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.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
.TH "PTHREAD_CANCEL" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" pthread_cancel
.SH NAME
pthread_cancel \- cancel execution of a thread
.SH SYNOPSIS
.LP
\fB#include <pthread.h>
.br
.sp
int pthread_cancel(pthread_t\fP \fIthread\fP\fB); \fP
\fB
.br
\fP
.SH DESCRIPTION
.LP
The \fIpthread_cancel\fP() function shall request that \fIthread\fP
be canceled. The target thread's cancelability state and
type determines when the cancellation takes effect. When the cancellation
is acted on, the cancellation cleanup handlers for
\fIthread\fP shall be called. When the last cancellation cleanup handler
returns, the thread-specific data destructor functions
shall be called for \fIthread\fP. When the last destructor function
returns, \fIthread\fP shall be terminated.
.LP
The cancellation processing in the target thread shall run asynchronously
with respect to the calling thread returning from
\fIpthread_cancel\fP().
.SH RETURN VALUE
.LP
If successful, the \fIpthread_cancel\fP() function shall return zero;
otherwise, an error number shall be returned to indicate
the error.
.SH ERRORS
.LP
The \fIpthread_cancel\fP() function may fail if:
.TP 7
.B ESRCH
No thread could be found corresponding to that specified by the given
thread ID.
.sp
.LP
The \fIpthread_cancel\fP() function shall not return an error code
of [EINTR].
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.LP
None.
.SH APPLICATION USAGE
.LP
None.
.SH RATIONALE
.LP
Two alternative functions were considered for sending the cancellation
notification to a thread. One would be to define a new
SIGCANCEL signal that had the cancellation semantics when delivered;
the other was to define the new \fIpthread_cancel\fP()
function, which would trigger the cancellation semantics.
.LP
The advantage of a new signal was that so much of the delivery criteria
were identical to that used when trying to deliver a
signal that making cancellation notification a signal was seen as
consistent. Indeed, many implementations implement cancellation
using a special signal. On the other hand, there would be no signal
functions that could be used with this signal except \fIpthread_kill\fP(),
and the behavior of the delivered cancellation signal would be unlike
any previously existing defined signal.
.LP
The benefits of a special function include the recognition that this
signal would be defined because of the similar delivery
criteria and that this is the only common behavior between a cancellation
request and a signal. In addition, the cancellation
delivery mechanism does not have to be implemented as a signal. There
are also strong, if not stronger, parallels with language
exception mechanisms than with signals that are potentially obscured
if the delivery mechanism is visibly closer to signals.
.LP
In the end, it was considered that as there were so many exceptions
to the use of the new signal with existing signals functions
it would be misleading. A special function has resolved this problem.
This function was carefully defined so that an implementation
wishing to provide the cancellation functions on top of signals could
do so. The special function also means that implementations
are not obliged to implement cancellation with signals.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIpthread_exit\fP() , \fIpthread_cond_timedwait\fP() , \fIpthread_join\fP()
, \fIpthread_setcancelstate\fP() , the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, \fI<pthread.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
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