Question

I have a CGI script running on “mongoose webserver” written in C++ (independent of mongoose specific APIs for portability in the future) on Ubuntu 10.04. Whenever I invoke the script from web browser (Chrome), the process works fine but when I run ps -al I see

F S   UID   PID  PPID  C PRI  NI ADDR SZ WCHAN  TTY          TIME CMD
4 S     0  3567  8877  0  80   0 - 23309 hrtime pts/0    00:00:00 mongoose
4 Z     0  3585  3567  7  80   0 -     0 exit   pts/0    00:00:00 test <defunct>

I use sudo kill -9 3567 in this case to kill the parent process. I have the following code in my script.

...
#include <sys/wait.h>
...

//==========================================================================
// Define the function to be called when ctrl-c (SIGINT) signal is sent to process
static void signal_callback_handler(int signum)
{ 
    point_of_inspection( __FILE__, __func__, __LINE__, ENABLE_LOG); // Entered the routine

    // Cleanup and close up stuff here
    while(1)
    {
        if (signum == SIGTERM)
        {
            error_log_report("caught signal - premature exit",CAUGHT_SIGNAL_ERROR,ENABLE_LOG);
            break;
        }
    }
    clean_exit();
    // Terminate program
    exit(signum);
}
//======================= Zombies or <defunct> handler ========================
// Signal handler to process terminated children
static void mysig(int nsig) 
{ 
    int nStatus, nPid; 
    while(1)
    {
        if (nsig == SIGCHLD)
        {
            nPid = waitpid(-1, &nStatus, WNOHANG); 
            if(nPid<0)
            {
                error_log_report("waitpid (nPid<0)",CAUGHT_SIGNAL_ERROR,ENABLE_LOG);         
                break;               
            }
            if(nPid==0)
            {
                error_log_report("Caught Signal - Zombies <defunct> (nPid==0)",CAUGHT_SIGNAL_ERROR,ENABLE_LOG);
                break;  
            }
        } 
    }
    clean_exit();
    exit(nsig);
} 

In the main function

 int main()
 {
  //some initialization variables
  ...

     // Register signal and signal handler
     signal(SIGTERM, signal_callback_handler);

     // To clean up terminated children
     signal(SIGCHLD, mysig); 
  ...

     return 0;
 }

However, It seems to not catch any signal triggered when the user closes web browser or navigates to a different page as I do not see any logs. I am wondering if this is a bug in mongoose or my script (I do not use any fork() process or threads in my script. But mongoose does use threads. Also I do not use any mongoose webserver specific APIs in my script.).

I am referring the signal tutorial from here http://orchard.wccnet.org/~chasselb/linux275/ClassNotes/process/sigbasics.htm and
http://www.gnu.org/s/hello/manual/libc/Process-Completion.html

Answer 1

They updated the code in mongoose.c file to reap zombies. The following is the portion of the code.

#if !defined(_WIN32) && !defined(__SYMBIAN32__)
  // Ignore SIGPIPE signal, so if browser cancels the request, it
  // won't kill the whole process.
  (void) signal(SIGPIPE, SIG_IGN);
  // Also ignoring SIGCHLD to let the OS to reap zombies properly.
  (void) signal(SIGCHLD, SIG_IGN);
#endif // !_WIN32