5a537261a6
In my example case, there are 2 threads - one is a worker thread created by OpenThreads::Thread. The other thread is the main thread i.e. the thread that is intrinsically created when you execute the application. The crucial problem is that for the main thread, OpenThreads::Thread::CurrentThread() will return null.
I'll demonstrate this by breaking ReentrantMutex::lock() into sub-statements:
1.) if (_threadHoldingMutex==OpenThreads::Thread::CurrentThread())
2.) if (_lockCount>0){
3.)
OpenThreads::ScopedLock<OpenThreads::Mutex> lock(_lockCountMutex);
++_lockCount;
return 0;
4.)
int result = Mutex::lock();
if (result==0)
{
OpenThreads::ScopedLock<OpenThreads::Mutex> lock(_lockCountMutex);
5.)
_threadHoldingMutex = OpenThreads::Thread::CurrentThread();
_lockCount = 1;
return result;
An error will occur in the following case:
1) The worker thread calls lock(), it gets to the start of statement 5.
2) The main thread calls lock(). Statement 1 is evaluated as true as _threadHoldingMutex is null, and OpenThreads::Thread::CurrentThread() returns null.
3) The worker thread executes statement 5.
4) The main thread executes statement 2 and evaluates it as true, because the worker thread has set _lockCount to 1. The main thread executes statement 3, and now can access the mutexed-data at the same time as the worker thread!
The simple solution to this is to always protect access to _lockCount and _threadHoldingMutex using _lockCountMutex. I have done this in the file I am submitting."
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| Atomic | ||
| Barrier | ||
| Block | ||
| Condition | ||
| Exports | ||
| Mutex | ||
| ReadWriteMutex | ||
| ReentrantMutex | ||
| ScopedLock | ||
| Thread | ||
| Version | ||