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wait_group.rs
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wait_group.rs
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use std::fmt;
use std::sync::{Arc, Condvar, Mutex};
/// `WaitGroup` provides synchronization on the completion of threads.
///
/// For each thread involved in the synchronization, `add(1)` should be
/// called. Just before a thread terminates, it should call `done`.
/// To synchronize, call `wait`, which will block until the number of `done`
/// calls corresponds to the number of `add(1)` calls.
///
/// # Example
///
/// ```
/// use std::thread;
///
/// let wg = chan::WaitGroup::new();
///
/// for _ in 0..4 {
/// wg.add(1);
/// let wg = wg.clone();
/// thread::spawn(move || {
/// // do some work.
///
/// // And now call done.
/// wg.done();
/// });
/// }
/// // Blocks until `wg.done()` is called for each thread we spawned.
/// wg.wait()
/// ```
#[derive(Clone)]
pub struct WaitGroup(Arc<WaitGroupInner>);
struct WaitGroupInner {
cond: Condvar,
count: Mutex<i32>,
}
impl WaitGroup {
/// Create a new wait group.
pub fn new() -> WaitGroup {
WaitGroup(Arc::new(WaitGroupInner {
cond: Condvar::new(),
count: Mutex::new(0),
}))
}
/// Add a new thread to the waitgroup.
///
/// # Failure
///
/// If the internal count drops below `0` as a result of calling `add`,
/// then this function panics.
pub fn add(&self, delta: i32) {
let mut count = self.0.count.lock().unwrap();
*count += delta;
assert!(*count >= 0);
self.0.cond.notify_all();
}
/// Mark a thread as having finished.
///
/// (This is equivalent to calling `add(-1)`.)
pub fn done(&self) {
self.add(-1);
}
/// Wait until all threads have completed.
///
/// This unblocks when the internal count is `0`.
pub fn wait(&self) {
let mut count = self.0.count.lock().unwrap();
while *count > 0 {
count = self.0.cond.wait(count).unwrap();
}
}
}
impl fmt::Debug for WaitGroup {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
let count = self.0.count.lock().unwrap();
write!(f, "WaitGroup {{ count: {:?} }}", *count)
}
}