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Full Discussion: Help understanding signals
Top Forums UNIX for Dummies Questions & Answers Help understanding signals Post 302464727 by joker40 on Wednesday 20th of October 2010 11:12:19 PM
Old 10-21-2010
Help understanding signals

I am having trouble with folowing
Code:
sigset_t s;    // now s represents set of signals
sigemptyset(&s) ; // initialize this set and exclude all the signals from it.is it empty?
sigaddset(&s,SIGILL);//this set containts only SIGILL signal
sigprocmask(SIG_BLOCK,&s,NULL);//lost on this one

Can anyone see my comment in the code and tell me if I am right. Last sigprocmask i read in documentation but I didnt really understand it.
Any help would be great
 

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SIGSETMASK(3)						   BSD Library Functions Manual 					     SIGSETMASK(3)

NAME
sigsetmask -- set current signal mask LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <signal.h> int sigsetmask(int mask); sigmask(signum); DESCRIPTION
This interface is made obsolete by: sigprocmask(2). sigsetmask() sets the current signal mask Signals are blocked from delivery if the corresponding bit in mask is a 1; the macro sigmask() is provided to construct the mask for a given signum. The system quietly disallows SIGKILL or SIGSTOP to be blocked. RETURN VALUES
The previous set of masked signals is returned. EXAMPLES
The following example using sigsetmask(): int omask; omask = sigblock(sigmask(SIGINT) | sigmask(SIGHUP)); ... sigsetmask(omask & ~(sigmask(SIGINT) | sigmask(SIGHUP))); Could be converted literally to: sigset_t set, oset; sigemptyset(&set); sigaddset(&set, SIGINT); sigaddset(&set, SIGHUP); sigprocmask(SIG_BLOCK, &set, &oset); ... sigdelset(&oset, SIGINT); sigdelset(&oset, SIGHUP); sigprocmask(SIG_SETMASK, &oset, NULL); Another, clearer, alternative is: sigset_t set; sigemptyset(&set); sigaddset(&set, SIGINT); sigaddset(&set, SIGHUP); sigprocmask(SIG_BLOCK, &set, NULL); ... sigprocmask(SIG_UNBLOCK, &set, NULL); To completely clear the signal mask using sigsetmask() one can do: (void) sigsetmask(0); Which can be expressed via sigprocmask(2) as: sigset_t eset; sigemptyset(&eset); (void) sigprocmask(SIG_SETMASK, &eset, NULL); SEE ALSO
kill(2), sigaction(2), sigprocmask(2), sigsuspend(2), sigblock(3), sigsetops(3), sigvec(3) HISTORY
The sigsetmask() function call appeared in 4.2BSD and has been deprecated. BSD
August 10, 2002 BSD
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