From: Karthik Gopalakrishnan (gopalakk_at_cse.ohio-state.edu)
Date: Thu Jan 29 2009 - 01:31:53 PST
Hi Paul.
Thanks. That confirms what I suspected. Even a Ctrl+C does not work
after restart. And I think I understand what you are saying wrt not
calling the do_real_work() function from the CR Callback. I will
restructure my program to avoid that. Could you please point me to a
suitable example in BLCR's 'tests' directory.
Thanks & Regards,
Karthik
On Thu, Jan 29, 2009 at 3:34 AM, Paul H. Hargrove <PHHargrove_at_lbl_dot_gov> wrote:
> I think the root of your problem is that BLCR invokes its callbacks with all
> signals blocked. This is preventing SIGCHLD from being delivered. You
> could unblock the signal yourself, but that is probably not the way to go
> (though I can't say for sure not seeing the full application). I think that
> perhaps you are not using the callback as we had intended (though I admit
> our documentation is a little "thin"). It was not our intention that the
> "normal" flow of your application would pickup in the callback, as your call
> to do_real_work() appears to. Instead it would be proper for the callback
> to raise some signal or otherwise "tell" the normal application flow (which
> is, I believe, currently just "while(1)") to do something.
>
> It is probably also worth noting that the child created by fork() inherits
> the signal mask of the parent, which in your case means the one spawned by
> the do_real_work() call in CR_Callback() is going to run with all signals
> blocked just as the callback does.
>
> Let us know if I have not been clear, or if you need more help.
>
> -Paul
>
> Karthik Gopalakrishnan wrote:
>>
>> Hello.
>>
>> I apologize for the long mail in advance. :-)
>>
>> I have an application which roughly works as follows:
>>
>> main()
>> {
>> do_cr_initialization();
>> do_real_work();
>> }
>>
>> do_real_work()
>> {
>> register(SIGCHLD_Handler);
>> fork();
>> if (child) {
>> do_stuff();
>> exit(0);
>> }
>> while(1);
>> }
>>
>> SIGCHLD_Handler()
>> {
>> wait_for_child();
>> exit(0);
>> }
>>
>> CR_Callback()
>> {
>> if (restarting)
>> do_real_work()
>> }
>>
>> do_stuff() is intelligent enough to continue from where it left off.
>> Now, under normal execution, after the do_stuff() completes & exit(0)
>> is called, SIGCHLD_Handler() is invoked which terminates the
>> application. However, when cr_restart is called after a checkpoint,
>> the application just "hangs" after do_stuff() completes the remaining
>> work & calls exit(0). SIGCHLD_Handler() is not invoked at restart at
>> all. The output of 'ps' shows the following:
>>
>> UID PID PPID C STIME TTY CMD
>> gopalakk 11886 12020 0 20:30 pts/0 a.out
>> gopalakk 12020 10333 0 20:30 pts/0 cr_restart context.11886
>> gopalakk 12026 11886 0 20:30 pts/0 [a.out] <defunct>
>>
>> Can someone explain what's going on here.
>>
>> Thanks & Regards,
>> Karthik
>>
>
>
> --
> Paul H. Hargrove PHHargrove_at_lbl_dot_gov
> Future Technologies Group Tel: +1-510-495-2352
> HPC Research Department Fax: +1-510-486-6900
> Lawrence Berkeley National Laboratory
>