From 5731cf99b697bd809b31d54fe86af957e298889a Mon Sep 17 00:00:00 2001
From: Chris Wilcox <crwilcox@google.com>
Date: Mon, 11 Mar 2019 15:26:44 -0700
Subject: [PATCH 1/2] Adds a ready event to BackgroundConsumer to allow waiting
 for the background thread to start

---
 api_core/google/api_core/bidi.py | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/api_core/google/api_core/bidi.py b/api_core/google/api_core/bidi.py
index 795a8d295f17..cd1e62e21bba 100644
--- a/api_core/google/api_core/bidi.py
+++ b/api_core/google/api_core/bidi.py
@@ -499,6 +499,7 @@ def __init__(self, bidi_rpc, on_response):
         self._wake = threading.Condition()
         self._thread = None
         self._operational_lock = threading.Lock()
+        self._ready = threading.Event()
 
     def _on_call_done(self, future):
         # Resume the thread if it's paused, this prevents blocking forever
@@ -507,6 +508,7 @@ def _on_call_done(self, future):
 
     def _thread_main(self):
         try:
+            self._ready.set()
             self._bidi_rpc.add_done_callback(self._on_call_done)
             self._bidi_rpc.open()
 
@@ -560,6 +562,11 @@ def start(self):
             )
             thread.daemon = True
             thread.start()
+            # Other parts of the code rely on `thread.is_alive` which
+            # isn't sufficient to know if a thread is active, just that it may
+            # soon be active. This can cause races. Further protect
+            # against races by using a ready event and wait on it to be set.
+            self._ready.wait()
             self._thread = thread
             _LOGGER.debug("Started helper thread %s", thread.name)
 
@@ -574,11 +581,12 @@ def stop(self):
                 self._thread.join()
 
             self._thread = None
+            self._ready.clear()
 
     @property
     def is_active(self):
         """bool: True if the background thread is active."""
-        return self._thread is not None and self._thread.is_alive()
+        return self._thread is not None and self._ready.is_set() and self._thread.is_alive()
 
     def pause(self):
         """Pauses the response stream.

From f1508edfe954ddd985956f553cf33b0d29c56711 Mon Sep 17 00:00:00 2001
From: Chris Wilcox <crwilcox@google.com>
Date: Mon, 11 Mar 2019 17:08:20 -0700
Subject: [PATCH 2/2] incorporate feedback from dpcollins to further limit the
 scope of ready

---
 api_core/google/api_core/bidi.py | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/api_core/google/api_core/bidi.py b/api_core/google/api_core/bidi.py
index cd1e62e21bba..68d13001a772 100644
--- a/api_core/google/api_core/bidi.py
+++ b/api_core/google/api_core/bidi.py
@@ -499,16 +499,15 @@ def __init__(self, bidi_rpc, on_response):
         self._wake = threading.Condition()
         self._thread = None
         self._operational_lock = threading.Lock()
-        self._ready = threading.Event()
 
     def _on_call_done(self, future):
         # Resume the thread if it's paused, this prevents blocking forever
         # when the RPC has terminated.
         self.resume()
 
-    def _thread_main(self):
+    def _thread_main(self, ready):
         try:
-            self._ready.set()
+            ready.set()
             self._bidi_rpc.add_done_callback(self._on_call_done)
             self._bidi_rpc.open()
 
@@ -557,8 +556,11 @@ def _thread_main(self):
     def start(self):
         """Start the background thread and begin consuming the thread."""
         with self._operational_lock:
+            ready = threading.Event()
             thread = threading.Thread(
-                name=_BIDIRECTIONAL_CONSUMER_NAME, target=self._thread_main
+                name=_BIDIRECTIONAL_CONSUMER_NAME,
+                target=self._thread_main,
+                args=(ready,)
             )
             thread.daemon = True
             thread.start()
@@ -566,7 +568,7 @@ def start(self):
             # isn't sufficient to know if a thread is active, just that it may
             # soon be active. This can cause races. Further protect
             # against races by using a ready event and wait on it to be set.
-            self._ready.wait()
+            ready.wait()
             self._thread = thread
             _LOGGER.debug("Started helper thread %s", thread.name)
 
@@ -581,12 +583,11 @@ def stop(self):
                 self._thread.join()
 
             self._thread = None
-            self._ready.clear()
 
     @property
     def is_active(self):
         """bool: True if the background thread is active."""
-        return self._thread is not None and self._ready.is_set() and self._thread.is_alive()
+        return self._thread is not None and self._thread.is_alive()
 
     def pause(self):
         """Pauses the response stream.