https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/concurrent/package-summary.html
https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/concurrent/package-summary.html#MemoryVisibility
    https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/concurrent/Executors.html
    https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/concurrent/ExecutorCompletionService.html

https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/concurrent/locks/package-summary.html
    https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/concurrent/locks/ReentrantReadWriteLock.html
https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/concurrent/atomic/package-summary.html