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Full Discussion: "No child processes" and waitpif
Top Forums Programming "No child processes" and waitpif Post 302296663 by Zipi on Wednesday 11th of March 2009 02:36:20 PM
Old 03-11-2009
"No child processes" and waitpif
Hi everybody,
i'm using a signal handler for the SIGCHLD signal.
Code:
void InstallNewSigChldHandler()
{     
    struct sigaction act;
    struct sigaction oldAct;
    act.sa_handler = CallWaitChildProcess;
 
    sigemptyset(&act.sa_mask);
    act.sa_flags = SA_NOCLDSTOP;

    if (sigaction(SIGCHLD, &act, &oldAct) < 0) 
    {
        cout<<"error in sigaction";
    }
}

The actual signal handler code is:
Code:
void CallWaitChildProcess(int signo) 
{
    int status, child_val, errStatus;

    pid_t retPid;
    retPid=waitpid(g_ChildProcessPid, &status, WNOHANG);
    errStatus=errno;
    if (retPid < 0) 
    {
        printf("waitpid failed.Error cause:%s",strerror(errStatus));
        return;
    }

    if(retPid==0)
    {
        printf("waitpid returned 0");
        return;
    }

    if (WIFEXITED(status))                /* did child exit normally? */
    {
        child_val = WEXITSTATUS(status); /* get child's exit status */
        printf("process pid:%d --> terminated normally with status %d\n", g_ChildProcessPid,child_val);
    }
}

I'm doing this cause i want to run two external programs from my main application,and catch their return code.So,i have the g_ChildProcessPid variable which holds the pid for the external program.

I expected that every other child would cause waitpid to return 0,since i specify the WNOHANG flag,but in my code i have some calls to the "system" function that cause a "No child processes" error.

For example,in a function i do:
Code:
sprintf(command,"rm %s/%s",getenv("LOG_DIR"),"test.log");
system(command);

This causes waitpid to fail,with the following error:
Code:
waitpid failed.Error cause:No child processes

Why?
 

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LEARN ABOUT OPENSOLARIS

siginterrupt

siginterrupt(3C)					   Standard C Library Functions 					  siginterrupt(3C)

NAME

       siginterrupt - allow signals to interrupt functions

SYNOPSIS

       #include <signal.h>

       int siginterrupt(int sig, int flag);

DESCRIPTION

       The  siginterrupt()  function  changes  the restart behavior when a function is interrupted by the specified signal. The function siginter-
       rupt(sig, flag) has an effect as if implemented as:

	 siginterrupt(int sig, int flag) {
	      int ret;
	      struct sigaction act;
	      (void) sigaction(sig, NULL, &act);
	      if (flag)
		   act.sa_flags &=  SA_RESTART;
	      else
		   act.sa_flags |= SA_RESTART;
	      ret = sigaction(sig, &act, NULL);
	      return ret;
	 }

RETURN VALUES

       Upon successful completion, siginterrupt() returns 0. Otherwise, -1 is returned and errno is set to indicate the error.

ERRORS

       The siginterrupt() function will fail if:

       EINVAL	 The sig argument is not a valid signal number.

USAGE

       The siginterrupt() function supports programs written to historical system interfaces. A standard-conforming application, when being  writ-
       ten or rewritten, should use sigaction(2) with the SA_RESTART flag instead of siginterrupt().

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       sigaction(2), signal.h(3HEAD), attributes(5), standards(5)

SunOS 5.11							    1 Sep 2003							  siginterrupt(3C)
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