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Revision 1.24, Sun Jun 13 19:17:06 2004 UTC (8 years, 11 months ago) by lha
Add list of async-signal-safe functions Approved by wiz
.\" $NetBSD: signal.3,v 1.24 2004/06/13 19:17:06 lha Exp $ .\" .\" Copyright (c) 1980, 1991, 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)signal.3 8.3 (Berkeley) 4/19/94 .\" .Dd June 11, 2004 .Dt SIGNAL 3 .Os .Sh NAME .Nm signal .Nd simplified software signal facilities .Sh LIBRARY .Lb libc .Sh SYNOPSIS .In signal.h .\" The following is Quite Ugly, but syntactically correct. Don't try to .\" fix it. .Ft void \*(lp* .Fn signal "int sig" "void \*(lp*func\*(rp\*(lpint\*(rp\*(rp\*(rp\*(lpint" .Sh DESCRIPTION This .Fn signal facility is a simplified interface to the more general .Xr sigaction 2 facility. .Pp Signals allow the manipulation of a process from outside its domain as well as allowing the process to manipulate itself or copies of itself (children). There are two general types of signals: those that cause termination of a process and those that do not. Signals which cause termination of a program might result from an irrecoverable error or might be the result of a user at a terminal typing the `interrupt' character. Signals are used when a process is stopped because it wishes to access its control terminal while in the background (see .Xr tty 4 ) . Signals are optionally generated when a process resumes after being stopped, when the status of child processes changes, or when input is ready at the control terminal. Most signals result in the termination of the process receiving them if no action is taken; some signals instead cause the process receiving them to be stopped, or are simply discarded if the process has not requested otherwise. Except for the .Dv SIGKILL and .Dv SIGSTOP signals, the .Fn signal function allows for a signal to be caught, to be ignored, or to generate an interrupt. See .Xr signal 7 for comprehensive list of supported signals. .Pp The .Fa func procedure allows a user to choose the action upon receipt of a signal. To set the default action of the signal to occur as listed above, .Fa func should be .Dv SIG_DFL . A .Dv SIG_DFL resets the default action. To ignore the signal .Fa func should be .Dv SIG_IGN . This will cause subsequent instances of the signal to be ignored and pending instances to be discarded. If .Dv SIG_IGN is not used, further occurrences of the signal are automatically blocked and .Fa func is called. .Pp The handled signal is unblocked when the function returns and the process continues from where it left off when the signal occurred. .Bf -symbolic Unlike previous signal facilities, the handler func() remains installed after a signal has been delivered. .Ef .Pp For some system calls, if a signal is caught while the call is executing and the call is prematurely terminated, the call is automatically restarted. (The handler is installed using the .Dv SA_RESTART flag with .Xr sigaction 2 ) . The affected system calls include .Xr read 2 , .Xr write 2 , .Xr sendto 2 , .Xr recvfrom 2 , .Xr sendmsg 2 and .Xr recvmsg 2 on a communications channel or a low speed device and during a .Xr ioctl 2 or .Xr wait 2 . However, calls that have already committed are not restarted, but instead return a partial success (for example, a short read count). .Pp When a process which has installed signal handlers forks, the child process inherits the signals. All caught signals may be reset to their default action by a call to the .Xr execve 2 function; ignored signals remain ignored. .Pp Only functions that are async-signal-safe can safely be used in signal handlers, see .Xr signal 7 for a complete list. .Sh RETURN VALUES The previous action is returned on a successful call. Otherwise, .Dv SIG_ERR is returned and the global variable .Va errno is set to indicate the error. .Sh ERRORS .Fn signal will fail and no action will take place if one of the following occur: .Bl -tag -width Er .It Bq Er EINVAL Specified .Em sig is not a valid signal number. .It Bq Er EINVAL An attempt is made to ignore or supply a handler for .Dv SIGKILL or .Dv SIGSTOP . .El .Sh SEE ALSO .Xr kill 1 , .Xr kill 2 , .Xr ptrace 2 , .Xr sigaction 2 , .Xr sigaltstack 2 , .Xr sigprocmask 2 , .Xr sigsuspend 2 , .Xr psignal 3 , .Xr setjmp 3 , .Xr strsignal 3 , .Xr tty 4 , .Xr signal 7 .Sh HISTORY This .Fn signal facility appeared in .Bx 4.0 .