Mutexes

These are functions prefixed with either pthread_mutex_ or pthread_mutexattr_. They apply to mutexes and their attribute objects.

Mutexes in Pthreads can be initialized, destroyed, locked, and unlocked. They can also have their behavior customized using a pthread_mutexattr_t structure, which has its corresponding pthread_mutexattr_* functions for initializing and destroying an attribute on it.

A basic use of a Pthread mutex using static initialization looks as follows:

static pthread_mutex_t func_mutex = PTHREAD_MUTEX_INITIALIZER; 
 
void func() { 
    pthread_mutex_lock(&func_mutex); 
 
    // Do something that's not thread-safe. 
 
    pthread_mutex_unlock(&func_mutex); 
} 

In this last bit of code, we use the PTHREAD_MUTEX_INITIALIZER macro, which initializes the mutex for us without having to type out the code for it every time. In comparison to other APIs, one has to manually initialize and destroy mutexes, though the use of macros helps somewhat.

After this, we lock and unlock the mutex. There's also the pthread_mutex_trylock() function, which is like the regular lock version, but which will return immediately if the referenced mutex is already locked instead of waiting for it to be unlocked.

In this example, the mutex is not explicitly destroyed. This is, however, a part of normal memory management in a Pthreads-based application.