Similar Synchronization Functions-Mutual Exclusion Locks

• "Initialize a Mutex"

• "Destroy a Mutex"

• "Acquire a Mutex"

• "Release a Mutex"

• "Try to Acquire a Mutex"

Initialize a Mutex

mutex_init(3T)

#include <synch.h>   (or
#include <thread.h>)

int mutex_init(mutex_t *mp, int type, void *arg)); 

Use mutex_init() to initialize the mutex pointed to by mp. The type can be one of the following (note that arg is currently ignored).

• USYNC_PROCESS The mutex can be used to synchronize threads in this and other processes.

• USYNC_THREAD The mutex can be used to synchronize threads in this process, only.

Mutexes can also be initialized by allocation in zeroed memory, in which case a type of USYNC_THREAD is assumed.

Multiple threads must not initialize the same mutex simultaneously. A mutex lock must not be reinitialized while other threads might be using it.

Mutexes with Intraprocess Scope

#include <thread.h>

mutex_t mp;
int ret;

/* to be used within this process only */
ret = mutex_init(&mp, USYNC_THREAD, 0); 

Mutexes with Interprocess Scope

#include <thread.h>

mutex_t mp;
int ret;

/* to be used among all processes */
ret = mutex_init(&mp, USYNC_PROCESS, 0); 

Destroy a Mutex

mutex_destroy(3T)

#include <thread.h>

int mutex_destroy (mutex_t *mp);

Use mutex_destroy() to destroy any state associated with the mutex pointed to by mp. Note that the space for storing the mutex is not freed.

Acquire a Mutex

mutex_lock(3T)

#include <thread.h>

int mutex_lock(mutex_t *mp);

Use mutex_lock() to lock the mutex pointed to by mp. When the mutex is already locked, the calling thread blocks until the mutex becomes available (blocked threads wait on a prioritized queue).

Release a Mutex

mutex_unlock(3T)

#include <thread.h>

int mutex_unlock(mutex_t *mp);

Use mutex_unlock() to unlock the mutex pointed to by mp. The mutex must be locked and the calling thread must be the one that last locked the mutex (the owner).

Try to Acquire a Mutex

mutex_trylock(3T)

#include <thread.h>

int mutex_trylock(mutex_t *mp);

Use mutex_trylock() to attempt to lock the mutex pointed to by mp. This function is a nonblocking version of mutex_lock().