src/libstd/sync/mpsc/blocking.rs

   1 // Copyright 2014 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.
   4 //
   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.
  10
  11 //! Generic support for building blocking abstractions.
  12
  13 use thread::{self, Thread};
  14 use sync::atomic::{AtomicBool, ATOMIC_BOOL_INIT, Ordering};
  15 use sync::Arc;
  16 use marker::{Sync, Send};
  17 use mem;
  18 use clone::Clone;
  19
  20 struct Inner {
  21     thread: Thread,
  22     woken: AtomicBool,
  23 }
  24
  25 unsafe impl Send for Inner {}
  26 unsafe impl Sync for Inner {}
  27
  28 #[derive(Clone)]
  29 pub struct SignalToken {
  30     inner: Arc<Inner>,
  31 }
  32
  33 pub struct WaitToken {
  34     inner: Arc<Inner>,
  35 }
  36
  37 impl !Send for WaitToken {}
  38
  39 impl !Sync for WaitToken {}
  40
  41 pub fn tokens() -> (WaitToken, SignalToken) {
  42     let inner = Arc::new(Inner {
  43         thread: thread::current(),
  44         woken: ATOMIC_BOOL_INIT,
  45     });
  46     let wait_token = WaitToken {
  47         inner: inner.clone(),
  48     };
  49     let signal_token = SignalToken {
  50         inner: inner
  51     };
  52     (wait_token, signal_token)
  53 }
  54
  55 impl SignalToken {
  56     pub fn signal(&self) -> bool {
  57         let wake = !self.inner.woken.compare_and_swap(false, true, Ordering::SeqCst);
  58         if wake {
  59             self.inner.thread.unpark();
  60         }
  61         wake
  62     }
  63
  64     /// Convert to an unsafe usize value. Useful for storing in a pipe's state
  65     /// flag.
  66     #[inline]
  67     pub unsafe fn cast_to_usize(self) -> usize {
  68         mem::transmute(self.inner)
  69     }
  70
  71     /// Convert from an unsafe usize value. Useful for retrieving a pipe's state
  72     /// flag.
  73     #[inline]
  74     pub unsafe fn cast_from_usize(signal_ptr: usize) -> SignalToken {
  75         SignalToken { inner: mem::transmute(signal_ptr) }
  76     }
  77
  78 }
  79
  80 impl WaitToken {
  81     pub fn wait(self) {
  82         while !self.inner.woken.load(Ordering::SeqCst) {
  83             thread::park()
  84         }
  85     }
  86 }