pthread_setcancelstate

       and type

SYNOPSIS
       #include <pthread.h>

       int pthread_setcancelstate(int state, int *oldstate);
       int pthread_setcanceltype(int type, int *oldtype);

       Compile and link with -pthread.

DESCRIPTION
       The pthread_setcancelstate() sets the cancelability state of the  call-
       ing  thread  to  the  value given in state.  The previous cancelability
       state of the thread is returned in the buffer pointed to  by  oldstate.
       The state argument must have one of the following values:

       PTHREAD_CANCEL_ENABLE
              The  thread  is  cancelable.   This is the default cancelability
              state in all new threads, including  the  initial  thread.   The
              thread's  cancelability type determines when a cancelable thread
              will respond to a cancellation request.

       PTHREAD_CANCEL_DISABLE
              The thread is not cancelable.   If  a  cancellation  request  is
              received, it is blocked until cancelability is enabled.

       The  pthread_setcanceltype() sets the cancelability type of the calling
       thread to the value given in type.  The previous cancelability type  of
       the  thread  is returned in the buffer pointed to by oldtype.  The type
       argument must have one of the following values:

       PTHREAD_CANCEL_DEFERRED
              A cancellation request is deferred until the thread next calls a
              function  that  is a cancellation point (see pthreads(7)).  This
              is the default cancelability type in all new threads,  including
              the initial thread.

       PTHREAD_CANCEL_ASYNCHRONOUS
              The  thread can be canceled at any time.  (Typically, it will be
              canceled immediately upon receiving a cancellation request,  but
              the system doesn't guarantee this.)

       The  set-and-get  operation  performed  by  each  of these functions is
       atomic with respect to other threads in the process  calling  the  same
       function.

RETURN VALUE
       On  success,  these functions return 0; on error, they return a nonzero
       error number.

ERRORS
       The pthread_setcancelstate() can fail with the following error:

       EINVAL Invalid value for state.
       Briefly  disabling  cancelability  is  useful if a thread performs some
       critical action that must not be interrupted by a cancellation request.
       Beware  of  disabling  cancelability for long periods, or around opera-
       tions that may block for long  periods,  since  that  will  render  the
       thread unresponsive to cancellation requests.

       Setting the cancelability type to PTHREAD_CANCEL_ASYNCHRONOUS is rarely
       useful.  Since the thread could be canceled  at  any  time,  it  cannot
       safely  reserve  resources  (e.g.,  allocating  memory with malloc(3)),
       acquire mutexes, semaphores, or locks, and so on.  Reserving  resources
       is  unsafe because the application has no way of knowing what the state
       of these resources is when the thread is canceled; that is, did cancel-
       lation  occur  before  the  resources  were  reserved,  while they were
       reserved, or after they were released?  Furthermore, some internal data
       structures  (e.g.,  the  linked list of free blocks managed by the mal-
       loc(3) family of functions) may be left in  an  inconsistent  state  if
       cancellation  occurs in the middle of the function call.  Consequently,
       clean-up handlers cease to be useful.  Functions  that  can  be  safely
       asynchronously   canceled   are   called  async-cancel-safe  functions.
       POSIX.1-2001 only requires that  pthread_cancel(3),  pthread_setcancel-
       state(), and pthread_setcanceltype() be async-cancel-safe.  In general,
       other library functions can't be safely called from  an  asynchronously
       cancelable  thread.  One of the few circumstances in which asynchronous
       cancelability is useful is for cancellation of a thread that  is  in  a
       pure compute-bound loop.

       The  Linux  threading  implementations  permit the oldstate argument of
       pthread_setcancelstate() to be NULL,  in  which  case  the  information
       about  the  previous cancelability state is not returned to the caller.
       Many other implementations also permit a  NULL  oldstat  argument,  but
       POSIX.1-2001  does  not  specify  this  point, so portable applications
       should always specify a non-NULL value in oldstate.  A precisely analo-
       gous set of statements applies for the oldtype argument of pthread_set-
       canceltype().

EXAMPLE
       See pthread_cancel(3).

SEE ALSO
       pthread_cancel(3),   pthread_cleanup_push(3),    pthread_testcancel(3),
       pthreads(7)

COLOPHON
       This  page  is  part of release 3.35 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://man7.org/linux/man-pages/.



Linux                             2008-11-24         PTHREAD_SETCANCELSTATE(3)
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