Re: [LTP] [PATCH] Synchronization between two processes

[Subrata Modak <subrata@linux.vnet.ibm.com>]

On Fri, 2009-05-15 at 08:45 -0500, Serge E. Hallyn wrote: 
> Quoting Gui Xiaohua (guixh@cn.fujitsu.com):
> > The child-process wait SIGUSR1 which would be sended by parent-process,
> > if the child-process execute sigtimedwait() after parent-process send 
> > the signal, it would never receive the SIGUSR1 from parent-process.
> > I cann't make sure the SIGUSR1 be sended after child-process execute 
> > sigtimedwait() with 100 percent, and i try my best.
> 
> Well, in theory I suppose this could happen, but you'd have to have
> a pretty bad scheduler if the parent can do a strcmp(buf, "c:go")
> between the pipe read and signal send, while the child goes straight
> from pipe write to sigtimedwait.
> 
> Have you seen this signal be missed?  If not, then I'd rather assume
> things are reasonable.  If you have seen this happen, then why not
> instead set up a SIGUSR1 handler in the child before doing the pipe
> write, then just sleep for 3 seconds instead of doing sigtimedwait?

Thanks Serge.

Gui,

Are you planning any further patch(s) for this ?

Regards--
Subrata

> 
> > Signed-off-by: Gui Xiaohua <guixh@cn.fujitsu.com>
> > --- testcases/kernel/containers/pidns/pidns12-old.c	2009-05-14 17:00:20.000000000 +0800
> > +++ testcases/kernel/containers/pidns/pidns12.c	2009-05-15 15:15:22.000000000 +0800
> > @@ -109,7 +109,7 @@ int child_fn(void *arg)
> >  	}
> > 
> >  	/* Set timeout for sigtimedwait */
> > -	timeout.tv_sec = 3;
> > +	timeout.tv_sec = 10;
> >  	timeout.tv_nsec = 0;
> > 
> >  	/* Set mask to wait for SIGUSR1 signal */
> > @@ -182,6 +182,9 @@ int main(int argc, char *argv[])
> >  		cleanup();
> >  	}
> > 
> > +	/*Try best to make sure the SIGUSR1 be sended after child-process execute sigtimedwait*/
> > +	sleep(5);
> > +
> >  	/* Send SIGUSR1 to container init */
> >  	if (kill(cpid, SIGUSR1) == -1) {
> >  		tst_resm(TBROK, "parent: kill() failed(%s).", strerror(errno));
> > 
> > 
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