NAME
pthread_cancel - cancel execution of a thread
SYNOPSIS
#include <pthread.h>
int pthread_cancel(pthread_t thread);
DESCRIPTION
The pthread_cancel() function shall request that thread 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 thread shall be called. When the last
cancellation cleanup handler returns, the thread-specific data
destructor functions shall be called for thread. When the last
destructor function returns, thread shall be terminated.
The cancellation processing in the target thread shall run
asynchronously with respect to the calling thread returning from
pthread_cancel().
RETURN VALUE
If successful, the pthread_cancel() function shall return zero;
otherwise, an error number shall be returned to indicate the error.
ERRORS
The pthread_cancel() function may fail if:
ESRCH No thread could be found corresponding to that specified by the
given thread ID.
The pthread_cancel() function shall not return an error code of
[EINTR].
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
None.
RATIONALE
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 pthread_cancel() function, which would trigger the
cancellation semantics.
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 pthread_kill(), and the behavior of the delivered
cancellation signal would be unlike any previously existing defined
signal.
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.
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.
FUTURE DIRECTIONS
None.
SEE ALSO
pthread_exit(3), pthread_cond_timedwait(3), pthread_join(3),
pthread_cleanup_pop(3), pthread_cleanup_push(3),
pthread_setcancelstate(3), pthread_setcanceltype(3),
pthread_testcancel(3), the Base Definitions volume of IEEE Std
1003.1-2001, <pthread.h>
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 .