A mutex (abbreviated Mutually Exclusive access) is a synchronization object, a variant of semaphore with k=1. A mutex is said to be seized by a task decreasing k. It is released when the task restores k. Mutexes are typically used to protect a shared resource from concurrent access. A task seizes (or acquires) the mutex, then accesses the resource, and after that releases the mutex.
A mutex is a low-level synchronization primitive exposed to deadlocking. A deadlock can occur with just two tasks and two mutexes (if each task attempts to acquire both mutexes, but in the opposite order). Entering the deadlock is usually aggravated by a race condition state, which leads to sporadic hangups, which are very difficult to track down.
To create a mutex operating system “object”:
HANDLE hMutex = CreateMutex(NULL, FALSE, NULL);
To lock the mutex:
To unlock the mutex
When the program is finished with the mutex:
Creating a mutex:
#include <pthread.h> pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t mutex; pthread_mutex_init(&mutex, NULL);
int error = pthread_mutex_lock(&mutex);
int error = pthread_mutex_unlock(&mutex);
Trying to lock (but do not wait if it can’t)
int error = pthread_mutex_trylock(&mutex);
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