RFR: 8142487: Cleanup sun.invoke.util.Wrapper zeroes to be both reliable and lazy

[John Rose]

On Nov 11, 2015, at 11:53 AM, Claes Redestad <claes.redestad at oracle.com> wrote:
> 
> Hi,
> 
> following-up on JDK-8141678[1]. So, it appears we want to avoid the fragility of keeping local copies of Byte/Short/Integer in Wrapper, and instead get the boxed zeroes lazily, when we actually need them.
> 
> It turns out simply fixing Wrapper.zero() would then regress things back a bit, since java.lang.invoke.LambdaForm itself eagerly generates a number of LambdaForms and NamedFunctions that touch a couple of Wrapper.zeros. By making the initialization of these lazy as well we not only avoid regression compared to JDK-8141678, but further remove another 9 LambdaForms from jigsaw startup (down from 74 to 65; down to 37 together with JDK-8142334[2]). An unneeded function (void zero_V) was removed in the process.

Making them lazy is fine, but this change is buggy, due to a large amount of cut-n-paste.

For example, this insertion looks wrong:
+    private static void createZeroForm(BasicType type) {
+        synchronized (LF_zero) {
+            final int ord = type.ordinal();
+            LambdaForm zeForm = LF_identity[ord];  <<< s.b. LF_zero???

For better maintainability, I think the zero and identity forms should be created together, not in separate twin code blocks.

I think this is a safer, saner way to inject laziness here:

- private static void createIdentityForms() {
+ // Create LF_zero, LF_identity, etc., for the given type.
+ private static void createIdentityForms(BasicType type) {

It means that groups of LFs get lazily created; if that is tolerable for the present purpose, it's easier to reason about.

— John