.\" Copyright (c) 1996 John Birrell <jb@cimlogic.com.au>.
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by John Birrell.
.\" 4. Neither the name of the author nor the names of any co-contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY JOHN BIRRELL AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" $FreeBSD: src/share/man/man3/pthread.3,v 1.33 2009/04/01 08:08:25 trhodes Exp $
.\"
.Dd April 8, 2010
.Dt PTHREAD 3
.Os
.Sh NAME
.Nm pthread
.Nd POSIX thread functions
.Sh LIBRARY
.Lb libpthread
.Sh SYNOPSIS
.In pthread.h
.Sh DESCRIPTION
POSIX threads are a set of functions that support applications with
requirements for multiple flows of control, called
.Em threads ,
within a process.
Multithreading is used to improve the performance of a
program.
.Pp
The POSIX thread functions are summarized in this section in the following
groups:
.Pp
.Bl -bullet -offset indent -compact
.It
Thread Routines
.It
Attribute Object Routines
.It
Mutex Routines
.It
Condition Variable Routines
.It
Read/Write Lock Routines
.It
Per-Thread Context Routines
.It
Cleanup Routines
.El
.Ss Thread Routines
.Bl -tag -width indent
.It Xo
.Ft int
.Fo pthread_create
.Fa "pthread_t *thread" "const pthread_attr_t *attr"
.Fa "void *\*[lp]*start_routine\*[rp]\*[lp]void *\*[rp]" "void *arg"
.Fc
.Xc
Creates a new thread of execution.
.It Xo
.Ft int
.Fn pthread_cancel "pthread_t thread"
.Xc
Cancels execution of a thread.
.It Xo
.Ft int
.Fn pthread_detach "pthread_t thread"
.Xc
Marks a thread for deletion.
.It Xo
.Ft int
.Fn pthread_equal "pthread_t t1" "pthread_t t2"
.Xc
Compares two thread IDs.
.It Xo
.Ft void
.Fn pthread_exit "void *value_ptr"
.Xc
Terminates the calling thread.
.It Xo
.Ft int
.Fn pthread_join "pthread_t thread" "void **value_ptr"
.Xc
Causes the calling thread to wait for the termination of the specified thread.
.It Xo
.Ft int
.Fn pthread_kill "pthread_t thread" "int sig"
.Xc
Delivers a signal to a specified thread.
.It Xo
.Ft int
.Fn pthread_once "pthread_once_t *once_control" "void \*[lp]*init_routine\*[rp]\*[lp]void\*[rp]"
.Xc
Calls an initialization routine once.
.It Xo
.Ft pthread_t
.Fn pthread_self void
.Xc
Returns the thread ID of the calling thread.
.It Xo
.Ft int
.Fn pthread_setcancelstate "int state" "int *oldstate"
.Xc
Sets the current thread's cancelability state.
.It Xo
.Ft int
.Fn pthread_setcanceltype "int type" "int *oldtype"
.Xc
Sets the current thread's cancelability type.
.It Xo
.Ft void
.Fn pthread_testcancel void
.Xc
Creates a cancellation point in the calling thread.
.It Xo
.Ft void
.Fn pthread_yield void
.Xc
Allows the scheduler to run another thread instead of the current one.
.El
.Ss Attribute Object Routines
.Bl -tag -width indent
.It Xo
.Ft int
.Fn pthread_attr_destroy "pthread_attr_t *attr"
.Xc
Destroy a thread attributes object.
.It Xo
.Ft int
.Fo pthread_attr_getinheritsched
.Fa "const pthread_attr_t *attr" "int *inheritsched"
.Fc
.Xc
Get the inherit scheduling attribute from a thread attributes object.
.It Xo
.Ft int
.Fo pthread_attr_getschedparam
.Fa "const pthread_attr_t *attr" "struct sched_param *param"
.Fc
.Xc
Get the scheduling parameter attribute from a thread attributes object.
