If the mutex is currently locked by another thread, execution of the calling thread is blocked until unlocked by the other thread (other non-locked threads continue their execution). If the mutex is currently locked by the same thread calling this function, it produces a deadlock (with undefined behavior).
Can you lock a locked mutex?
Use pthread_mutex_lock(3THR) to lock the mutex pointed to by mutex . When pthread_mutex_lock() returns, the mutex is locked and the calling thread is the owner. If the mutex is already locked and owned by another thread, the calling thread blocks until the mutex becomes available.
What happens if you try to lock a locked mutex?
Locks a mutex object, which identifies a mutex. 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.
Can another thread unlock mutex?
If a thread attempts to unlock a mutex that it has not locked or a mutex which is unlocked, undefined behavior results. As user562734’s answer says, the answer is no – you cannot unlock a thread that was locked by another thread .
How do I know if mutex is locked?
The mutex object referenced by mutex shall be locked by a call to pthread_mutex_lock() that returns zero or [EOWNERDEAD] . If the mutex is already locked by another thread, the calling thread shall block until the mutex becomes available.
Is locking a mutex expensive?
Locking unlocked mutex is really cheap . Unlocking mutex w/o contention is cheap too.
What is the overhead of locking?
lock overhead: the extra resources for using locks , like the memory space allocated for locks, the CPU time to initialize and destroy locks, and the time for acquiring or releasing locks.
Can a mutex be locked more than once?
Can a mutex be locked more than once? A mutex is a lock. Only one state (locked/unlocked) is associated with it. However, a recursive mutex can be locked more than once (POSIX compliant systems), in which a count is associated with it, yet retains only one state (locked/unlocked).
Can a thread lock a mutex twice?
Mutexes guarantee that only one thread can lock a given mutex . ... Non-recursive mutexes can’t be locked several times by the same thread. If a mutex is locked twice by a thread, the result is undefined, it might throw an error or the thread could be blocked forever.
Is std :: mutex recursive?
std::recursive_mutex
A recursive mutex is a lockable object , just like mutex , but allows the same thread to acquire multiple levels of ownership over the mutex object.
How do I unlock mutex?
Usepthread_mutex_unlock(3THR) to unlock the mutex pointed to by mutex . (For Solaris threads, see “mutex_unlock(3THR)”.) pthread_mutex_unlock() releases the mutex object referenced by mutex. The manner in which a mutex is released is dependent upon the mutex’s type attribute.
When a mutex is no longer needed it delete?
Mutex . Generally, CLI objects don’t need deletion, because the platform is managed. But with Mutex , you need to call IDisposable. Dispose() when this object is no longer needed, and this interface method is implemented by System.
What is the difference between semaphore and mutex?
A mutex is an object but semaphore is an integer variable. ... A mutex object allows multiple process threads to access a single shared resource but only one at a time. On the other hand, semaphore allows multiple process threads to access the finite instance of the resource until available.
Is mutex a lock?
A mutex is the same as a lock but it can be system wide (shared by multiple processes). A semaphore does the same as a mutex but allows x number of threads to enter, this can be used for example to limit the number of cpu, io or ram intensive tasks running at the same time.
What is the difference between Unique_lock and Lock_guard?
A lock_guard always holds a lock from its construction to its destruction. A unique_lock can be created without immediately locking , can unlock at any point in its existence, and can transfer ownership of the lock from one instance to another.
What is pthread_cond_signal?
The pthread_cond_signal() function wakes up at least one thread that is currently waiting on the condition variable specified by cond. If no threads are currently blocked on the condition variable, this call has no effect.
