These are mutexes that work in both multi-processing and
multi-threading netplex environments. They are implemented on top of
Netplex_semaphore, and use the same name space for named objects.
For implementation issues, see
It is not required to create mutexes: A mutex is automatically created when the name is used for the first time. Mutexes are initially always in unlocked state.
Mutexes do not stack: A container cannot lock a mutex several times. (The second lock attempt would result in a deadlock.)
There is no deadlock detection.
If a container holding mutexes terminates the mutexes are automatically unlocked.
Mutex are not owned by their container. It is allowed that a different container unlocks the mutex.
Technically, a mutex named
n is implemented by a semaphore
If the mutex is locked, the semaphore has the value 0, and if it is
unlocked, it has value 1.
Thread safety: Full. The functions can be called from any thread.
val plugin :
To enable mutexes, call the controller's
with this object as argument. This can e.g. be done in the
post_add_hook of the processor.
The following functions can only be invoked in container
contexts. Outside of such a context the exception
Netplex_cenv.Not_in_container_thread is raised.
val access :
string -> mutex
Access the named mutex. If the mutex does not exist, it is created in unlocked state
val lock :
mutex -> unit
Wait until the mutex is free, and locks it
val unlock :
mutex -> unit
Unlocks the mutex. This is a no-op if the mutex is not locked