[sheepdog] [PATCH v2] lib/logger: nonblocking waitpid to avoid sheep process cannot exit

[Hitoshi Mitake]

At Wed, 11 Jun 2014 10:53:35 +0800,
Ruoyu wrote:
> 
> Sometimes sheep process cannot exit as we expected. I think the
> point might be the sequential problem by using waitpid, the
> system call waiting for process to change state.
> 
> Current log_close function calling waitpid as a void method. It
> will block the main process. Suppose this situation:
> 
> Father: --> active=false --------------------------------> waitpid
> Child: -------------> active=true --> while(active) do sth. -->
> 
> The log process will loop forever so that the main process cannot
> exit.
> 
> Therefore, it is better to retrieve the return value and pass the
> nonblocking flag WNOHANG to it. Moreover, reset share memory flag
> before each time calling waitpid.
> 
> Signed-off-by: Ruoyu <liangry at ucweb.com>
> ---
>  lib/logger.c | 26 ++++++++++++++++++++------
>  1 file changed, 20 insertions(+), 6 deletions(-)

Looks good to me.
Reviewed-by: Hitoshi Mitake <mitake.hitoshi at lab.ntt.co.jp>

Thanks,
Hitoshi

> 
> diff --git a/lib/logger.c b/lib/logger.c
> index 6829f45..3815ee4 100644
> --- a/lib/logger.c
> +++ b/lib/logger.c
> @@ -711,13 +711,27 @@ 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);
> +	pid_t pid;
> +
> +	if (!la)
> +		return;
>  
> -		syslog(LOG_WARNING, "logger pid %d stopped\n", logger_pid);
> -		closelog();
> -		free_logarea();
> +	while (true) {
> +		la->active = false;
> +		pid = waitpid(logger_pid, NULL, WNOHANG);
> +		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
> 
> 
> -- 
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