StackOverflow2013

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copied!<p>I just found a huge memory leak, so I am going to call the code that created the leak to be <em>wrong</em> and my fix that does not leak as <em>right</em>.</p> <p>Here is the old code: (This is a common pattern I have seen all over)</p> <pre><code>class Singleton { static Singleton getInstance() {...} void addListener(Listener listener) {...} void removeListener(Listener listener) {...} } class Leaky { Leaky() { // If the singleton changes the widget we need to know so register a listener Singleton singleton = Singleton.getInstance(); singleton.addListener(new Listener() { void handleEvent() { doSomething(); } }); } void doSomething() {...} } // Elsewhere while (1) { Leaky leaky = new Leaky(); // ... do stuff // leaky falls out of scope } </code></pre> <p>Clearly, this is bad. Many Leaky's are being created and never get garbage collected because the listeners keep them alive.</p> <p>Here was my alternative that fixed my memory leak. This works because I only care about the event listener while the object exists. The listener should not keep the object alive.</p> <pre><code>class Singleton { static Singleton getInstance() {...} void addListener(Listener listener) {...} void removeListener(Listener listener) {...} } class NotLeaky { private NotLeakyListener listener; NotLeaky() { // If the singleton changes the widget we need to know so register a listener Singleton singleton = Singleton.getInstance(); listener = new NotLeakyListener(this, singleton); singleton.addListener(listener); } void doSomething() {...} protected void finalize() { try { if (listener != null) listener.dispose(); } finally { super.finalize(); } } private static class NotLeakyListener implements Listener { private WeakReference<NotLeaky> ownerRef; private Singleton eventer; NotLeakyListener(NotLeaky owner, Singleton e) { ownerRef = new WeakReference<NotLeaky>(owner); eventer = e; } void dispose() { if (eventer != null) { eventer.removeListener(this); eventer = null; } } void handleEvent() { NotLeaky owner = ownerRef.get(); if (owner == null) { dispose(); } else { owner.doSomething(); } } } } // Elsewhere while (1) { NotLeaky notleaky = new NotLeaky(); // ... do stuff // notleaky falls out of scope } </code></pre>

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