11-06-2008
Signals...
(posted this in the scripting forum as well, but figured it should go here) So, what's going on is this:
For our program, we had to create our own shell, and if the user pressed ctrl-c just at the cmdline, then this signal would be ignored, but if there is a foreground process running, let's say, "sleep 10", and ctrl-c was pressed, then this process would be terminated... however, my problem lies within background processes... when I press ctrl-c after running something like "sleep 10 &", where the '&' indicates it's a background process, it uses the correct if branch of my SIGINT_handler, but it terminates the process.... so it's definitely something wrong with either the handler, or the installation of the signal.
What I don't get is... if the ctrl-c at the command line doesn't quit the program, why would it terminate my background process? Is it because the parent process just puts the ctrl-c onto the child processes? If so, is there a way to add something to my SIGINT_handler to make it ignore this signal?
****Let me just say that I have successfully been able to ignore the signal for a background process, but this way doesn't use my SIGINT_handler, which I do want it to use so some text gets printed. The way I'm talking of is just using "signal(SIGINT, SIG_IGN)", but like I said, doesn't use my SIGINT_handler...
This is my SIGINT_handler:
void SIGINT_handler(int sig)
{
if (foreground_pid == 0)
{
fprintf(stderr, "\nSIGINT ignored\n");
}
else
{
kill(foreground_pid, SIGINT);
foreground_pid = 0;
}
}
And then when I install the handler/signal, I use signal(SIGINT, SIGINT_handler) and also set foreground_pid in its respective spot... so if anyone can help, that'd be awesome, and if you need to see more code or some things are unclear, ask. Thanks.
10 More Discussions You Might Find Interesting
1. Programming
does the way of handling, interrupting signals in HP-UX same as that of solaris. If there is difference than what it is.?:confused: (1 Reply)
Discussion started by: kapilv
1 Replies
2. Programming
How can use signals in a C program If i want a child program to signal it's parent program that it(child) program has completed the task that it was assigned.:confused: (2 Replies)
Discussion started by: kapilv
2 Replies
3. UNIX for Dummies Questions & Answers
can any one give me an example of a concurrency program in threads and signals, i.e how to deliver messages between threads using signals. thanks (0 Replies)
Discussion started by: moe_7
0 Replies
4. Programming
can any one give me an example of a concurrency program in threads and signals, i.e how to deliver messages between threads using signals. thanks (2 Replies)
Discussion started by: moe_7
2 Replies
5. OS X (Apple)
Hi,
In our program, we are using SIGTERM and i tired to put break point in this function. But my debuger is unable to brake at that point.
I am working on Mac X and using XCode.
Thanks (0 Replies)
Discussion started by: Saurabh78
0 Replies
6. Programming
Hi,
In our program, we are using SIGTERM and i tired to put break point in this function. But my debuger is unable to brake at that point.
I am working on Mac X and using XCode.
Thanks (1 Reply)
Discussion started by: Saurabh78
1 Replies
7. UNIX for Dummies Questions & Answers
I am having trouble with folowing
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... (3 Replies)
Discussion started by: joker40
3 Replies
8. UNIX for Dummies Questions & Answers
I have following problem with this code..
First time trough the main loop.....
perror gives ....blocked signal:success(all other times gives illlegal seek)
Should every time trought the main loop be success??
And the perror otside of main loop...didn't change mask:success
That line of code... (2 Replies)
Discussion started by: joker40
2 Replies
9. UNIX for Dummies Questions & Answers
I know how to add signal to a set. But what if I want to add 2 or 3 signals to the set.
I know I can use sigaddset (&set,SIGBUS)....but what if I want to add SIGBUS and SIGALRM at once. Do i have to do it like this..
sigaddset (&set,SIGBUS);
sigaddset (&set,SIGALRM);
Is there another way to... (0 Replies)
Discussion started by: joker40
0 Replies
10. UNIX for Advanced & Expert Users
Hi All,
The problem statement is as below:
Problem: A process (exe) is getting executed in background. The output of this process is getting logged in a file. After successfully running for some time the process gets terminated. In the log file following is present:
^M[7m Interrupt ^M[27m... (8 Replies)
Discussion started by: Praty.27
8 Replies
LEARN ABOUT CENTOS
readkey
readkey(3alleg4) Allegro manual readkey(3alleg4)
NAME
readkey - Returns the next character from the keyboard buffer. Allegro game programming library.
SYNOPSIS
#include <allegro.h>
int readkey();
DESCRIPTION
Returns the next character from the keyboard buffer, in ASCII format. If the buffer is empty, it waits until a key is pressed. You can see
if there are queued keypresses with keypressed().
The low byte of the return value contains the ASCII code of the key, and the high byte the scancode. The scancode remains the same whatever
the state of the shift, ctrl and alt keys, while the ASCII code is affected by shift and ctrl in the normal way (shift changes case,
ctrl+letter gives the position of that letter in the alphabet, eg. ctrl+A = 1, ctrl+B = 2, etc). Pressing alt+key returns only the scan-
code, with a zero ASCII code in the low byte. For example:
int val;
...
val = readkey();
if ((val & 0xff) == 'd') /* by ASCII code */
allegro_message("You pressed 'd'
");
if ((val >> 8) == KEY_SPACE) /* by scancode */
allegro_message("You pressed Space
");
if ((val & 0xff) == 3) /* ctrl+letter */
allegro_message("You pressed Control+C
");
if (val == (KEY_X << 8)) /* alt+letter */
allegro_message("You pressed Alt+X
");
This function cannot return character values greater than 255. If you need to read Unicode input, use ureadkey() instead.
SEE ALSO
install_keyboard(3alleg4), ureadkey(3alleg4), keypressed(3alleg4), clear_keybuf(3alleg4), simulate_keypress(3alleg4)
Allegro version 4.4.2 readkey(3alleg4)