[jdk17u-dev] RFR: 8324646: Avoid Class.forName in SecureRandom constructor

[Oli Gillespie]

Improve performance of SecureRandom constructor by backporting (both clean) two changes:

1. [JDK-8280970](https://bugs.openjdk.org/browse/JDK-8280970) removes some unused code in Provider.java. This is not really functionally needed, but it changes the same areas of code and makes the actual performance fix apply cleanly.
2. [JDK-8324646](https://bugs.openjdk.org/browse/JDK-8324646) is the actual performance fix - avoiding Class.forName calls in every construction.

Note - because of the unused code still present in JDK17, there is actually an alternative fix which makes use of it, which is very simple:


diff --git a/src/java.base/share/classes/java/security/Provider.java b/src/java.base/share/classes/java/security/Provider.java
index af8ebeeda57..28bf642d0c8 100644
--- a/src/java.base/share/classes/java/security/Provider.java
+++ b/src/java.base/share/classes/java/security/Provider.java
@@ -1851,7 +1851,7 @@ public abstract class Provider extends Properties {
                         null : constructorParameter.getClass();
                 } else {
                     ctrParamClz = cap.constructorParameterClassName == null?
-                        null : Class.forName(cap.constructorParameterClassName);
+                        null : cap.getConstructorParameterClass(); // actually make use of the cached class!
                     if (constructorParameter != null) {
                         if (ctrParamClz == null) {
                             throw new InvalidParameterException


This has the same performance benefits as making the two backports. But, it means 17 will be diverged from later versions, and I think the backported fix is cleaner overall.

Benchmark results (`make test TEST=micro:org.openjdk.bench.java.security.SecureRandomBench`):


Before: 2614 ± 127  ns/op
 After: 2150 ± 116  ns/op

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

Commit messages:
 - Backport 8ef918d6678437a5b351b172bb4cf144eeaa975f
 - Backport 63e11cfa3f887515ca36ab5147c3e6fa540978d3

Changes: https://git.openjdk.org/jdk17u-dev/pull/2310/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=2310&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8324646
  Stats: 70 lines in 2 files changed: 47 ins; 10 del; 13 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/2310.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/2310/head:pull/2310

PR: https://git.openjdk.org/jdk17u-dev/pull/2310