Question

I am writing a program with a few critical sections. The thing is I need to check the value of a mutex in an if statement.

I would like to do something like this:

if pthread_mutex(&mutex) == 0 // locked 
  // Do something
else if pthread_mutex(&mutex) == 1 // unlocked 
 // Do something else

Is this possible?

Answer 1

You want pthread_mutex_trylock().

From that link:

The pthread_mutex_trylock() function shall be equivalent to pthread_mutex_lock(), except that if the mutex object referenced by mutex is currently locked (by any thread, including the current thread), the call shall return immediately.

…

Return values

…

The pthread_mutex_trylock() function shall return zero if a lock on the mutex object referenced by mutex is acquired. Otherwise, an error number is returned to indicate the error

So your code would go like this:

pthread_mutex_t *m = /* ... */;

if (pthread_mutex_trylock(m) == 0)
{
    /* Success!  This thread now owns the lock. */
}
else
{
    /* Fail!  This thread doesn't own the lock.  Do something else... */
}