using per-key basis queue (#5420)

* adding KeyPromiseQueue

* nit

* removing secondary object and using a tuple

* using array

* nits

* some tests

* Minor refinements

* removing old adapter

* dummy change, travis test not found

* travis test missing, dummy change

* revrting mistake

* reverting mistake

* indentation fix

* additional tests for coverage

* extending coverage

* nits

* fixing mistake

* better code

src/Adapters/Cache/RedisCacheAdapter/index.js

@@ -0,0 +1,101 @@
+import redis from 'redis';
+import logger from '../../../logger';
+import { KeyPromiseQueue } from './KeyPromiseQueue';
+
+const DEFAULT_REDIS_TTL = 30 * 1000; // 30 seconds in milliseconds
+const FLUSH_DB_KEY = '__flush_db__';
+
+function debug() {
+  logger.debug.apply(logger, ['RedisCacheAdapter', ...arguments]);
+}
+
+const isValidTTL = ttl => typeof ttl === 'number' && ttl > 0;
+
+export class RedisCacheAdapter {
+  constructor(redisCtx, ttl = DEFAULT_REDIS_TTL) {
+    this.ttl = isValidTTL(ttl) ? ttl : DEFAULT_REDIS_TTL;
+    this.client = redis.createClient(redisCtx);
+    this.queue = new KeyPromiseQueue();
+  }
+
+  get(key) {
+    debug('get', key);
+    return this.queue.enqueue(
+      key,
+      () =>
+        new Promise(resolve => {
+          this.client.get(key, function(err, res) {
+            debug('-> get', key, res);
+            if (!res) {
+              return resolve(null);
+            }
+            resolve(JSON.parse(res));
+          });
+        })
+    );
+  }
+
+  put(key, value, ttl = this.ttl) {
+    value = JSON.stringify(value);
+    debug('put', key, value, ttl);
+
+    if (ttl === 0) {
+      // ttl of zero is a logical no-op, but redis cannot set expire time of zero
+      return this.queue.enqueue(key, () => Promise.resolve());
+    }
+
+    if (ttl === Infinity) {
+      return this.queue.enqueue(
+        key,
+        () =>
+          new Promise(resolve => {
+            this.client.set(key, value, function() {
+              resolve();
+            });
+          })
+      );
+    }
+
+    if (!isValidTTL(ttl)) {
+      ttl = this.ttl;
+    }
+
+    return this.queue.enqueue(
+      key,
+      () =>
+        new Promise(resolve => {
+          this.client.psetex(key, ttl, value, function() {
+            resolve();
+          });
+        })
+    );
+  }
+
+  del(key) {
+    debug('del', key);
+    return this.queue.enqueue(
+      key,
+      () =>
+        new Promise(resolve => {
+          this.client.del(key, function() {
+            resolve();
+          });
+        })
+    );
+  }
+
+  clear() {
+    debug('clear');
+    return this.queue.enqueue(
+      FLUSH_DB_KEY,
+      () =>
+        new Promise(resolve => {
+          this.client.flushdb(function() {
+            resolve();
+          });
+        })
+    );
+  }
+}
+
+export default RedisCacheAdapter;