1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
|
// Copyright 2013 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::cast;
use std::libc::c_int;
use std::rt::rtio::{Callback, RemoteCallback};
use std::unstable::sync::Exclusive;
use uvll;
use super::{Loop, UvHandle};
// The entire point of async is to call into a loop from other threads so it
// does not need to home.
pub struct AsyncWatcher {
handle: *uvll::uv_async_t,
// A flag to tell the callback to exit, set from the dtor. This is
// almost never contested - only in rare races with the dtor.
exit_flag: Exclusive<bool>
}
struct Payload {
callback: ~Callback,
exit_flag: Exclusive<bool>,
}
impl AsyncWatcher {
pub fn new(loop_: &mut Loop, cb: ~Callback) -> AsyncWatcher {
let handle = UvHandle::alloc(None::<AsyncWatcher>, uvll::UV_ASYNC);
assert_eq!(unsafe {
uvll::uv_async_init(loop_.handle, handle, async_cb)
}, 0);
let flag = Exclusive::new(false);
let payload = ~Payload { callback: cb, exit_flag: flag.clone() };
unsafe {
let payload: *u8 = cast::transmute(payload);
uvll::set_data_for_uv_handle(handle, payload);
}
return AsyncWatcher { handle: handle, exit_flag: flag, };
}
}
impl UvHandle<uvll::uv_async_t> for AsyncWatcher {
fn uv_handle(&self) -> *uvll::uv_async_t { self.handle }
unsafe fn from_uv_handle<'a>(_: &'a *uvll::uv_async_t) -> &'a mut AsyncWatcher {
fail!("async watchers can't be built from their handles");
}
}
extern fn async_cb(handle: *uvll::uv_async_t, status: c_int) {
assert!(status == 0);
let payload: &mut Payload = unsafe {
cast::transmute(uvll::get_data_for_uv_handle(handle))
};
// The synchronization logic here is subtle. To review,
// the uv async handle type promises that, after it is
// triggered the remote callback is definitely called at
// least once. UvRemoteCallback needs to maintain those
// semantics while also shutting down cleanly from the
// dtor. In our case that means that, when the
// UvRemoteCallback dtor calls `async.send()`, here `f` is
// always called later.
// In the dtor both the exit flag is set and the async
// callback fired under a lock. Here, before calling `f`,
// we take the lock and check the flag. Because we are
// checking the flag before calling `f`, and the flag is
// set under the same lock as the send, then if the flag
// is set then we're guaranteed to call `f` after the
// final send.
// If the check was done after `f()` then there would be a
// period between that call and the check where the dtor
// could be called in the other thread, missing the final
// callback while still destroying the handle.
let should_exit = unsafe {
payload.exit_flag.with_imm(|&should_exit| should_exit)
};
payload.callback.call();
if should_exit {
unsafe { uvll::uv_close(handle, close_cb) }
}
}
extern fn close_cb(handle: *uvll::uv_handle_t) {
// drop the payload
let _payload: ~Payload = unsafe {
cast::transmute(uvll::get_data_for_uv_handle(handle))
};
// and then free the handle
unsafe { uvll::free_handle(handle) }
}
impl RemoteCallback for AsyncWatcher {
fn fire(&mut self) {
unsafe { uvll::uv_async_send(self.handle) }
}
}
impl Drop for AsyncWatcher {
fn drop(&mut self) {
unsafe {
self.exit_flag.with(|should_exit| {
// NB: These two things need to happen atomically. Otherwise
// the event handler could wake up due to a *previous*
// signal and see the exit flag, destroying the handle
// before the final send.
*should_exit = true;
uvll::uv_async_send(self.handle)
})
}
}
}
#[cfg(test)]
mod test_remote {
use std::rt::rtio::{Callback, RemoteCallback};
use std::rt::thread::Thread;
use super::AsyncWatcher;
use super::super::local_loop;
// Make sure that we can fire watchers in remote threads and that they
// actually trigger what they say they will.
#[test]
fn smoke_test() {
struct MyCallback(Option<Chan<int>>);
impl Callback for MyCallback {
fn call(&mut self) {
// this can get called more than once, but we only want to send
// once
let MyCallback(ref mut s) = *self;
if s.is_some() {
s.take_unwrap().send(1);
}
}
}
let (port, chan) = Chan::new();
let cb = ~MyCallback(Some(chan));
let watcher = AsyncWatcher::new(&mut local_loop().loop_,
cb as ~Callback);
let thread = do Thread::start {
let mut watcher = watcher;
watcher.fire();
};
assert_eq!(port.recv(), 1);
thread.join();
}
}
|
