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.
37 use std::rt::local::Local;
38 use std::rt::rtio::LocalIo;
39 use std::rt::task::{Task, BlockedTask};
42 use queue::{Queue, QueuePool};
44 /// A handle to a remote libuv event loop. This handle will keep the event loop
45 /// alive while active in order to ensure that a homing operation can always be
48 /// Handles are clone-able in order to derive new handles from existing handles
49 /// (very useful for when accepting a socket from a server).
50 pub struct HomeHandle {
56 pub fn new(id: uint, pool: &mut QueuePool) -> HomeHandle {
57 HomeHandle { queue: pool.queue(), id: id }
60 fn send(&mut self, task: BlockedTask) {
61 self.queue.push(task);
65 impl Clone for HomeHandle {
66 fn clone(&self) -> HomeHandle {
68 queue: self.queue.clone(),
74 pub fn local_id() -> uint {
75 let mut io = match LocalIo::borrow() {
76 Some(io) => io, None => return 0,
80 let (_vtable, ptr): (uint, uint) = cast::transmute(io);
86 fn home<'r>(&'r mut self) -> &'r mut HomeHandle;
88 /// This function will move tasks to run on their home I/O scheduler. Note
89 /// that this function does *not* pin the task to the I/O scheduler, but
90 /// rather it simply moves it to running on the I/O scheduler.
91 fn go_to_IO_home(&mut self) -> uint {
92 let _f = ForbidUnwind::new("going home");
94 let cur_loop_id = local_id();
95 let destination = self.home().id;
97 // Try at all costs to avoid the homing operation because it is quite
98 // expensive. Hence, we only deschedule/send if we're not on the correct
99 // event loop. If we're already on the home event loop, then we're good
100 // to go (remember we have no preemption, so we're guaranteed to stay on
101 // this event loop as long as we avoid the scheduler).
102 if cur_loop_id != destination {
103 let cur_task: Box<Task> = Local::take();
104 cur_task.deschedule(1, |task| {
105 self.home().send(task);
109 // Once we wake up, assert that we're in the right location
110 assert_eq!(local_id(), destination);
116 /// Fires a single homing missile, returning another missile targeted back
117 /// at the original home of this task. In other words, this function will
118 /// move the local task to its I/O scheduler and then return an RAII wrapper
119 /// which will return the task home.
120 fn fire_homing_missile(&mut self) -> HomingMissile {
121 HomingMissile { io_home: self.go_to_IO_home() }
125 /// After a homing operation has been completed, this will return the current
126 /// task back to its appropriate home (if applicable). The field is used to
127 /// assert that we are where we think we are.
128 pub struct HomingMissile {
133 /// Check at runtime that the task has *not* transplanted itself to a
134 /// different I/O loop while executing.
135 pub fn check(&self, msg: &'static str) {
136 assert!(local_id() == self.io_home, "{}", msg);
140 impl Drop for HomingMissile {
142 let _f = ForbidUnwind::new("leaving home");
144 // It would truly be a sad day if we had moved off the home I/O
145 // scheduler while we were doing I/O.
146 self.check("task moved away from the home scheduler");
153 use green::{SchedPool, PoolConfig};
154 use std::rt::rtio::RtioUdpSocket;
155 use std::io::test::next_test_ip4;
156 use std::task::TaskOpts;
159 use super::super::local_loop;
161 // On one thread, create a udp socket. Then send that socket to another
162 // thread and destroy the socket on the remote thread. This should make sure
163 // that homing kicks in for the socket to go back home to the original
164 // thread, close itself, and then come back to the last thread.
166 fn test_homing_closes_correctly() {
167 let (tx, rx) = channel();
168 let mut pool = SchedPool::new(PoolConfig {
170 event_loop_factory: ::event_loop,
173 pool.spawn(TaskOpts::new(), proc() {
174 let listener = UdpWatcher::bind(local_loop(), next_test_ip4());
175 tx.send(listener.unwrap());
178 let task = pool.task(TaskOpts::new(), proc() {
181 pool.spawn_sched().send(sched::TaskFromFriend(task));
187 fn test_homing_read() {
188 let (tx, rx) = channel();
189 let mut pool = SchedPool::new(PoolConfig {
191 event_loop_factory: ::event_loop,
194 pool.spawn(TaskOpts::new(), proc() {
195 let addr1 = next_test_ip4();
196 let addr2 = next_test_ip4();
197 let listener = UdpWatcher::bind(local_loop(), addr2);
198 tx.send((listener.unwrap(), addr1));
199 let mut listener = UdpWatcher::bind(local_loop(), addr1).unwrap();
200 listener.sendto([1, 2, 3, 4], addr2).unwrap();
203 let task = pool.task(TaskOpts::new(), proc() {
204 let (mut watcher, addr) = rx.recv();
205 let mut buf = [0, ..10];
206 assert_eq!(watcher.recvfrom(buf).unwrap(), (4, addr));
208 pool.spawn_sched().send(sched::TaskFromFriend(task));