native: Use WNOHANG before signaling

src/libnative/io/process.rs

@@ -134,6 +134,18 @@ impl rtio::RtioProcess for Process {
     }
 
     fn kill(&mut self, signum: int) -> Result<(), io::IoError> {
+        // On linux (and possibly other unices), a process that has exited will
+        // continue to accept signals because it is "defunct". The delivery of
+        // signals will only fail once the child has been reaped. For this
+        // reason, if the process hasn't exited yet, then we attempt to collect
+        // their status with WNOHANG.
+        if self.exit_code.is_none() {
+            match waitpid_nowait(self.pid) {
+                Some(code) => { self.exit_code = Some(code); }
+                None => {}
+            }
+        }
+
         // if the process has finished, and therefore had waitpid called,
         // and we kill it, then on unix we might ending up killing a
         // newer process that happens to have the same (re-used) id
@@ -662,6 +674,31 @@ fn free_handle(_handle: *()) {
     // unix has no process handle object, just a pid
 }
 
+#[cfg(unix)]
+fn translate_status(status: c_int) -> p::ProcessExit {
+    #[cfg(target_os = "linux")]
+    #[cfg(target_os = "android")]
+    mod imp {
+        pub fn WIFEXITED(status: i32) -> bool { (status & 0xff) == 0 }
+        pub fn WEXITSTATUS(status: i32) -> i32 { (status >> 8) & 0xff }
+        pub fn WTERMSIG(status: i32) -> i32 { status & 0x7f }
+    }
+
+    #[cfg(target_os = "macos")]
+    #[cfg(target_os = "freebsd")]
+    mod imp {
+        pub fn WIFEXITED(status: i32) -> bool { (status & 0x7f) == 0 }
+        pub fn WEXITSTATUS(status: i32) -> i32 { status >> 8 }
+        pub fn WTERMSIG(status: i32) -> i32 { status & 0o177 }
+    }
+
+    if imp::WIFEXITED(status) {
+        p::ExitStatus(imp::WEXITSTATUS(status) as int)
+    } else {
+        p::ExitSignal(imp::WTERMSIG(status) as int)
+    }
+}
+
 /**
  * Waits for a process to exit and returns the exit code, failing
  * if there is no process with the specified id.
@@ -723,33 +760,31 @@ fn waitpid(pid: pid_t) -> p::ProcessExit {
     #[cfg(unix)]
     fn waitpid_os(pid: pid_t) -> p::ProcessExit {
         use std::libc::funcs::posix01::wait;
-
-        #[cfg(target_os = "linux")]
-        #[cfg(target_os = "android")]
-        mod imp {
-            pub fn WIFEXITED(status: i32) -> bool { (status & 0xff) == 0 }
-            pub fn WEXITSTATUS(status: i32) -> i32 { (status >> 8) & 0xff }
-            pub fn WTERMSIG(status: i32) -> i32 { status & 0x7f }
+        let mut status = 0 as c_int;
+        match retry(|| unsafe { wait::waitpid(pid, &mut status, 0) }) {
+            -1 => fail!("unknown waitpid error: {}", super::last_error()),
+            _ => translate_status(status),
         }
+    }
+}
 
-        #[cfg(target_os = "macos")]
-        #[cfg(target_os = "freebsd")]
-        mod imp {
-            pub fn WIFEXITED(status: i32) -> bool { (status & 0x7f) == 0 }
-            pub fn WEXITSTATUS(status: i32) -> i32 { status >> 8 }
-            pub fn WTERMSIG(status: i32) -> i32 { status & 0o177 }
-        }
+fn waitpid_nowait(pid: pid_t) -> Option<p::ProcessExit> {
+    return waitpid_os(pid);
 
+    // This code path isn't necessary on windows
+    #[cfg(windows)]
+    fn waitpid_os(_pid: pid_t) -> Option<p::ProcessExit> { None }
+
+    #[cfg(unix)]
+    fn waitpid_os(pid: pid_t) -> Option<p::ProcessExit> {
+        use std::libc::funcs::posix01::wait;
         let mut status = 0 as c_int;
-        match retry(|| unsafe { wait::waitpid(pid, &mut status, 0) }) {
-            -1 => fail!("unknown waitpid error: {}", super::last_error()),
-            _ => {
-                if imp::WIFEXITED(status) {
-                    p::ExitStatus(imp::WEXITSTATUS(status) as int)
-                } else {
-                    p::ExitSignal(imp::WTERMSIG(status) as int)
-                }
-            }
+        match retry(|| unsafe {
+            wait::waitpid(pid, &mut status, libc::WNOHANG)
+        }) {
+            n if n == pid => Some(translate_status(status)),
+            0 => None,
+            n => fail!("unknown waitpid error `{}`: {}", n, super::last_error()),
         }
     }
 }

