Multithreaded Programming Guide

Initialize a Mutex

Use mutex_init(3C) to initialize the mutex pointed to by mp. For POSIX threads, see Initializing a Mutex.

mutex_init(3C) Syntax

#include <synch.h> 
#include <thread.h>

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

The type can be one of the following values.

When a process fails while holding a USYNC_PROCESS lock, subsequent requestors of that lock hang. This behavior is a problem for systems that share locks with client processes because the client processes can be abnormally killed. To avoid the problem of hanging on a lock held by a dead process, use USYNC_PROCESS_ROBUST to lock the mutex. USYNC_PROCESS_ROBUST adds two capabilities:

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 the mutex.

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); 

Mutexes With Interprocess Scope-Robust

#include <thread.h>

mutex_t mp;
int ret;

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

mutex_init Return Values

mutex_init() returns 0 if successful. When any of the following conditions is detected, mutex_init() fails and returns the corresponding value.


EFAULT

Description:

mp points to an illegal address.


EINVAL

Description:

The value specified by mp is invalid.


ENOMEM

Description:

System has insufficient memory to initialize the mutex.


EAGAIN

Description:

System has insufficient resources to initialize the mutex.


EBUSY

Description:

System detected an attempt to reinitialize an active mutex.