Executor框架：任务与执行的解耦🏗️

Executor框架：不关心怎么执行，只关心执行什么！任务提交和执行完全解耦。

一、Executor框架层次

Executor (顶层接口)
  ↓
ExecutorService (生命周期管理)
  ↓
AbstractExecutorService (模板方法)
  ↓
ThreadPoolExecutor (核心实现)

Callable/Runnable (任务抽象)
  ↓
Future (结果获取)
  ↓
FutureTask (结果实现)

二、核心接口

Executor

public interface Executor {
    void execute(Runnable command);
}

最简单实现：

// 直接执行
class DirectExecutor implements Executor {
    public void execute(Runnable r) {
        r.run();  // 调用者线程执行
    }
}

// 新线程执行
class ThreadPerTaskExecutor implements Executor {
    public void execute(Runnable r) {
        new Thread(r).start();
    }
}

ExecutorService

public interface ExecutorService extends Executor {
    void shutdown();
    List<Runnable> shutdownNow();
    boolean isShutdown();
    boolean isTerminated();
    
    <T> Future<T> submit(Callable<T> task);
    <T> Future<T> submit(Runnable task, T result);
    Future<?> submit(Runnable task);
}

三、设计思想

1. 任务抽象

// Runnable：无返回值
Runnable task = () -> System.out.println("Hello");

// Callable：有返回值
Callable<String> task = () -> "Result";

2. 执行策略

// 策略1：单线程串行
ExecutorService executor = Executors.newSingleThreadExecutor();

// 策略2：固定线程池
ExecutorService executor = Executors.newFixedThreadPool(10);

// 策略3：缓存线程池
ExecutorService executor = Executors.newCachedThreadPool();

// 策略4：定时任务
ScheduledExecutorService executor = Executors.newScheduledThreadPool(5);

3. 结果获取

Future<String> future = executor.submit(() -> "Result");
String result = future.get();  // 阻塞获取结果

四、生命周期管理

RUNNING → SHUTDOWN → STOP → TIDYING → TERMINATED

executor.shutdown();           // 优雅关闭
executor.shutdownNow();        // 立即关闭
executor.awaitTermination(...); // 等待终止

五、使用示例

ExecutorService executor = Executors.newFixedThreadPool(10);

// 提交任务
List<Future<Integer>> futures = new ArrayList<>();

for (int i = 0; i < 100; i++) {
    final int taskId = i;
    Future<Integer> future = executor.submit(() -> {
        // 任务逻辑
        return taskId * 2;
    });
    futures.add(future);
}

// 获取结果
for (Future<Integer> future : futures) {
    Integer result = future.get();
    System.out.println(result);
}

executor.shutdown();

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