mirror of https://github.com/mkerrisk/man-pages
121 lines
4.5 KiB
Plaintext
121 lines
4.5 KiB
Plaintext
.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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.TH "PTHREAD_SETCANCELSTATE" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
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.\" pthread_setcancelstate
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.SH NAME
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pthread_setcancelstate, pthread_setcanceltype, pthread_testcancel
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\- set cancelability state
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.SH SYNOPSIS
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.LP
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\fB#include <pthread.h>
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.br
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.sp
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int pthread_setcancelstate(int\fP \fIstate\fP\fB, int *\fP\fIoldstate\fP\fB);
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.br
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int pthread_setcanceltype(int\fP \fItype\fP\fB, int *\fP\fIoldtype\fP\fB);
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.br
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void pthread_testcancel(void); \fP
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\fB
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.br
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\fP
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.SH DESCRIPTION
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.LP
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The \fIpthread_setcancelstate\fP() function shall atomically both
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set the calling thread's cancelability state to the indicated
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\fIstate\fP and return the previous cancelability state at the location
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referenced by \fIoldstate\fP. Legal values for
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\fIstate\fP are PTHREAD_CANCEL_ENABLE and PTHREAD_CANCEL_DISABLE.
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.LP
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The \fIpthread_setcanceltype\fP() function shall atomically both set
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the calling thread's cancelability type to the indicated
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\fItype\fP and return the previous cancelability type at the location
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referenced by \fIoldtype\fP. Legal values for \fItype\fP
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are PTHREAD_CANCEL_DEFERRED and PTHREAD_CANCEL_ASYNCHRONOUS.
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.LP
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The cancelability state and type of any newly created threads, including
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the thread in which \fImain\fP() was first invoked,
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shall be PTHREAD_CANCEL_ENABLE and PTHREAD_CANCEL_DEFERRED respectively.
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.LP
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The \fIpthread_testcancel\fP() function shall create a cancellation
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point in the calling thread. The
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\fIpthread_testcancel\fP() function shall have no effect if cancelability
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is disabled.
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.SH RETURN VALUE
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.LP
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If successful, the \fIpthread_setcancelstate\fP() and \fIpthread_setcanceltype\fP()
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functions shall return zero; otherwise, an
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error number shall be returned to indicate the error.
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.SH ERRORS
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.LP
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The \fIpthread_setcancelstate\fP() function may fail if:
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.TP 7
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.B EINVAL
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The specified state is not PTHREAD_CANCEL_ENABLE or PTHREAD_CANCEL_DISABLE.
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.sp
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.LP
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The \fIpthread_setcanceltype\fP() function may fail if:
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.TP 7
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.B EINVAL
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The specified type is not PTHREAD_CANCEL_DEFERRED or PTHREAD_CANCEL_ASYNCHRONOUS.
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.sp
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.LP
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These functions shall not return an error code of [EINTR].
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.LP
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\fIThe following sections are informative.\fP
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.SH EXAMPLES
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.LP
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None.
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.SH APPLICATION USAGE
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.LP
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None.
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.SH RATIONALE
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.LP
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The \fIpthread_setcancelstate\fP() and \fIpthread_setcanceltype\fP()
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functions control the points at which a thread may be
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asynchronously canceled. For cancellation control to be usable in
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modular fashion, some rules need to be followed.
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.LP
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An object can be considered to be a generalization of a procedure.
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It is a set of procedures and global variables written as a
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unit and called by clients not known by the object. Objects may depend
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on other objects.
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.LP
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First, cancelability should only be disabled on entry to an object,
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never explicitly enabled. On exit from an object, the
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cancelability state should always be restored to its value on entry
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to the object.
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.LP
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This follows from a modularity argument: if the client of an object
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(or the client of an object that uses that object) has
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disabled cancelability, it is because the client does not want to
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be concerned about cleaning up if the thread is canceled while
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executing some sequence of actions. If an object is called in such
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a state and it enables cancelability and a cancellation request
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is pending for that thread, then the thread is canceled, contrary
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to the wish of the client that disabled.
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.LP
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Second, the cancelability type may be explicitly set to either \fIdeferred\fP
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or \fIasynchronous\fP upon entry to an object.
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But as with the cancelability state, on exit from an object the cancelability
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type should always be restored to its value on entry
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to the object.
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.LP
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Finally, only functions that are cancel-safe may be called from a
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thread that is asynchronously cancelable.
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.SH FUTURE DIRECTIONS
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.LP
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None.
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.SH SEE ALSO
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.LP
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\fIpthread_cancel\fP() , the Base Definitions volume of IEEE\ Std\ 1003.1-2001,
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\fI<pthread.h>\fP
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.SH COPYRIGHT
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Portions of this text are reprinted and reproduced in electronic form
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from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
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-- Portable Operating System Interface (POSIX), The Open Group Base
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Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group. In the
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event of any discrepancy between this version and the original IEEE and
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The Open Group Standard, the original IEEE and The Open Group Standard
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is the referee document. The original Standard can be obtained online at
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http://www.opengroup.org/unix/online.html .
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