perf(cache): improve cache and reduce Memory Usages (hexojs#3756)

* test(cache): verify whether the cache works properly
* fix(fragment_cache): reset the cache on generateBefore event so we can enable cache on watch mode.
* fix(cache): disable save cache for rendered contents when generate files. Added at (hexojs@e8e45ed#diff-b9bb6fa7bb069bab9948daba90c6c3b2). Should enable save cache for rendered contents when run server mode.

lib/hexo/index.js

@@ -51,6 +51,7 @@ function Hexo(base = process.cwd(), args = {}) {
     silent: Boolean(args.silent),
     env: process.env.NODE_ENV || 'development',
     version: pkg.version,
+    cmd: args._ ? args._[0] : '',
     init: false
   };
 
@@ -253,11 +254,16 @@ Hexo.prototype.load = function(callback) {
       this.source.process(),
       this.theme.process()
     ]);
-  }).then(() => this._generate({cache: true})).asCallback(callback);
+  }).then(() => this._generate({cache: false})).asCallback(callback);
 };
 
 Hexo.prototype.watch = function(callback) {
-  this._watchBox = debounce(() => this._generate({cache: false}), 100);
+  let useCache = false;
+  if (this.env.cmd.startsWith('s')) {
+    // enable cache when run hexo server
+    useCache = true;
+  }
+  this._watchBox = debounce(() => this._generate({cache: useCache}), 100);
 
   return loadDatabase(this).then(() => {
     this.log.info('Start processing');
@@ -270,7 +276,7 @@ Hexo.prototype.watch = function(callback) {
     this.source.on('processAfter', this._watchBox);
     this.theme.on('processAfter', this._watchBox);
 
-    return this._generate({cache: false});
+    return this._generate({cache: useCache});
   }).asCallback(callback);
 };
 
@@ -345,6 +351,8 @@ const createLoadThemeRoute = function(generatorResult, locals, ctx) {
   const layout = unique(castArray(generatorResult.layout));
   const layoutLength = layout.length;
 
+  // allways use cache in fragment_cache
+  locals.cache = true;
   return () => {
     if (useCache && routeCache.has(generatorResult)) return routeCache.get(generatorResult);
 
@@ -355,7 +363,9 @@ const createLoadThemeRoute = function(generatorResult, locals, ctx) {
       if (view) {
         log.debug(`Rendering HTML ${name}: ${chalk.magenta(path)}`);
         return view.render(locals).tap(result => {
-          routeCache.set(generatorResult, result);
+          if (useCache) {
+            routeCache.set(generatorResult, result);
+          }
         }).tapCatch(err => {
           log.error({ err }, `Render HTML failed: ${chalk.magenta(path)}`);
         });

lib/plugins/helper/fragment_cache.js

@@ -1,7 +1,10 @@
 'use strict';
 
 module.exports = ctx => {
-  const cache = {};
+  let cache = {};
+
+  // reset cache for watch mode
+  ctx.on('generateBefore', () => { cache = {}; });
 
   return function fragmentCache(id, fn) {
     if (this.cache && cache[id] != null) return cache[id];

test/scripts/helpers/fragment_cache.js

@@ -1,7 +1,9 @@
 'use strict';
 
 describe('fragment_cache', () => {
-  const fragment_cache = require('../../../lib/plugins/helper/fragment_cache')();
+  const Hexo = require('../../../lib/hexo');
+  const hexo = new Hexo(__dirname);
+  const fragment_cache = require('../../../lib/plugins/helper/fragment_cache')(hexo);
 
   fragment_cache.call({cache: true}, 'foo', () => 123);
 
@@ -12,4 +14,11 @@ describe('fragment_cache', () => {
   it('cache disabled', () => {
     fragment_cache.call({cache: false}, 'foo', () => 456).should.eql(456);
   });
+
+  it('should reset cache on generateBefore', () => {
+    fragment_cache.call({cache: true}, 'foo', () => 789).should.eql(456);
+    // reset cache
+    hexo.emit('generateBefore');
+    fragment_cache.call({cache: true}, 'foo', () => 789).should.eql(789);
+  });
 });

test/scripts/hexo/hexo.js

@@ -62,6 +62,7 @@ describe('Hexo', () => {
       silent: false,
       env: process.env.NODE_ENV || 'development',
       version,
+      cmd: '',
       init: false
     });
     hexo.config_path.should.eql(pathFn.join(__dirname, '_config.yml'));
@@ -452,17 +453,41 @@ describe('Hexo', () => {
   it('_generate() - reset cache for new route', () => {
     let count = 0;
 
-    hexo.theme.setView('test.swig', '{{ page.count }}');
+    hexo.theme.setView('test.swig', '{{ page.count() }}');
 
     hexo.extend.generator.register('test', () => ({
       path: 'test',
       layout: 'test',
-      data: {count: count++}
+      data: {count: () => count++}
     }));
 
     // First generation
-    return hexo._generate({cache: true}).then(() => checkStream(route.get('test'), '0')).then(() => // Second generation
-      hexo._generate({cache: true})).then(() => checkStream(route.get('test'), '1'));
+    return hexo._generate({cache: true})
+      .then(() => checkStream(route.get('test'), '0'))
+      .then(() => checkStream(route.get('test'), '0')) // should return cached result
+      .then(() => hexo._generate({cache: true})) // Second generation
+      .then(() => checkStream(route.get('test'), '1'))
+      .then(() => checkStream(route.get('test'), '1')); // should return cached result
+  });
+
+  it('_generate() - cache disabled and use new route', () => {
+    let count = 0;
+
+    hexo.theme.setView('test.swig', '{{ page.count() }}');
+
+    hexo.extend.generator.register('test', () => ({
+      path: 'test',
+      layout: 'test',
+      data: {count: () => count++}
+    }));
+
+    // First generation
+    return hexo._generate({cache: false})
+      .then(() => checkStream(route.get('test'), '0'))
+      .then(() => checkStream(route.get('test'), '1'))
+      .then(() => hexo._generate({cache: false})) // Second generation
+      .then(() => checkStream(route.get('test'), '2'))
+      .then(() => checkStream(route.get('test'), '3'));
   });
 
   it('_generate() - cache disabled & update template', () => {
@@ -473,10 +498,24 @@ describe('Hexo', () => {
       layout: 'test'
     }));
 
-    return hexo._generate({cache: false}).then(() => checkStream(route.get('test'), '0')).then(() => {
-      hexo.theme.setView('test.swig', '1');
-      return checkStream(route.get('test'), '1');
-    });
+    return hexo._generate({cache: false})
+      .then(() => checkStream(route.get('test'), '0'))
+      .then(() => hexo.theme.setView('test.swig', '1'))
+      .then(() => checkStream(route.get('test'), '1'));
+  });
+
+  it('_generate() - cache enabled & update template', () => {
+    hexo.theme.setView('test.swig', '0');
+
+    hexo.extend.generator.register('test', () => ({
+      path: 'test',
+      layout: 'test'
+    }));
+
+    return hexo._generate({cache: true})
+      .then(() => checkStream(route.get('test'), '0'))
+      .then(() => hexo.theme.setView('test.swig', '1'))
+      .then(() => checkStream(route.get('test'), '0')); // should return cached result
   });
 
   it('execFilter()', () => {