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PTHREAD_SETCANCELSTATE(3)  Linux Programmer's Manual PTHREAD_SETCANCELSTATE(3)

NAME
       pthread_setcancelstate, pthread_setcanceltype - set cancelability state
       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.

       The pthread_setcanceltype() can fail with the following error:

       EINVAL Invalid value for type.

ATTRIBUTES
   Multithreading (see pthreads(7))
       The pthread_setcancelstate() and pthread_setcanceltype() functions  are
       thread-safe.

CONFORMING TO
       POSIX.1-2001.

NOTES
       For details of what happens when a thread is canceled, see pthread_can-
       cel(3).

       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.

   Asynchronous cancelability
       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 requires  only  that  pthread_can-
       cel(3), pthread_setcancelstate(), 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.

   Portability notes
       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 3.74 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest     version     of     this    page,    can    be    found    at
       http://www.kernel.org/doc/man-pages/.

Linux                             2014-05-13         PTHREAD_SETCANCELSTATE(3)

Czas wygenerowania: 0.00053 sek.


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