Add an example that uses napa.sync.Lock (#179)

* Add example for napa/sync/Lock

* Update link to sync.md

* Update example and rename to 'synchronized-loading'

* Update README and API docs: add synchronized loading example

* Resolve comments

* fix grammer

README.md

@@ -31,9 +31,10 @@ zone1.execute(
 ```
 More examples:
 * [Estimate PI in parallel](./examples/tutorial/estimate-pi-in-parallel)
+* [Max sub-matrix of 1s with layered parallelism](./examples/tutorial/max-square-sub-matrix)
 * [Parallel Quick Sort](./examples/tutorial/parallel-quick-sort)
 * [Recursive Fibonacci with multiple JavaScript threads](./examples/tutorial/recursive-fibonacci)
-* [Max sub-matrix of 1s with layered parallelism](./examples/tutorial/max-square-sub-matrix)
+* [Synchronized loading](./examples/tutorial/synchronized-loading)
 
 ## Features
 - Multi-threaded JavaScript runtime

docs/api/sync.md

@@ -35,6 +35,9 @@ catch(error) {
     console.log(error);
 }
 ```
+
+An example [Synchronized Loading](./../../examples/tutorial/synchronized-loading) demonstrated how to implement a shared, lazy-loading phone book.
+
 <!--
 ### <a name="lock-guard-func-promise-any-promise-any"></a> lock.guard(func: () => Promise\<any>): Promise\<any>
 

examples/tutorial/synchronized-loading/README.md

@@ -0,0 +1,22 @@
+# Synchronized loading
+This example implements a shared phone book component. The component will not load data until the first lookup request happens. When it starts to load data, it ensures the loading will run only once. 
+
+The component is implemented using lazy-loading pattern with the use of [`napa.sync.Lock`](./../../../docs/api/sync.md#interface-lock).
+
+## How to run
+1. Go to directory of "examples/tutorial/synchronized-loading"
+2. Run "npm install" to install napajs
+3. Run "node synchronized-loading.js"
+
+## Program output
+The output below shows one possible result. The sequence of the output may be different but the data loading will always run once only.
+```
+[lookupPhoneNumber] Start to lookup phone number of david.
+[lookupPhoneNumber] Start to lookup phone number of wade.
+[load_data] loading...
+[lookupPhoneNumber] Start to lookup phone number of lisa.
+[lookupPhoneNumber] wade : <not found>.
+[lookupPhoneNumber] lisa : 567-888-9999.
+[lookupPhoneNumber] david : 123-444-5555.
+[run] All operations are completed.
+```

examples/tutorial/synchronized-loading/package.json

@@ -0,0 +1,9 @@
+{
+    "name": "napajs-tutorial",
+    "version": "0.1.0",
+    "author": "napajs",
+    "main": "./synchronized-loading.js",
+    "dependencies": {
+        "napajs": ">= 0.1.8"
+    }
+}

examples/tutorial/synchronized-loading/phone-book-data.json

@@ -0,0 +1,6 @@
+{
+    "ashley": "123-456-7890",
+    "david": "123-444-5555",
+    "lisa": "567-888-9999",
+    "tony": "456-789-0000"
+}

examples/tutorial/synchronized-loading/phone-book.js

@@ -0,0 +1,40 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT license.
+
+const napa = require("napajs");
+const store = napa.store.getOrCreate('my-phone-book');
+
+const initialize = function () {
+    store.set('_loadLock', napa.sync.createLock());
+}
+
+const load_data = function () {
+    // load data. This function should run only once.
+    console.log('[load_data] loading...');
+
+    const fs = require('fs');
+    let phoneBookData = JSON.parse(fs.readFileSync('./phone-book-data.json').toString());
+
+    for (let name in phoneBookData) {
+        store.set(name, phoneBookData[name]);
+    }
+    store.set('_loaded', true);
+}
+
+let loaded = false;
+const lookup = function (name) {
+    if (!loaded) {
+        const lock = store.get('_loadLock');
+        lock.guardSync(function() {
+            if (!store.get('_loaded')) {
+                load_data();
+            }
+        });
+        loaded = true;
+    }
+
+    return store.get(name);
+};
+
+module.exports.initialize = initialize;
+module.exports.lookup = lookup;

examples/tutorial/synchronized-loading/synchronized-loading.js

@@ -0,0 +1,42 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT license.
+
+const napa = require("napajs");
+
+// Change this value to control number of napa workers initialized.
+const NUMBER_OF_WORKERS = 4;
+
+// Create a napa zone with number_of_workers napa workers.
+const zone = napa.zone.create('zone', { workers: NUMBER_OF_WORKERS });
+
+function run() {
+    // Initialize the phone book component
+    const phoneBook = require('./phone-book');
+    phoneBook.initialize();
+
+    // Setup all workers with functions to be executed.
+    zone.broadcast(' \
+        var napa = require("napajs"); \
+        var zone = napa.zone.get("zone"); \
+        var phoneBook = require("./phone-book"); \
+    ');
+    zone.broadcast(lookupPhoneNumber.toString());
+
+    var tasks = [];
+    tasks.push(zone.execute('', 'lookupPhoneNumber', ['david']));
+    tasks.push(zone.execute('', 'lookupPhoneNumber', ['lisa']));
+    tasks.push(zone.execute('', 'lookupPhoneNumber', ['wade']));
+
+    Promise.all(tasks).then(function () {
+        console.log('[run] All operations are completed.');
+    });
+}
+
+function lookupPhoneNumber(name) {
+    console.log(`[lookupPhoneNumber] Start to lookup phone number of ${name}.`);
+    var n = phoneBook.lookup(name);
+    console.log(`[lookupPhoneNumber] ${name} : ${n ? n : '<not found>'}.`);
+}
+
+// Run program.
+run();