12-02-2011
Quote:
Originally Posted by
DendyGamer
Why "signal safety" may change something? Signals are blocked, when signal action called.
It means, you're not allowed to call pthread_join(*s,NULL); inside a signal handler, and the results can't be predicted when you do so. It may work and betray you in strange ways later. It may do incorrect things in a less than obvious way. It may blow up immediately. It may work in this system but fail when ported to another system or your kernel is upgraded. In short, you're not supposed to do it.
The only signal-safe IPC I know of is sem_wait.
10 More Discussions You Might Find Interesting
1. Programming
I am trying to send a SIGUSR1 to a set of process. Please tell
me how to do. I've tried the system call raise(int sig) but it just
raise a signal of to the 'current process.'
My program is about a network chat server. When a client
connects in, The main process will fork a new process... (1 Reply)
Discussion started by: Namely
1 Replies
2. UNIX for Advanced & Expert Users
hi
I have created a application which uses SIGUSR2. It send this signal to server and waits for signal SIGUSR2 from server after server performing some operation server sends SIGUSR2 back to the application. The application then quits.
This works fine which ran from terminal , but when I... (3 Replies)
Discussion started by: khan_069
3 Replies
3. Programming
I am using the signal function, and passing it a function named quit procedure...I get the following warning....
passing arg2 of signal from incompatible pointer type...
void quit_procedure(void); //this is the way i define my prototype...
signal(SIGINT, quit_procedure);
Please guide... (5 Replies)
Discussion started by: jacques83
5 Replies
4. Programming
#include<signal.h>
void suicide();
main()
{
printf("use CTRL \\ for exiting \n");
//signal(SIGINT,SIG_DFL);
signal(SIGQUIT,suicide);
for (;;);
}
void suicide()
{ printf("hello here you r in the suicide code ");
}
i was just starting with signals .. and tried this ,, but in the... (10 Replies)
Discussion started by: narendra.pant
10 Replies
5. Programming
Hi,
I have a daq program that runs in an infinite loop until it receives SIGINT. A handler catches the signal and sets a flag to stop the while loop. After the loop some things have to be cleaned up.
The problem is that I want my main while loop to wait until the next full second begins, to... (2 Replies)
Discussion started by: soeckel
2 Replies
6. Programming
i wrote handler for sigsegv such that i can allocate memory for a variable to which
sigsegv generated for illlegal acces of memory.
my code is
#include <signal.h>
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
char *j;
void segv_handler(int dummy)
{
j=(char *)malloc(10);
... (4 Replies)
Discussion started by: pavan6754
4 Replies
7. Programming
hi friends i have a problem in signal handling ...
let me explain my problem clearly..
i have four process ..
main process forks two child process and each child process again forks another new process respectively...
the problem is whenever i kill the child process it is reforking and the... (2 Replies)
Discussion started by: senvenugopal
2 Replies
8. Programming
Hi all,
Sorry about the title,at first i decided to ask a problem about the signal mechanism,however,i'm now figured it out.Sorry to forget modify the title:wall:.I had a small problem that if i use the code which is commented,the code would get a segment fault,while the above code NOT.what's... (4 Replies)
Discussion started by: homeboy
4 Replies
9. Programming
i m unble to execute code of
signal handler using
a) Wait b) Waitpid (1 Reply)
Discussion started by: madhura
1 Replies
10. Linux
hey,
i have been facing a very fatel error with dovecot..
i am getting this error in my dovecot.log file
dovecot: Feb 13 15:21:02 Fatal: chdir(/var/mail/folders/user1) failed with uid 1001: Permission denied
dovecot: Feb 13 15:21:02 Error: child 18732 (imap) returned error 89
dovecot: Feb... (3 Replies)
Discussion started by: htshshrm2
3 Replies
LEARN ABOUT NETBSD
signal
SIGNAL(3) BSD Library Functions Manual SIGNAL(3)
NAME
signal -- simplified software signal facilities
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <signal.h>
void (*
signal(int sig, void (*func)(int)))(int);
DESCRIPTION
This signal() facility is a simplified interface to the more general sigaction(2) facility.
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' char-
acter. Signals are used when a process is stopped because it wishes to access its control terminal while in the background (see 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
SIGKILL and SIGSTOP signals, the signal() function allows for a signal to be caught, to be ignored, or to generate an interrupt. See
signal(7) for comprehensive list of supported signals.
The 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, func should be SIG_DFL. A SIG_DFL resets the default action. To ignore the signal func should be SIG_IGN. This will cause subse-
quent instances of the signal to be ignored and pending instances to be discarded. If SIG_IGN is not used, further occurrences of the signal
are automatically blocked and func is called.
The handled signal is unblocked when the function returns and the process continues from where it left off when the signal occurred. Unlike
previous signal facilities, the handler func() remains installed after a signal has been delivered.
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 SA_RESTART flag with sigaction(2)). The affected system calls include read(2), write(2),
sendto(2), recvfrom(2), sendmsg(2) and recvmsg(2) on a communications channel or a low speed device and during a ioctl(2) or wait(2). How-
ever, calls that have already committed are not restarted, but instead return a partial success (for example, a short read count).
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 execve(2) function; ignored signals remain ignored.
Only functions that are async-signal-safe can safely be used in signal handlers, see signal(7) for a complete list.
RETURN VALUES
The previous action is returned on a successful call. Otherwise, SIG_ERR is returned and the global variable errno is set to indicate the
error.
ERRORS
signal() will fail and no action will take place if one of the following occur:
[EINVAL] Specified sig is not a valid signal number.
[EINVAL] An attempt is made to ignore or supply a handler for SIGKILL or SIGSTOP.
SEE ALSO
kill(1), kill(2), ptrace(2), sigaction(2), sigaltstack(2), sigprocmask(2), sigsuspend(2), psignal(3), setjmp(3), strsignal(3), tty(4),
signal(7)
HISTORY
This signal() facility appeared in 4.0BSD.
BSD
June 11, 2004 BSD