Fix pty read sometimes not triggering draw

There was a lot of complexity around the threadsafe `Flag` type and
waking up the event loop. The idea was to prevent unnecessary calls to
the glutin window's wakeup_event_loop() method which can be expensive.
This complexity made it difficult to get synchronization between the pty
reader and the render thread correct. Now, the `dirty` flag on the
terminal is also used to prevent spurious wakeups. It is only changed
when the mutex is held, so race conditions associated with that flag
shouldn't happen.

1 files changed, 8 insertions, 3 deletions

diff --git a/src/event_loop.rs b/src/event_loop.rs
index a6eed40e..d1c52367 100644
--- a/src/event_loop.rs
+++ b/src/event_loop.rs
@@ -211,9 +211,14 @@ impl<Io> EventLoop<Io>
                         state.parser.advance(&mut *terminal, *byte, &mut self.pty);
                     }
 
-                    terminal.dirty = true;
-
-                    self.display.notify();
+                    // Only request a draw if one hasn't already been requested.
+                    //
+                    // This is a performance optimization even if only for X11
+                    // which is very expensive to hammer on the even loop wakeup
+                    if !terminal.dirty {
+                        self.display.notify();
+                        terminal.dirty = true;
+                    }
                 },
                 Err(err) => {
                     match err.kind() {