.It Xo
.Ft int
.Fn pthread_attr_getschedpolicy "const pthread_attr_t *attr" "int *policy"
.Xc
Get the scheduling policy attribute from a thread attributes object.
.It Xo
.Ft int
.Fn pthread_attr_getscope "const pthread_attr_t *attr" "int *contentionscope"
.Xc
Get the contention scope attribute from a thread attributes object.
.It Xo
.Ft int
.Fn pthread_attr_getstacksize "const pthread_attr_t *attr" "size_t *stacksize"
.Xc
Get the stack size attribute from a thread attributes object.
.It Xo
.Ft int
.Fn pthread_attr_getstackaddr "const pthread_attr_t *attr" "void **stackaddr"
.Xc
Get the stack address attribute from a thread attributes object.
.It Xo
.Ft int
.Fn pthread_attr_getdetachstate "const pthread_attr_t *attr" "int *detachstate"
.Xc
Get the detach state attribute from a thread attributes object.
.It Xo
.Ft int
.Fn pthread_attr_init "pthread_attr_t *attr"
.Xc
Initialize a thread attributes object with default values.
.It Xo
.Ft int
.Fn pthread_attr_setinheritsched "pthread_attr_t *attr" "int inheritsched"
.Xc
Set the inherit scheduling attribute in a thread attributes object.
.It Xo
.Ft int
.Fo pthread_attr_setschedparam
.Fa "pthread_attr_t *attr" "const struct sched_param *param"
.Fc
.Xc
Set the scheduling parameter attribute in a thread attributes object.
.It Xo
.Ft int
.Fn pthread_attr_setschedpolicy "pthread_attr_t *attr" "int policy"
.Xc
Set the scheduling policy attribute in a thread attributes object.
.It Xo
.Ft int
.Fn pthread_attr_setscope "pthread_attr_t *attr" "int contentionscope"
.Xc
Set the contention scope attribute in a thread attributes object.
.It Xo
.Ft int
.Fn pthread_attr_setstacksize "pthread_attr_t *attr" "size_t stacksize"
.Xc
Set the stack size attribute in a thread attributes object.
.It Xo
.Ft int
.Fn pthread_attr_setstackaddr "pthread_attr_t *attr" "void *stackaddr"
.Xc
Set the stack address attribute in a thread attributes object.
.It Xo
.Ft int
.Fn pthread_attr_setdetachstate "pthread_attr_t *attr" "int detachstate"
.Xc
Set the detach state in a thread attributes object.
.El
.Ss Mutex Routines
.Bl -tag -width indent
.It Xo
.Ft int
.Fn pthread_mutexattr_destroy "pthread_mutexattr_t *attr"
.Xc
Destroy a mutex attributes object.
.It Xo
.Ft int
.Fn pthread_mutexattr_getprioceiling "pthread_mutexattr_t *attr" "int *ceiling"
.Xc
Obtain priority ceiling attribute of mutex attribute object.
.It Xo
.Ft int
.Fn pthread_mutexattr_getprotocol "pthread_mutexattr_t *attr" "int *protocol"
.Xc
Obtain protocol attribute of mutex attribute object.
.It Xo
.Ft int
.Fn pthread_mutexattr_gettype "pthread_mutexattr_t *attr" "int *type"
.Xc
Obtain the mutex type attribute in the specified mutex attributes object.
.It Xo
.Ft int
.Fn pthread_mutexattr_init "pthread_mutexattr_t *attr"
.Xc
Initialize a mutex attributes object with default values.
.It Xo
.Ft int
.Fn pthread_mutexattr_setprioceiling "pthread_mutexattr_t *attr" "int ceiling"
.Xc
Set priority ceiling attribute of mutex attribute object.
.It Xo
.Ft int
.Fn pthread_mutexattr_setprotocol "pthread_mutexattr_t *attr" "int protocol"
.Xc
Set protocol attribute of mutex attribute object.
.It Xo
.Ft int
.Fn pthread_mutexattr_settype "pthread_mutexattr_t *attr" "int type"
.Xc
Set the mutex type attribute that is used when a mutex is created.
