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.
34 use std::rt::local::Local;
35 use std::rt::rtio::LocalIo;
36 use std::rt::task::{Task, BlockedTask};
39 use queue::{Queue, QueuePool};
41 /// A handle to a remote libuv event loop. This handle will keep the event loop
42 /// alive while active in order to ensure that a homing operation can always be
45 /// Handles are clone-able in order to derive new handles from existing handles
46 /// (very useful for when accepting a socket from a server).
47 pub struct HomeHandle {
53 pub fn new(id: uint, pool: &mut QueuePool) -> HomeHandle {
54 HomeHandle { queue: pool.queue(), id: id }
57 fn send(&mut self, task: BlockedTask) {
58 self.queue.push(task);
62 impl Clone for HomeHandle {
63 fn clone(&self) -> HomeHandle {
65 queue: self.queue.clone(),
72 fn home<'r>(&'r mut self) -> &'r mut HomeHandle;
74 /// This function will move tasks to run on their home I/O scheduler. Note
75 /// that this function does *not* pin the task to the I/O scheduler, but
76 /// rather it simply moves it to running on the I/O scheduler.
77 fn go_to_IO_home(&mut self) -> uint {
78 let _f = ForbidUnwind::new("going home");
80 let mut cur_task: ~Task = Local::take();
82 let mut io = cur_task.local_io().expect("libuv must have I/O");
86 // Try at all costs to avoid the homing operation because it is quite
87 // expensive. Hence, we only deschedule/send if we're not on the correct
88 // event loop. If we're already on the home event loop, then we're good
89 // to go (remember we have no preemption, so we're guaranteed to stay on
90 // this event loop as long as we avoid the scheduler).
91 if cur_loop_id != self.home().id {
92 cur_task.deschedule(1, |task| {
93 self.home().send(task);
97 // Once we wake up, assert that we're in the right location
99 let mut io = LocalIo::borrow().expect("libuv must have I/O");
102 assert_eq!(cur_loop_id, self.home().id);
106 Local::put(cur_task);
111 /// Fires a single homing missile, returning another missile targeted back
112 /// at the original home of this task. In other words, this function will
113 /// move the local task to its I/O scheduler and then return an RAII wrapper
114 /// which will return the task home.
115 fn fire_homing_missile(&mut self) -> HomingMissile {
116 HomingMissile { io_home: self.go_to_IO_home() }
120 /// After a homing operation has been completed, this will return the current
121 /// task back to its appropriate home (if applicable). The field is used to
122 /// assert that we are where we think we are.
123 struct HomingMissile {
128 /// Check at runtime that the task has *not* transplanted itself to a
129 /// different I/O loop while executing.
130 pub fn check(&self, msg: &'static str) {
131 let mut io = LocalIo::borrow().expect("libuv must have I/O");
132 assert!(io.get().id() == self.io_home, "{}", msg);
136 impl Drop for HomingMissile {
138 let _f = ForbidUnwind::new("leaving home");
140 // It would truly be a sad day if we had moved off the home I/O
141 // scheduler while we were doing I/O.
142 self.check("task moved away from the home scheduler");
149 use green::{SchedPool, PoolConfig};
150 use std::rt::rtio::RtioUdpSocket;
151 use std::io::test::next_test_ip4;
152 use std::task::TaskOpts;
155 use super::super::local_loop;
157 // On one thread, create a udp socket. Then send that socket to another
158 // thread and destroy the socket on the remote thread. This should make sure
159 // that homing kicks in for the socket to go back home to the original
160 // thread, close itself, and then come back to the last thread.
162 fn test_homing_closes_correctly() {
163 let (port, chan) = Chan::new();
164 let mut pool = SchedPool::new(PoolConfig {
166 event_loop_factory: None,
169 do pool.spawn(TaskOpts::new()) {
170 let listener = UdpWatcher::bind(local_loop(), next_test_ip4());
171 chan.send(listener.unwrap());
174 let task = do pool.task(TaskOpts::new()) {
177 pool.spawn_sched().send(sched::TaskFromFriend(task));
183 fn test_homing_read() {
184 let (port, chan) = Chan::new();
185 let mut pool = SchedPool::new(PoolConfig {
187 event_loop_factory: None,
190 do pool.spawn(TaskOpts::new()) {
191 let addr1 = next_test_ip4();
192 let addr2 = next_test_ip4();
193 let listener = UdpWatcher::bind(local_loop(), addr2);
194 chan.send((listener.unwrap(), addr1));
195 let mut listener = UdpWatcher::bind(local_loop(), addr1).unwrap();
196 listener.sendto([1, 2, 3, 4], addr2);
199 let task = do pool.task(TaskOpts::new()) {
200 let (mut watcher, addr) = port.recv();
201 let mut buf = [0, ..10];
202 assert_eq!(watcher.recvfrom(buf).unwrap(), (4, addr));
204 pool.spawn_sched().send(sched::TaskFromFriend(task));