fix view cache singleflight

.gitignore

@@ -44,5 +44,6 @@ src/config/config.local*
 src/config/sequelize.json
 lib/*
 .nyc_output
+nohup.out
 yarn.lock
 package-lock.json

src/middlewares/view_cache.js

@@ -74,49 +74,103 @@ function ViewCacheMiddleware(cache, logger) {
       ttl,
       headersFilter,
       namespace,
+      lockNamespace,
       hashStrategy
     } = Object.assign({
       ttl: 60,
       headersFilter: defaultHeadersFilter,
       hashStrategy: defaultHashStrategy,
-      namespace: 'view'
+      namespace: 'view',
+      lockNamespace: 'view:lock'
     }, options);
+
+    const getCache = async (ns, key) => await cache.namespace(ns).get(key) || {
+      headers: [],
+      body: null
+    };
+
     return wrapper(async (req, res, next) => {
       const cacheKey = requestToCacheKey(req, hashStrategy);
-      const {
-        headers: cachedHeaders = [],
-        body: cachedBody
-      } = await cache.namespace(namespace).get(cacheKey)
-      || {
-        headers: [],
-        body: null
-      };
-      if (req.query.flush !== 'true' && cachedBody) {
+
+      //加锁避免缓存失效风暴
+      const lockTTL = ttl - 1;
+
+      const sendHit = (headers, body) => {
         logger.debug('View cache hit by key %s', cacheKey);
-        if (cachedHeaders.length > 0) {
-          cachedHeaders.forEach(([key, value]) => {
+        if (headers.length > 0) {
+          headers.forEach(([key, value]) => {
             res.setHeader(key, value);
           });
         }
         res.setHeader('X-View-Cache-Hit', cacheKey);
-        res.send(cachedBody);
+        res.send(body);
+      };
+
+      //重设send方法
+      const resetSend = () => {
+        res.realSend = res.realSend || res.send; //eslint-disable-line no-param-reassign
+        res.send = (body) => { //eslint-disable-line no-param-reassign
+          logger.debug('View cache missed by key %s, creating...', cacheKey);
+          res.setHeader('X-View-Cache-Miss', cacheKey);
+          res.setHeader('X-View-Cache-Expire-At', moment().add(ttl, 'minute').format('YYYY-MM-DD HH:mm:ss Z'));
+          res.setHeader('X-View-Cache-Created-At', moment().format('YYYY-MM-DD HH:mm:ss Z'));
+          res.realSend(body);
+          const headers = headersFilter && util.isFunction(headersFilter) ?
+            headersFilter(res) : defaultHeadersFilter(res);
+          if (res.statusCode <= 500) {
+            cache.namespace(namespace).set(cacheKey, { headers, body }, ttl).then((ret) => {
+              if (ret === null) {
+                logger.error('View cache set failed for return %s', ret);
+              }
+              if (lockTTL > 0) {
+                cache.namespace(lockNamespace).del(cacheKey);
+              }
+            }).catch((e) => {
+              logger.error('View cache set failed for %s', cacheKey, e);
+            });
+          } else if (lockTTL > 0) {
+            cache.namespace(lockNamespace).del(cacheKey);
+          }
+        };
+      };
+
+      const spinCache = async () => {
+        const retry = await getCache(namespace, cacheKey);
+        if (retry && retry.body) {
+          return sendHit(retry.headers, retry.body);
+        }
+        //这里再次判断锁是否存在, 如果锁已经被释放, 代表缓存可能已经过期,则重新设置
+        const lockRet = await cache.namespace(lockNamespace).set(cacheKey, 1, lockTTL, 'nx');
+        if (lockRet) {
+          resetSend();
+          return next();
+        }
+
+        //自旋
+        setTimeout(spinCache, 0);
+        logger.info('View cache is spinning...');
+        return true;
+      };
+
+      const {
+        headers: cachedHeaders,
+        body: cachedBody
+      } = await getCache(namespace, cacheKey);
+      if (req.query.flush !== 'true' && cachedBody) {
+        sendHit(cachedHeaders, cachedBody);
         return;
       }
-      res.realSend = res.send; //eslint-disable-line no-param-reassign
-      res.send = (body) => { //eslint-disable-line no-param-reassign
-        logger.debug('View cache missed by key %s, creating...', cacheKey);
-        res.setHeader('X-View-Cache-Miss', cacheKey);
-        res.setHeader('X-View-Cache-Expire-At', moment().add(ttl, 'minute').format('YYYY-MM-DD HH:mm:ss Z'));
-        res.setHeader('X-View-Cache-Created-At', moment().format('YYYY-MM-DD HH:mm:ss Z'));
-        res.realSend(body);
-        const headers = headersFilter && util.isFunction(headersFilter) ?
-          headersFilter(res) : defaultHeadersFilter(res);
-        if (res.statusCode <= 500) {
-          cache.namespace(namespace).set(cacheKey, { headers, body }, ttl).catch((e) => {
-            logger.error('View cache set failed for %s', cacheKey, e);
-          });
+
+      if (lockTTL > 0) {
+        const lockRet = await cache.namespace(lockNamespace).set(cacheKey, 1, lockTTL, 'nx');
+        if (lockRet === null) {
+          //get cache again
+          await spinCache();
+          return;
         }
-      };
+      }
+
+      resetSend();
       next();
     });
   };

