1 // Copyright 2013 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! Homing I/O implementation
13 //! In libuv, whenever a handle is created on an I/O loop it is illegal to use
14 //! that handle outside of that I/O loop. We use libuv I/O with our green
15 //! scheduler, and each green scheduler corresponds to a different I/O loop on a
16 //! different OS thread. Green tasks are also free to roam among schedulers,
17 //! which implies that it is possible to create an I/O handle on one event loop
18 //! and then attempt to use it on another.
20 //! In order to solve this problem, this module implements the notion of a
21 //! "homing operation" which will transplant a task from its currently running
22 //! scheduler back onto the original I/O loop. This is accomplished entirely at
23 //! the librustuv layer with very little cooperation from the scheduler (which
24 //! we don't even know exists technically).
26 //! These homing operations are completed by first realizing that we're on the
27 //! wrong I/O loop, then descheduling ourselves, sending ourselves to the
28 //! correct I/O loop, and then waking up the I/O loop in order to process its
29 //! local queue of tasks which need to run.
31 //! This enqueueing is done with a concurrent queue from libstd, and the
32 //! signalling is achieved with an async handle.
36 use std::rt::local::Local;
37 use std::rt::rtio::LocalIo;
38 use std::rt::task::{Task, BlockedTask};
41 use queue::{Queue, QueuePool};
43 /// A handle to a remote libuv event loop. This handle will keep the event loop
44 /// alive while active in order to ensure that a homing operation can always be
47 /// Handles are clone-able in order to derive new handles from existing handles
48 /// (very useful for when accepting a socket from a server).
49 pub struct HomeHandle {
55 pub fn new(id: uint, pool: &mut QueuePool) -> HomeHandle {
56 HomeHandle { queue: pool.queue(), id: id }
59 fn send(&mut self, task: BlockedTask) {
60 self.queue.push(task);
64 impl Clone for HomeHandle {
65 fn clone(&self) -> HomeHandle {
67 queue: self.queue.clone(),
74 fn home<'r>(&'r mut self) -> &'r mut HomeHandle;
76 /// This function will move tasks to run on their home I/O scheduler. Note
77 /// that this function does *not* pin the task to the I/O scheduler, but
78 /// rather it simply moves it to running on the I/O scheduler.
79 fn go_to_IO_home(&mut self) -> uint {
80 let _f = ForbidUnwind::new("going home");
82 let mut cur_task: ~Task = Local::take();
84 let mut io = cur_task.local_io().expect("libuv must have I/O");
88 // Try at all costs to avoid the homing operation because it is quite
89 // expensive. Hence, we only deschedule/send if we're not on the correct
90 // event loop. If we're already on the home event loop, then we're good
91 // to go (remember we have no preemption, so we're guaranteed to stay on
92 // this event loop as long as we avoid the scheduler).
93 if cur_loop_id != self.home().id {
94 cur_task.deschedule(1, |task| {
95 self.home().send(task);
99 // Once we wake up, assert that we're in the right location
101 let mut io = LocalIo::borrow().expect("libuv must have I/O");
104 assert_eq!(cur_loop_id, self.home().id);
108 Local::put(cur_task);
113 /// Fires a single homing missile, returning another missile targeted back
114 /// at the original home of this task. In other words, this function will
115 /// move the local task to its I/O scheduler and then return an RAII wrapper
116 /// which will return the task home.
117 fn fire_homing_missile(&mut self) -> HomingMissile {
118 HomingMissile { io_home: self.go_to_IO_home() }
122 /// After a homing operation has been completed, this will return the current
123 /// task back to its appropriate home (if applicable). The field is used to
124 /// assert that we are where we think we are.
125 struct HomingMissile {
130 /// Check at runtime that the task has *not* transplanted itself to a
131 /// different I/O loop while executing.
132 pub fn check(&self, msg: &'static str) {
133 let mut io = LocalIo::borrow().expect("libuv must have I/O");
134 assert!(io.get().id() == self.io_home, "{}", msg);
138 impl Drop for HomingMissile {
140 let _f = ForbidUnwind::new("leaving home");
142 // It would truly be a sad day if we had moved off the home I/O
143 // scheduler while we were doing I/O.
144 self.check("task moved away from the home scheduler");
151 use green::{SchedPool, PoolConfig};
152 use std::rt::rtio::RtioUdpSocket;
153 use std::io::test::next_test_ip4;
154 use std::task::TaskOpts;
157 use super::super::local_loop;
159 // On one thread, create a udp socket. Then send that socket to another
160 // thread and destroy the socket on the remote thread. This should make sure
161 // that homing kicks in for the socket to go back home to the original
162 // thread, close itself, and then come back to the last thread.
164 fn test_homing_closes_correctly() {
165 let (port, chan) = Chan::new();
166 let mut pool = SchedPool::new(PoolConfig {
168 event_loop_factory: None,
171 do pool.spawn(TaskOpts::new()) {
172 let listener = UdpWatcher::bind(local_loop(), next_test_ip4());
173 chan.send(listener.unwrap());
176 let task = do pool.task(TaskOpts::new()) {
179 pool.spawn_sched().send(sched::TaskFromFriend(task));
185 fn test_homing_read() {
186 let (port, chan) = Chan::new();
187 let mut pool = SchedPool::new(PoolConfig {
189 event_loop_factory: None,
192 do pool.spawn(TaskOpts::new()) {
193 let addr1 = next_test_ip4();
194 let addr2 = next_test_ip4();
195 let listener = UdpWatcher::bind(local_loop(), addr2);
196 chan.send((listener.unwrap(), addr1));
197 let mut listener = UdpWatcher::bind(local_loop(), addr1).unwrap();
198 listener.sendto([1, 2, 3, 4], addr2);
201 let task = do pool.task(TaskOpts::new()) {
202 let (mut watcher, addr) = port.recv();
203 let mut buf = [0, ..10];
204 assert_eq!(watcher.recvfrom(buf).unwrap(), (4, addr));
206 pool.spawn_sched().send(sched::TaskFromFriend(task));