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Get a mutex type
#include <pthread.h> int pthread_mutexattr_gettype( const pthread_mutexattr_t * attr, int * type );
- A pointer to the pthread_mutexattr_t object that you want to get the attribute from.
- A pointer to a location where the function can store the type.
Use the -l c option to qcc to link against this library. This library is usually included automatically.
The pthread_mutexattr_gettype() function gets the mutex type attribute in the type parameter. Valid mutex types include:
- No deadlock detection. A thread that attempts to relock this mutex without first unlocking it deadlocks. Attempts to unlock a mutex locked by a different thread or attempts to unlock an unlocked mutex result in undefined behavior.
- Provides error checking.
A thread returns with an error when it attempts to:
- Relock this mutex without first unlocking it.
- Unlock a mutex that another thread has locked.
- Unlock an unlocked mutex.
- A thread that attempts to relock this mutex without first unlocking it succeeds in locking the mutex. The relocking deadlock that can occur with mutexes of type PTHREAD_MUTEX_NORMAL can't occur with this mutex type. Multiple locks of this mutex require the same number of unlocks to release the mutex before another thread can acquire the mutex. A thread that attempts to unlock a mutex that another thread has locked, or unlock an unlocked mutex, returns with an error.
- The default value of the type attribute. Attempts to recursively lock a mutex of this type, or unlock a mutex of this type that isn't locked by the calling thread, or unlock a mutex of this type that isn't locked, results in undefined behavior.
Zero, and the value of the type attribute of attr is stored in the object referenced by the type parameter; otherwise, an error.
- Invalid value specified by attr.
An application shouldn't use a PTHREAD_MUTEX_RECURSIVE mutex with condition variables because the implicit unlock performed for a pthread_cond_wait() or pthread_cond_timedwait() may not actually release the mutex (if it's been locked multiple times). If this happens, no other thread can satisfy the condition of the predicate.