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
164
165
166
167
168
169
170
171
//! An implementation of IPC locks, guaranteed to be released if a process dies
//!
//! This module implements a locking server/client where the main `cargo fix`
//! process will start up a server and then all the client processes will
//! connect to it. The main purpose of this file is to ensure that each crate
//! (aka file entry point) is only fixed by one process at a time, currently
//! concurrent fixes can't happen.
//!
//! The basic design here is to use a TCP server which is pretty portable across
//! platforms. For simplicity it just uses threads as well. Clients connect to
//! the main server, inform the server what its name is, and then wait for the
//! server to give it the lock (aka write a byte).
use std::collections::HashMap;
use std::io::{BufRead, BufReader, Read, Write};
use std::net::{SocketAddr, TcpListener, TcpStream};
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::{Arc, Mutex};
use std::thread::{self, JoinHandle};
use anyhow::{Context, Error};
pub struct LockServer {
listener: TcpListener,
addr: SocketAddr,
threads: HashMap<String, ServerClient>,
done: Arc<AtomicBool>,
}
pub struct LockServerStarted {
done: Arc<AtomicBool>,
addr: SocketAddr,
thread: Option<JoinHandle<()>>,
}
pub struct LockServerClient {
_socket: TcpStream,
}
struct ServerClient {
thread: Option<JoinHandle<()>>,
lock: Arc<Mutex<(bool, Vec<TcpStream>)>>,
}
impl LockServer {
pub fn new() -> Result<LockServer, Error> {
let listener = TcpListener::bind("127.0.0.1:0")
.with_context(|| "failed to bind TCP listener to manage locking")?;
let addr = listener.local_addr()?;
Ok(LockServer {
listener,
addr,
threads: HashMap::new(),
done: Arc::new(AtomicBool::new(false)),
})
}
pub fn addr(&self) -> &SocketAddr {
&self.addr
}
pub fn start(self) -> Result<LockServerStarted, Error> {
let addr = self.addr;
let done = self.done.clone();
let thread = thread::spawn(|| {
self.run();
});
Ok(LockServerStarted {
addr,
thread: Some(thread),
done,
})
}
fn run(mut self) {
while let Ok((client, _)) = self.listener.accept() {
if self.done.load(Ordering::SeqCst) {
break;
}
// Learn the name of our connected client to figure out if it needs
// to wait for another process to release the lock.
let mut client = BufReader::new(client);
let mut name = String::new();
if client.read_line(&mut name).is_err() {
continue;
}
let client = client.into_inner();
// If this "named mutex" is already registered and the thread is
// still going, put it on the queue. Otherwise wait on the previous
// thread and we'll replace it just below.
if let Some(t) = self.threads.get_mut(&name) {
let mut state = t.lock.lock().unwrap();
if state.0 {
state.1.push(client);
continue;
}
drop(t.thread.take().unwrap().join());
}
let lock = Arc::new(Mutex::new((true, vec![client])));
let lock2 = lock.clone();
let thread = thread::spawn(move || {
loop {
let mut client = {
let mut state = lock2.lock().unwrap();
if state.1.is_empty() {
state.0 = false;
break;
} else {
state.1.remove(0)
}
};
// Inform this client that it now has the lock and wait for
// it to disconnect by waiting for EOF.
if client.write_all(&[1]).is_err() {
continue;
}
let mut dst = Vec::new();
drop(client.read_to_end(&mut dst));
}
});
self.threads.insert(
name,
ServerClient {
thread: Some(thread),
lock,
},
);
}
}
}
impl Drop for LockServer {
fn drop(&mut self) {
for (_, mut client) in self.threads.drain() {
if let Some(thread) = client.thread.take() {
drop(thread.join());
}
}
}
}
impl Drop for LockServerStarted {
fn drop(&mut self) {
self.done.store(true, Ordering::SeqCst);
// Ignore errors here as this is largely best-effort
if TcpStream::connect(&self.addr).is_err() {
return;
}
drop(self.thread.take().unwrap().join());
}
}
impl LockServerClient {
pub fn lock(addr: &SocketAddr, name: impl AsRef<[u8]>) -> Result<LockServerClient, Error> {
let mut client =
TcpStream::connect(&addr).with_context(|| "failed to connect to parent lock server")?;
client
.write_all(name.as_ref())
.and_then(|_| client.write_all(b"\n"))
.with_context(|| "failed to write to lock server")?;
let mut buf = [0];
client
.read_exact(&mut buf)
.with_context(|| "failed to acquire lock")?;
Ok(LockServerClient { _socket: client })
}
}