Any object in Java can be used as a lock using a synchronized block. This will also automatically take care of releasing the lock when an exception occurs. Object someObject = …; synchronized (someObject) { … } You can read more about this here: Intrinsic Locks and Synchronization
TL;DR: The ForkJoinPool uses daemon threads, whereas the ExecutorService is using non-daemon threads. The latter keep the JVM alive; the former do not. Also, the main thread is a non-daemon thread and when you block it waiting for the CompletableFuture to complete it remains alive (thus keeping the JVM alive). Daemon vs Non-Daemon Threads A … Read more
ExecutorService ExecutorService executor=Executors.newFixedThreadPool(50); It is simple and easy to use. It hides low level details of ThreadPoolExecutor. Prefer this one when number of Callable/Runnable tasks are small in number and piling of tasks in unbounded queue does not increase memory & degrade the performance of the system. If you have CPU/Memory constraints, use ThreadPoolExecutor with … Read more
The Oracle’s implementation[1] of parallel stream uses the current thread and in addition to that, if needed, also the threads that compose the default fork join pool ForkJoinPool.commonPool(), which has a default size equal to one less than the number of cores of your CPU. That default size of the common pool can be changed … Read more
In summary, you can think of it that way: shutdown() will just tell the executor service that it can’t accept new tasks, but the already submitted tasks continue to run shutdownNow() will do the same AND will try to cancel the already submitted tasks by interrupting the relevant threads. Note that if your tasks ignore … Read more
If you’re simply locking an object, I’d prefer to use synchronized Example: Lock.acquire(); doSomethingNifty(); // Throws a NPE! Lock.release(); // Oh noes, we never release the lock! You have to explicitly do try{} finally{} everywhere. Whereas with synchronized, it’s super clear and impossible to get wrong: synchronized(myObject) { doSomethingNifty(); } That said, Locks may be … Read more