Mayank Jain <[EMAIL PROTECTED]> wrote: On 12/25/05, Gora Mohanty wrote:
>> Um, what do you mean by a "non-blocking wait." Calling
>> wait()/waitpid() means that you *want* the parent process to
>> wait for the child to finish processing (or, some other
>> condition occurs, as specified in the 3rd argument).
> What if i want just to check the status of the child? Is it alive or
> not? I dont want to *wait*...
As Manish suggests, checking the return value of waitpid() with the
WNOHANG option will tell you whether the child exited immediately.
With WNOHANG, if the return value is 0, the child has not yet exited
(really, not changed state), else if the return value is non-zero, then
it is the PID of the child process that changed state. If you want to
be informed as and when the child exits, a much better way than
looping is to set up the child to signal the parent.
Also, I did not notice this in my initial reading of your message, but
there is no need to loop around waitpid(). A single call is sufficient.
Try the following code (note that I have added an immediate exit in the
child):
#include <unistd.h>
#include <sys/types.h>
#include <stdio.h>
#include <sys/wait.h>
#include <stdlib.h>
int main()
{
pid_t child = 0;
int status = 0;
printf("forking!\n");
child = fork();
if(child == 0)
{
exit(0);
printf("Inside child\n");
sleep(2);
printf("Finishing if\n");
}
else
{
pid_t retval;
printf("Inside Parent\nCalling waitpid\n");
retval = waitpid(child, &status, WNOHANG);
if(WIFEXITED(status))
{
printf("Child exited: waitpid returned %d\n", retval);
}
printf("Finishing else\n");
}
return 0;
}
With this, you should get some process ID for the return value of
waitpid(). If you remove the exit(0) in the child, you should get zero
for the retunr value. Is that what you wanted?
Regards,
Gora
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