Method lock class added

appmixer-lib.js

@@ -5,7 +5,8 @@ module.exports = {
     db: require('./db/db'),
     redis: require('./db/redis'),
     lock: {
-        mutex: require('./lock/mutex')
+        mutex: require('./lock/mutex'),
+        method: require('./lock/method')
     },
     util: {
         array: require('./util/array'),

lock/method.js

@@ -0,0 +1,48 @@
+'use strict';
+const Promise = require('bluebird');
+const check = require('check-types');
+
+/**
+ * This class provides func to execute function only once (when called multiple times from
+ * various resources) and return the same result to all callers.
+ */
+class Method {
+
+    constructor() {
+
+        this.inProgress = false;
+        this.callbacks = [];
+    }
+
+    /**
+     * @param {function} func
+     * @return {Promise<void>}
+     * @public
+     */
+    async call(func) {
+
+        check.assert.function(func, 'Invalid function.');
+
+        if (this.inProgress) {
+            return new Promise((resolve, reject) => {
+                this.callbacks.push({ resolve, reject });
+            });
+        }
+
+        try {
+            this.inProgress = true;
+            const result = await func();
+            this.inProgress = false;
+            while (this.callbacks.length > 0) {
+                this.callbacks.pop().resolve(result);
+            }
+        } catch (err) {
+            this.inProgress = false;
+            while (this.callbacks.length > 0) {
+                this.callbacks.pop().reject(err);
+            }
+        }
+    }
+}
+
+module.exports = Method;