RFR: 8078641: MethodHandle.asTypeCache can retain classes from unloading
Mandy Chung
mchung at openjdk.java.net
Mon Aug 30 23:58:31 UTC 2021
On Wed, 25 Aug 2021 09:31:51 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:
> `MethodHandle.asTypeCache` keeps a strong reference to adapted `MethodHandle` and it can introduce a class loader leak through its `MethodType`.
>
> Proposed fix introduces a 2-level cache (1 element each) where 1st level can only contain `MethodHandle`s which are guaranteed to not introduce any dependencies on new class loaders compared to the original `MethodHandle`. 2nd level is backed by a `SoftReference` and is used as a backup when the result of `MethodHandle.asType()` conversion can't populate the higher level cache.
>
> The fix is based on [the work](http://cr.openjdk.java.net/~plevart/jdk9-dev/MethodHandle.asTypeCacheLeak/) made by Peter Levart @plevart back in 2015.
>
> Testing: tier1 - tier6
Thanks for fixing this. JEP 416 depends on this.
src/java.base/share/classes/java/lang/invoke/MethodHandle.java line 966:
> 964: }
> 965:
> 966: private static boolean isSystemLoader(ClassLoader loader) {
These are builtin loaders. This method may be better to rename to `isBuiltinLoader`.
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Marked as reviewed by mchung (Reviewer).
PR: https://git.openjdk.java.net/jdk/pull/5246
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