run all ready tasks prior to calling poll in poll_loop.py (#84)

This ensures we make as much progress as possible and accumulate as many
`pollable`s as possible prior to calling `poll`.  Previously, we were
accidentally limiting concurrency (and potentially getting stuck in cases where
there were interdepdencencies between tasks) by only running one task per loop.

Signed-off-by: Joel Dice <joel.dice@fermyon.com>

bundled/poll_loop.py

@@ -125,10 +125,11 @@ def run_until_complete(self, future):
         self.running = True
         asyncio.events._set_running_loop(self)
         while self.running and not future.done():
-            handle = self.handles[0]
-            self.handles = self.handles[1:]
-            if not handle._cancelled:
-                handle._run()
+            handles = self.handles
+            self.handles = []
+            for handle in handles:
+                if not handle._cancelled:
+                    handle._run()
 
             if self.wakers:
                 [pollables, wakers] = list(map(list, zip(*self.wakers)))