Signal Handling 2

[SwapSawe]

Dear All,

I am required to send a signal from one program to another program so as to execute the specified function. I am familiar with raise() and signal() ie. what they do. But I am unable to use them. Can anyone be kind enough to give me a sample source code.

Thanx,
SwapSawe.

 

[rbobbitt]

Set up the signal handler in the process that wants to catch the signal:

#include <signal.h>

/* ... */

signal(SIGUSR1,handler);

In the process that sends the signal, call raise():

#include <signal.h>

if (raise(SIGUSR1)!=0) {
/* failure */

/* ... */

SIGUSR1 might not be available for your system though, in which case you'll obviously have to use a different signal.

Russ
bobbitts@hotmail.com

http://home.earthlink.net/~bobbitts

 

[sramki]

There is also another way of sending signals .

Set up the signal handler in the process that wants to catch the signal:

#include <signal.h>

/* ... */

signal(SIGUSR1,handler);

The handler fucntion will be called as soon as the signal SIGUSR1 is invoked .

In the process that sends the signal, call kill();
This takes 2 parameters .
#include <signal.h>

kill(PID,SIGNAL-TO-BE-SENT);
eg: kill(pid,SIGUSR1);

regards
sramki

 

[rbobbitt]

Right (what was I thinking), of course if you're sending a signal to another process you'll need kill() as raise() will only send a signal to the process that calls raise().

Russ
bobbitts@hotmail.com

http://home.earthlink.net/~bobbitts

 

[sramki]

kill would be a better choice than raise .

more efficient and reliable also

regards
ramki

 

[rbobbitt]

what makes kill more efficient and reliable than raise()?

Russ
bobbitts@hotmail.com

http://home.earthlink.net/~bobbitts

 

[sramki]

It is possible to send a signal to a specified process group using the kill system call .
where as raise sends a signal to the current process
only .

regards
ramki

 

[smaniraja]

The signals can be sent to the program through the system calls, keyboard and through command line. We can use the raise() and kill() system calls to send a signal, Ctrl C is an example for sending signal through keyboard and kill command is used to send signals form command line itself to a specific process.

Program for Handling the Ctrl C.

#include <signal.h>
#include <sys/types.h>
#include <unistd.h>

void Handle_function()
{
...
printf(&quot;Ctrl Pressed...&quot;
...
}

int main()
{
...
/* Handler to catch the INT ( Ctrl C)
signal(SIGINT, Handle_function);
...
}


Now the signal (Ctrl C) can be send to the program by pressing Ctrl C, or by giving the command kill -INT {process ID of the above program } or by calling the kill or raise system call from another program.

If we want to send a signal to a another program then the process Id of that program is required

kill( {process Id of the program [ signal handler ] }, SIGINT);

Regards
Maniraja S

 

[rbobbitt]

Maybe this is a misunderstanding of language. raise() is just as efficient and reliable as kill() given that your intent is to send a signal() to the same process that you call raise() in. In fact one could argue that raise() is even more efficient and reliable than kill() in this context because it doesn't require the programmer to call getpid() to get its process id. raise() is equivalent to calling kill(getpid(),SIGNAL_TO_SEND)

You might say kill() is more /versatile/ than raise() because you're not limited to sending signals just to the calling process, and I suspect this is what you meant after seeing your explanation.

Russ
bobbitts@hotmail.com

http://home.earthlink.net/~bobbitts