std: Add a process::exit function

This commit is an implementation of [RFC #1011][rfc] which adds an `exit`
function to the standard library for immediately terminating the current process
with a specified exit code.

[rfc]: rust-lang/rfcs#1011

Author: alexcrichton

src/libstd/process.rs

@@ -527,6 +527,22 @@ impl Child {
     }
 }
 
+/// Terminates the current process with the specified exit code.
+///
+/// This function will never return and will immediately terminate the current
+/// process. The exit code is passed through to the underlying OS and will be
+/// available for consumption by another process.
+///
+/// Note that because this function never returns, and that it terminates the
+/// process, no destructors on the current stack or any other thread's stack
+/// will be run. If a clean shutdown is needed it is recommended to only call
+/// this function at a known point where there are no more destructors left
+/// to run.
+#[stable(feature = "rust1", since = "1.0.0")]
+pub fn exit(code: i32) -> ! {
+    ::sys::os::exit(code)
+}
+
 #[cfg(test)]
 mod tests {
     use io::ErrorKind;

src/libstd/sys/unix/os.rs

@@ -505,3 +505,7 @@ pub fn home_dir() -> Option<PathBuf> {
         }
     }
 }
+
+pub fn exit(code: i32) -> ! {
+    unsafe { libc::exit(code as c_int) }
+}

src/libstd/sys/windows/c.rs

@@ -433,6 +433,7 @@ extern "system" {
                             TokenHandle: *mut libc::HANDLE) -> libc::BOOL;
     pub fn GetCurrentProcess() -> libc::HANDLE;
     pub fn GetStdHandle(which: libc::DWORD) -> libc::HANDLE;
+    pub fn ExitProcess(uExitCode: libc::UINT) -> !;
 }
 
 #[link(name = "userenv")]

src/libstd/sys/windows/os.rs

@@ -379,3 +379,7 @@ pub fn home_dir() -> Option<PathBuf> {
         }, super::os2path).ok()
     })
 }
+
+pub fn exit(code: i32) -> ! {
+    unsafe { libc::ExitProcess(code as libc::UINT) }
+}

src/test/run-pass/process-exit.rs

@@ -0,0 +1,31 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use std::env;
+use std::process::{self, Command, Stdio};
+
+fn main() {
+    let args: Vec<String> = env::args().collect();
+    if args.len() > 1 && args[1] == "child" {
+        child();
+    } else {
+        parent();
+    }
+}
+
+fn parent() {
+    let args: Vec<String> = env::args().collect();
+    let status = Command::new(&args[0]).arg("child").status().unwrap();
+    assert_eq!(status.code(), Some(2));
+}
+
+fn child() -> i32 {
+    process::exit(2);
+}