pthread_mutexattr_settype()

Arguments:

attr

A pointer to the pthread_mutexattr_t object that you want to set the attribute in.

type

The new type; one of:

• PTHREAD_MUTEX_NORMAL — 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.
• PTHREAD_MUTEX_ERRORCHECK — 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, or unlock an unlocked mutex.
• PTHREAD_MUTEX_RECURSIVE — 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.
• PTHREAD_MUTEX_DEFAULT — the default value of the type attribute. In QNX Neutrino, PTHREAD_MUTEX_DEFAULT mutexes are treated in the same way as PTHREAD_MUTEX_ERRORCHECK ones.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The pthread_mutexattr_settype() function sets the mutex type in the mutex attribute object attr to the value given by type.

Returns:

EOK

Success.

EINVAL

The value specified by attr or type is invalid.

Classification:

POSIX 1003.1

Caveats:

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.