[sheepdog] [PATCH] lib/logger: nonblocking waitpid to avoid sheep process cannot exit

[Hitoshi Mitake]

At Wed, 11 Jun 2014 10:30:01 +0800,
Ruoyu wrote:
> 
> 
> On 2014年06月11日 10:09, Hitoshi Mitake wrote:
> > At Wed, 11 Jun 2014 11:05:53 +0900,
> > Hitoshi Mitake wrote:
> >> At Tue, 10 Jun 2014 18:22:11 +0800,
> >> Ruoyu wrote:
> >>> Sometimes sheep process cannot exit as we expected. I think the
> >>> problem might be waitpid, the system call waiting for process to
> >>> change state.
> >>>
> >>> Current log_close function calling waitpid as a void method. It is
> >>> better to retrieve the return value and pass the nonblocking flag,
> >>> that is WNOHANG, to it.
> >>>
> >>> Signed-off-by: Ruoyu <liangry at ucweb.com>
> >>> ---
> >>>   lib/logger.c | 24 ++++++++++++++++++------
> >>>   1 file changed, 18 insertions(+), 6 deletions(-)
> >>>
> >>> diff --git a/lib/logger.c b/lib/logger.c
> >>> index 6829f45..79c60a7 100644
> >>> --- a/lib/logger.c
> >>> +++ b/lib/logger.c
> >>> @@ -711,13 +711,25 @@ int log_init(const char *program_name, enum log_dst_type type, int level,
> >>>   
> >>>   void log_close(void)
> >>>   {
> >>> -	if (la) {
> >>> -		la->active = false;
> >>> -		waitpid(logger_pid, NULL, 0);
> >>> +	if (!la)
> >>> +		return;
> >>>   
> >>> -		syslog(LOG_WARNING, "logger pid %d stopped\n", logger_pid);
> >>> -		closelog();
> >>> -		free_logarea();
> >>> +	while (true) {
> >>> +		la->active = false;
> > Seems that the above assignment statement can be placed before the loop.
> >
> > Thanks,
> > Hitoshi
> No, there is a sequential problem inter process if the statement is 
> placed before the loop.
> 
> Suppose this situation:
> 
> Father process: -----> active = false 
> ---------------------------------------------------------------------------> 
> waitpid
> Child process: -------------------------------> active = true -----> 
> while (active) do something ----->
> 
> The log process will loop forever so that main process cannot exit.

Ah, sorry, I missed the case. You are correct.

Thanks,
Hitoshi

> >>> +		pid_t pid = waitpid(logger_pid, NULL, WNOHANG);
> >> Interleaved statement and declaration is not allowed in the current
> >> coding style of sheepdog.
> >> # Personally I really like it but it is denied in the past.
> >>
> >> Other part looks good and quite reasonable to me.
> >>
> >> Thanks,
> >> Hitoshi
> >>
> >>> +		if (pid == 0) {
> >>> +			usleep(100000);
> >>> +			continue;
> >>> +		} else if (pid > 0) {
> >>> +			syslog(LOG_WARNING, "logger pid %d stopped\n",
> >>> +					logger_pid);
> >>> +			closelog();
> >>> +			free_logarea();
> >>> +			break;
> >>> +		} else {
> >>> +			syslog(LOG_ERR, "waitpid() failure\n");
> >>> +			exit(1);
> >>> +		}
> >>>   	}
> >>>   }
> >>>   
> >>> -- 
> >>> 1.8.3.2
> >>>
> >>>
> >>> -- 
> >>> sheepdog mailing list
> >>> sheepdog at lists.wpkg.org
> >>> http://lists.wpkg.org/mailman/listinfo/sheepdog
> 
>