PTHREAD_CANCEL(3)          POSIX Programmer's Manual         PTHREAD_CANCEL(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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 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.

       If an implementation detects use of a thread ID after the end of its
       lifetime, it is recommended that the function should fail and report an
       [ESRCH] error.

FUTURE DIRECTIONS
       None.

SEE ALSO
       pthread__exit(), pthread__cond__timedwait(), pthread__join(),
       pthread__setcancelstate()

       The Base Definitions volume of POSIX.1-2017, <pthread.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                    PTHREAD_CANCEL(3)