.It Xo
.Ft int
.Fn pthread_mutex_destroy "pthread_mutex_t *mutex"
.Xc
Destroy a mutex.
.It Xo
.Ft int
.Fo pthread_mutex_init
.Fa "pthread_mutex_t *mutex" "const pthread_mutexattr_t *attr"
.Fc
.Xc
Initialize a mutex with specified attributes.
.It Xo
.Ft int
.Fn pthread_mutex_lock "pthread_mutex_t *mutex"
.Xc
Lock a mutex and block until it becomes available.
.It Xo
.Ft int
.Fo pthread_mutex_timedlock
.Fa "pthread_mutex_t *mutex" "const struct timespec *abstime"
.Fc
.Xc
Lock a mutex and block until it becomes available or until the timeout expires.
.It Xo
.Ft int
.Fn pthread_mutex_trylock "pthread_mutex_t *mutex"
.Xc
Try to lock a mutex, but do not block if the mutex is locked by another thread,
including the current thread.
.It Xo
.Ft int
.Fn pthread_mutex_unlock "pthread_mutex_t *mutex"
.Xc
Unlock a mutex.
.El
.Ss Condition Variable Routines
.Bl -tag -width indent
.It Xo
.Ft int
.Fn pthread_condattr_destroy "pthread_condattr_t *attr"
.Xc
Destroy a condition variable attributes object.
.It Xo
.Ft int
.Fn pthread_condattr_init "pthread_condattr_t *attr"
.Xc
Initialize a condition variable attributes object with default values.
.It Xo
.Ft int
.Fn pthread_cond_broadcast "pthread_cond_t *cond"
.Xc
Unblock all threads currently blocked on the specified condition variable.
.It Xo
.Ft int
.Fn pthread_cond_destroy "pthread_cond_t *cond"
.Xc
Destroy a condition variable.
.It Xo
.Ft int
.Fn pthread_cond_init "pthread_cond_t *cond" "const pthread_condattr_t *attr"
.Xc
Initialize a condition variable with specified attributes.
.It Xo
.Ft int
.Fn pthread_cond_signal "pthread_cond_t *cond"
.Xc
Unblock at least one of the threads blocked on the specified condition variable.
.It Xo
.Ft int
.Fo pthread_cond_timedwait
.Fa "pthread_cond_t *cond" "pthread_mutex_t *mutex"
.Fa "const struct timespec *abstime"
.Fc
.Xc
Wait no longer than the specified time for a condition
and lock the specified mutex.
.It Xo
.Ft int
.Fn pthread_cond_wait "pthread_cond_t *" "pthread_mutex_t *mutex"
.Xc
Wait for a condition and lock the specified mutex.
.El
.Ss Read/Write Lock Routines
.Bl -tag -width indent
.It Xo
.Ft int
.Fn pthread_rwlock_destroy "pthread_rwlock_t *lock"
.Xc
Destroy a read/write lock object.
.It Xo
.Ft int
.Fo pthread_rwlock_init
.Fa "pthread_rwlock_t *lock" "const pthread_rwlockattr_t *attr"
.Fc
.Xc
Initialize a read/write lock object.
.It Xo
.Ft int
.Fn pthread_rwlock_rdlock "pthread_rwlock_t *lock"
.Xc
Lock a read/write lock for reading, blocking until the lock can be
acquired.
.It Xo
.Ft int
.Fn pthread_rwlock_tryrdlock "pthread_rwlock_t *lock"
.Xc
Attempt to lock a read/write lock for reading, without blocking if the
lock is unavailable.
.It Xo
.Ft int
.Fn pthread_rwlock_trywrlock "pthread_rwlock_t *lock"
.Xc
Attempt to lock a read/write lock for writing, without blocking if the
lock is unavailable.
.It Xo
.Ft int
.Fn pthread_rwlock_unlock "pthread_rwlock_t *lock"
.Xc
Unlock a read/write lock.
