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Drop Pool job_sender explicitly using ManuallyDrop #21

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Drop Pool job_sender explicitly using ManuallyDrop #21

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16 changes: 10 additions & 6 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -55,7 +55,7 @@ use std::thread::{self, JoinHandle};
use std::sync::mpsc::{channel, Sender, Receiver, SyncSender, sync_channel, RecvError};
use std::sync::{Arc, Mutex};
use std::marker::PhantomData;
use std::mem;
use std::mem::{self, ManuallyDrop};

enum Message {
NewJob(Thunk<'static>),
Expand All @@ -76,15 +76,19 @@ type Thunk<'a> = Box<FnBox + Send + 'a>;

impl Drop for Pool {
fn drop(&mut self) {
self.job_sender = None;
// Explicitly drop job_sender before the threads, to ensure
// channel is already closed by the time threads are joined.
unsafe {
ManuallyDrop::drop(&mut self.job_sender);
}
}
}

/// A threadpool that acts as a handle to a number
/// of threads spawned at construction.
pub struct Pool {
threads: Vec<ThreadData>,
job_sender: Option<Sender<Message>>
job_sender: ManuallyDrop<Sender<Message>>,
}

struct ThreadData {
Expand Down Expand Up @@ -162,7 +166,7 @@ impl Pool {

Pool {
threads: threads,
job_sender: Some(job_sender),
job_sender: ManuallyDrop::new(job_sender),
}
}

Expand Down Expand Up @@ -210,13 +214,13 @@ impl<'pool, 'scope> Scope<'pool, 'scope> {
let b = unsafe {
mem::transmute::<Thunk<'scope>, Thunk<'static>>(Box::new(f))
};
self.pool.job_sender.as_ref().unwrap().send(Message::NewJob(b)).unwrap();
self.pool.job_sender.send(Message::NewJob(b)).unwrap();
}

/// Blocks until all currently queued jobs have run to completion.
pub fn join_all(&self) {
for _ in 0..self.pool.threads.len() {
self.pool.job_sender.as_ref().unwrap().send(Message::Join).unwrap();
self.pool.job_sender.send(Message::Join).unwrap();
}

// Synchronize/Join with threads
Expand Down