316 lines
8.1 KiB
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316 lines
8.1 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of PTHREAD_SETCANCELSTATE</TITLE>
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</HEAD><BODY>
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<H1>PTHREAD_SETCANCELSTATE</H1>
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Section: Linux Programmer's Manual (3)<BR>Updated: 2019-10-10<BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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pthread_setcancelstate, pthread_setcanceltype -
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set cancelability state and type
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<PRE>
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<B>#include <<A HREF="file:///usr/include/pthread.h">pthread.h</A>></B>
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<B>int pthread_setcancelstate(int </B><I>state</I><B>, int *</B><I>oldstate</I><B>);</B>
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<B>int pthread_setcanceltype(int </B><I>type</I><B>, int *</B><I>oldtype</I><B>);</B>
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Compile and link with <I>-pthread</I>.
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</PRE>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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The
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<B>pthread_setcancelstate</B>()
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sets the cancelability state of the calling thread to the value
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given in
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<I>state</I>.
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The previous cancelability state of the thread is returned
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in the buffer pointed to by
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<I>oldstate</I>.
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The
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<I>state</I>
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argument must have one of the following values:
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<DL COMPACT>
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<DT id="1"><B>PTHREAD_CANCEL_ENABLE</B>
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<DD>
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The thread is cancelable.
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This is the default cancelability state in all new threads,
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including the initial thread.
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The thread's cancelability type determines when a cancelable thread
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will respond to a cancellation request.
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<DT id="2"><B>PTHREAD_CANCEL_DISABLE</B>
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<DD>
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The thread is not cancelable.
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If a cancellation request is received,
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it is blocked until cancelability is enabled.
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</DL>
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<P>
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The
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<B>pthread_setcanceltype</B>()
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sets the cancelability type of the calling thread to the value
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given in
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<I>type</I>.
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The previous cancelability type of the thread is returned
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in the buffer pointed to by
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<I>oldtype</I>.
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The
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<I>type</I>
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argument must have one of the following values:
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<DL COMPACT>
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<DT id="3"><B>PTHREAD_CANCEL_DEFERRED</B>
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<DD>
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A cancellation request is deferred until the thread next calls
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a function that is a cancellation point (see
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<B><A HREF="/cgi-bin/man/man2html?7+pthreads">pthreads</A></B>(7)).
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This is the default cancelability type in all new threads,
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including the initial thread.
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<DT id="4"><DD>
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Even with deferred cancellation, a
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cancellation point in an asynchronous signal handler may still
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be acted upon and the effect is as if it was an asynchronous
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cancellation.
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<DT id="5"><B>PTHREAD_CANCEL_ASYNCHRONOUS</B>
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<DD>
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The thread can be canceled at any time.
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(Typically,
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it will be canceled immediately upon receiving a cancellation request,
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but the system doesn't guarantee this.)
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</DL>
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<P>
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The set-and-get operation performed by each of these functions
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is atomic with respect to other threads in the process
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calling the same function.
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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On success, these functions return 0;
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on error, they return a nonzero error number.
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<A NAME="lbAF"> </A>
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<H2>ERRORS</H2>
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The
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<B>pthread_setcancelstate</B>()
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can fail with the following error:
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<DL COMPACT>
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<DT id="6"><B>EINVAL</B>
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<DD>
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Invalid value for
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<I>state</I>.
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</DL>
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<P>
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The
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<B>pthread_setcanceltype</B>()
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can fail with the following error:
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<DL COMPACT>
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<DT id="7"><B>EINVAL</B>
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<DD>
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Invalid value for
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<I>type</I>.
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</DL>
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<A NAME="lbAG"> </A>
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<H2>ATTRIBUTES</H2>
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For an explanation of the terms used in this section, see
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<B><A HREF="/cgi-bin/man/man2html?7+attributes">attributes</A></B>(7).
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<TABLE BORDER>
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<TR VALIGN=top><TD><B>Interface</B></TD><TD><B>Attribute</B></TD><TD><B>Value</B><BR></TD></TR>
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<TR VALIGN=top><TD>
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<B>pthread_setcancelstate</B>(),
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<B>pthread_setcanceltype</B>()
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</TD><TD>Thread safety</TD><TD>
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MT-Safe
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<BR></TD></TR>
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<TR VALIGN=top><TD>
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<B>pthread_setcancelstate</B>(),
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<B>pthread_setcanceltype</B>()
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</TD><TD>Async-cancel-safety</TD><TD>
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AC-Safe
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<BR></TD></TR>
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</TABLE>
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<A NAME="lbAH"> </A>
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<H2>CONFORMING TO</H2>
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POSIX.1-2001, POSIX.1-2008.
