rust-chg: remove SIGCHLD handler which won't work in oxidized chg

Since pager is managed by the Rust part, the C code doesn't know the pager
pid. I could make the Rust part teach the pid to C, but still installing
SIGCHLD handler seems horrible idea since we no longer use handcrafted
low-level process management functions.

Instead, I'm thinking of adding async handler to send SIGPIPE at the exit
of the pager.

rust/chg/src/sighandlers.c

@@ -1,177 +1,151
 /*
  * Signal handlers for cHg
  *
  * Copyright 2011, 2018 Yuya Nishihara <[e-mail]>
  *
  * This software may be used and distributed according to the terms of the
  * GNU General Public License version 2 or any later version.
  */
 
 #include <assert.h>
 #include <errno.h>
 #include <signal.h>
 #include <string.h>
-#include <sys/wait.h>
 #include <unistd.h>
 
-#ifdef __GNUC__
-#define UNUSED_ __attribute__((unused))
-#else
-#define UNUSED_
-#endif
-
-static pid_t pagerpid = 0;
 static pid_t peerpgid = 0;
 static pid_t peerpid = 0;
 
 static void forwardsignal(int sig)
 {
 	assert(peerpid > 0);
 	(void)kill(peerpid, sig);
 }
 
 static void forwardsignaltogroup(int sig)
 {
 	/* prefer kill(-pgid, sig), fallback to pid if pgid is invalid */
 	pid_t killpid = peerpgid > 1 ? -peerpgid : peerpid;
 	(void)kill(killpid, sig);
 }
 
 static void handlestopsignal(int sig)
 {
 	sigset_t unblockset, oldset;
 	struct sigaction sa, oldsa;
 	if (sigemptyset(&unblockset) < 0)
 		return;
 	if (sigaddset(&unblockset, sig) < 0)
 		return;
 	memset(&sa, 0, sizeof(sa));
 	sa.sa_handler = SIG_DFL;
 	sa.sa_flags = SA_RESTART;
 	if (sigemptyset(&sa.sa_mask) < 0)
 		return;
 
 	forwardsignal(sig);
 	if (raise(sig) < 0) /* resend to self */
 		return;
 	if (sigaction(sig, &sa, &oldsa) < 0)
 		return;
 	if (sigprocmask(SIG_UNBLOCK, &unblockset, &oldset) < 0)
 		return;
 	/* resent signal will be handled before sigprocmask() returns */
 	if (sigprocmask(SIG_SETMASK, &oldset, NULL) < 0)
 		return;
 	if (sigaction(sig, &oldsa, NULL) < 0)
 		return;
 }
 
-static void handlechildsignal(int sig UNUSED_)
-{
-	if (peerpid == 0 || pagerpid == 0)
-		return;
-	/* if pager exits, notify the server with SIGPIPE immediately.
-	 * otherwise the server won't get SIGPIPE if it does not write
-	 * anything. (issue5278) */
-	if (waitpid(pagerpid, NULL, WNOHANG) == pagerpid)
-		kill(peerpid, SIGPIPE);
-}
-
 /*
  * Installs signal handlers.
  *
  * Returns 0 on success, -1 on error and errno is set appropriately.
  * Installed handlers wouldn't be cleaned up on error.
  */
 int setupsignalhandler(pid_t pid, pid_t pgid)
 {
 	if (pid <= 0) {
 		errno = EINVAL;
 		return -1;
 	}
 	peerpid = pid;
 	peerpgid = (pgid <= 1 ? 0 : pgid);
 
 	struct sigaction sa;
 	memset(&sa, 0, sizeof(sa));
 
 	/* deadly signals meant to be sent to a process group:
 	 * - SIGHUP: usually generated by the kernel, when termination of a
 	 *   process causes that process group to become orphaned
 	 * - SIGINT: usually generated by the terminal */
 	sa.sa_handler = forwardsignaltogroup;
 	sa.sa_flags = SA_RESTART;
 	if (sigemptyset(&sa.sa_mask) < 0)
 		return -1;
 	if (sigaction(SIGHUP, &sa, NULL) < 0)
 		return -1;
 	if (sigaction(SIGINT, &sa, NULL) < 0)
 		return -1;
 
 	/* terminate frontend by double SIGTERM in case of server freeze */
 	sa.sa_handler = forwardsignal;
 	sa.sa_flags |= SA_RESETHAND;
 	if (sigaction(SIGTERM, &sa, NULL) < 0)
 		return -1;
 
