有哪些更复杂的并发编程概念可以进一步学习？

1. 并发集合：Java 提供了一套并发集合类，如 ConcurrentHashMap，ConcurrentLinkedQueue 和 CopyOnWriteArrayList 等，可以在并发环境下使用，而不需担心线程安全问题。

2. 原子变量: java.util.concurrent.atomic 包提供了一组原子变量类，如 AtomicInteger，AtomicLong，AtomicReference 等，可以在并发环境下进行线程安全的操作。

3. 信号量（Semaphore）：如果你需要限制某些资源的并发访问数量，你可能需要研究一下信号量。这是一个可以控制同时访问特定资源的线程数的计数器。

4. CountDownLatch 和 CyclicBarrier：这两个类可以帮助你协调多线程之间的操作，例如，可以使一个线程等待其它线程完成各自的工作后再执行。

5. Callable 和 FutureTask：除了Runnable接口，Java还提供了Callable接口，它允许有返回值的任务。FutureTask 可以将 Callable 任务转换为 Future 对象，从而获取任务的运行结果。

6. 线程安全的数据类型：例如 ReentrantLock、ReentrantReadWriteLock 和 StampedLock。这些工具可以帮助你在处理复杂的并发情况时，保证数据的一致性。

7. Fork/Join 框架：这个框架可以帮助你并行的执行任务，利用多核处理器的优势，提高 java 程序的性能。

以下为Java示例：

       并发集合（ConcurrentHashMap）：

import java.util.concurrent.*;

public class Main {
    public static void main(String[] args) {
        ConcurrentHashMap<String, Integer> map = new ConcurrentHashMap<>();
        map.put("One", 1);
        map.put("Two", 2);
        map.put("Three", 3);

        map.forEach((k, v) -> System.out.println(k + " = " + v));
    }
}

原子变量（AtomicInteger）：

import java.util.concurrent.atomic.*;

public class Main {
  public static void main(String[] args) {
    AtomicInteger atomicInt = new AtomicInteger(0);
    atomicInt.incrementAndGet();
    System.out.println(atomicInt); //Prints 1
  }
}

信号量（Semaphore）：

import java.util.concurrent.*;

public class Main {
  public static void main(String[] args) {
    Semaphore semaphore = new Semaphore(1); // Only one thread can acquire at a time
    try {
      semaphore.acquire();
      // critical section here
    } catch (InterruptedException e) {
      e.printStackTrace();
    } finally {
      semaphore.release(); // release the permit
    }
  }
}

CountDownLatch：

import java.util.concurrent.*;

public class Main {
  public static void main(String[] args) throws InterruptedException {
    CountDownLatch latch = new CountDownLatch(3); // three threads to wait for

    new Thread(() -> { System.out.println("Thread 1 finished"); latch.countDown(); }).start();
    new Thread(() -> { System.out.println("Thread 2 finished"); latch.countDown(); }).start();
    new Thread(() -> { System.out.println("Thread 3 finished"); latch.countDown(); }).start();

    latch.await(); // wait for all three threads to finish
    System.out.println("All threads finished"); // print after all threads have finished
  }
}

Callable 和 FutureTask：

import java.util.concurrent.*;

public class Main {
  public static void main(String[] args) throws ExecutionException, InterruptedException {
    Callable<Integer> task = () -> {
      TimeUnit.SECONDS.sleep(1);
      return 123;
    };
    FutureTask<Integer> futureTask = new FutureTask<>(task);
    new Thread(futureTask).start();
    System.out.println("futureTask.get() = " + futureTask.get()); // Will output: futureTask.get() = 123
  }
}

线程安全的数据类型（ReentrantLock）：

import java.util.concurrent.locks.*;

public class Counter {
    private final ReentrantLock lock = new ReentrantLock();
    private int count = 0;

    public void increment() {
        lock.lock();
        try {
            count++;
        } finally {
            lock.unlock();
        }
    }

    public void decrement() {
        lock.lock();
        try {
            count--;
        } finally {
            lock.unlock();
        }
    }

    public int value() {
        lock.lock();
        try {
            return count;
        } finally {
            lock.unlock();
        }
    }
}

Fork/Join 框架：

import java.util.concurrent.*;

class SimpleRecursiveTask extends RecursiveTask<Integer> {

    private int simulatedWork;

    public SimpleRecursiveTask(int simulatedWork) {
        this.simulatedWork = simulatedWork;
    }

    @Override
    protected Integer compute() {

        if(simulatedWork > 100) {

            System.out.println("Parallel execution and split task : " + simulatedWork);

            SimpleRecursiveTask simpleRecursiveTask1 = new SimpleRecursiveTask(simulatedWork/2);
            SimpleRecursiveTask simpleRecursiveTask2 = new SimpleRecursiveTask(simulatedWork/2);

            simpleRecursiveTask1.fork();
            simpleRecursiveTask2.fork();

            int solution = 0;
            solution = solution + simpleRecursiveTask1.join();
            solution = solution + simpleRecursiveTask2.join();

            return solution;

        } else {
            System.out.println("No need for parallel execution, sequential algorithm is ok. " + simulatedWork);
            return 2 * simulatedWork;
        }
    }
}

public class Main {
    public static void main(String[] args) {

        ForkJoinPool forkJoinPool = new ForkJoinPool(Runtime.getRuntime().availableProcessors());
        SimpleRecursiveTask simpleRecursiveAction = new SimpleRecursiveTask(120);

        System.out.println(forkJoinPool.invoke(simpleRecursiveAction));
    }
}