RFR: 8333716: Shenandoah: Check for disarmed method before taking the nmethod lock [v2]

[Neethu Prasad]

> **Notes**
> We are spending significant time on acquiring the per-nmethod as all the
> threads are in same nmethod.
> Adding double-check lock by calling is_armed before lock acquisition.
> 
> **Verification**
> 1. hotspot_gc tests
> 
> 2.
> 
> dev-dsk-neethp-jdk-2c-ad54955c % jdk/build/linux-x86_64-server-release/images/jdk/bin/java -Xmx1g -Xms1g -XX:+UseShenandoahGC -Xlog:gc ManyThreadsStacks.java 2>&1 | grep "marking roots"  
> [0.617s][info][gc] GC(0) Concurrent marking roots 5.553ms
> [0.643s][info][gc] GC(1) Concurrent marking roots 3.148ms
> [0.666s][info][gc] GC(2) Concurrent marking roots 3.219ms
> [0.687s][info][gc] GC(3) Concurrent marking roots 2.796ms
> [0.708s][info][gc] GC(4) Concurrent marking roots 2.892ms
> [0.946s][info][gc] GC(5) Concurrent marking roots 3.393ms
> [1.023s][info][gc] GC(6) Concurrent marking roots 2.710ms
> [1.095s][info][gc] GC(7) Concurrent marking roots 2.466ms
> [1.173s][info][gc] GC(8) Concurrent marking roots 2.734ms
> [1.247s][info][gc] GC(9) Concurrent marking roots 2.706ms
> [1.325s][info][gc] GC(10) Concurrent marking roots 2.451ms
> [1.397s][info][gc] GC(11) Concurrent marking roots 2.381ms
> [1.477s][info][gc] GC(12) Concurrent marking roots 2.411ms
> [1.555s][info][gc] GC(13) Concurrent marking roots 2.222ms
> [1.628s][info][gc] GC(14) Concurrent marking roots 2.599ms

Neethu Prasad has updated the pull request incrementally with one additional commit since the last revision:

  Update full name

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/19587/files
  - new: https://git.openjdk.org/jdk/pull/19587/files/65123cd0..9649f1e3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19587&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19587&range=00-01

  Stats: 0 lines in 0 files changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/19587.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19587/head:pull/19587

PR: https://git.openjdk.org/jdk/pull/19587