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diff --git a/lib/CallbackWrapper.jsm b/lib/CallbackWrapper.jsm
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+/*******************************************************************************
+
+    ηMatrix - a browser extension to black/white list requests.
+    Copyright (C) 2014-2019 The uMatrix/uBlock Origin authors
+    Copyright (C) 2019 Alessio Vanni
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see {http://www.gnu.org/licenses/}.
+
+    Home: https://gitlab.com/vannilla/ematrix
+    uMatrix Home: https://github.com/gorhill/uMatrix
+*/
+
+'use strict';
+
+var EXPORTED_SYMBOLS = ['CallbackWrapper'];
+
+var junkyard = [];
+
+var CallbackWrapper = function (messageManager, channelName,
+				listenerId, requestId) {
+    // This allows to avoid creating a closure for every single
+    // message which expects an answer. Having a closure created
+    // each time a message is processed has been always bothering
+    // me. Another benefit of the implementation here is to reuse
+    // the callback proxy object, so less memory churning.
+    //
+    // https://developers.google.com/speed/articles/optimizing-javascript
+    // "Creating a closure is significantly slower then creating
+    // an inner function without a closure, and much slower than
+    // reusing a static function"
+    //
+    // http://hacksoflife.blogspot.ca/2015/01/the-four-horsemen-of-performance.html
+    // "the dreaded 'uniformly slow code' case where every
+    // function takes 1% of CPU and you have to make one hundred
+    // separate performance optimizations to improve performance
+    // at all"
+    //
+    // http://jsperf.com/closure-no-closure/2
+    this.callback = this.proxy.bind(this); // bind once
+    this.init(messageManager, channelName, listenerId, requestId);
+};
+
+CallbackWrapper.factory = function (messageManager, channelName,
+				    listenerId, requestId) {
+    let wrapper = junkyard.pop();
+    if (wrapper) {
+        wrapper.init(messageManager, channelName, listenerId, requestId);
+        return wrapper;
+    }
+    
+    return new CallbackWrapper(messageManager, channelName,
+			       listenerId, requestId);
+};
+
+CallbackWrapper.prototype.init = function (messageManager, channelName,
+					   listenerId, requestId) {
+    this.messageManager = messageManager;
+    this.channelName = channelName;
+    this.listenerId = listenerId;
+    this.requestId = requestId;
+};
+
+CallbackWrapper.prototype.proxy = function (response) {
+    let message = JSON.stringify({
+        requestId: this.requestId,
+        channelName: this.channelName,
+        msg: response !== undefined ? response : null
+    });
+
+    if (this.messageManager.sendAsyncMessage) {
+        this.messageManager.sendAsyncMessage(this.listenerId, message);
+    } else {
+        this.messageManager.broadcastAsyncMessage(this.listenerId, message);
+    }
+
+    // Mark for reuse
+    this.messageManager = this.channelName =
+	this.requestId = this.listenerId = null;
+    
+    junkyard.push(this);
+};