2008-11-14 17:22:19 +00:00
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.\" Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk
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.\" <mtk.manpages@gmail.com>
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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2008-11-24 18:21:03 +00:00
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.TH PTHREAD_SETCANCELSTATE 3 2008-11-24 "Linux" "Linux Programmer's Manual"
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2008-11-14 17:22:19 +00:00
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.SH NAME
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pthread_setcancelstate, pthread_setcanceltype \-
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set cancelability state and type
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.SH SYNOPSIS
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.nf
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.B #include <pthread.h>
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.BI "int pthread_setcancelstate(int " state ", int *" oldstate );
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.BI "int pthread_setcanceltype(int " type ", int *" oldtype );
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.sp
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Compile and link with \fI\-pthread\fP.
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.SH DESCRIPTION
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The
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.BR pthread_setcancelstate ()
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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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.IR state .
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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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.IR oldstate .
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The
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.I state
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argument must have one of the following values:
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.TP
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.B PTHREAD_CANCEL_ENABLE
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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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.TP
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.B PTHREAD_CANCEL_DISABLE
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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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.PP
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The
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.BR pthread_setcanceltype ()
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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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.IR type .
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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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.IR oldtype .
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The
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.I type
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argument must have one of the following values:
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.TP
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.B PTHREAD_CANCEL_DEFERRED
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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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.BR pthreads (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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.TP
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.B PTHREAD_CANCEL_ASYNCHRONOUS
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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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.PP
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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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.SH RETURN VALUE
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On success, these functions return 0;
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intro.1, time.1, adjtimex.2, capget.2, eventfd.2, fcntl.2, getrlimit.2, getsockopt.2, gettimeofday.2, intro.2, ioctl_list.2, ioperm.2, mlock.2, pivot_root.2, poll.2, prctl.2, ptrace.2, sched_setscheduler.2, select_tut.2, semget.2, sigaltstack.2, signalfd.2, sysctl.2, timer_settime.2, timerfd_create.2, wait.2, CPU_SET.3, argz_add.3, assert_perror.3, atexit.3, backtrace.3, bcmp.3, clearenv.3, ctime.3, dl_iterate_phdr.3, dlopen.3, ecvt.3, errno.3, error.3, ether_aton.3, exit.3, fenv.3, ferror.3, finite.3, flockfile.3, fnmatch.3, fpathconf.3, fpclassify.3, ftime.3, ftok.3, ftw.3, fwide.3, getaddrinfo.3, gethostbyname.3, getlogin.3, getnameinfo.3, getnetent.3, getopt.3, getprotoent.3, getrpcent.3, getservent.3, glob.3, hsearch.3, inet.3, isalpha.3, iswalnum.3, iswalpha.3, iswblank.3, iswcntrl.3, iswctype.3, iswdigit.3, iswgraph.3, iswlower.3, iswprint.3, iswpunct.3, iswspace.3, iswupper.3, iswxdigit.3, longjmp.3, lsearch.3, malloc.3, matherr.3, mblen.3, mbsinit.3, mbtowc.3, on_exit.3, printf.3, pthread_attr_init.3, pthread_attr_setaffinity_np.3, pthread_attr_setdetachstate.3, pthread_attr_setguardsize.3, pthread_attr_setinheritsched.3, pthread_attr_setschedparam.3, pthread_attr_setschedpolicy.3, pthread_attr_setscope.3, pthread_attr_setstack.3, pthread_attr_setstackaddr.3, pthread_attr_setstacksize.3, pthread_cancel.3, pthread_cleanup_push.3, pthread_equal.3, pthread_getattr_np.3, pthread_getcpuclockid.3, pthread_setaffinity_np.3, pthread_setcancelstate.3, pthread_setconcurrency.3, pthread_setschedparam.3, pthread_setschedprio.3, ptsname.3, putenv.3, putgrent.3, raise.3, rcmd.3, regex.3, rexec.3, rpc.3, rpmatch.3, rtnetlink.3, scandir.3, sem_init.3, setaliasent.3, setbuf.3, setenv.3, setjmp.3, signbit.3, stdio_ext.3, strtod.3, strtol.3, strtoul.3, system.3, termios.3, timeradd.3, tzset.3, ualarm.3, wctomb.3, xdr.3, st.4, tty_ioctl.4, core.5, elf.5, proc.5, bootparam.7, capabilities.7, icmp.7, ip.7, ipv6.7, math_error.7, mdoc.samples.7, mq_overview.7, pthreads.7, raw.7, regex.7, socket.7, tcp.7, tzselect.8: Global fix: s/non-zero/nonzero/
The tendency in English, as prescribed in style guides like
Chicago MoS, is towards removing hyphens after prefixes
like "non-" etc.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
2010-01-16 16:40:55 +00:00
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on error, they return a nonzero error number.
