feat: Add caching capability to circuits

nodeshift · Mar 7, 2017 · 0b717f6 · 0b717f6
1 parent 6c14b39
commit 0b717f6
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Showing 3 changed files with 61 additions and 1 deletion.
diff --git a/lib/circuit.js b/lib/circuit.js
@@ -11,6 +11,7 @@ const PENDING_CLOSE = Symbol('pending-close');
 const FALLBACK_FUNCTION = Symbol('fallback');
 const NUM_FAILURES = Symbol('num-failures');
 const STATUS = Symbol('status');
+const CACHE = new WeakMap();
 
 /**
  * @class CircuitBreaker
@@ -62,6 +63,9 @@ class CircuitBreaker extends EventEmitter {
 
     this.on('open', _startTimer(this));
     this.on('success', () => this.close());
+    if (this.options.cache) {
+      CACHE.set(this, undefined);
+    }
   }
 
   /**
@@ -165,6 +169,12 @@ class CircuitBreaker extends EventEmitter {
    * @fires CircuitBreaker#timeout
    */
   fire () {
+    if (CACHE.get(this) !== undefined) {
+      this.emit('cacheHit');
+      return CACHE.get(this);
+    } else {
+      this.emit('cacheMiss');
+    }
     const args = Array.prototype.slice.call(arguments);
     /**
      * Emitted when the circuit breaker action is executed
@@ -185,7 +195,7 @@ class CircuitBreaker extends EventEmitter {
 
     let timeout;
     let timeoutError = false;
-    return new this.Promise((resolve, reject) => {
+    const value = new this.Promise((resolve, reject) => {
       timeout = setTimeout(
         () => {
           timeoutError = true;
@@ -222,6 +232,17 @@ class CircuitBreaker extends EventEmitter {
         handleError(error, this, timeout, args, resolve, reject);
       }
     });
+    if (this.options.cache) {
+      CACHE.set(this, value);
+    }
+    return value;
+  }
+
+  /**
+   * Clears the cache of this {@link CircuitBreaker}
+   */
+  clearCache () {
+    CACHE.set(this, undefined);
   }
 }
 

diff --git a/lib/status.js b/lib/status.js
@@ -33,13 +33,23 @@ class Status {
      * The number of times this circuit breaker has timed out
      */
     this.timeouts = 0;
+    /**
+     * The number of times the cache is used
+     */
+    this.cacheHit = 0;
+    /**
+     * The number of times the cache is missed
+     */
+    this.cacheMiss = 0;
     this[CIRCUIT_BREAKER] = circuit;
     circuit.on('success', () => this.successes++);
     circuit.on('failure', () => this.failures++);
     circuit.on('fallback', () => this.fallbacks++);
     circuit.on('timeout', () => this.timeouts++);
     circuit.on('fire', () => this.fires++);
     circuit.on('reject', () => this.rejects++);
+    circuit.on('cacheHit', () => this.cacheHit++);
+    circuit.on('cacheMiss', () => this.cacheMiss++);
   }
 }
 

diff --git a/test/test.js b/test/test.js
@@ -40,6 +40,35 @@ test('Passes parameters to the circuit function', (t) => {
     .catch(t.fail);
 });
 
+test('Using cache', (t) => {
+  t.plan(3);
+  const expected = 34;
+  const options = {
+    cache: true
+  };
+  const breaker = cb(passFail, options);
+
+  breaker.fire(expected)
+    .then((arg) => t.equals(arg, expected, `cache hits:misses ${breaker.status.cacheHit}:${breaker.status.cacheMiss}`))
+    .catch(t.fail)
+    .then(() => {
+      breaker.fire(expected)
+        .then((arg) => {
+          t.equals(arg, expected, `cache hits:misses ${breaker.status.cacheHit}:${breaker.status.cacheMiss}`);
+          breaker.clearCache();
+        })
+        .catch(t.fail)
+        .then(() => {
+          breaker.fire(expected)
+            .then((arg) => {
+              t.equals(arg, expected, `cache hits:misses ${breaker.status.cacheHit}:${breaker.status.cacheMiss}`);
+            })
+            .then(t.end)
+            .catch(t.fail);
+        });
+    });
+});
+
 test('Fails when the circuit function fails', (t) => {
   t.plan(1);
   const breaker = cb(passFail);