create_mutex — Create a mutual exclusion synchronization object.
create_mutex( : : AttribName, AttribValue : MutexHandle)
A mutex is a synchronization object that negotiates mutual exclusion among threads of a single process to avoid simultaneous modifications on common resources such as global variables. A mutex has two possible states: unlocked, i.e., not owned by any thread, and locked, i.e., owned by one certain thread. Threads attempting to lock a mutex that is already owned by another thread, i.e., locked, wait until the owning thread unlocks the mutex first. Unlike events, a thread has to own a mutex to unlock it.
create_mutex allocates and initializes the mutex object according to
the attributes specified in AttribName and AttribValue.
AttribName specifies the attribute class and AttribValue
the kind of the mutex. The description beneath lists all mutex kinds
supported by following classes:
empty string sets the default attributes.
specifies what happens if a thread attempts to lock a mutex that is already owned:
simply suspends the calling thread (default). The behavior is undefined, if the thread is already owner of the mutex.
a fast mutex implementation that is busy waiting for the signaled mutex. The behavior is undefined, if the thread is already owner of the mutex.
suspends the calling thread if the thread is not owner of the mutex. But a recursive mutex can be acquired again by the owning thread. A recursive mutex does not become unlocked until the number of unlock requests equals the number of successful lock requests.
The mutex is unlocked when created.
AttribName (input_control) number(-array) → (string / integer / real)
Mutex attribute class.
Default value: []
List of values: 'type'
AttribValue (input_control) number(-array) → (string / integer / real)
Mutex attribute kind.
Number of elements: AttribValue == AttribName
Default value: []
List of values: 'recursive', 'sleep', 'spin'
MutexHandle (output_control) mutex → (handle)
Mutex synchronization object.
create_mutex returns 2 (H_MSG_TRUE) if all parameters are correct.
If necessary, an exception is raised.
Foundation