Use all redis pipelines as context managers to ensure that they are always cleaned up properly, especially in the case of exceptions

celery/backends/redis.py

@@ -164,13 +164,13 @@ class RedisBackend(KeyValueStoreBackend):
         return self.ensure(self._set, (key, value), **retry_policy)
 
     def _set(self, key, value):
-        pipe = self.client.pipeline()
-        if self.expires:
-            pipe.setex(key, value, self.expires)
-        else:
-            pipe.set(key, value)
-        pipe.publish(key, value)
-        pipe.execute()
+        with self.client.pipeline() as pipe:
+            if self.expires:
+                pipe.setex(key, value, self.expires)
+            else:
+                pipe.set(key, value)
+            pipe.publish(key, value)
+            pipe.execute()
 
     def delete(self, key):
         self.client.delete(key)
@@ -209,21 +209,23 @@ class RedisBackend(KeyValueStoreBackend):
         client = self.client
         jkey = self.get_key_for_group(gid, '.j')
         result = self.encode_result(result, state)
-        _, readycount, _ = client.pipeline()                            \
-            .rpush(jkey, self.encode([1, tid, state, result]))          \
-            .llen(jkey)                                                 \
-            .expire(jkey, 86400)                                        \
-            .execute()
+        with client.pipeline() as pipe:
+            _, readycount, _ = pipe                                         \
+                .rpush(jkey, self.encode([1, tid, state, result]))          \
+                .llen(jkey)                                                 \
+                .expire(jkey, 86400)                                        \
+                .execute()
 
         try:
             callback = maybe_signature(request.chord, app=app)
             total = callback['chord_size']
             if readycount == total:
                 decode, unpack = self.decode, self._unpack_chord_result
-                resl, _ = client.pipeline()     \
-                    .lrange(jkey, 0, total)     \
-                    .delete(jkey)               \
-                    .execute()
+                with client.pipeline() as pipe:
+                    resl, _, = pipe                 \
+                        .lrange(jkey, 0, total)     \
+                        .delete(jkey)               \
+                        .execute()
                 try:
                     callback.delay([unpack(tup, decode) for tup in resl])
                 except Exception as exc: