239 lines
5.9 KiB
Groff
239 lines
5.9 KiB
Groff
.\" $NetBSD: setjmp.3,v 1.18 2021/05/24 23:59:59 riastradh Exp $
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.\"
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.\" Copyright (c) 1990, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" the American National Standards Committee X3, on Information
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.\" Processing Systems.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)setjmp.3 8.1 (Berkeley) 6/4/93
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.\"
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.Dd June 1, 2008
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.Dt SETJMP 3
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.Os
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.Sh NAME
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.Nm sigsetjmp ,
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.Nm siglongjmp ,
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.Nm setjmp ,
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.Nm longjmp ,
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.Nm _setjmp ,
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.Nm _longjmp ,
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.Nm longjmperror
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.Nd non-local jumps
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In setjmp.h
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.Ft int
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.Fn sigsetjmp "sigjmp_buf env" "int savemask"
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.Ft void
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.Fn siglongjmp "sigjmp_buf env" "int val"
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.Ft int
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.Fn setjmp "jmp_buf env"
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.Ft void
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.Fn longjmp "jmp_buf env" "int val"
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.Ft int
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.Fn _setjmp "jmp_buf env"
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.Ft void
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.Fn _longjmp "jmp_buf env" "int val"
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.Ft void
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.Fn longjmperror void
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.Sh DESCRIPTION
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The
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.Fn sigsetjmp ,
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.Fn setjmp ,
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and
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.Fn _setjmp
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functions save their calling environment in
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.Fa env .
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Each of these functions returns 0.
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.Pp
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The corresponding
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.Fn longjmp
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functions restore the environment saved by the most recent
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invocation of the respective
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.Fn setjmp
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function.
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They then return so that program execution continues as if the corresponding
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invocation of the
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.Fn setjmp
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call had just returned the value specified by
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.Fa val ,
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instead of 0.
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The
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.Fn longjmp
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functions cannot cause
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.Fn setjmp
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to return 0; if
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.Fa val
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is 0,
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.Fn setjmp
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returns 1 instead.
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.Pp
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Pairs of calls may be intermixed, i.e., both
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.Fn sigsetjmp
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and
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.Fn siglongjmp
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as well as
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.Fn setjmp
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and
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.Fn longjmp
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combinations may be used in the same program.
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However, individual calls may not, e.g., the
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.Fa env
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argument to
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.Fn setjmp
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may not be passed to
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.Fn siglongjmp .
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.Pp
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The
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.Fn longjmp
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routines may not be called after the routine which called the
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.Fn setjmp
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routines returns.
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.Pp
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All accessible objects have values as of the time
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.Fn longjmp
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routine was called, except that the values of objects of automatic storage
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invocation duration that do not have the
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.Li volatile
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type and have been changed between the
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.Fn setjmp
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invocation and
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.Fn longjmp
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call are indeterminate.
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.Pp
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The
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.Fn setjmp Ns / Ns Fn longjmp
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function pairs save and restore the signal mask while
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.Fn _setjmp Ns / Ns Fn _longjmp
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function pairs save and restore only the register set and the stack.
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(See
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.Fn sigprocmask 2 . )
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.Pp
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The
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.Fn sigsetjmp Ns / Ns Fn siglongjmp
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function pairs save and restore the signal mask if the argument
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.Fa savemask
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is non-zero.
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Otherwise, only the register set and the stack are saved.
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.Pp
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In other words,
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.Fn setjmp Ns / Ns Fn longjmp
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are functionally equivalent to
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.Fn sigsetjmp Ns / Ns Fn siglongjmp
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when
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.Fn sigsetjmp
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is called with a non-zero
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.Fa savemask
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argument.
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Conversely,
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.Fn _setjmp Ns / Ns Fn _longjmp
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are functionally equivalent to
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.Fn sigsetjmp Ns / Ns Fn siglongjmp
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when
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.Fn sigsetjmp
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is called with a zero-value
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.Fa savemask .
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.Pp
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The
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.Fn sigsetjmp Ns / Ns Fn siglongjmp
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interfaces are preferred for maximum portability.
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.Sh ERRORS
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If the contents of the
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.Fa env
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are corrupted or correspond to an environment that has already returned,
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the
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.Fn longjmp
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routine calls the routine
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.Xr longjmperror 3 .
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If
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.Fn longjmperror
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returns, the program is aborted (see
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.Xr abort 3 ) .
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The default version of
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.Fn longjmperror
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prints the message
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.Dq Li longjmp botch
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to standard error and returns.
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User programs wishing to exit more gracefully should write their own
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versions of
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.Fn longjmperror .
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.Sh SEE ALSO
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.Xr sigaction 2 ,
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.Xr sigaltstack 2 ,
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.Xr sigprocmask 2 ,
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.Xr pthread_sigmask 3 ,
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.Xr signal 3
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.Sh STANDARDS
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The
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.Fn setjmp
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and
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.Fn longjmp
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functions conform to
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.St -ansiC .
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The
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.Fn sigsetjmp
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and
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.Fn siglongjmp
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functions conform to
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.St -p1003.1-90 .
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.Sh CAVEATS
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Historically, on
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.At V ,
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the
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.Fn setjmp Ns / Ns Fn longjmp
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functions have been equivalent to the
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.Bx
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.Fn _setjmp Ns / Ns Fn _longjmp
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functions and do not restore the signal mask.
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Because of this discrepancy, the
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.Fn sigsetjmp Ns / Ns Fn siglongjmp
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interfaces should be used if portability is desired.
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.Pp
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Use of
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.Fn longjmp
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or
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.Fn siglongjmp
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from inside a signal handler is not as easy as it might seem.
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Generally speaking, all possible code paths between the
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.Fn setjmp
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and
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.Fn longjmp
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must be signal race safe.
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Furthermore, the code paths must not do resource management
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(such as
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.Xr open 2
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or
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.Xr close 2 )
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without blocking the signal in question, or resources might
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be mismanaged.
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Obviously this makes
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.Fn longjmp
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much less useful than previously thought.
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