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POError with signal handling for processes in linux
 

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  1. POError with signal handling for processes in linux
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    <p>The following is the code fragment :</p> <pre><code>#include&lt;sys/types.h&gt; #include&lt;stdio.h&gt; #include&lt;signal.h&gt; #include&lt;stdlib.h&gt; #include&lt;unistd.h&gt; #include&lt;string.h&gt; sig_atomic_t child1 ; sig_atomic_t child2 ; void child1_handler( int sig_num ) { int ret ; if(sig_num == SIGUSR2 ) { printf("\n Recieved sigusr2 for child1\n"); ret = kill( getppid() , SIGUSR2 ) ; if( ret != 0 ) kill( getpid() , SIGTERM ); } else if(sig_num == SIGUSR1 ) { /* child 1 does something */ printf("\n Recieved sigusr1 for child1\n"); printf("\n child 1 is doing \n"); kill( child2 , SIGUSR2 ); } } void child2_handler( int sig_num ) { if( sig_num == SIGUSR2 ) { /* child2 does somethign */ printf("\n Recieved sigusr2 for child2\n"); printf("\n child2 is doing \n"); kill( child1 , SIGUSR2 ); kill( getpid() , SIGTERM ); } } void parent_handler( int sig_num ) { int ret ; if( sig_num == SIGUSR2 ) { printf("\n Recieved sigusr2 for parent\n"); ret = kill( child1 , SIGUSR1 ) ; if( ret != 0 ) { /* parent does something */ printf( "\n Parent does something \n" ); exit(0); } } } int main() { struct sigaction sa_parent , sa_child1 , sa_child2 ; pid_t temp_id1 , temp_id2 ; int temp ; memset(&amp;sa_parent , 0 , sizeof(sa_parent) ) ; memset(&amp;sa_child1 , 0 , sizeof(sa_child1) ) ; memset(&amp;sa_child2 , 0 , sizeof(sa_child2) ) ; /* parent */ printf( " \n Inside parent \n" ); sa_parent.sa_handler = &amp;parent_handler ; sigaction( SIGUSR2 , &amp;sa_parent , NULL ); temp_id1 = fork() ; if( temp_id1 == 0 ) { child1 = getpid() ; /* child1 */ printf("\n inside child1 \n" ); sa_child1.sa_handler = &amp;child1_handler ; sigaction( SIGUSR1 , &amp;sa_child1 , NULL ) ; sigaction( SIGUSR2 , &amp;sa_child1 , NULL ) ; temp_id2 = fork() ; if( temp_id2 == 0 ) { child2 = getpid() ; /* child2 */ printf( "\n inside child2 \n" ); sa_child2.sa_handler = &amp;child2_handler ; sigaction( SIGUSR2 , &amp;sa_child2 , NULL ); kill( child1 , SIGUSR2 ); } wait(&amp;temp); } wait(&amp;temp); return 0 ; } </code></pre> <p>I am expecting the output to depict that first </p> <pre><code>child1 is doing child2 is doing parent does something </code></pre> <p>However the output produced is as given below.. </p> <pre><code>Inside parent inside child1 inside child2 Recieved sigusr2 for child1 Recieved sigusr2 for parent Recieved sigusr1 for child1 child 1 is doing Recieved sigusr2 for child1 User defined signal 1 [ what is going wrong ? ] </code></pre> <p>Please ignore the "recieved sign" and "Inside..." lines as they were meant to mark locations in code.</p>
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    1. USJohn Kugelman
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    1. COWhy is your code indented in an apparently random fashion?
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      1. UScaf
    2. COYou might consider just using sigemptyset() instead of memset(). memset() is not guaranteed to exclude all signals. That's a side note, not quite related to your question, but thought I'd point it out.
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      1. POError with signal handling for processes in linux
      1. USTim Post
 

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