Help on calling signal with SIGUSR1 signum

oceanfun · 06-02-2006, 08:09 PM

Hi guys,
I have a problem in my program when calling system function 'signal' with SIGUSR1. Something like this:

void SignalHandle(int iSigNo) {
printf("Got SIGUSR1 handled.\n");
}

int main() {
signal(SIGUSR1, SignalHandle);

ClassA aobj;
aobj.start();

return 0;
}

ClassA {
void start();
};

ClassA::start() {
while(true) {
// something got done in here
}
}

Goal: I want to print out the "Got SIGUSR1 handled" line when executed command "kill -SIGUSR1 <pid>" without terminating my application (which I expect what it should be.)

Problem: The program printed out the line, but it's also killed (which I don't want to). Anyone see what I am doing wrong here? How to fix it please.

Thanks in advance for your help.

OceanFun

jonaskoelker · 06-04-2006, 03:29 PM

Hello, and welcome to LQ.

Firstly, when posting code, please enclose it in code tags:

Code:

[ code ] like this, but without spaces [ /code ]

Secondly, I've tested your program, with "// something got done in here" replaced by "while (true) sleep(1);". I then went on to do "while true; do killall -USR1 a.out; done", and it happily printed out a message ad infinitum.

That leads me to believe that the error is a sympton of whatever it is you have replaced by "//something got done in here". Please post the code here, or--if it's more than, say, 20 lines--in a pastebin or on your website, so we can have a look at it.

oceanfun · 06-05-2006, 05:33 PM

Quote:

Originally Posted by jonaskoelker

Hello, and welcome to LQ.

Firstly, when posting code, please enclose it in code tags:

Code:

[ code ] like this, but without spaces [ /code ]

Secondly, I've tested your program, with "// something got done in here" replaced by "while (true) sleep(1);". I then went on to do "while true; do killall -USR1 a.out; done", and it happily printed out a message ad infinitum.

That leads me to believe that the error is a sympton of whatever it is you have replaced by "//something got done in here". Please post the code here, or--if it's more than, say, 20 lines--in a pastebin or on your website, so we can have a look at it.

Thanks for your respond. So your replacement would be like this:

Code:

while(true) {
while(true)
  sleep(1);
}

Due to the complication of the project policies, I can't post the whole code. But it would do something like this:

Code:

while(true) {
  int iResult = select(maxFd+1, readFd, NULL, NULL, NULL); // where maxFd and readFd are ClassA variables
  if (iResult == -1) {
     printf("Error at select statement.\n");
     exit(1);
  }
  if (FD_ISSET(fd1, &readFd)) {
     // do something
  }
  if (FD_ISSET(fd2, &readFd)) {
     // do other thing
  }
}

Anycomment would be appreciated.
OceanFun

oceanfun · 06-05-2006, 07:30 PM

Additional information:

It printed:

Got SIGUSR1 handled.
Error at select statement.

then the program exited. I am wondering it is because of the select statement returned with -1. What is going on here? Thanks.

oceanfun · 06-05-2006, 08:25 PM

Never mind. I got it resolved. Just in case someone has the same problem. Here is the solution. Since the select statement got the errno = 4 (EINTR), I need to handle that error case. Instead of exiting I have to reset the fd set and continue to loop back to call the select statement.

Code:

while(true) {
  setFds(); // function to set fds
  int iResult = select(maxFd+1, readFd, NULL, NULL, NULL); // where maxFd and readFd are ClassA variables
  if (iResult == -1) {
     printf("Error at select statement.\n");
     if (errno != EINTR) {
        exit(1);
     }
     continue;
  }
  if (FD_ISSET(fd1, &readFd)) {
     // do something
  }
  if (FD_ISSET(fd2, &readFd)) {
     // do other thing
  }
}

Regards,
OceanFun.