From 0a55e42ef67888e411987d6ae53c925f13026bb5 Mon Sep 17 00:00:00 2001
From: rh389 <roberthogan@blueyonder.co.uk>
Date: Fri, 28 Apr 2017 03:47:19 -0700
Subject: [PATCH] Refactor MessageQueue

Summary:
Looking to address a few new `FlowFixMe`s I had to do some minor refactoring of `MessageQueue`. Has the advantage of (IMO) making things clearer by removing a redundant counter and some gratuitous bitwise operations.

Previously `_callbacks` was an array of `?Function`s where even elements were failure callbacks and odd elements were successes. Each new call incremented `_callID` by one and `_callbackID` by two. I've changed this to use two arrays `_successCallbacks` and `_failureCallbacks` indexed by `callID`. That made the `_callbackID` counter unnecessary and reduced the need for computed indices.

Tested with flow and a quick play with UIExplorer.
Closes https://github.com/facebook/react-native/pull/11986

Differential Revision: D4962162

Pulled By: javache

fbshipit-source-id: 17dddfedc0cb5950dbdd9bd06fae6eb6de4c4a7d
---
 Libraries/BatchedBridge/MessageQueue.js | 58 ++++++++++---------------
 1 file changed, 24 insertions(+), 34 deletions(-)

diff --git a/Libraries/BatchedBridge/MessageQueue.js b/Libraries/BatchedBridge/MessageQueue.js
index ac4c2a2bc..1248f3b09 100644
--- a/Libraries/BatchedBridge/MessageQueue.js
+++ b/Libraries/BatchedBridge/MessageQueue.js
@@ -44,8 +44,8 @@ const DEBUG_INFO_LIMIT = 32;
 class MessageQueue {
   _callableModules: {[key: string]: Object};
   _queue: [Array<number>, Array<number>, Array<any>, number];
-  _callbacks: [];
-  _callbackID: number;
+  _successCallbacks: Array<?Function>;
+  _failureCallbacks: Array<?Function>;
   _callID: number;
   _inCall: number;
   _lastFlush: number;
@@ -60,8 +60,8 @@ class MessageQueue {
   constructor() {
     this._callableModules = {};
     this._queue = [[], [], [], 0];
-    this._callbacks = [];
-    this._callbackID = 0;
+    this._successCallbacks = [];
+    this._failureCallbacks = [];
     this._callID = 0;
     this._lastFlush = 0;
     this._eventLoopStartTime = new Date().getTime();
@@ -143,22 +143,17 @@ class MessageQueue {
   enqueueNativeCall(moduleID: number, methodID: number, params: Array<any>, onFail: ?Function, onSucc: ?Function) {
     if (onFail || onSucc) {
       if (__DEV__) {
-        const callId = this._callbackID >> 1;
-        this._debugInfo[callId] = [moduleID, methodID];
-        if (callId > DEBUG_INFO_LIMIT) {
-          delete this._debugInfo[callId - DEBUG_INFO_LIMIT];
+        this._debugInfo[this._callID] = [moduleID, methodID];
+        if (this._callID > DEBUG_INFO_LIMIT) {
+          delete this._debugInfo[this._callID - DEBUG_INFO_LIMIT];
         }
       }
-      onFail && params.push(this._callbackID);
-      /* $FlowFixMe(>=0.38.0 site=react_native_fb,react_native_oss) - Flow error
-       * detected during the deployment of v0.38.0. To see the error, remove
-       * this comment and run flow */
-      this._callbacks[this._callbackID++] = onFail;
-      onSucc && params.push(this._callbackID);
-      /* $FlowFixMe(>=0.38.0 site=react_native_fb,react_native_oss) - Flow error
-       * detected during the deployment of v0.38.0. To see the error, remove
-       * this comment and run flow */
-      this._callbacks[this._callbackID++] = onSucc;
+      // Encode callIDs into pairs of callback identifiers by shifting left and using the rightmost bit
+      // to indicate fail (0) or success (1)
+      onFail && params.push(this._callID << 1);
+      onSucc && params.push((this._callID << 1) | 1);
+      this._successCallbacks[this._callID] = onSucc;
+      this._failureCallbacks[this._callID] = onFail;
     }
 
     if (__DEV__) {
@@ -255,13 +250,16 @@ class MessageQueue {
   __invokeCallback(cbID: number, args: Array<any>) {
     this._lastFlush = new Date().getTime();
     this._eventLoopStartTime = this._lastFlush;
-    const callback = this._callbacks[cbID];
+
+    // The rightmost bit of cbID indicates fail (0) or success (1), the other bits are the callID shifted left.
+    const callID = cbID >>> 1;
+    const callback = (cbID & 1) ? this._successCallbacks[callID] : this._failureCallbacks[callID];
 
     if (__DEV__) {
-      const debug = this._debugInfo[cbID >> 1];
+      const debug = this._debugInfo[callID];
       const module = debug && this._remoteModuleTable[debug[0]];
       const method = debug && this._remoteMethodTable[debug[0]][debug[1]];
-      if (callback == null) {
+      if (!callback) {
         let errorMessage = `Callback with id ${cbID}: ${module}.${method}() not found`;
         if (method) {
           errorMessage = `The callback ${method}() exists in module ${module}, `
@@ -278,21 +276,13 @@ class MessageQueue {
       }
       Systrace.beginEvent(
         `MessageQueue.invokeCallback(${profileName}, ${stringifySafe(args)})`);
-    } else {
-      if (!callback) {
-        return;
-      }
     }
 
-    /* $FlowFixMe(>=0.38.0 site=react_native_fb,react_native_oss) - Flow error
-     * detected during the deployment of v0.38.0. To see the error, remove this
-     * comment and run flow */
-    this._callbacks[cbID & ~1] = null;
-    /* $FlowFixMe(>=0.38.0 site=react_native_fb,react_native_oss) - Flow error
-     * detected during the deployment of v0.38.0. To see the error, remove this
-     * comment and run flow */
-    this._callbacks[cbID |  1] = null;
-    // $FlowIssue(>=0.35.0) #14551610
+    if (!callback) {
+      return;
+    }
+
+    this._successCallbacks[callID] = this._failureCallbacks[callID] = null;
     callback.apply(null, args);
 
     if (__DEV__) {