.It Xo
.Ft int
.Fn pthread_rwlock_wrlock "pthread_rwlock_t *lock"
.Xc
Lock a read/write lock for writing, blocking until the lock can be
acquired.
.It Xo
.Ft int
.Fn pthread_rwlockattr_destroy "pthread_rwlockattr_t *attr"
.Xc
Destroy a read/write lock attribute object.
.It Xo
.Ft int
.Fo pthread_rwlockattr_getpshared
.Fa "const pthread_rwlockattr_t *attr" "int *pshared"
.Fc
.Xc
Retrieve the process shared setting for the read/write lock attribute
object.
.It Xo
.Ft int
.Fn pthread_rwlockattr_init "pthread_rwlockattr_t *attr"
.Xc
Initialize a read/write lock attribute object.
.It Xo
.Ft int
.Fn pthread_rwlockattr_setpshared "pthread_rwlockattr_t *attr" "int pshared"
.Xc
Set the process shared setting for the read/write lock attribute object.
.El
.Ss Per-Thread Context Routines
.Bl -tag -width indent
.It Xo
.Ft int
.Fn pthread_key_create "pthread_key_t *key" "void \*[lp]*routine\*[rp]\*[lp]void *\*[rp]"
.Xc
Create a thread-specific data key.
.It Xo
.Ft int
.Fn pthread_key_delete "pthread_key_t key"
.Xc
Delete a thread-specific data key.
.It Xo
.Ft "void *"
.Fn pthread_getspecific "pthread_key_t key"
.Xc
Get the thread-specific value for the specified key.
.It Xo
.Ft int
.Fn pthread_setspecific "pthread_key_t key" "const void *value_ptr"
.Xc
Set the thread-specific value for the specified key.
.El
.Ss Cleanup Routines
.Bl -tag -width indent
.It Xo
.Ft int
.Fo pthread_atfork
.Fa "void \*[lp]*prepare\*[rp]\*[lp]void\*[rp]"
.Fa "void \*[lp]*parent\*[rp]\*[lp]void\*[rp]"
.Fa "void \*[lp]*child\*[rp]\*[lp]void\*[rp]"
.Fc
.Xc
Register fork handlers
.It Xo
.Ft void
.Fn pthread_cleanup_pop "int execute"
.Xc
Remove the routine at the top of the calling thread's cancellation cleanup
stack and optionally invoke it.
.It Xo
.Ft void
.Fn pthread_cleanup_push "void \*[lp]*routine\*[rp]\*[lp]void *\*[rp]" "void *routine_arg"
.Xc
Push the specified cancellation cleanup handler onto the calling thread's
cancellation stack.
.El
.Sh IMPLEMENTATION NOTES
The current
.Dx
POSIX thread implementation is built in the library
.Sy libthread_xu
which contains both thread-safe libc functions and the thread functions.
Another thread library,
.Sy libc_r ,
is available for testing purposes.
.Pp
In
.Dx ,
it is possible to switch the threading library used by dynamically linked
binaries at execution time by re-linking
.Pa /usr/lib/libpthread.so.x
to a different library in
.Pa /usr/lib/thread .
At link time,
.Xr ld 1
reads the
.Sy SONAME
of
.Pa libpthread.so ,
which is set to
.Pa libpthread.so.0
(or a higher major, if there were ABI changes).
For normal libraries
.Pa libfoo.so
is usually a symlink to
.Pa libfoo.so.3
which also has its
.Sy SONAME
set to
.Pa libfoo.so.3 ,
so that if
.Pa libfoo.so.4
is installed, programs will still continue to use
.Pa libfoo.so.3
and not follow the symlink
.Pa libfoo.so
to the newer (and possibly incompatible)
.Pa libfoo.so.4 .
What we do for
.Pa libpthread.so
is approximately the opposite:
.Pa libpthread.so
is not a symlink but nevertheless has its
.Sy SONAME
set to
.Pa libpthread.so.0 .
