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

use jobserver_crate::{Client, HelperThread, Acquired};
use lazy_static::lazy_static;
use std::sync::{Condvar, Arc, Mutex};
use std::mem;

#[derive(Default)]
struct LockedProxyData {
    /// The number of free thread tokens, this may include the implicit token given to the process
    free: usize,

    /// The number of threads waiting for a token
    waiters: usize,

    /// The number of tokens we requested from the server
    requested: usize,

    /// Stored tokens which will be dropped when we no longer need them
    tokens: Vec<Acquired>,
}

impl LockedProxyData {
    fn request_token(&mut self, thread: &Mutex<HelperThread>) {
        self.requested += 1;
        thread.lock().unwrap().request_token();
    }

    fn release_token(&mut self, cond_var: &Condvar) {
        if self.waiters > 0 {
            self.free += 1;
            cond_var.notify_one();
        } else {
            if self.tokens.is_empty() {
                // We are returning the implicit token
                self.free += 1;
            } else {
                // Return a real token to the server
                self.tokens.pop().unwrap();
            }
        }
    }

    fn take_token(&mut self, thread: &Mutex<HelperThread>) -> bool {
        if self.free > 0 {
            self.free -= 1;
            self.waiters -= 1;

            // We stole some token reqested by someone else
            // Request another one
            if self.requested + self.free < self.waiters {
                self.request_token(thread);
            }

            true
        } else {
            false
        }
    }

    fn new_requested_token(&mut self, token: Acquired, cond_var: &Condvar) {
        self.requested -= 1;

        // Does anything need this token?
        if self.waiters > 0 {
            self.free += 1;
            self.tokens.push(token);
            cond_var.notify_one();
        } else {
            // Otherwise we'll just drop it
            mem::drop(token);
        }
    }
}

#[derive(Default)]
struct ProxyData {
    lock: Mutex<LockedProxyData>,
    cond_var: Condvar,
}

/// A helper type which makes managing jobserver tokens easier.
/// It also allows you to treat the implicit token given to the process
/// in the same manner as requested tokens.
struct Proxy {
    thread: Mutex<HelperThread>,
    data: Arc<ProxyData>,
}

lazy_static! {
    // We can only call `from_env` once per process

    // Note that this is unsafe because it may misinterpret file descriptors
    // on Unix as jobserver file descriptors. We hopefully execute this near
    // the beginning of the process though to ensure we don't get false
    // positives, or in other words we try to execute this before we open
    // any file descriptors ourselves.
    //
    // Pick a "reasonable maximum" if we don't otherwise have
    // a jobserver in our environment, capping out at 32 so we
    // don't take everything down by hogging the process run queue.
    // The fixed number is used to have deterministic compilation
    // across machines.
    //
    // Also note that we stick this in a global because there could be
    // multiple rustc instances in this process, and the jobserver is
    // per-process.
    static ref GLOBAL_CLIENT: Client = unsafe {
        Client::from_env().unwrap_or_else(|| {
            Client::new(32).expect("failed to create jobserver")
        })
    };

    static ref GLOBAL_PROXY: Proxy = {
        let data = Arc::new(ProxyData::default());

        Proxy {
            data: data.clone(),
            thread: Mutex::new(client().into_helper_thread(move |token| {
                data.lock.lock().unwrap().new_requested_token(token.unwrap(), &data.cond_var);
            }).unwrap()),
        }
    };
}

pub fn client() -> Client {
    GLOBAL_CLIENT.clone()
}

pub fn acquire_thread() {
    GLOBAL_PROXY.acquire_token();
}

pub fn release_thread() {
    GLOBAL_PROXY.release_token();
}

impl Proxy {
    fn release_token(&self) {
        self.data.lock.lock().unwrap().release_token(&self.data.cond_var);
    }

    fn acquire_token(&self) {
        let mut data = self.data.lock.lock().unwrap();
        data.waiters += 1;
        if data.take_token(&self.thread) {
            return;
        }
        // Request a token for us
        data.request_token(&self.thread);
        loop {
            data = self.data.cond_var.wait(data).unwrap();
            if data.take_token(&self.thread) {
                return;
            }
        }
    }
}