RE: [LIP] SIGCHLD behaviour...

On Thu, 15 Apr 2004, Sameer Oak wrote:
> ok. but why is it needed to set the action to ignore explicitly?
It is required by POSIX.
> 
> > Else, even though the default action is ignore, it will never be delivered
> > to the process.
> ...
> the default action of SIGCHLD is to ignore, thus that is never delivered to
> the parent.
> 
> the ``else'' and ``even though'' have a bit of irony. kindly explain if
> am getting it wrong.
signalling has two parts : 1. generation and 2. delivery
generation : 
1. Default action (ignore)
The siginfo_t table of the destination process is untouched. handler =
SIG_DFL
2. eXPLICITLY setting ignore
The siginfo_t table should add one entry with handler = SIG_IGN.

Ignore is an action.

Delivery : 
If the action is to ignore, do_signal() will continue with the next signal.
if handler == SIG_IGN, and signal number is SIGCHLD, kernel willdo
    sys_wait4().
if default action (i.e, to ignore), handler is SIG_DFL, there will not be
    any sys_wait4(), but the loop will continue with next signal processing.
HTH.

> 
> > And init will have to take care fo zonbies and other children.
> ...
> this sounds bit different to me! init becomes parent of all the orphan
> processes and thus clears the zombies
> from process table.
> in what all circumstances does init handle zombies? i've never seen init
> clearing zombies if SIGCHLD is
> ignored by either explicitly setting it to SIG_IGN or not setting it.
> kindly explain.
Sorry, I should have said "If parent dies, init will have3 to clear zonbies"
> -



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