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.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
.TH "PTHREAD_SETCANCELSTATE" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" pthread_setcancelstate
.SH 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.
.SH NAME
pthread_setcancelstate, pthread_setcanceltype, pthread_testcancel
\- set cancelability state
.SH SYNOPSIS
.LP
\fB#include <pthread.h>
.br
.sp
int pthread_setcancelstate(int\fP \fIstate\fP\fB, int *\fP\fIoldstate\fP\fB);
.br
int pthread_setcanceltype(int\fP \fItype\fP\fB, int *\fP\fIoldtype\fP\fB);
.br
void pthread_testcancel(void); \fP
\fB
.br
\fP
.SH DESCRIPTION
.LP
The \fIpthread_setcancelstate\fP() function shall atomically both
set the calling thread's cancelability state to the indicated
\fIstate\fP and return the previous cancelability state at the location
referenced by \fIoldstate\fP. Legal values for
\fIstate\fP are PTHREAD_CANCEL_ENABLE and PTHREAD_CANCEL_DISABLE.
.LP
The \fIpthread_setcanceltype\fP() function shall atomically both set
the calling thread's cancelability type to the indicated
\fItype\fP and return the previous cancelability type at the location
referenced by \fIoldtype\fP. Legal values for \fItype\fP
are PTHREAD_CANCEL_DEFERRED and PTHREAD_CANCEL_ASYNCHRONOUS.
.LP
The cancelability state and type of any newly created threads, including
the thread in which \fImain\fP() was first invoked,
shall be PTHREAD_CANCEL_ENABLE and PTHREAD_CANCEL_DEFERRED respectively.
.LP
The \fIpthread_testcancel\fP() function shall create a cancellation
point in the calling thread. The
\fIpthread_testcancel\fP() function shall have no effect if cancelability
is disabled.
.SH RETURN VALUE
.LP
If successful, the \fIpthread_setcancelstate\fP() and \fIpthread_setcanceltype\fP()
functions shall return zero; otherwise, an
error number shall be returned to indicate the error.
.SH ERRORS
.LP
The \fIpthread_setcancelstate\fP() function may fail if:
.TP 7
.B EINVAL
The specified state is not PTHREAD_CANCEL_ENABLE or PTHREAD_CANCEL_DISABLE.
.sp
.LP
The \fIpthread_setcanceltype\fP() function may fail if:
.TP 7
.B EINVAL
The specified type is not PTHREAD_CANCEL_DEFERRED or PTHREAD_CANCEL_ASYNCHRONOUS.
.sp
.LP
These functions shall not return an error code of [EINTR].
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.LP
None.
.SH APPLICATION USAGE
.LP
None.
.SH RATIONALE
.LP
The \fIpthread_setcancelstate\fP() and \fIpthread_setcanceltype\fP()
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.
.LP
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.
.LP
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.
.LP
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.
.LP
Second, the cancelability type may be explicitly set to either \fIdeferred\fP
or \fIasynchronous\fP 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.
.LP
Finally, only functions that are cancel-safe may be called from a
thread that is asynchronously cancelable.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIpthread_cancel\fP(), the Base Definitions volume of IEEE\ Std\ 1003.1-2001,
\fI<pthread.h>\fP
.SH 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 .
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