Fix deadlock if compute function throw a RuntimeException

[imario42]

If the computeIfAbsent methods fails with a runtime exception, successive calls to computeIfAbsent lock due to a call to oldValue.waitForValue which never will receive a value then.

A test case to reproduce this behavior - the second computeIfAbsent will never return and your app is frozen.
The pull request restores the previous state of the cache on RuntimeException and the test will finish correctly.

`public class TestGuava extends TestCase
{
private Cache<String, Boolean> cache = CacheBuilder.newBuilder()
.maximumSize(10000)
.expireAfterAccess(30, TimeUnit.SECONDS)
.build();
private Map<String, Boolean> cacheMap = cache.asMap();

private final static Boolean TEST_BOOLEAN = new Boolean(true);
public void testComputeException()
{
    try
    {
        cacheMap.computeIfAbsent("a", key ->
        {
            throw new IllegalArgumentException();
        });

        fail();
    }
    catch (Exception e)
    {
        // expected
    }

    Boolean ret = cacheMap.computeIfAbsent("a", key -> {
        return TEST_BOOLEAN;
    });

    assertEquals(Boolean.TRUE, ret);
    assertSame(TEST_BOOLEAN, ret);

    ret = cacheMap.computeIfAbsent("a", key -> {
        return new Boolean(true); // should not create a new entry
    });

    assertEquals(Boolean.TRUE, ret);
    assertSame(TEST_BOOLEAN, ret);
}

}`

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[imario42]

I signed it!

[googlebot]

CLAs look good, thanks!

[ben-manes]

This should rethrow Throwable in case of an Error.

[imario42]

@ben-manes : You mean instead of catching "just" the RuntimeException (which actually is rethrown) to catch a Throwable, right? Else, I don't know which "Error" you mean.

[ben-manes]

Yes, use Throwable. Otherwise a java.lang.Error or sneakily thrown checked exception will not be handled.

[imario42]

Well, thanks to Java 8 that one was easy to fix. Done!

[imario42]

I'd like to ask if there is something else I can do that this fix gets merged?

[schlosna]

I would also like to see this fix merged and released soon as I've seen a couple separate projects hit deadlocks on cache compute and the fix for #2743 did not fully handle the above mentioned failure cases.

Thanks!

[dawid-stosur]

We also experienced this issue on PROD so also would like to see it merged and released ASAP as we use this cache extensively in our projects.

[imario42]

Maybe have a look at https://github.com/ben-manes/caffeine which does not suffer from this bug?

[ben-manes]

I think this was fixed in 8210828 (25.1)

[netdpb]

Closing this PR as it looks like the bug was fixed.