RFR: 8261354: SIGSEGV at MethodIteratorHost [v2]

[Jaroslav Bachorik]

> The `MethodIteratorHost` will iterate over previous versions of redefined classes but the number of methods in that class is retrieved only for the current version. 
> Since the previous versions may theoretically, and before JDK 15 also practically, contain fewer methods than the current version (hotspot did support adding `private static` methods during retransformation) this can lead to SIGSEGV when the iterator tries accessing out-of-range method element.
> 
> Although for after JDK 15 it is not possible to have differing number of methods between multiple versions of a retransformed class it feels right not to rely on the implementation detail and re-retrieve the number of methods per each class version.
> 
> All jdk_jfr tests are passing on Linux x64 and MacOS x64

Jaroslav Bachorik has updated the pull request incrementally with one additional commit since the last revision:

  Remove unused filter

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4143/files
  - new: https://git.openjdk.java.net/jdk/pull/4143/files/96ddee5b..3da48b92

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4143&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4143&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4143.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4143/head:pull/4143

PR: https://git.openjdk.java.net/jdk/pull/4143