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2008-11-14 17:22:19 +00:00
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.SH ERRORS
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The
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.BR pthread_setcancelstate ()
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can fail with the following error:
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.TP
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.B EINVAL
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Invalid value for
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.IR state .
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.PP
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The
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.BR pthread_setcanceltype ()
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can fail with the following error:
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.TP
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.B EINVAL
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Invalid value for
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.IR type .
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.\" .SH VERSIONS
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.\" Available since glibc 2.0
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.SH CONFORMING TO
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POSIX.1-2001.
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.SH NOTES
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For details of what happens when a thread is canceled, see
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.BR pthread_cancel (3).
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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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Setting the cancelability type to
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.B PTHREAD_CANCEL_ASYNCHRONOUS
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is rarely useful.
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Since the thread could be canceled at
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.I any
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2008-11-24 18:21:03 +00:00
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time, it cannot safely reserve resources (e.g., allocating memory with
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.BR malloc (3)),
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acquire mutexes, semaphores, or locks, and so on.
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2008-11-24 22:35:16 +00:00
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Reserving resources is unsafe because the application has no way of
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2008-11-24 18:21:03 +00:00
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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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2008-11-24 22:46:21 +00:00
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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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.BR malloc (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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2008-11-24 18:21:03 +00:00
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Consequently, clean-up handlers cease to be useful.
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Functions that can be safely asynchronously canceled are called
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2008-11-26 02:44:53 +00:00
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.IR "async-cancel-safe functions" .
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2008-11-24 18:21:03 +00:00
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POSIX.1-2001 only requires that
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2008-11-14 17:22:19 +00:00
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.BR pthread_cancel (3),
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.BR pthread_setcancelstate (),
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and
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.BR pthread_setcanceltype ()
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2008-11-24 18:21:03 +00:00
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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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2008-11-14 17:22:19 +00:00
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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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The Linux threading implementations permit the
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.I oldstate
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argument of
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.BR pthread_setcancelstate ()
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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
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argument,
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.\" It looks like at least Solaris, FreeBSD and Tru64 support this.
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but POSIX.1-2001 does not specify this point,
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so portable applications should always specify a non-NULL value in
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.IR oldstate .
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A precisely analogous set of statements applies for the
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.I oldtype
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argument of
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.BR pthread_setcanceltype ().
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.SH EXAMPLE
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See
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.BR pthread_cancel (3).
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.SH SEE ALSO
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.BR pthread_cancel (3),
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clock_nanosleep.2, getpriority.2, kexec_load.2, nanosleep.2, nice.2, sched_setaffinity.2, timer_create.2, timer_delete.2, timer_settime.2, utime.2, btowc.3, futimes.3, log.3, pthread_attr_setguardsize.3, pthread_kill_other_threads_np.3, pthread_setaffinity_np.3, pthread_setcancelstate.3, pthread_setschedparam.3, pthread_setschedprio.3, pthread_tryjoin_np.3, strcoll.3, strcpy.3, string.3, strxfrm.3, networks.5, aio.7, sigevent.7, udplite.7: SEE ALSO: Place entries in correct order
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
2010-11-01 05:34:26 +00:00
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.BR pthread_cleanup_push (3),
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2008-11-14 17:22:19 +00:00
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.BR pthread_testcancel (3),
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.BR pthreads (7)
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