add taskQueue based on generator.

Author: front-thinking

TaskQueue.js

@@ -52,4 +52,55 @@ class TaskQueue {
             this.running++;
         }
     }
-};
+};
+
+
+/*
+* A taskQueue based on generator which implement producer-consumer pattern.
+* To understand this class, you need know generator\co\producer-consumer, etc.
+* */
+"use strict";
+
+const co = require('co');
+
+class TaskQueue {
+    constructor(concurrency) {
+        this.concurrency = concurrency;
+        this.running = 0;
+        this.taskQueue = [];
+        this.consumerQueue = [];
+        this.spawnWorkers(concurrency);
+    }
+
+    pushTask(task) {
+        if (this.consumerQueue.length !== 0) {
+            this.consumerQueue.shift()(null, task);
+        } else {
+            this.taskQueue.push(task);
+        }
+    }
+
+    spawnWorkers(concurrency) {
+        const self = this;
+        for(let i = 0; i < concurrency; i++) {
+            co(function* () {
+                while(true) {
+                    const task = yield self.nextTask();
+                    yield task;
+                }
+            });
+        }
+    }
+
+    nextTask() {
+        return callback => {
+            if(this.taskQueue.length !== 0) {
+                return callback(null, this.taskQueue.shift());
+            }
+
+            this.consumerQueue.push(callback);
+        }
+    }
+}
+
+module.exports = TaskQueue;