...
   context->event_stack_lock = 0;

A thread reschedule could happen between the test in the "while" and setting 
the lock to "1". The 2 threads could both think the lock is free and both enter 
the critical section at the same time.
Better would be to use a Mutex:
   context->event_stack_mutex = sceKernelCreateMutex("Event Stack", PSP_MUTEX_ATTR_ALLOW_RECURSIVE, 0, NULL);

   sceKernelLockMutex(context->event_stack_mutex, 1, NULL);
   ...do something...
   sceKernelUnlockMutex(context->event_stack_mutex, 1);

The attribute PSP_MUTEX_ATTR_ALLOW_RECURSIVE allows a thread to lock again a 
mutex when it has already been locked by himself. This could be useful to also 
protect the sequence below, see Issue 2 (_spawnLocalEvent will again lock the 
mutex):

   sceKernelLockMutex(context->event_stack_mutex, 1, NULL);
   _spawnLocalEvent(context, ADHOC_MATCHING_EVENT_ESTABLISHED, sendermac, 0, NULL);
   _spawnLocalEvent(context, ADHOC_MATCHING_EVENT_ACCEPT, sendermac, optlen, opt);
   sceKernelUnlockMutex(context->event_stack_mutex, 1);

Original issue reported on code.google.com by [email protected] on 12 Jul 2012 at 7:20