Make sure handler.flush() doesn't deadlock. (#1112)

Author: gukoff

contrib/opencensus-ext-azure/opencensus/ext/azure/log_exporter/__init__.py

@@ -106,6 +106,20 @@ def log_record_to_envelope(self, record):
         raise NotImplementedError  # pragma: NO COVER
 
     def flush(self, timeout=None):
+        if self._queue.is_empty():
+            return
+
+        # We must check the worker thread is alive, because otherwise flush
+        # is useless. Also, it would deadlock if no timeout is given, and the
+        # queue isn't empty.
+        # This is a very possible scenario during process termination, when
+        # atexit first calls handler.close() and then logging.shutdown(),
+        # that in turn calls handler.flush() without arguments.
+        if not self._worker.is_alive():
+            logger.warning("Can't flush %s, worker thread is dead. "
+                           "Any pending messages will be lost.", self)
+            return
+
         self._queue.flush(timeout=timeout)
 
 

opencensus/common/schedule/__init__.py

@@ -112,6 +112,9 @@ def _gets(self, count, timeout):
     def gets(self, count, timeout):
         return tuple(self._gets(count, timeout))
 
+    def is_empty(self):
+        return not self._queue.qsize()
+
     def flush(self, timeout=None):
         if self._queue.qsize() == 0:
             return 0
@@ -124,7 +127,7 @@ def flush(self, timeout=None):
             return
         elapsed_time = time.time() - start_time
         wait_time = timeout and max(timeout - elapsed_time, 0)
-        if event.wait(timeout):
+        if event.wait(wait_time):
             return time.time() - start_time  # time taken to flush
 
     def put(self, item, block=True, timeout=None):