NonblockingQueue has been removed from the mainline since JDK-8371922, but it's still used in the Leyden premain branch:
https://github.com/openjdk/leyden/commit/fa117d9ac2a31f71da13039b6456cbb9103afec7
https://github.com/openjdk/leyden/commit/0518a5d203f4938e6d3b2b042b27ecd8cd217150
For the time being, I have restored this class in Leyden.
We should investigate if the Leyden changes in compileBroker.cpp can be implemented with an alternative design.
https://github.com/openjdk/leyden/commit/fa117d9ac2a31f71da13039b6456cbb9103afec7
https://github.com/openjdk/leyden/commit/0518a5d203f4938e6d3b2b042b27ecd8cd217150
For the time being, I have restored this class in Leyden.
We should investigate if the Leyden changes in compileBroker.cpp can be implemented with an alternative design.