Re: A (dumb?) waitpid(2) question

[Steven Rostedt <rostedt@goodmis.org>]

On Tue, 2004-12-21 at 19:26 -0500, usvyatsky, ilya wrote:
> As dumb as it seems, I am seing a weird behavior on my RH3.0 box
> (2.4.21-20.Elsmp kernel).
> 
> It looks like (contrary to the man page and POSIX .1) waitpid(2) does not
> return upon a SIGALRM.
> 
> I am porting an old piece of Solaris userland code (stripped from all useful
> functionality):

I changed your code with the following:

@@ -25,11 +25,15 @@
     if (child_pid) {
         /* parent */
         int status = 0, timeout = 1;
+       struct sigaction sa;
+       sa.sa_handler = sig_handler;
+       sa.sa_flags = SA_NOMASK;

         do {
             printf("Parent: setting an alarm for %d seconds\n", timeout);

-            signal(SIGALRM, sig_handler);
+           sigaction(SIGALRM, &sa,NULL);
+//            signal(SIGALRM, sig_handler);
             alarm(timeout);

             printf("Parent: waiting for a child %d\n", child_pid);


And got the following result:

$ ./alarmit
Child:  sleeping for 6 seconds
Parent: setting an alarm for 1 seconds
Parent: waiting for a child 25926
Alarm!!!
Parent: wait was interrupted by a signalParent: setting an alarm for 1 seconds
Parent: waiting for a child -1
Alarm!!!
Parent: wait was interrupted by a signalParent: setting an alarm for 1 seconds
Parent: waiting for a child -1
Alarm!!!
Parent: wait was interrupted by a signalParent: setting an alarm for 1 seconds
Parent: waiting for a child -1
Alarm!!!
Parent: wait was interrupted by a signalParent: setting an alarm for 1 seconds
Parent: waiting for a child -1
Alarm!!!
Parent: wait was interrupted by a signalParent: setting an alarm for 1 seconds
Parent: waiting for a child -1
Child:  exiting
Parent: child 25926 terminated normally with status 0


> Is it a bug or a feature?

I guess it's a feature, and the default signal function must have
SA_RESTART set.

> Any suggestions would be greatly appreciated...
> 

Use sigaction instead of signal.


-- Steve