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PROLOG |NAME |SYNOPSIS |DESCRIPTION |RETURN VALUE |ERRORS |EXAMPLES |APPLICATION USAGE |RATIONALE |FUTURE DIRECTIONS |SEE ALSO |COPYRIGHT | |
PTHREAD_...CELSTATE(3P) POSIX Programmer's ManualPTHREAD_...CELSTATE(3P)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.
pthread_setcancelstate, pthread_setcanceltype, pthread_testcancel — set cancelability state
#include <pthread.h> int pthread_setcancelstate(intstate, int *oldstate); int pthread_setcanceltype(inttype, int *oldtype); void pthread_testcancel(void);
Thepthread_setcancelstate() function shall atomically both set the calling thread's cancelability state to the indicatedstate and return the previous cancelability state at the location referenced byoldstate. Legal values forstate are PTHREAD_CANCEL_ENABLE and PTHREAD_CANCEL_DISABLE. Thepthread_setcanceltype() function shall atomically both set the calling thread's cancelability type to the indicatedtype and return the previous cancelability type at the location referenced byoldtype. Legal values fortype are PTHREAD_CANCEL_DEFERRED and PTHREAD_CANCEL_ASYNCHRONOUS. The cancelability state and type of any newly created threads, including the thread in whichmain() was first invoked, shall be PTHREAD_CANCEL_ENABLE and PTHREAD_CANCEL_DEFERRED respectively. Thepthread_testcancel() function shall create a cancellation point in the calling thread. Thepthread_testcancel() function shall have no effect if cancelability is disabled.
If successful, thepthread_setcancelstate() andpthread_setcanceltype() functions shall return zero; otherwise, an error number shall be returned to indicate the error.
Thepthread_setcancelstate() function may fail if:EINVALThe specified state is not PTHREAD_CANCEL_ENABLE or PTHREAD_CANCEL_DISABLE. Thepthread_setcanceltype() function may fail if:EINVALThe 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.
None.
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 callpthread_setcancelstate() from a signal handler since it is not currently required to be async-signal-safe. On implementations wherepthread_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 makepthread_setcancelstate() async-signal-safe.
Thepthread_setcancelstate() andpthread_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 eitherdeferred orasynchronous 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.
Thepthread_setcancelstate() function may be added to the table of async-signal-safe functions inSection 2.4.3,Signal Actions.
pthread_cancel(3p) The Base Definitions volume of POSIX.1‐2017,pthread.h(0p)
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 athttp://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, seehttps://www.kernel.org/doc/man-pages/reporting_bugs.html .IEEE/The Open Group 2017PTHREAD_...CELSTATE(3P)Pages that refer to this page:pthread.h(0p), pthread_cancel(3p), pthread_cleanup_pop(3p), pthread_testcancel(3p)
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