test/middlewares/view_cache.js

@@ -61,23 +61,61 @@ test('Request hash', (t) => {
   );
 });
 
-//FIXME: this assert not work!!
-// test('View cache', (t) => {
-//   t.plan(1);
-//   const req = mockRequest({
-//     method: 'GET', url: '/'
-//   });
-//   req.route = {};
-//   const res = mockResponse();
-//   const middleware = DI.get('view_cache')(60);
-//   res.on('end', () => {
-//     cache.namespace('view').has('get/unknown:043fe182887af19ba0be0cb494b75c9c').then((v) => {
-//       t.true(v);
-//     });
-//   });
-//
-//   middleware(req, res, () => {
-//     res.send('something');
-//   });
-// });
+test('View cache', async (t) => {
+  const req = mockRequest({
+    method: 'GET', url: '/'
+  });
+  req.route = {};
+  const res = mockResponse();
+  const middleware = DI.get('view_cache')(60);
+
+  await middleware(req, res, () => {
+    res.send('something');
+  });
+
+  //走缓存, 所以next中断言不执行
+  await middleware(req, res, () => {
+    t.true(false);
+  });
+
+  const v = await cache.namespace('view').has('get/unknown/:5bb7eb919a5d177089d48a9ab171fc4e');
+  t.true(v);
+
+  t.is(await cache.namespace('view').flush(), 1);
+  t.is(await cache.namespace('view:lock').flush(), 0);
+});
+
+test('View lock', async (t) => {
+  const req = mockRequest({
+    method: 'GET', url: '/'
+  });
+  req.route = {};
+  const res = mockResponse();
+  const middleware = DI.get('view_cache')(60);
 
+  await middleware(req, res, () => {
+    // 不执行send
+  });
+
+  const locked = await cache.namespace('view:lock').has('get/unknown/:5bb7eb919a5d177089d48a9ab171fc4e');
+  t.true(locked);
+
+  //此时资源被锁定, 无法缓存
+  await middleware(req, res, (v) => {
+    res.send('something');
+  });
+  let v = await cache.namespace('view').has('get/unknown/:5bb7eb919a5d177089d48a9ab171fc4e');
+  t.false(v);
+
+  t.is(await cache.namespace('view:lock').flush(), 1);
+
+  //延迟500ms, 确保当lock 被释放后, 缓存被设置成功
+  const s = new Promise(resolve => setTimeout(resolve, 500));
+  await s;
+
+  v = await cache.namespace('view').has('get/unknown/:5bb7eb919a5d177089d48a9ab171fc4e');
+  t.true(v);
+
+  t.is(await cache.namespace('view').flush(), 1);
+
+});