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.