RFR: 6983726: remove Proxy from MethodHandleProxies.asInterfaceInstance SAM conversion [v3]
Chen Liang
liach at openjdk.org
Wed Mar 29 01:04:44 UTC 2023
> As John Rose has pointed out in this issue, the current j.l.r.Proxy based implementation of MethodHandleProxies.asInterface has a few issues:
> 1. Exposes too much information via Proxy supertype (and WrapperInstance interface)
> 2. Does not allow future expansion to support SAM[^1] abstract classes
> 3. Slow (in fact, very slow)
>
> This patch addresses all 3 problems:
> 1. It implements proxies with one hidden class for each requested interface and replaced WrapperInstance inheritance with an annotation. This can avoid unexpected passing of `instanceof`, and avoids the nasty problem of exporting a JDK interface to a dynamic module to ensure access.
> 2. This patch obtains already generated classes from a ClassValue by the requested interface type; the ClassValue can later be updated to compute implementation generation for abstract classes as well.
> 3. This patch's generated hidden classes has acceptable call and creation performance compared to the baseline; though the methods to access wrapper information see huge performance drops, they are not anticipated to be used in a very frequent basis, while the old implementation's wrapper access methods are more optimized (2ns/op) than interface implementation methods (6ns/op). [Oracle JDK 20 vs this](https://jmh.morethan.io/?gists=bf98de7b2128e7e5d14e697fd9921eb9,e5115a2a8fa0a45159e15fab0d95b5d8)
>
> Additionally, an obsolete `ProxyForMethodHandle` test was removed, for it's no longer applicable. Tests in `jdk/java/lang/invoke` and `jdk/java/lang/reflect` pass.
>
> Alternative implementation:
> [An alternative implementation](https://github.com/openjdk/jdk/commit/72dbf9d4e01c455854d9b865cb2a47c38f37a8e0) was to generate a proxy class for each methodhandle than sharing across methodhandles. That implementation was abandoned for its bad proxy creation performance, despite it having excellent call performance. [Alternative implementation vs this](https://jmh.morethan.io/?gists=08abb39f224574550925beb8be1b2f59,e5115a2a8fa0a45159e15fab0d95b5d8)
>
> In addition, I have a question: in [8161245](https://bugs.openjdk.org/browse/JDK-8161245) it seems some fields can be optimized as seen in [ciField.cpp](https://github.com/openjdk/jdk/blob/6aec6f3a842ead30b26cd31dc57a2ab268f67875/src/hotspot/share/ci/ciField.cpp#L219). Does it affect the execution performance of MethodHandle in hidden classes' Condy vs. MethodHandle in regular final field in hidden classes?
>
> [^1]: single abstract method
Chen Liang has updated the pull request incrementally with one additional commit since the last revision:
rethrow error
-------------
Changes:
- all: https://git.openjdk.org/jdk/pull/13197/files
- new: https://git.openjdk.org/jdk/pull/13197/files/0158ffe5..fade6200
Webrevs:
- full: https://webrevs.openjdk.org/?repo=jdk&pr=13197&range=02
- incr: https://webrevs.openjdk.org/?repo=jdk&pr=13197&range=01-02
Stats: 2 lines in 1 file changed: 2 ins; 0 del; 0 mod
Patch: https://git.openjdk.org/jdk/pull/13197.diff
Fetch: git fetch https://git.openjdk.org/jdk.git pull/13197/head:pull/13197
PR: https://git.openjdk.org/jdk/pull/13197
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