CONCURRENCY is calculated at runtime based on min(cores / 2, 12) * CONCURRENCY_FACTOR. This is enabled in test/TestCommon.gmk (via JDK-8196197) and take effect to most components (jdk, jaxp, hotspot, nashorn) since they use (include) test/TestCommon.gmk.

BUT the calculate concurrency logic is NOT in langtools tests since test/langtools/Makefile does NOT use test/TestCommon.gmk (see more: JDK-8170629).

Calculate concurrency logic should also be enabled for langtools tests. (or/and, test/langtools/Makefile should be improved to use test/TestCommon.gmk as other components)