PTHREAD_SETCANCELSTATE(P) POSIX Programmer's Manual PTHREAD_SETCANCELSTATE(P)
pthread_setcancelstate, pthread_setcanceltype, pthread_testcancel - set cancelability
int pthread_setcancelstate(int state, int *oldstate);
int pthread_setcanceltype(int type, int *oldtype);
The pthread_setcancelstate() function shall atomically both set the calling thread's can-
celability 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
The pthread_setcanceltype() function shall atomically both set the calling thread's cance-
lability 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
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
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.
If successful, the pthread_setcancelstate() and pthread_setcanceltype() functions shall
return zero; otherwise, an error number shall be returned to indicate the error.
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.
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 proce-
dures 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, con-
trary 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 asyn-
pthread_cancel() , the Base Definitions volume of IEEE Std 1003.1-2001, <pthread.h>
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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 PTHREAD_SETCANCELSTATE(P)