xref: /openbsd-src/lib/libpthread/man/pthread_mutex_lock.3 (revision 86f9d4cdda0e0267dccd8755ac0035525579c4a7)

.\" $OpenBSD: pthread_mutex_lock.3,v 1.11 2013/06/05 03:44:50 tedu Exp $
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.\" Copyright (c) 1997 Brian Cully <shmit@kublai.com>
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.\" $FreeBSD: pthread_mutex_lock.3,v 1.5 1999/08/28 00:03:07 peter Exp $
.\"
.Dd $Mdocdate: June 5 2013 $
.Dt PTHREAD_MUTEX_LOCK 3
.Os
.Sh NAME
.Nm pthread_mutex_lock ,
.Nm pthread_mutex_timedlock ,
.Nm pthread_mutex_trylock
.Nd lock a mutex
.Sh SYNOPSIS
.In pthread.h
.Ft int
.Fn pthread_mutex_lock "pthread_mutex_t *mutex"
.Ft int
.Fn pthread_mutex_timedlock "pthread_mutex_t *mutex" "const struct timespec *abstime"
.Ft int
.Fn pthread_mutex_trylock "pthread_mutex_t *mutex"
.Sh DESCRIPTION
The
.Fn pthread_mutex_lock
function locks
.Fa mutex .
If the mutex is currently locked by another thread,
the calling thread will block until the
mutex becomes available.
.Pp
If the mutex is currently locked by the calling thread,
then the behavior depends on the type of the mutex.
If
.Fa mutex
is of type
.Dv PTHREAD_MUTEX_NORMAL ,
then the calling thread will deadlock and never return from
.Fn pthread_mutex_lock .
If
.Fa mutex
is of type
.Dv PTHREAD_MUTEX_ERRORCHECK ,
then
.Er EDEADLK
is immediately returned.
If
.Fa mutex
is of type
.Dv PTHREAD_MUTEX_RECURSIVE ,
then the recursion count on the mutex is incremented.
.Pp
The
.Fn pthread_mutex_timedlock
function locks
.Fa mutex
like
.Fn pthread_mutex_lock
except that it will not block or deadlock past the system time
specified in
.Fa abstime .
If that time is reached without being able to lock
.Fa mutex ,
then it returns
.Er ETIMEDOUT .
.Pp
The
.Fn pthread_mutex_trylock
function locks
.Fa mutex
like
.Fn pthread_mutex_lock
except that if
.Fa mutex
is locked by another thread,
or is locked by the calling thread and is not of type
.Dv PTHREAD_MUTEX_RECURSIVE ,
then it will immediately return
.Er EBUSY .
.Sh RETURN VALUES
If successful,
.Fn pthread_mutex_lock ,
.Fn pthread_mutex_timedlock ,
and
.Fn pthread_mutex_trylock
will return zero, otherwise an error number will be returned to
indicate the error.
.Sh ERRORS
.Fn pthread_mutex_lock ,
.Fn pthread_mutex_timedlock ,
and
.Fn pthread_mutex_trylock
will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The value specified by
.Fa mutex
is invalid.
.It Bq Er EAGAIN
The mutex is of type
.Dv PTHREAD_MUTEX_RECURSIVE
and the maximum recursion count has been reached.
.El
.Pp
In addition,
.Fn pthread_mutex_lock
and
.Fn pthread_mutex_timedlock
may return the following error:
.Bl -tag -width Er
.It Bq Er EDEADLK
The mutex is of type
.Dv PTHREAD_MUTEX_ERRORCHECK
and is already locked by the calling thread.
.El
.Pp
.Fn pthread_mutex_timedlock
may return the following error:
.Bl -tag -width Er
.It Bq Er ETIMEDOUT
The mutex could not be locked and the specified time was reached.
.El
.Pp
.Fn pthread_mutex_trylock
may return the following error:
.Bl -tag -width Er
.It Bq Er EBUSY
The mutex could not be locked because it was already locked.
.El
.Sh SEE ALSO
.Xr pthread_mutex_destroy 3 ,
.Xr pthread_mutex_init 3 ,
.Xr pthread_mutex_unlock 3 ,
.Xr pthread_mutexattr_settype 3
.Sh STANDARDS
.Fn pthread_mutex_lock ,
.Fn pthread_mutex_timedlock ,
and
.Fn pthread_mutex_trylock
conform to
.St -p1003.1-2008 .