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.\" $FreeBSD: src/lib/libpthread/man/pthread_mutexattr.3,v 1.8 2002/09/16 19:29:29 mini Exp $
.Dd June 12, 2016
.Dt PTHREAD_MUTEXATTR 3
.Os
.Sh NAME
.Nm pthread_mutexattr_init ,
.Nm pthread_mutexattr_destroy ,
.Nm pthread_mutexattr_setprioceiling ,
.Nm pthread_mutexattr_getprioceiling ,
.Nm pthread_mutexattr_setprotocol ,
.Nm pthread_mutexattr_getprotocol ,
.Nm pthread_mutexattr_settype ,
.Nm pthread_mutexattr_gettype ,
.Nm pthread_mutexattr_getpshared ,
.Nm pthread_mutexattr_setpshared
.Nd mutex attribute operations
.Sh LIBRARY
.Lb libpthread
.Sh SYNOPSIS
.In pthread.h
.Ft int
.Fn pthread_mutexattr_init "pthread_mutexattr_t *attr"
.Ft int
.Fn pthread_mutexattr_destroy "pthread_mutexattr_t *attr"
.Ft int
.Fn pthread_mutexattr_setprioceiling \
"pthread_mutexattr_t *attr" "int prioceiling"
.Ft int
.Fn pthread_mutexattr_getprioceiling \
"pthread_mutexattr_t *attr" "int *prioceiling"
.Ft int
.Fn pthread_mutexattr_setprotocol \
"pthread_mutexattr_t *attr" "int protocol"
.Ft int
.Fn pthread_mutexattr_getprotocol \
"pthread_mutexattr_t *attr" "int *protocol"
.Ft int
.Fn pthread_mutexattr_settype "pthread_mutexattr_t *attr" "int type"
.Ft int
.Fn pthread_mutexattr_gettype \
"pthread_mutexattr_t * restrict attr" "int * restrict type"
.Ft int
.Fn pthread_mutexattr_getpshared \
"const pthread_mutexattr_t * __restrict attr" "int * __restrict pshared"
.Ft int
.Fn pthread_mutexattr_setpshared \
"pthread_mutexattr_t * attr" "int pshared"
.Sh DESCRIPTION
Mutex attributes are used to specify parameters to
.Fn pthread_mutex_init .
Like with thread attributes,
one attribute object can be used in multiple calls to
.Xr pthread_mutex_init 3 ,
with or without modifications between calls.
.Pp
The
.Fn pthread_mutexattr_init
function initializes
.Fa attr
with all the default mutex attributes.
.Pp
The
.Fn pthread_mutexattr_destroy
function destroys
.Fa attr .
.Pp
The
.Fn pthread_mutexattr_settype
functions set the mutex
.Fa type
value of the attribute.
Valid mutex types are:
.Bl -tag -width "XXX" -offset 2n
.It Dv PTHREAD_MUTEX_NORMAL
This type of mutex does not check for usage errors.
It will deadlock if reentered, and result in undefined behavior if a
locked mutex is unlocked by another thread.
Attempts to unlock an already unlocked
.Dv PTHREAD_MUTEX_NORMAL
mutex will result in undefined behavior.
.It Dv PTHREAD_MUTEX_ERRORCHECK
These mutexes do check for usage errors.
If an attempt is made to relock a
.Dv PTHREAD_MUTEX_ERRORCHECK
mutex without first dropping the lock, an error will be returned.
If a thread attempts to unlock a
.Dv PTHREAD_MUTEX_ERRORCHECK
mutex that is locked by another thread, an error will be returned.
If a thread attempts to unlock a
.Dv PTHREAD_MUTEX_ERRORCHECK
thread that is unlocked, an error will be returned.
.It Dv PTHREAD_MUTEX_RECURSIVE
These mutexes allow recursive locking.
An attempt to relock a
.Dv PTHREAD_MUTEX_RECURSIVE
mutex that is already locked by the same thread succeeds.
