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I'm developing an application on an embedded linux OS (uClinux) and I need to be able to lock the mutex more than once (by the same thread).
I have a mutex and a mutexattr defined and initialized as follows:
pthread_mutexattr_t waiting_barcode_mutexattr;
pthread_mutex_t waiting_barcode_mutex;
pthread_mutexattr_init(&waiting_barcode_mutexattr);
pthread_mutexattr_settype(&waiting_barcode_mutexattr, PTHREAD_MUTEX_RECURSIVE);
pthread_mutex_init(&waiting_barcode_mutex, &waiting_barcode_mutexattr);
But when I try to acquire the lock twice it blocks on the second lock:
pthread_mutex_lock(&waiting_barcode_mutex);
pthread_mutex_lock(&waiting_barcode_mutex);
Am I initializing it wrong or is there a better way of accomplishing the same?
Thanks in advance.
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A recursive type mutex permits a thread to lock many times. That is, a thread attempting to relock this mutex without first unlocking will succeed. This type of mutex must be unlocked the same number to times it is locked before the mutex will be returned to an unlocked state.
Recursive locks: A recursive lock is a lock that has been taken by a thread several times without having been released.
Typically, threads cannot acquire locks twice in a row: a thread must release an acquired lock before attempting to acquire it again. However, reentrant locks can be acquired multiple times by the same thread. Reentrant locks allow code to acquire a lock before calling other functions that acquire the same lock.
The major drawback of a mutex lock is that it lets the thread spinlock if the lock is not available. While one thread has acquired the lock and is in its critical section, all other threads attempting to acquire the lock are in a loop where the thread periodically checks whether the lock is available.
(Just realised I didn't mark this question as answered)
Taken from the Conclusions in the question:
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