ExecutorService shutdown in finalize()

Question

I've got a class which manages a cache of objects.
The cache is cleaned once an hour via ScheduledExecutorService.
Is it ok to shutdown the ExecutorService via the class finalize() method?

@Override
protected void finalize() throws Throwable {
    EXECUTOR_SERVICE.shutdownNow();
}

I'm currently running on Java 6.

Note that `finalize` is deprecated in Java 9. See [the javadoc](https://docs.oracle.com/javase/9/docs/api/java/lang/Object.html#finalize--) for an explanation of the shortcomings of using that method. — assylias, Apr 27 '18 at 12:50
I would probably implement AutoCloseable and provide an awaitTermination(long, TimeUnit) and shutdownNow() there. — Johannes, Apr 27 '18 at 12:59
@Andrew When the container, which may be EJB for example (and the JVM) shuts down, why shouldn't it be invoked? — LppEdd, Apr 27 '18 at 13:08
Don't use finalize. Finalize is not the Java equivalent of C's destructor. — DwB, Apr 27 '18 at 18:19

Bill K · Answer 1 · 2018-04-27T18:19:22.213

1

I recommend looking at the WeakReference class and it's use as a finalizer.

It is still dependent on the GC's reachability calculations which means it might not be called immediately, but it gets rid of the chance of zombie objects and a few other problems that plague the finalize pattern.

edited Apr 27 '18 at 18:19

answered Apr 27 '18 at 18:13

Bill K

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score 1 · Accepted Answer · answered Apr 27 '18 at 18:25

There is no "call-this-last" method in Java. The finalize method is actually a "eat-memory-and-maybe-don't-even-call-me" method in Java.

The ExecutorService has shutdown and a shutdownNow. Use these, but not in a finalize method.

Call shutdown when your app knows that it "wants to stop soonish". Call shutdownNow when your app knows that it "wants to stop asap, but maybe not immediately`.

There is no way to instruct the ExecutorService to "stop now, don't wait".

Here is a Brief ExecutorService Tutorial on Baeldung.

ExecutorService shutdown in finalize()

2 Answers2