dam@us.ibm.com wrote:
> I'm porting some code from LINUX to AIX and am hitting a problem in the
> SIGCHLD handler. Here is the code
>
> static void child_handler(int sig)
> {
> int n, status;
> for (n = 0; wait4(-1, &status, WNOHANG, NULL) > 0; n++) ;
> if (n == 0)
> printf("Didn't reap any childred\n");
> signal(sig, child_handler);
> }
>
> The problem is that wait4 (which isn't even listed in the AIX 5.2 tech
> ref) must not be working as expeced since when it exits the loop, "n"
> is still equal to 0, then when the signal() call is made at the end of
> the function, the child_handler get control right back and eventually
> overruns the stack. Can anybody see why it is acting this way? Since
> the code doesn't seem to do anything with the child, I changed the code
> to ignore this signal and it seems to work OK, but I'd still like to
> understand what is happening in case I do need to handle it in the
> future.
> Thanks.

Replace the wait4() call with a waitpid() call...
....like this:
for(n=0;waitpid(-1, &status, WNOHANG) > 0; n++) ;

Or, compile the existing code with the BSD library:
cc -o demo demo.c -D_BSD -lbsd

Both will work...

The current problem is that child process is not "seen" by the wait4()
call,
so that when "signal" is rearmed, it immediately goes (recursively)
into the
child_handler() function.

If you're not opposed to making other fixes, I would suggest you
convert
the "main" signal() call, into a sigaction() call... eliminating the
need
to "re-arm" signal handling in child_handler.

HTH,
-tony