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<A NAME="lbAI"> </A>
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<H2>NOTES</H2>
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For details of what happens when a thread is canceled, see
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<B><A HREF="/cgi-bin/man/man2html?3+pthread_cancel">pthread_cancel</A></B>(3).
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<P>
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Briefly disabling cancelability is useful
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if a thread performs some critical action
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that must not be interrupted by a cancellation request.
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Beware of disabling cancelability for long periods,
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or around operations that may block for long periods,
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since that will render the thread unresponsive to cancellation requests.
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<A NAME="lbAJ"> </A>
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<H3>Asynchronous cancelability</H3>
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Setting the cancelability type to
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<B>PTHREAD_CANCEL_ASYNCHRONOUS</B>
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is rarely useful.
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Since the thread could be canceled at
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<I>any</I>
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time, it cannot safely reserve resources (e.g., allocating memory with
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<B><A HREF="/cgi-bin/man/man2html?3+malloc">malloc</A></B>(3)),
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acquire mutexes, semaphores, or locks, and so on.
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Reserving resources is unsafe because the application has no way of
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knowing what the state of these resources is when the thread is canceled;
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that is, did cancellation occur before the resources were reserved,
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while they were reserved, or after they were released?
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Furthermore, some internal data structures
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(e.g., the linked list of free blocks managed by the
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<B><A HREF="/cgi-bin/man/man2html?3+malloc">malloc</A></B>(3)
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family of functions) may be left in an inconsistent state
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if cancellation occurs in the middle of the function call.
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Consequently, clean-up handlers cease to be useful.
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<P>
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Functions that can be safely asynchronously canceled are called
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<I>async-cancel-safe functions</I>.
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POSIX.1-2001 and POSIX.1-2008 require only that
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<B><A HREF="/cgi-bin/man/man2html?3+pthread_cancel">pthread_cancel</A></B>(3),
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<B>pthread_setcancelstate</B>(),
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and
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<B>pthread_setcanceltype</B>()
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be async-cancel-safe.
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In general, other library functions
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can't be safely called from an asynchronously cancelable thread.
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<P>
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One of the few circumstances in which asynchronous cancelability is useful
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is for cancellation of a thread that is in a pure compute-bound loop.
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<A NAME="lbAK"> </A>
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<H3>Portability notes</H3>
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The Linux threading implementations permit the
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<I>oldstate</I>
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argument of
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<B>pthread_setcancelstate</B>()
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to be NULL, in which case the information about the previous
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cancelability state is not returned to the caller.
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Many other implementations also permit a NULL
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<I>oldstat</I>
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argument,
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but POSIX.1 does not specify this point,
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so portable applications should always specify a non-NULL value in
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<I>oldstate</I>.
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A precisely analogous set of statements applies for the
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<I>oldtype</I>
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argument of
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<B>pthread_setcanceltype</B>().
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<A NAME="lbAL"> </A>
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<H2>EXAMPLE</H2>
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See
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<B><A HREF="/cgi-bin/man/man2html?3+pthread_cancel">pthread_cancel</A></B>(3).
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<A NAME="lbAM"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?3+pthread_cancel">pthread_cancel</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+pthread_cleanup_push">pthread_cleanup_push</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+pthread_testcancel">pthread_testcancel</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?7+pthreads">pthreads</A></B>(7)
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<A NAME="lbAN"> </A>
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<H2>COLOPHON</H2>
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This page is part of release 5.05 of the Linux
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<I>man-pages</I>
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project.
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A description of the project,
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information about reporting bugs,
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and the latest version of this page,
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can be found at
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<A HREF="https://www.kernel.org/doc/man-pages/.">https://www.kernel.org/doc/man-pages/.</A>
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="8"><A HREF="#lbAB">NAME</A><DD>
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<DT id="9"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="10"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="11"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="12"><A HREF="#lbAF">ERRORS</A><DD>
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<DT id="13"><A HREF="#lbAG">ATTRIBUTES</A><DD>
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<DT id="14"><A HREF="#lbAH">CONFORMING TO</A><DD>
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<DT id="15"><A HREF="#lbAI">NOTES</A><DD>
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<DL>
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<DT id="16"><A HREF="#lbAJ">Asynchronous cancelability</A><DD>
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<DT id="17"><A HREF="#lbAK">Portability notes</A><DD>
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</DL>
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<DT id="18"><A HREF="#lbAL">EXAMPLE</A><DD>
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<DT id="19"><A HREF="#lbAM">SEE ALSO</A><DD>
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<DT id="20"><A HREF="#lbAN">COLOPHON</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:05:53 GMT, March 31, 2021
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