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.\" $FreeBSD: src/lib/libpthread/man/pthread_cancel.3,v 1.7 2002/09/16 19:29:28 mini Exp $
.Dd July 9, 2010
.Dt PTHREAD_CANCEL 3
.Os
.Sh NAME
.Nm pthread_cancel
.Nd cancel execution of a thread
.Sh LIBRARY
.Lb libpthread
.Sh SYNOPSIS
.In pthread.h
.Ft int
.Fn pthread_cancel "pthread_t thread"
.Sh DESCRIPTION
The
.Fn pthread_cancel
function requests that
.Fa thread
be canceled.
The target thread's cancelability state and type determines
whether and when the target thread reacts to the cancellation request.
.Bl -enum -offset 2n
.It
The cancelability
.Em state
of a thread is determined by the
.Xr pthread_setcancelstate 3
function.
The state can be either:
.Bl -bullet -offset 2n
.It
.Dv PTHREAD_CANCEL_ENABLE :
the cancelability type determines when the actual cancellation occurs.
This is the default.
.It
.Dv PTHREAD_CANCEL_DISABLE :
the request from
.Fn pthread_cancel
remains queued until the cancellation is enabled by the thread.
.El
.It
The cancellation
.Em type
of a thread is determined by the
.Xr pthread_setcanceltype 3
function.
The type can be either:
.Bl -bullet -offset 2n
.It
.Dv PTHREAD_CANCEL_DEFERRED :
the cancellation will be delayed until the thread calls
a function that is a cancellation point.
This is the default.
The available cancellation points are listed in
.Xr pthread_setcanceltype 3 .
.It
.Dv PTHREAD_CANCEL_ASYNCHRONOUS :
the thread can be canceled at any time.
.El
.El
.Pp
When the thread reacts to the cancellation request, the following occur:
.Bl -enum -offset 2n
.It
The cancellation cleanup handlers for the thread are called; see
.Xr pthread_cleanup_push 3 .
.It
When the last cancellation cleanup handler returns,
the thread-specific data destructor functions will be called for the thread.
.It
When the last destructor function returns, the thread will be terminated; see
.Xr pthread_exit 3 .
.El
.Pp
The cancellation processing in the target thread runs asynchronously with
respect to the calling thread returning from
.Fn pthread_cancel .
.Pp
A status of
.Dv PTHREAD_CANCELED
is made available to any threads joining with the target.
The symbolic
constant
.Dv PTHREAD_CANCELED
expands to a constant expression of type
.Ft (void *) ,
whose value matches no pointer to an object in memory nor the value
.Dv NULL .
.Sh RETURN VALUES
If successful,  the
.Fn pthread_cancel
functions will return zero.
Otherwise an error number will be returned to
indicate the error.
.Sh ERRORS
The
.Fn pthread_cancel
function may fail if:
.Bl -tag -width Er
.It Bq Er ESRCH
No thread could be found corresponding to that specified by the given
thread ID.
.El
.Sh SEE ALSO
.Xr pthread_cleanup_pop 3 ,
.Xr pthread_join 3 ,
.Xr pthread_testcancel 3
.Sh STANDARDS
The function conforms to
.St -p1003.1-2001 .