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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 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  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.
FUTURE DIRECTIONS
       None.
SEE ALSO
       pthread_exit(),  pthread_cond_timedwait(), pthread_join(), pthread_set-
       cancelstate(), 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 .

IEEE/The Open Group                  2003                   PTHREAD_CANCEL(3P)