 	/* notify the worker about window resize events */
 	sa.sa_flags = SA_RESTART;
 	if (sigaction(SIGWINCH, &sa, NULL) < 0)
 		return -1;
 	/* forward user-defined signals */
 	if (sigaction(SIGUSR1, &sa, NULL) < 0)
 		return -1;
 	if (sigaction(SIGUSR2, &sa, NULL) < 0)
 		return -1;
 	/* propagate job control requests to worker */
 	sa.sa_handler = forwardsignal;
 	sa.sa_flags = SA_RESTART;
 	if (sigaction(SIGCONT, &sa, NULL) < 0)
 		return -1;
 	sa.sa_handler = handlestopsignal;
 	sa.sa_flags = SA_RESTART;
 	if (sigaction(SIGTSTP, &sa, NULL) < 0)
 		return -1;
-	/* get notified when pager exits */
-	sa.sa_handler = handlechildsignal;
-	sa.sa_flags = SA_RESTART;
-	if (sigaction(SIGCHLD, &sa, NULL) < 0)
-		return -1;
 
 	return 0;
 }
 
 /*
  * Restores signal handlers to the default, and masks SIGINT.
  *
  * Returns 0 on success, -1 on error and errno is set appropriately.
  */
 int restoresignalhandler(void)
 {
 	struct sigaction sa;
 	memset(&sa, 0, sizeof(sa));
 	sa.sa_handler = SIG_DFL;
 	sa.sa_flags = SA_RESTART;
 	if (sigemptyset(&sa.sa_mask) < 0)
 		return -1;
 
 	if (sigaction(SIGHUP, &sa, NULL) < 0)
 		return -1;
 	if (sigaction(SIGTERM, &sa, NULL) < 0)
 		return -1;
 	if (sigaction(SIGWINCH, &sa, NULL) < 0)
 		return -1;
 	if (sigaction(SIGCONT, &sa, NULL) < 0)
 		return -1;
 	if (sigaction(SIGTSTP, &sa, NULL) < 0)
 		return -1;
-	if (sigaction(SIGCHLD, &sa, NULL) < 0)
-		return -1;
 
 	/* ignore Ctrl+C while shutting down to make pager exits cleanly */
 	sa.sa_handler = SIG_IGN;
 	if (sigaction(SIGINT, &sa, NULL) < 0)
 		return -1;
 
 	peerpid = 0;
 	return 0;
 }

rust/chg/src/uihandler.rs

@@ -1,83 +1,87
 // Copyright 2018 Yuya Nishihara <[e-mail]>
 //
 // This software may be used and distributed according to the terms of the
 // GNU General Public License version 2 or any later version.
 
 use futures::Future;
 use futures::future::IntoFuture;
 use std::io;
 use std::os::unix::io::AsRawFd;
 use std::os::unix::process::ExitStatusExt;
 use std::process::{Command, Stdio};
 use tokio;
 use tokio_process::{ChildStdin, CommandExt};
 
 use super::message::CommandSpec;
 use super::procutil;
 
 /// Callback to process shell command requests received from server.
 pub trait SystemHandler: Sized {
     type PagerStdin: AsRawFd;
     type SpawnPagerResult: IntoFuture<Item = (Self, Self::PagerStdin), Error = io::Error>;
     type RunSystemResult: IntoFuture<Item = (Self, i32), Error = io::Error>;
 
     /// Handles pager command request.
     ///
     /// Returns the pipe to be attached to the server if the pager is spawned.
     fn spawn_pager(self, spec: CommandSpec) -> Self::SpawnPagerResult;
 
     /// Handles system command request.
     ///
     /// Returns command exit code (positive) or signal number (negative).
     fn run_system(self, spec: CommandSpec) -> Self::RunSystemResult;
 }
 
 /// Default cHg implementation to process requests received from server.
 pub struct ChgUiHandler {
 }
 
 impl ChgUiHandler {
     pub fn new() -> ChgUiHandler {
         ChgUiHandler {}
     }
 }
 
 impl SystemHandler for ChgUiHandler {
     type PagerStdin = ChildStdin;
     type SpawnPagerResult = io::Result<(Self, Self::PagerStdin)>;
     type RunSystemResult = Box<dyn Future<Item = (Self, i32), Error = io::Error> + Send>;
 
     fn spawn_pager(self, spec: CommandSpec) -> Self::SpawnPagerResult {
         let mut pager = new_shell_command(&spec)
             .stdin(Stdio::piped())
             .spawn_async()?;
         let pin = pager.stdin().take().unwrap();
         procutil::set_blocking_fd(pin.as_raw_fd())?;
+        // TODO: if pager exits, notify the server with SIGPIPE immediately.
+        // otherwise the server won't get SIGPIPE if it does not write
+        // anything. (issue5278)
+        // kill(peerpid, SIGPIPE);
         tokio::spawn(pager.map(|_| ()).map_err(|_| ()));  // just ignore errors
         Ok((self, pin))
     }
 
     fn run_system(self, spec: CommandSpec) -> Self::RunSystemResult {
         let fut = new_shell_command(&spec)
             .spawn_async()
             .into_future()
             .flatten()
             .map(|status| {
                 let code = status.code().or_else(|| status.signal().map(|n| -n))
                     .expect("either exit code or signal should be set");
                 (self, code)
             });
         Box::new(fut)
     }
 }
 
 fn new_shell_command(spec: &CommandSpec) -> Command {
     let mut builder = Command::new("/bin/sh");
     builder
         .arg("-c")
         .arg(&spec.command)
         .current_dir(&spec.current_dir)
         .env_clear()
         .envs(spec.envs.iter().cloned());
     builder
  }