Java多线程中的主动等待与优雅终止：break和join()的应用

public class PrinterThread extends Thread {
    private String letter;
    private int internal;
    private int amount;

    public PrinterThread(String letter, int internal, int amount){
        this.letter = letter;
        this.internal = internal;
        this.amount = amount;
    }

    @Override
    public void run(){
        for (int i = 1; i <= amount; i++) {
            System.out.println(letter);
            try {
                Thread.sleep(internal); // 模拟耗时操作
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt(); // 重新设置中断状态
                System.err.println(letter + " 线程被中断。");
            }
        }
        System.out.println(letter + " 线程完成。");
    }
}

public class Main {
    public static void main(String[] args) {
        PrinterThread printerThreadA = new PrinterThread("A", 1, 1000);
        PrinterThread printerThreadB = new PrinterThread("B", 1, 1000);
        PrinterThread printerThreadC = new PrinterThread("C", 1, 1); // C线程很快完成
        PrinterThread printerThreadD = new PrinterThread("D", 5, 50);

        printerThreadA.start();
        printerThreadB.start();
        printerThreadC.start();

        // 主动等待 printerThreadD 启动的条件
        while(!printerThreadD.isAlive()){ // 循环检查D是否已启动
            if (!printerThreadA.isAlive() || !printerThreadB.isAlive() || !printerThreadC.isAlive()) {
                printerThreadD.start(); // 条件满足，启动D
            }
        }
        System.out.println("主线程逻辑继续执行...");
    }
}

// ... (PrinterThread 类保持不变) ...

public class MainOptimized {
    public static void main(String[] args) {
        PrinterThread printerThreadA = new PrinterThread("A", 1, 1000);
        PrinterThread printerThreadB = new PrinterThread("B", 1, 1000);
        PrinterThread printerThreadC = new PrinterThread("C", 1, 1);
        PrinterThread printerThreadD = new PrinterThread("D", 5, 50);

        printerThreadA.start();
        printerThreadB.start();
        printerThreadC.start();

        while(!printerThreadD.isAlive()){
            if (!printerThreadA.isAlive() || !printerThreadB.isAlive() || !printerThreadC.isAlive()) {
                printerThreadD.start();
                break; // 条件满足，启动D后立即跳出循环
            }
            // 考虑在此处添加 Thread.sleep() 以避免完全的忙等待，
            // 但更好的做法是使用更高级的同步机制。
            try {
                Thread.sleep(10); // 稍微休眠，减少CPU占用
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            }
        }
        System.out.println("主线程逻辑继续执行...");
    }
}

// ... (PrinterThread 类保持不变) ...

public class MainGracefulTermination {
    public static void main(String[] args) throws InterruptedException { // join() 可能抛出 InterruptedException
        PrinterThread printerThreadA = new PrinterThread("A", 1, 1000);
        PrinterThread printerThreadB = new PrinterThread("B", 1, 1000);
        PrinterThread printerThreadC = new PrinterThread("C", 1, 1);
        PrinterThread printerThreadD = new PrinterThread("D", 5, 50);

        printerThreadA.start();
        printerThreadB.start();
        printerThreadC.start();

        while(!printerThreadD.isAlive()){
            if (!printerThreadA.isAlive() || !printerThreadB.isAlive() || !printerThreadC.isAlive()) {
                printerThreadD.start();
                break;
            }
            try {
                Thread.sleep(10); // 避免过快的忙等待
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            }
        }
        System.out.println("主线程已启动所有子线程，并等待它们完成...");

        // 使用 join() 方法确保主线程等待所有子线程完成
        printerThreadA.join();
        printerThreadB.join();
        printerThreadC.join();
        printerThreadD.join();

        System.out.println("所有子线程已完成，主线程即将退出。");
    }
}