What does QMutex do?
The QMutex class provides access serialization between threads.
What happens when mutex is locked?
Mutexes are used to protect shared resources. If the mutex is already locked by another thread, the thread waits for the mutex to become available. The thread that has locked a mutex becomes its current owner and remains the owner until the same thread has unlocked it.
How do mutex locks work?
Mutex lock will only be released by the thread who locked it. So this ensures that once a thread has locked a piece of code then no other thread can execute the same region until it is unlocked by the thread who locked it.
Can another thread unlock mutex?
A thread attempting to unlock a mutex which another thread has locked will return with an error. A thread attempting to unlock an unlocked mutex will return with an error. Attempting to recursively lock a mutex of this type results in undefined behavior.
What happens if you forget to unlock the mutex?
Mutexes work like toilets. Once you go inside and lock the door, everyone else has to wait until you unlock the door and come out. If you never do that, everyone else (in theory) will have to wait infinitely.
What is Pthread_cond_signal?
The pthread_cond_signal() call unblocks at least one of the threads that are blocked on the specified condition variable cond (if any threads are blocked on cond).
What is pthread_mutex_lock used for?
Once the mutex is initialized, threads can use pthread_mutex_lock and pthread_mutex_unlock functions correspondingly. pthread_mutex_lock locks the mutex object passed as the only argument. If the mutex was already locked, the calling thread gets blocked until the mutex becomes available.
What does Pthread cond wait do?
The pthread_cond_wait() function blocks the calling thread, waiting for the condition specified by cond to be signaled or broadcast to. When pthread_cond_wait() is called, the calling thread must have mutex locked.
What is Pthread_mutex_recursive?
PTHREAD_MUTEX_RECURSIVE: Recursive type. This mutex type allows the same thread to lock the mutex multiple times before it is unlocked. Recursive mutex maintains the count of locks that will not be released if the number of unlocks and the number of locks are different, and no other thread can lock this mutex.
How to unlock and relock a qmutex?
You can unlock and relock the mutex with unlock () and relock (). If locked, the mutex will be unlocked when the QMutexLocker is destroyed. For example, this complex function locks a QMutex upon entering the function and unlocks the mutex at all the exit points:
What is the default mode of qmutex?
The mutex is created in an unlocked state. If mode is QMutex::Recursive, a thread can lock the same mutex multiple times and the mutex won’t be unlocked until a corresponding number of unlock () calls have been made. The default is QMutex::NonRecursive.
What happens to the mutex when the qmutex is destroyed?
If locked, the mutex will be unlocked when the QMutexLocker is destroyed. For example, this complex function locks a QMutex upon entering the function and unlocks the mutex at all the exit points: This example function will get more complicated as it is developed, which increases the likelihood that errors will occur.
What is the use of mutex block function in Qt?
This function was introduced in Qt 5.7. Locks the mutex. If another thread has locked the mutex then this call will block until that thread has unlocked it. Calling this function multiple times on the same mutex from the same thread is allowed if this mutex is a recursive mutex.