项目 更喜欢并发实用程序来等待和通知

<code class="java">Map<String, String> map = new ConcurrentHashMap<>();
String result = map.putIfAbsent("key", "value");
if (result == null) {
    System.out.println("Value inserted.");
} else {
    System.out.println("Key already exists with value: " + result);
}</code>

<code class="java">public static long time(Executor executor, int concurrency, Runnable action) throws InterruptedException {
    CountDownLatch ready = new CountDownLatch(concurrency);
    CountDownLatch start = new CountDownLatch(1);
    CountDownLatch done = new CountDownLatch(concurrency);

    for (int i = 0; i < concurrency; i++) {
        executor.execute(() -> {
            try {
                ready.countDown(); // Signal ready
                start.await();     // Wait for start signal
                action.run();
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            } finally {
                done.countDown(); // Signal done
            }
        });
    }

    ready.await();   // Wait for all threads to be ready
    long startTime = System.nanoTime();
    start.countDown(); // Trigger start
    done.await();     // Wait for all threads to finish
    return System.nanoTime() - startTime;
}</code>

<code class="java">synchronized (lock) {
    while (!condition) {
        lock.wait();
    }
}</code>