An equivalent number of
.Xr pthread_mutex_unlock 3
calls are needed before the mutex will wake another thread waiting
on this lock.
If a thread attempts to unlock a
.Dv PTHREAD_MUTEX_RECURSIVE
mutex that is locked by another thread, an error will be returned.
If a thread attempts to unlock a
.Dv PTHREAD_MUTEX_RECURSIVE
thread that is unlocked, an error will be returned.
.Pp
It is advised that
.Dv PTHREAD_MUTEX_RECURSIVE
mutexes are not used with condition variables.
This is because of the implicit unlocking done by
.Xr pthread_cond_wait 3
and
.Xr pthread_cond_timedwait 3 .
.It Dv PTHREAD_MUTEX_DEFAULT
Also this type of mutex will cause undefined behavior if reentered.
Unlocking a
.Dv PTHREAD_MUTEX_DEFAULT
mutex locked by another thread will result in undefined behavior.
Attempts to unlock an already unlocked
.Dv PTHREAD_MUTEX_DEFAULT
mutex will result in undefined behavior.
.Pp
This is the default mutex type for
.Fn pthread_mutexattr_init .
.El
.Pp
The
.Fn pthread_mutexattr_gettype
functions copy the type value of the attribute to the location
pointed to by the second parameter.
.Pp
The
.Fn pthread_mutexattr_getpshared
function obtains the value of the process-shared attribute from
the attributes object referenced by
.Fa attr .
.Pp
The
.Fn pthread_mutexattr_setpshared
function is used to set the process-shared attribute in an initialised
attributes object referenced by
.Fa attr .
.Pp
The
.Fn pthread_mutexattr_getprotocol
and
.Fn pthread_mutexattr_setprotocol
functions shall get and set the protocol attribute of a mutex attributes
object pointed to by
.Fa attr
which was previously created by the function
.Fn pthread_mutexattr_init .
.Pp
The
.Fn pthread_mutexattr_getprioceiling
and
.Fn pthread_mutexattr_setprioceiling
functions, shall get and set the priority ceiling attribute of a mutex attributes
object pointed to by
.Fa attr
which was previously created by the function
.Fn pthread_mutexattr_init .
.Sh RETURN VALUES
If successful, these functions return 0.
Otherwise, an error number is returned to indicate the error.
.Sh ERRORS
The
.Fn pthread_mutexattr_init
function shall fail if:
.Bl -tag -width Er
.It Bq Er ENOMEM
Insufficient memory exists to initialize the mutex attributes object.
.El
.Pp
The
.Fn pthread_mutexattr_settype
function shall fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The value specified either by
.Fa type
or
.Fa attr
is invalid.
.El
.Pp
No error numbers are defined for the
.Fn pthread_mutexattr_destroy
and
.Fn pthread_mutexattr_gettype
functions.
.Pp
.Fn pthread_mutexattr_setprioceiling
may fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
Invalid value for
.Fa attr ,
or invalid value for
.Fa prioceiling .
.El
.Pp
.Fn pthread_mutexattr_getprioceiling
may fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
Invalid value for
.Fa attr .
.El
.Pp
.Fn pthread_mutexattr_setprotocol
may fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
Invalid value for
.Fa attr ,
or invalid value for
.Fa protocol .
.El
.Pp
.Fn pthread_mutexattr_getprotocol
may fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
Invalid value for
.Fa attr .
.El
.Pp
.Fn pthread_mutexattr_getpshared
and
.Fn pthread_mutexattr_setpshared
may fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
the value specified by
.Fa attr
is invalid.
.El
.Sh SEE ALSO
.Xr pthread_mutex_init 3
.Sh STANDARDS
These functions conform to
.St -p1003.1-2001 .
.Sh BUGS
The
.Fn pthread_mutexattr_getpshared
and
.Fn pthread_mutexattr_setpshared
functions are hidden by default since only thread shared attributes
are supported.