VMS Help DCE_THREADS, Application Routines, pthread_setcancel  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  NAME

      pthread_setcancel - Enables or disables the current thread's
                          general cancelability

  SYNOPSIS

      #include <pthread.h>

      int pthread_setcancel( int state );

  PARAMETERS

      state                State of general cancelability set for the
                           calling thread.  On return, receives the
                           prior state of general cancelability.  Valid
                           values are as follows:

                           CANCEL_ON    General cancelability is enabled.

                           CANCEL_OFF   General cancelability is disabled.

  DESCRIPTION

  The pthread_setcancel() routine enables or disables the current thread's
  general cancelability and returns the previous cancelability state to
  the state parameter.
  When general cancelability is set to CANCEL_OFF, a cancel cannot be
  delivered to the thread, even if a cancelable routine is called or asyn-
  chronous cancelability is enabled.

  When a thread is created, the default general cancelability state is
  CANCEL_ON.

  POSSIBLE DANGERS OF DISABLING CANCELABILITY

  The most important use of cancels is to ensure that indefinite wait
  operations are terminated. For example, a thread waiting on some network
  connection, which may take days to respond (or may never respond), is
  normally made cancelable.

  However, when cancelability is disabled, no routine is cancelable. Waits
  must be completed normally before a cancel can be delivered. As a
  result, the program stops working and the user is unable to cancel the
  operation.

  When disabling cancelability, be sure that no long waits can occur or
  that it is necessary for other reasons to defer cancels around that par-
  ticular region of code.

  RETURN VALUES

  If the function fails, errno may be set to one of the following values:

    Return       Error      Description
    ___________________________________________________________
    CANCEL_ON               Asynchronous cancelability was on.

    CANCEL_OFF              Asynchronous cancelability was off.

    -1           [EINVAL]   The specified state is not CANCEL_ON
                            or CANCEL_OFF.

  RELATED INFORMATION

      FUNCTIONS:  pthread_cancel
                  pthread_setasynccancel
                  pthread_testcancel