????

• Java 5?? ???? java.util.concurrent ????? ?? ??? ??? ????? ??????.
• ?? ? ??? ????? ??? ??? ?????.
• ? ???? ???? ???? ?? ???? ??? ??? ???? ?????.

java.util.concurrent? ??? ????
???? ????:

• Executor Framework: ?? 80?? ??? ??? ??
• ?? ???: ??, ???, ?? ?? ?? ???? ?????? ???? ?????.
• ??? ??: CountDownLatch, Semaphore, CyclicBarrier, Exchanger ? Phaser? ??? ??? ? ??

?? ???

??:

• ???? ?? ?? ???
• ?? ??? ??? ???? ????.
• putIfAbsent? ?? ??? ??? ??? ???? ??????. ?: ?????? ??? ? ??:

Map<String, String> map = new ConcurrentHashMap<>();
String result = map.putIfAbsent("key", "value");
if (result == null) {
    System.out.println("Valor inserido.");
} else {
    System.out.println("Chave já existente com valor: " + result);
}

??:

• ???? ???? ?????(Collections.synchronizedMap).
• ?? ??????? ??? ?? ???????.

????
??: ??? ?? ??.

???? ??? ??? ?:

• CountDownLatch: ??? ??? ?? ??? ??.
• ????: ?? ???? ?? ???? ?????.
• CyclicBarrier: ??? ??? ?? ???? ???
• Phaser: ?? ? ?? ??? ???.

?? ?: CountDownLatch? ??? ?? ???
??: ?? ???? ?? ??? ??? ?????.

??:

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(); // Indica que está pronto
                start.await();     // Aguarda o sinal de início
                action.run();
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            } finally {
                done.countDown(); // Indica que terminou
            }
        });
    }

    ready.await();   // Aguarda todas as threads ficarem prontas
    long startTime = System.nanoTime();
    start.countDown(); // Dispara o sinal de início
    done.await();     // Aguarda todas as threads finalizarem
    return System.nanoTime() - startTime;
}

??:

• 3?? ??? ?????: ??(?? ?? ??), ??(?? ???), ??(??).
• System.nanoTime? ???? ?? ??? ???? ?????.

???? ??? ?? ??
??? ?? ?? ???? ?????.
?? ??:

1. ??? ??? ?? ?? ??? ?????.

synchronized (lock) {
    while (!condition) {
        lock.wait();
    }
}

1. ???? ?? ?? ??? ???????.
2. notify? ?? ???? ???,notifyAll? ?????.

??

• ???? ??? ?? ????? ?????.
• ??? ? ?? ?? ???? ????? ????.
• CyclicBarrier ?? Phaser? ?? ?? ??? ?? ? ?? ?? ??? ??? ? ????

?? ??

? ??? ?? ?? ? ??? ?? ??? ????? ?????.? ?? ?????. ??? ??? PHP ??? ????? ?? ?? ??? ?????!