pthread_setcancelstate

PTHREAD_SETCANCELSTATE(3P)  POSIX Programmer's Manual PTHREAD_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
       In order to write a signal handler for an asynchronous signal which can
       run safely in a cancellable thread, pthread_setcancelstate() must be used
       to disable cancellation for the duration of any calls that the signal
       handler makes which are cancellation points. However, the standard does
       not permit strictly conforming applications to call
       pthread_setcancelstate() from a signal handler since it is not currently
       required to be async-signal-safe. On implementations where
       pthread_setcancelstate() is not async-signal-safe, alternatives are to
       ensure either that the corresponding signals are blocked during execution
       of functions that are not async-cancel-safe or that cancellation is
       disabled during times when those signals could be delivered.
       Implementations are strongly encouraged to make pthread_setcancelstate()
       async-signal-safe.

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
       The pthread_setcancelstate() function may be added to the table of async-
       signal-safe functions in Section 2.4.3, Signal Actions.

SEE ALSO
       pthread_cancel()

       The Base Definitions volume of POSIX.1‐2017, <pthread.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       Any typographical or formatting errors that appear in this page are most
       likely to have been introduced during the conversion of the source files
       to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                   2017            PTHREAD_SETCANCELSTATE(3P)