.Pa libpthread.so.0 ,
however, is a symlink to the threading library of the user's choice.
The linker will use the default threading library which
.Pa libpthread.so
is linked to, but the runtime linker will instead follow the symlink.
.Pp
.Pa libc.so
defines all pthread functions as weak symbols except for
.Fn pthread_create
(which is defined by libpthread.so.x to satisfy
.Xr ld 1 ) .
At execution time,
.Xr rtld 1
will resolve all these references to the strong symbols from the thread
library.
.Pp
By default,
.Sy libc_r
is built as part of a 'make buildworld'.
To disable the build of
.Fa libc_r
you must supply the '-DNO_LIBC_R' option to
.Xr make 1
(or set it in
.Xr make.conf 5 ) .
.Pp
Another
.Xr make.conf 5
option,
.Va THREAD_LIB ,
can be used to override the system's default threading library.
.Pp
A
.Dx
specific option exists in
.Xr gcc 1
to simplify the linking of threaded processes.
.Nm gcc Fl pthread
links a threaded process against
.Pa libpthread.so
instead of
.Fa libc .
.Sh SEE ALSO
.Xr pthread_atfork 3 ,
.Xr pthread_cancel 3 ,
.Xr pthread_cleanup_pop 3 ,
.Xr pthread_cleanup_push 3 ,
.Xr pthread_condattr_destroy 3 ,
.Xr pthread_condattr_init 3 ,
.Xr pthread_cond_broadcast 3 ,
.Xr pthread_cond_destroy 3 ,
.Xr pthread_cond_init 3 ,
.Xr pthread_cond_signal 3 ,
.Xr pthread_cond_timedwait 3 ,
.Xr pthread_cond_wait 3 ,
.Xr pthread_create 3 ,
.Xr pthread_detach 3 ,
.Xr pthread_equal 3 ,
.Xr pthread_exit 3 ,
.Xr pthread_getspecific 3 ,
.Xr pthread_join 3 ,
.Xr pthread_key_delete 3 ,
.Xr pthread_kill 3 ,
.Xr pthread_mutexattr_destroy 3 ,
.Xr pthread_mutexattr_getprioceiling 3 ,
.Xr pthread_mutexattr_getprotocol 3 ,
.Xr pthread_mutexattr_gettype 3 ,
.Xr pthread_mutexattr_init 3 ,
.Xr pthread_mutexattr_setprioceiling 3 ,
.Xr pthread_mutexattr_setprotocol 3 ,
.Xr pthread_mutexattr_settype 3 ,
.Xr pthread_mutex_destroy 3 ,
.Xr pthread_mutex_init 3 ,
.Xr pthread_mutex_lock 3 ,
.Xr pthread_mutex_trylock 3 ,
.Xr pthread_mutex_unlock 3 ,
.Xr pthread_once 3 ,
.Xr pthread_rwlockattr_destroy 3 ,
.Xr pthread_rwlockattr_getpshared 3 ,
.Xr pthread_rwlockattr_init 3 ,
.Xr pthread_rwlockattr_setpshared 3 ,
.Xr pthread_rwlock_destroy 3 ,
.Xr pthread_rwlock_init 3 ,
.Xr pthread_rwlock_rdlock 3 ,
.Xr pthread_rwlock_unlock 3 ,
.Xr pthread_rwlock_wrlock 3 ,
.Xr pthread_self 3 ,
.Xr pthread_setcancelstate 3 ,
.Xr pthread_setcanceltype 3 ,
.Xr pthread_setspecific 3 ,
.Xr pthread_testcancel 3
.Sh STANDARDS
The functions with the
.Nm pthread_
prefix and not
.Nm _np
suffix or
.Nm pthread_rwlock
prefix conform to
.St -p1003.1-96 .
.Pp
The functions with the
.Nm pthread_
prefix and
.Nm _np
suffix are non-portable extensions to POSIX threads.
.Pp
The functions with the
.Nm pthread_rwlock
prefix are extensions created by The Open Group as part of the
.St -susv2 .