Question

Most of the examples I’m looking at on the Web have pthread_mutex_t sitting at the top of the file in the global space and I think I read somewhere that Linux mutexes have to be global. Is this true?

edit:
I have some Win32 multithreading code that I’m porting over to Linux. For the windows code, there are several wrapper functions that encapsulate things like mutex creation and locking/unlocking. My understanding is that every synchronization primitive that’s created through one of the Create() API calls in Windows returns a HANDLE that can be stored in an instance field and then used later. In this case, it’s used in the Lock() function, which is wrapper around WaitForSingleObject(). For Linux, could I simply store the mutex in an instance field and call pthread_mutex_lock()/pthread_cond_wait() in the Lock() function and expect the same behavior as on Windows?

Nv_Mutex::Nv_Mutex(Nv_XprocessID name)
{

#if defined(WIN32)
    if((handle = ::CreateMutexA(0, false, name)) == NULL)
    {
        throw Nv_EXCEPTION(XCPT_ResourceAllocationFailure, GetLastError());
    }

    isCreator = !(::GetLastError() == ERROR_ALREADY_EXISTS);
#else
    if (name == Nv_XprocessID_NULL) {
        /*
        pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;                     // Fast
        pthread_mutex_t recmutex = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;     // Recursive
        pthread_mutex_t errchkmutex = PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP; // Errorcheck
        */
        mutex = PTHREAD_MUTEX_INITIALIZER;
        // attributes??

        if (pthread_mutex_init(&mutex, NULL) != 0) {
            throw Nv_EXCEPTION(XCPT_ResourceAllocationFailure, GetLastError());
        }
    }
    else {
        // insert code for named mutex (needed for shared mutex across processes) here.
    }

    //isCreator = !(GetLastError() == EBUSY);
#endif
}

bool                
Nv_Mutex::Lock(const char *f, int l, Nv_uint32 timeout)
{

    switch(WaitForSingleObject(handle, timeout))
    {
        case WAIT_OBJECT_0:
            file = f;
            line = l;
            return true;

        case WAIT_TIMEOUT:
            return false;
    }

    throw Nv_EXCEPTION(XCPT_WaitFailed, GetLastError());
}

Answer 1

No, they can scoped. There is nothing special about the actual mutex pointer.