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fix deadlock in queue drop #3903

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Dec 19, 2016
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fix deadlock in queue drop #3903

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34 changes: 19 additions & 15 deletions ethcore/src/verification/queue/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -137,7 +137,7 @@ pub struct VerificationQueue<K: Kind> {
max_queue_size: usize,
max_mem_use: usize,
scale_verifiers: bool,
verifier_handles: Vec<JoinHandle<()>>,
verifier_handles: Vec<JoinHandle<()>>,
state: Arc<(Mutex<State>, Condvar)>,
}

Expand Down Expand Up @@ -225,8 +225,8 @@ impl<K: Kind> VerificationQueue<K> {

let num_cpus = ::num_cpus::get();
let max_verifiers = min(num_cpus, MAX_VERIFIERS);
let default_amount = max(1, min(max_verifiers, config.verifier_settings.num_verifiers));
let state = Arc::new((Mutex::new(State::Work(default_amount)), Condvar::new()));
let default_amount = max(1, min(max_verifiers, config.verifier_settings.num_verifiers));
let state = Arc::new((Mutex::new(State::Work(default_amount)), Condvar::new()));
let mut verifier_handles = Vec::with_capacity(max_verifiers);

debug!(target: "verification", "Allocating {} verifiers, {} initially active", max_verifiers, default_amount);
Expand All @@ -248,11 +248,11 @@ impl<K: Kind> VerificationQueue<K> {
.spawn(move || {
panic_handler.catch_panic(move || {
VerificationQueue::verify(
verification,
engine,
wait,
ready,
empty,
verification,
engine,
wait,
ready,
empty,
state,
i,
)
Expand Down Expand Up @@ -299,11 +299,11 @@ impl<K: Kind> VerificationQueue<K> {

debug!(target: "verification", "verifier {} sleeping", id);
state.1.wait(&mut cur_state);
debug!(target: "verification", "verifier {} waking up", id);
debug!(target: "verification", "verifier {} waking up", id);
}

if let State::Exit = *cur_state {
debug!(target: "verification", "verifier {} exiting", id);
if let State::Exit = *cur_state {
debug!(target: "verification", "verifier {} exiting", id);
break;
}
}
Expand All @@ -326,7 +326,7 @@ impl<K: Kind> VerificationQueue<K> {
}

if let State::Exit = *state.0.lock() {
debug!(target: "verification", "verifier {} exiting", id);
debug!(target: "verification", "verifier {} exiting", id);
return;
}
}
Expand Down Expand Up @@ -681,8 +681,12 @@ impl<K: Kind> Drop for VerificationQueue<K> {
*self.state.0.lock() = State::Exit;
self.state.1.notify_all();

// wake up all threads waiting for more work.
self.more_to_verify.notify_all();
// acquire this lock to force threads to reach the waiting point
// if they're in-between the exit check and the more_to_verify wait.
{
let _more = self.verification.more_to_verify.lock().unwrap();
self.more_to_verify.notify_all();
}

// wait for all verifier threads to join.
for thread in self.verifier_handles.drain(..) {
Expand Down Expand Up @@ -811,7 +815,7 @@ mod tests {
fn readjust_verifiers() {
let queue = get_test_queue(true);

// put all the verifiers to sleep to ensure
// put all the verifiers to sleep to ensure
// the test isn't timing sensitive.
*queue.state.0.lock() = State::Work(0);

Expand Down