Subj : sigwait() is not catching SIGUSR1 signal
To   : comp.programming.threads,comp.unix.programmer
From : neelakantan
Date : Thu Mar 10 2005 11:19 pm

Hi,
      
     i have a problem with sigwait() in a multithreaded program. 

     In this program some thread will be generating the signal SIGUSR1 at 
     some time(asynchronously) and there is a dedicated thread for handling 
     the asynchronous(SIGUSR1 in my case) signals.
 
     The sinal handling thread uses sigwait() to catch the signal, however 
     the signal is not caught by the sigwait() function. I have blocked the 
     signal SIGUSR1 before the threads are created aswell before the sigwait() 
     is called.

     I have included a variant of the program. 

     Any help will be highly appreciated.

     Thanks and regards,

     Neelakantan
    
***************************************************************** 
     OS : Redhat 9 kernel version 2.4.20

     Compiler: g++ (GCC) 3.2.2 20030222 (Red Hat Linux 3.2.2-5).

     Note: if i send the signal SIGUSR1 from the command prompt, 
           the signal has been caught.

****************   sinal.cpp ************************************
#include<iostream>
#include<pthread.h>
#include<signal.h>
#include<errno.h>
#include<unistd.h>
using namespace std;
void* fun(void* arg)
{
        int i = 0;
        while(i<10)
        {
          sleep(2);
          kill(getpid(),SIGUSR1);
          cout << "SIGUSR1 Has been sent" << i++ << endl;
        }
        return NULL;
}
int main()
{
        pthread_t tid;
        sigset_t set;
        sigemptyset(&set);
        sigaddset(&set, SIGUSR1);
        sigaddset(&set, SIGINT);
        pthread_sigmask(SIG_BLOCK, &set, NULL);
        int status = pthread_create(&tid,0,fun,0);
        if (status != 0)
        {
          cout << "Thread Creation Failed" << endl;
          exit(0);
        }
        int signal = 0;
        while(true)
        {
          sigwait(&set,&signal);
          if (signal == SIGUSR1)
           {
                cout << "SIGUSR1 signal recieved" << endl;
                break;
           }
          if(signal == SIGINT)
           {
                cout << "SIGINT signal recieved" << endl;
                break;
           }
        }
        cout << "Main is exiting" << endl;
        exit(0);
}
******************* signal.cpp ends ***************************

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