`jmod`/`jlink` are executed during build time to produce the `jmod` and the base modules image. On slow hardware (Raspberry Pi -class, for example) and/or slow VMs (debug, interpreter-only, for example) this takes a while. Profiling shows the considerable time is spent on hashing modules either for writing out the ModuleHash attribute or for verifying the hashes are good.
Those paths can be parallelized to make them quite faster. The major contributors to module hashing are `java.base`, `jdk.desktop` and `jdk.localedata`, so we have a significant opportunity for parallelism here. Motivational improvements on `make clean-images images`: # x86_64 Server, release # Baseline real 0m11.895s user 1m4.526s sys 0m10.715s # Patched real 0m10.701s ; <--- 1.1x improvement user 1m5.097s sys 0m11.260s # x86_64 Zero, release # Baseline real 5m20.335s user 7m7.791s sys 0m7.258s # Patched real 2m23.551s ; <--- 2.23x improvement user 7m14.442s sys 0m7.856s Additional testing: - [x] Linux x86_64 fastdebug, `java/util/jar` - [x] Linux x86_64 fastdebug, `tools/jmod` - [x] Linux x86_64 fastdebug, `tools/jlink` - [x] Linux x86_64 fastdebug `tier1` ------------- Commit messages: - Fix Changes: https://git.openjdk.org/jdk/pull/10060/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10060&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8293017 Stats: 60 lines in 2 files changed: 40 ins; 10 del; 10 mod Patch: https://git.openjdk.org/jdk/pull/10060.diff Fetch: git fetch https://git.openjdk.org/jdk pull/10060/head:pull/10060 PR: https://git.openjdk.org/jdk/pull/10060