src/libstd/io/process.rs

@@ -331,7 +331,9 @@ impl Process {
     /// signals (SIGTERM/SIGKILL/SIGINT) are translated to `TerminateProcess`.
     ///
     /// Additionally, a signal number of 0 can check for existence of the target
-    /// process.
+    /// process. Note, though, that on some platforms signals will continue to
+    /// be successfully delivered if the child has exited, but not yet been
+    /// reaped.
     pub fn kill(id: libc::pid_t, signal: int) -> IoResult<()> {
         LocalIo::maybe_raise(|io| io.kill(id, signal))
     }
@@ -342,8 +344,16 @@ impl Process {
     /// Sends the specified signal to the child process, returning whether the
     /// signal could be delivered or not.
     ///
-    /// Note that this is purely a wrapper around libuv's `uv_process_kill`
-    /// function.
+    /// Note that signal 0 is interpreted as a poll to check whether the child
+    /// process is still alive or not. If an error is returned, then the child
+    /// process has exited.
+    ///
+    /// On some unix platforms signals will continue to be received after a
+    /// child has exited but not yet been reaped. In order to report the status
+    /// of signal delivery correctly, unix implementations may invoke
+    /// `waitpid()` with `WNOHANG` in order to reap the child as necessary.
+    ///
+    /// # Errors
     ///
     /// If the signal delivery fails, the corresponding error is returned.
     pub fn signal(&mut self, signal: int) -> IoResult<()> {
@@ -833,4 +843,17 @@ mod tests {
         p.signal_kill().unwrap();
         assert!(!p.wait().success());
     })
+
+    iotest!(fn test_zero() {
+        let mut p = sleeper();
+        p.signal_kill().unwrap();
+        for _ in range(0, 20) {
+            if p.signal(0).is_err() {
+                assert!(!p.wait().success());
+                return
+            }
+            timer::sleep(100);
+        }
+        fail!("never saw the child go away");
+    })
 }

src/libstd/libc.rs

@@ -2356,6 +2356,8 @@ pub mod consts {
 
             pub static CLOCK_REALTIME: c_int = 0;
             pub static CLOCK_MONOTONIC: c_int = 1;
+
+            pub static WNOHANG: c_int = 1;
         }
         pub mod posix08 {
         }
@@ -2802,6 +2804,8 @@ pub mod consts {
 
             pub static CLOCK_REALTIME: c_int = 0;
             pub static CLOCK_MONOTONIC: c_int = 4;
+
+            pub static WNOHANG: c_int = 1;
         }
         pub mod posix08 {
         }
@@ -3187,6 +3191,8 @@ pub mod consts {
             pub static PTHREAD_CREATE_JOINABLE: c_int = 1;
             pub static PTHREAD_CREATE_DETACHED: c_int = 2;
             pub static PTHREAD_STACK_MIN: size_t = 8192;
+
+            pub static WNOHANG: c_int = 1;
         }
         pub mod posix08 {
         }

src/test/run-pass/core-run-destroy.rs

@@ -22,6 +22,12 @@ extern crate native;
 extern crate green;
 extern crate rustuv;
 
+use std::io::Process;
+
+macro_rules! succeed( ($e:expr) => (
+    match $e { Ok(..) => {}, Err(e) => fail!("failure: {}", e) }
+) )
+
 macro_rules! iotest (
     { fn $name:ident() $b:block $($a:attr)* } => (
         mod $name {
@@ -53,28 +59,29 @@ fn start(argc: int, argv: **u8) -> int {
 }
 
 iotest!(fn test_destroy_once() {
-    #[cfg(not(target_os="android"))]
-    static mut PROG: &'static str = "echo";
-
-    #[cfg(target_os="android")]
-    static mut PROG: &'static str = "ls"; // android don't have echo binary
-
-    let mut p = unsafe {Process::new(PROG, []).unwrap()};
-    p.signal_exit().unwrap(); // this shouldn't crash (and nor should the destructor)
+    let mut p = sleeper();
+    match p.signal_exit() {
+        Ok(()) => {}
+        Err(e) => fail!("error: {}", e),
+    }
 })
 
+#[cfg(unix)]
+pub fn sleeper() -> Process {
+    Process::new("sleep", [~"1000"]).unwrap()
+}
+#[cfg(windows)]
+pub fn sleeper() -> Process {
+    // There's a `timeout` command on windows, but it doesn't like having
+    // its output piped, so instead just ping ourselves a few times with
+    // gaps inbetweeen so we're sure this process is alive for awhile
+    Process::new("ping", [~"127.0.0.1", ~"-n", ~"1000"]).unwrap()
+}
+
 iotest!(fn test_destroy_twice() {
-    #[cfg(not(target_os="android"))]
-    static mut PROG: &'static str = "echo";
-    #[cfg(target_os="android")]
-    static mut PROG: &'static str = "ls"; // android don't have echo binary
-
-    let mut p = match unsafe{Process::new(PROG, [])} {
-        Ok(p) => p,
-        Err(e) => fail!("wut: {}", e),
-    };
-    p.signal_exit().unwrap(); // this shouldnt crash...
-    p.signal_exit().unwrap(); // ...and nor should this (and nor should the destructor)
+    let mut p = sleeper();
+    succeed!(p.signal_exit()); // this shouldnt crash...
+    let _ = p.signal_exit(); // ...and nor should this (and nor should the destructor)
 })
 
 pub fn test_destroy_actually_kills(force: bool) {