The source code

    /**
     * @class Ext.util.TaskRunner
     * Provides the ability to execute one or more arbitrary tasks in a multithreaded
     * manner.  Generally, you can use the singleton {@link Ext.TaskMgr} instead, but
     * if needed, you can create separate instances of TaskRunner.  Any number of
     * separate tasks can be started at any time and will run independently of each
     * other. Example usage:
     * <pre><code>
    // Start a simple clock task that updates a div once per second
    var updateClock = function(){
        Ext.fly('clock').update(new Date().format('g:i:s A'));
    }
    var task = {
        run: updateClock,
        interval: 1000 //1 second
    }
    var runner = new Ext.util.TaskRunner();
    runner.start(task);

    // equivalent using TaskMgr
    Ext.TaskMgr.start({
        run: updateClock,
        interval: 1000
    });

     * </code></pre>
     * <p>See the {@link #start} method for details about how to configure a task object.</p>
     * Also see {@link Ext.util.DelayedTask}.
     *
     * @constructor
     * @param {Number} interval (optional) The minimum precision in milliseconds supported by this TaskRunner instance
     * (defaults to 10)
     */
    Ext.util.TaskRunner = function(interval){
        interval = interval || 10;
        var tasks = [],
        	removeQueue = [],
        	id = 0,
        	running = false,

        	// private
        	stopThread = function(){
    	        running = false;
    	        clearInterval(id);
    	        id = 0;
    	    },

        	// private
        	startThread = function(){
    	        if(!running){
    	            running = true;
    	            id = setInterval(runTasks, interval);
    	        }
    	    },

        	// private
        	removeTask = function(t){
    	        removeQueue.push(t);
    	        if(t.onStop){
    	            t.onStop.apply(t.scope || t);
    	        }
    	    },

        	// private
        	runTasks = function(){
    	    	var rqLen = removeQueue.length,
    	    		now = new Date().getTime();

    	        if(rqLen > 0){
    	            for(var i = 0; i < rqLen; i++){
    	                tasks.remove(removeQueue[i]);
    	            }
    	            removeQueue = [];
    	            if(tasks.length < 1){
    	                stopThread();
    	                return;
    	            }
    	        }
    	        for(var i = 0, t, itime, rt, len = tasks.length; i < len; ++i){
    	            t = tasks[i];
    	            itime = now - t.taskRunTime;
    	            if(t.interval <= itime){
    	                rt = t.run.apply(t.scope || t, t.args || [++t.taskRunCount]);
    	                t.taskRunTime = now;
    	                if(rt === false || t.taskRunCount === t.repeat){
    	                    removeTask(t);
    	                    return;
    	                }
    	            }
    	            if(t.duration && t.duration <= (now - t.taskStartTime)){
    	                removeTask(t);
    	            }
    	        }
    	    };

        /**
         * Starts a new task.
         * @method start
         * @param {Object} task <p>A config object that supports the following properties:<ul>
         * <li><code>run</code> : Function<div class="sub-desc"><p>The function to execute each time the task is invoked. The
         * function will be called at each interval and passed the <code>args</code> argument if specified, and the
         * current invocation count if not.</p>
         * <p>If a particular scope (<code>this</code> reference) is required, be sure to specify it using the <code>scope</code> argument.</p>
         * <p>Return <code>false</code> from this function to terminate the task.</p></div></li>
         * <li><code>interval</code> : Number<div class="sub-desc">The frequency in milliseconds with which the task
         * should be invoked.</div></li>
         * <li><code>args</code> : Array<div class="sub-desc">(optional) An array of arguments to be passed to the function
         * specified by <code>run</code>. If not specified, the current invocation count is passed.</div></li>
         * <li><code>scope</code> : Object<div class="sub-desc">(optional) The scope (<tt>this</tt> reference) in which to execute the
         * <code>run</code> function. Defaults to the task config object.</div></li>
         * <li><code>duration</code> : Number<div class="sub-desc">(optional) The length of time in milliseconds to invoke
         * the task before stopping automatically (defaults to indefinite).</div></li>
         * <li><code>repeat</code> : Number<div class="sub-desc">(optional) The number of times to invoke the task before
         * stopping automatically (defaults to indefinite).</div></li>
         * </ul></p>
         * <p>Before each invocation, Ext injects the property <code>taskRunCount</code> into the task object so
         * that calculations based on the repeat count can be performed.</p>
         * @return {Object} The task
         */
        this.start = function(task){
            tasks.push(task);
            task.taskStartTime = new Date().getTime();
            task.taskRunTime = 0;
            task.taskRunCount = 0;
            startThread();
            return task;
        };

        /**
         * Stops an existing running task.
         * @method stop
         * @param {Object} task The task to stop
         * @return {Object} The task
         */
        this.stop = function(task){
            removeTask(task);
            return task;
        };

        /**
         * Stops all tasks that are currently running.
         * @method stopAll
         */
        this.stopAll = function(){
            stopThread();
            for(var i = 0, len = tasks.length; i < len; i++){
                if(tasks[i].onStop){
                    tasks[i].onStop();
                }
            }
            tasks = [];
            removeQueue = [];
        };
    };

    /**
     * @class Ext.TaskMgr
     * @extends Ext.util.TaskRunner
     * A static {@link Ext.util.TaskRunner} instance that can be used to start and stop arbitrary tasks.  See
     * {@link Ext.util.TaskRunner} for supported methods and task config properties.
     * <pre><code>
    // Start a simple clock task that updates a div once per second
    var task = {
        run: function(){
            Ext.fly('clock').update(new Date().format('g:i:s A'));
        },
        interval: 1000 //1 second
    }
    Ext.TaskMgr.start(task);
    </code></pre>
     * <p>See the {@link #start} method for details about how to configure a task object.</p>
     * @singleton
     */
    Ext.TaskMgr = new Ext.util.TaskRunner();