Fix assumption about queue order. Fixes #216 .
The mpmc queue can fill slots out of order if a context switch occurs
between "reserving" a slot and marking that slot as filled.
So, insertion into slot 2 can look successful (and cause mio to
increment its own queue length counts) before an insertion into slot 1
is fully committed.
So, then when mio actually reads the queue, it gets None, because
slot 1, the "next" slot, isn't completely done yet. Yielding the
scheduler to other threads will allow the partially-committed slot
to finish committing, and the queue will eventually be seen as having
both elements, slots 1 and 2.
diff --git a/src/event_loop.rs b/src/event_loop.rs
index 5d27e64..44f68cc 100644
--- a/src/event_loop.rs
+++ b/src/event_loop.rs
@@ -3,7 +3,7 @@
use notify::Notify;
use timer::{Timer, Timeout, TimerResult};
use std::default::Default;
-use std::{io, fmt, usize};
+use std::{io, fmt, thread, usize};
/// Configure EventLoop runtime details
#[derive(Copy, Clone, Debug)]
@@ -309,11 +309,18 @@
fn notify(&mut self, handler: &mut H, mut cnt: usize) {
while cnt > 0 {
- let msg = self.notify.poll()
- .expect("[BUG] at this point there should always be a message");
-
- handler.notify(self, msg);
- cnt -= 1;
+ match self.notify.poll() {
+ Some(msg) => {
+ handler.notify(self, msg);
+ cnt -= 1;
+ },
+ // If we expect messages, but the queue seems empty, a context
+ // switch has occurred in the queue's push() method between
+ // reserving a slot and marking that slot; let's spin for
+ // what should be a very brief period of time until the push
+ // is done.
+ None => thread::yield_now(),
+ }
}
}
