1 files changed, 71 insertions, 9 deletions
diff --git a/src/python/grpcio_health_checking/grpc_health/v1/health.py b/src/python/grpcio_health_checking/grpc_health/v1/health.py
index 0583659428..0a5bbb5504 100644
--- a/src/python/grpcio_health_checking/grpc_health/v1/health.py
+++ b/src/python/grpcio_health_checking/grpc_health/v1/health.py
@@ -23,15 +23,61 @@ from grpc_health.v1 import health_pb2_grpc as _health_pb2_grpc
 SERVICE_NAME = _health_pb2.DESCRIPTOR.services_by_name['Health'].full_name
 
 
+class _Watcher():
+
+    def __init__(self):
+        self._condition = threading.Condition()
+        self._responses = list()
+        self._open = True
+
+    def __iter__(self):
+        return self
+
+    def _next(self):
+        with self._condition:
+            while not self._responses and self._open:
+                self._condition.wait()
+            if self._responses:
+                return self._responses.pop(0)
+            else:
+                raise StopIteration()
+
+    def next(self):
+        return self._next()
+
+    def __next__(self):
+        return self._next()
+
+    def add(self, response):
+        with self._condition:
+            self._responses.append(response)
+            self._condition.notify()
+
+    def close(self):
+        with self._condition:
+            self._open = False
+            self._condition.notify()
+
+
 class HealthServicer(_health_pb2_grpc.HealthServicer):
     """Servicer handling RPCs for service statuses."""
 
     def __init__(self):
-        self._server_status_lock = threading.Lock()
+        self._lock = threading.RLock()
         self._server_status = {}
+        self._watchers = {}
+
+    def _on_close_callback(self, watcher, service):
+
+        def callback():
+            with self._lock:
+                self._watchers[service].remove(watcher)
+            watcher.close()
+
+        return callback
 
     def Check(self, request, context):
-        with self._server_status_lock:
+        with self._lock:
             status = self._server_status.get(request.service)
             if status is None:
                 context.set_code(grpc.StatusCode.NOT_FOUND)
@@ -39,14 +85,30 @@ class HealthServicer(_health_pb2_grpc.HealthServicer):
             else:
                 return _health_pb2.HealthCheckResponse(status=status)
 
+    def Watch(self, request, context):
+        service = request.service
+        with self._lock:
+            status = self._server_status.get(service)
+            if status is None:
+                status = _health_pb2.HealthCheckResponse.SERVICE_UNKNOWN  # pylint: disable=no-member
+            watcher = _Watcher()
+            watcher.add(_health_pb2.HealthCheckResponse(status=status))
+            if service not in self._watchers:
+                self._watchers[service] = set()
+            self._watchers[service].add(watcher)
+            context.add_callback(self._on_close_callback(watcher, service))
+        return watcher
+
     def set(self, service, status):
         """Sets the status of a service.
 
-    Args:
-        service: string, the name of the service.
-            NOTE, '' must be set.
-        status: HealthCheckResponse.status enum value indicating
-            the status of the service
-    """
-        with self._server_status_lock:
+        Args:
+          service: string, the name of the service. NOTE, '' must be set.
+          status: HealthCheckResponse.status enum value indicating the status of
+            the service
+        """
+        with self._lock:
             self._server_status[service] = status
+            if service in self._watchers:
+                for watcher in self._watchers[service]:
+                    watcher.add(_health_pb2.HealthCheckResponse(status=status))