Make sure _PushStatus operations are run in order (parse-community#2367)

Author: flovilmart

src/pushStatusHandler.js

@@ -20,7 +20,7 @@ export default function pushStatusHandler(config) {
   let pushStatus;
   let objectId = newObjectId();
   let database = config.database;
-
+  let lastPromise;
   let setInitial = function(body = {}, where, options = {source: 'rest'}) {
     let now = new Date();
     let data =  body.data || {};
@@ -41,19 +41,23 @@ export default function pushStatusHandler(config) {
       ACL: {}
     }
 
-    return database.create(PUSH_STATUS_COLLECTION, object).then(() => {
+    lastPromise = database.create(PUSH_STATUS_COLLECTION, object).then(() => {
       pushStatus = {
         objectId
       };
       return Promise.resolve(pushStatus);
     });
+    return lastPromise;
   }
 
   let setRunning = function(installations) {
     logger.verbose('sending push to %d installations', installations.length);
-    return database.update(PUSH_STATUS_COLLECTION,
-      {status:"pending", objectId: objectId},
-      {status: "running", updatedAt: new Date() });
+    lastPromise = lastPromise.then(() => {
+      return database.update(PUSH_STATUS_COLLECTION,
+        {status:"pending", objectId: objectId},
+        {status: "running", updatedAt: new Date() });
+    });
+    return lastPromise;
   }
 
   let complete = function(results) {
@@ -87,7 +91,10 @@ export default function pushStatusHandler(config) {
       }, update);
     }
     logger.verbose('sent push! %d success, %d failures', update.numSent, update.numFailed);
-    return database.update(PUSH_STATUS_COLLECTION, {status:"running", objectId }, update);
+    lastPromise = lastPromise.then(() => {
+      return database.update(PUSH_STATUS_COLLECTION, {status:"running", objectId }, update);
+    });
+    return lastPromise;
   }
 
   let fail = function(err) {
@@ -97,7 +104,10 @@ export default function pushStatusHandler(config) {
       updatedAt: new Date()
     }
     logger.info('warning: error while sending push', err);
-    return database.update(PUSH_STATUS_COLLECTION, { objectId }, update);
+    lastPromise = lastPromise.then(() => {
+      return database.update(PUSH_STATUS_COLLECTION, { objectId }, update);
+    });
+    return lastPromise;
   }
 
   return Object.freeze({