Subject: Re: [PATCH 3/3] daemon: explicitly allow EINTR during poll()

From: Junio C Hamano <[email-masked]>
Date: Tue, 24 Jun 2025 08:43:25 -0700

"Carlo Marcelo Arenas Belón via GitGitGadget"
<[email-masked]> writes:

> -static void child_handler(int signo UNUSED)
> +static void child_handler(int signo)
>  {
>  	/*
> -	 * Otherwise empty handler because systemcalls will get interrupted
> -	 * upon signal receipt
> +	 * Empty handler because systemcalls should get interrupted
> +	 * upon signal receipt.
>  	 */
> +#ifdef NO_SIGINTERRUPT
> +	/* SysV needs the handler to be rearmed */
> +	signal(signo, child_handler);
> +#endif
>  }

On NO_SIGINTERRUPT systems, signo is UNUSED, isn't it?

Can we abstract this a bit better?  #if/#else/#endif sprinkled
everywhere is simply an eyesore.

>  static int set_reuse_addr(int sockfd)
> @@ -1118,8 +1122,10 @@ static void socksetup(struct string_list *listen_addr, int listen_port, struct s
>  
>  static int service_loop(struct socketlist *socklist)
>  {
> -	struct pollfd *pfd;
> +#ifndef NO_SIGINTERRUPT
>  	struct sigaction sa;
> +#endif
> +	struct pollfd *pfd;
>  	CALLOC_ARRAY(pfd, socklist->nr);
>  
> @@ -1128,14 +1134,22 @@ static int service_loop(struct socketlist *socklist)
>  		pfd[i].events = POLLIN;
>  	}
>  
> +#ifdef NO_SIGINTERRUPT
> +	signal(SIGCHLD, child_handler);
> +#else
>  	sigemptyset(&sa.sa_mask);
>  	sa.sa_flags = SA_NOCLDSTOP | SA_RESTART;
>  	sa.sa_handler = child_handler;
>  	sigaction(SIGCHLD, &sa, NULL);
> +#endif
>  
>  	for (;;) {
>  		check_dead_children();
>  
> +#ifndef NO_SIGINTERRUPT
> +		sa.sa_flags &= ~SA_RESTART;
> +		sigaction(SIGCHLD, &sa, NULL);
> +#endif
>  		if (poll(pfd, socklist->nr, -1) < 0) {
>  			if (errno != EINTR) {
>  				logerror("Poll failed, resuming: %s",
> @@ -1144,6 +1158,10 @@ static int service_loop(struct socketlist *socklist)
>  			}
>  			continue;
>  		}
> +#ifndef NO_SIGINTERRUPT
> +		sa.sa_flags |= SA_RESTART;
> +		sigaction(SIGCHLD, &sa, NULL);
> +#endif