RFR: 6983726: remove Proxy from MethodHandleProxies.asInterfaceInstance SAM conversion [v9]

[ExE Boss]

On Thu, 6 Apr 2023 20:47:10 GMT, Chen Liang <liach at openjdk.org> wrote:

>> 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 a check to the class data. 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 call performance on par with those of lambda expressions; the creation performance is slightly less than that of LambdaMetafactory: https://jmh.morethan.io/?gist=fcb946d83ee4ac7386901795ca49b224
>> 
>> Additionally, an obsolete `ProxyForMethodHandle` test was removed, for it's no longer applicable.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.
>> 
>> [^1]: single abstract method
>
> Chen Liang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Require an original lookup in constructor arguments to prevent unintended instantiation

src/java.base/share/classes/java/lang/invoke/MethodHandleProxies.java line 317:

> 315:                 cob.aload(1);
> 316:                 cob.invokevirtual(CD_MethodHandles_Lookup, "lookupClass", MTD_Class);
> 317:                 cob.constantInstruction(proxyDesc);

This probably can’t use `LDC` of `CONSTANT_Class`, as that can’t refer to hidden classes:
Suggestion:

                cob.aload(0);
                cob.invokevirtual(CD_Object, "getClass", MTD_Class);


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Having a helper constant bootstrap of the following form would allow to obtain the current class using a dynamic constant:

public static final Class<?> lookupClass(
	final MethodHandles.Lookup lookup,
	final String name,
	@SuppressWarnings("rawtypes") // needed to allow `Class.class`
	final Class<? extends Class> type
) {
	requireNonNull(lookup);
	requireNonNull(type);
	if (type != Class.class) {
		throw new IllegalArgumentException();
	}
	return lookup.lookupClass();
}

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/13197#discussion_r1160636661