如何在Servlet中集成memcached？ Tomcat和内存泄漏

Question

Searching memcached java in google, the first result is Using Memcached with Java .

The guy (who calls himself Just some Random Asshole in the Internet! ) proposes a Singleton based on net.spy.memcached . It basically creates 20 threads and connections by creating 20 instances of MemcachedClient. For every request it chooses one at random.

However those threads and connections are never closed and they pile up every time I hot swap the application during development (with warnings from Tomcat 7).

SEVERE: The web application [/MyAppName] appears to have started a thread named
[...] but has failed to stop it. This is very likely to create a memory leak.

By looking at MemcachedClient JavaDoc, I see a method called shutdown with the only description being "Shut down immediately." Shut down what? The client? The server? I suppose is the client, since it's in MemcachedClient and I suppose that this method would close the connection and terminate the thread. EDIT : yes, it shuts down the client.

Question 1 How to force the execution of cleanup code in Tomcat 7, before the application is hot swapped?

Question 2 Is this approach of using memcached (with cleanup code), correct or is better I start over in a different way?

Answer 1

I think creating 20 memcache clients is silly - that's like creating 20 separate copies of your DB connection pool. The idea with that client is that it multiplexes a variety of requests with asynch IO. http://code.google.com/p/spymemcached/wiki/Optimizations

As far as shutting it down, simply call: yourClient.shutdown() to shutdown immediately, or yourClient.shutdown(3, TimeUnit.SECONDS) for example, to allow some time for a more graceful shutdown.

That could be called from your Servlet's .destroy method, or a context listener for your whole WAR.

Answer 2

我对memcached一无所知，但您可能可以编写一个自定义上下文侦听器，并在上下文侦听器中放入某种关闭挂钩，以便在上下文关闭时可以遍历单例中的项目并将其关闭。

Answer 3

It turned out that it was a bug of Java AWS SDK and was not related to memcached. Version 1.2.2 of Java AWS SDK has this bug fixed.