Multithreading: ReentrantLock.tryLock avoids blocking forever

tryLock(timeout, unit) gives up and returns false instead of waiting indefinitely for a lock that is already held. This lets a thread fail fast or fall back to other work rather than deadlocking.

Code

ReentrantLock lock = new ReentrantLock();
lock.lock();
boolean[] acquired = new boolean[1];
Thread other = new Thread(() -> {
    try {
        acquired[0] = lock.tryLock(10, TimeUnit.MILLISECONDS);
    } catch (InterruptedException e) { }
});
other.start();
other.join();
System.out.println("Other thread acquired the held lock: " + acquired[0]);
lock.unlock();

Output

Other thread acquired the held lock: false