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

["Serge E. Hallyn" <serue@us.ibm.com>]

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?

> 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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