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PTHREAD_CANCEL(3P)         POSIX Programmer's Manual        PTHREAD_CANCEL(3P)
PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the  corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.
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  can-
       cellation  cleanup  handlers  for thread shall be called. When the last
       cancellation cleanup handler returns, the thread-specific data destruc-
       tor  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  asyn-
       chronously   with   respect   to  the  calling  thread  returning  from
       pthread_cancel().
RETURN VALUE
       If successful, the pthread_cancel() function shall return zero;  other-
       wise, 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 can-
       cellation 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  sig-
       nals 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  func-
       tion 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_set-
       cancelstate()
       The Base Definitions volume of POSIX.1-2008, <pthread.h>
COPYRIGHT
       Portions  of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
       cal  and  Electronics  Engineers,  Inc  and  The  Open Group.  (This is
       POSIX.1-2008 with the 2013 Technical Corrigendum  1  applied.)  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.unix.org/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.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                   PTHREAD_CANCEL(3P)