pthread_setcanceltype

PTHREAD_SETCANCELSTATE(3P) POSIX Programmer's ManualPTHREAD_SETCANCELSTATE(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_setcancelstate, pthread_setcanceltype, pthread_testcancel - set
       cancelability state

SYNOPSIS
       #include <pthread.h>

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


DESCRIPTION
       The pthread_setcancelstate() function shall atomically both set the
       calling thread's cancelability state to the indicated state and return
       the previous cancelability state at the location referenced by
       oldstate. Legal values for state are PTHREAD_CANCEL_ENABLE and
       PTHREAD_CANCEL_DISABLE.

       The pthread_setcanceltype() function shall atomically both set the
       calling thread's cancelability type to the indicated type and return
       the previous cancelability type at the location referenced by oldtype.
       Legal values for type are PTHREAD_CANCEL_DEFERRED and
       PTHREAD_CANCEL_ASYNCHRONOUS.

       The cancelability state and type of any newly created threads,
       including the thread in which main() was first invoked, shall be
       PTHREAD_CANCEL_ENABLE and PTHREAD_CANCEL_DEFERRED respectively.

       The pthread_testcancel() function shall create a cancellation point in
       the calling thread. The pthread_testcancel() function shall have no
       effect if cancelability is disabled.

RETURN VALUE
       If successful, the pthread_setcancelstate() and pthread_setcanceltype()
       functions shall return zero; otherwise, an error number shall be
       returned to indicate the error.

ERRORS
       The pthread_setcancelstate() function may fail if:

       EINVAL The specified state is not PTHREAD_CANCEL_ENABLE or
              PTHREAD_CANCEL_DISABLE.


       The pthread_setcanceltype() function may fail if:

       EINVAL The specified type is not PTHREAD_CANCEL_DEFERRED or
              PTHREAD_CANCEL_ASYNCHRONOUS.


       These functions shall not return an error code of [EINTR].

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       None.

RATIONALE
       The pthread_setcancelstate() and pthread_setcanceltype() functions
       control the points at which a thread may be asynchronously canceled.
       For cancellation control to be usable in modular fashion, some rules
       need to be followed.

       An object can be considered to be a generalization of a procedure.  It
       is a set of procedures and global variables written as a unit and
       called by clients not known by the object. Objects may depend on other
       objects.

       First, cancelability should only be disabled on entry to an object,
       never explicitly enabled. On exit from an object, the cancelability
       state should always be restored to its value on entry to the object.

       This follows from a modularity argument: if the client of an object (or
       the client of an object that uses that object) has disabled
       cancelability, it is because the client does not want to be concerned
       about cleaning up if the thread is canceled while executing some
       sequence of actions. If an object is called in such a state and it
       enables cancelability and a cancellation request is pending for that
       thread, then the thread is canceled, contrary to the wish of the client
       that disabled.

       Second, the cancelability type may be explicitly set to either deferred
       or asynchronous upon entry to an object.  But as with the cancelability
       state, on exit from an object the cancelability type should always be
       restored to its value on entry to the object.

       Finally, only functions that are cancel-safe may be called from a
       thread that is asynchronously cancelable.

FUTURE DIRECTIONS
       None.

SEE ALSO
       pthread_cancel(), 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_SETCANCELSTATE(3P)