Standard C Library Functions pthread_mutex_lock(3C)
NAME
pthread_mutex_lock, pthread_mutex_trylock,
pthread_mutex_unlock - lock or unlock a mutex
SYNOPSIS
cc -mt [ flag... ] file... -lpthread [ library... ]
#include
int pthread_mutex_lock(pthread_mutex_t *mutex);
int pthread_mutex_trylock(pthread_mutex_t *mutex);
int pthread_mutex_unlock(pthread_mutex_t *mutex);
DESCRIPTION
The mutex object referenced by mutex is locked by callingpthread_mutex_lock(). If the mutex is already locked, the
calling thread blocks until the mutex becomes available. This operation returns with the mutex object referenced by mutex in the locked state with the calling thread as its owner.If the mutex type is PTHREAD_MUTEX_NORMAL, deadlock detec-
tion is not provided. Attempting to relock the mutex causes deadlock. If a thread attempts to unlock a mutex that it has not locked or a mutex that is unlocked, undefined behavior results.If the mutex type is PTHREAD_MUTEX_ERRORCHECK, then error
checking is provided. If a thread attempts to relock a mutex that it has already locked, an error will be returned. If a thread attempts to unlock a mutex that it has not locked or a mutex which is unlocked, an error will be returned.If the mutex type is PTHREAD_MUTEX_RECURSIVE, then the
mutex maintains the concept of a lock count. When a thread successfully acquires a mutex for the first time, the lock count is set to 1. Every time a thread relocks this mutex, the lock count is incremented by one. Each time the thread unlocks the mutex, the lock count is decremented by one. When the lock count reaches 0, the mutex becomes available for other threads to acquire. If a thread attempts to unlock a mutex that it has not locked or a mutex that is unlocked, an error will be returned.SunOS 5.11 Last change: 11 Nov 2008 1
Standard C Library Functions pthread_mutex_lock(3C)
If the mutex type is PTHREAD_MUTEX_DEFAULT, attempting to
recursively lock the mutex results in undefined behavior. Attempting to unlock the mutex if it was not locked by the calling thread results in undefined behavior. Attempting to unlock the mutex if it is not locked results in undefined behavior.The pthread_mutex_trylock() function is identical to
pthread_mutex_lock() except that if the mutex object refer-
enced by mutex is currently locked (by any thread, including the current thread), the call fails immediately with EBUSY.The pthread_mutex_unlock() function releases the mutex
object referenced by mutex. The manner in which a mutex is released is dependent upon the mutex's type attribute. If there are threads blocked on the mutex object referenced bymutex when pthread_mutex_unlock() is called, resulting in
the mutex becoming available, the scheduling policy is used to determine which thread will acquire the mutex. (In thecase of PTHREAD_MUTEX_RECURSIVE mutexes, the mutex becomes
available when the count reaches 0 and the calling thread no longer has any locks on this mutex.) If a signal is delivered to a thread waiting for a mutex,upon return from the signal handler the thread resumes wait-
ing for the mutex as if it was not interrupted.RETURN VALUES
If successful, the pthread_mutex_lock() and
pthread_mutex_unlock() functions return 0. Otherwise, an
error number is returned to indicate the error.The pthread_mutex_trylock() function returns 0 if a lock
on the mutex object referenced by mutex is acquired. Other-
wise, an error number is returned to indicate the error.ERRORS
The pthread_mutex_lock() and pthread_mutex_trylock() func-
tions will fail if:EAGAIN The mutex could not be acquired because the max-
imum number of recursive locks for mutex has been exceeded. EINVAL The mutex was created with the protocol attributehaving the value PTHREAD_PRIO_PROTECT and the cal-
ling thread's priority is higher than the mutex'sSunOS 5.11 Last change: 11 Nov 2008 2
Standard C Library Functions pthread_mutex_lock(3C)
current priority ceiling. EPERM The mutex was created with the protocol attributehaving the value PTHREAD_PRIO_PROTECT and the cal-
ling thread is not in the real-time class
(SCHED_RR or SCHED_FIFO scheduling class).
The pthread_mutex_trylock() function will fail if:
EBUSY The mutex could not be acquired because it was already locked.The pthread_mutex_lock(), pthread_mutex_trylock() and
pthread_mutex_unlock() functions may fail if:
EINVAL The value specified by mutex does not refer to an initialized mutex object.The pthread_mutex_lock() function may fail if:
EDEADLK The current thread already owns the mutex. ENOMEM The limit on the number of simultaneously held mutexes has been exceeded.The pthread_mutex_unlock() function will fail if:
EPERM The mutex type is PTHREAD_MUTEX_ERRORCHECK or the
mutex is a robust mutex, and the current thread does not own the mutex.When a thread makes a call to pthread_mutex_lock() or
pthread_mutex_trylock(), if the mutex is initialized with
the robustness attribute having the valuePTHREAD_MUTEX_ROBUST (see pthread_mutexattr_getrobust(3C)),
the call will return these error values if: EOWNERDEAD The last owner of this mutex died whileholding the mutex, or the process con-
taining the owner of the mutex unmappedSunOS 5.11 Last change: 11 Nov 2008 3
Standard C Library Functions pthread_mutex_lock(3C)
the memory containing the mutex or per-
formed one of the exec(2) functions. This mutex is now owned by the caller. The caller must now attempt to make the state protected by the mutex consistent. If it is able to clean up the state, then itshould call pthread_mutex_consistent()
for the mutex and unlock the mutex. Sub-
sequent calls to pthread_mutex_lock() and
pthread_mutex_trylock() will behave nor-
mally, as before. If the caller is not able to clean up the state,pthread_mutex_consistent() should not be
called for the mutex, but the mutex should be unlocked. Subsequent calls topthread_mutex_lock() and
pthread_mutex_trylock() will fail to
acquire the mutex with the error value ENOTRECOVERABLE. If the owner who acquired the lock with EOWNERDEAD dies, the next owner will acquire the lock with EOWNERDEAD.ENOTRECOVERABLE The mutex trying to be acquired was pro-
tecting the state that has been left irrecoverable by the mutex's last owner. The mutex has not been acquired. This condition can occur when the lock was previously acquired with EOWNERDEAD, and the owner was not able to clean up thestate and unlocked the mutex without cal-
ling pthread_mutex_consistent().
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:SunOS 5.11 Last change: 11 Nov 2008 4
Standard C Library Functions pthread_mutex_lock(3C)
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Interface Stability | Committed ||_____________________________|_____________________________|
| MT-Level | MT-Safe |
|_____________________________|_____________________________|
| Standard | See standards(5). ||_____________________________|_____________________________|
SEE ALSO
pthread_mutex_consistent(3C), pthread_mutex_init(3C),
pthread_mutexattr_setprotocol(3C),
pthread_mutexattr_setrobust(3C),
pthread_mutexattr_settype(3C), attributes(5), standards(5)
NOTES In the current implementation of threads,pthread_mutex_lock(), pthread_mutex_unlock(), mutex_lock(),
mutex_unlock(), pthread_mutex_trylock(), and mutex_trylock()
do not validate the mutex type. Therefore, an uninitializedmutex or a mutex with an invalid type does not return EIN-
VAL. Interfaces for mutexes with an invalid type have unspecified behavior. Uninitialized mutexes that are allocated locally may contain junk data. Such mutexes need to be initialized usingpthread_mutex_init() or mutex_init().
SunOS 5.11 Last change: 11 Nov 2008 5