LockSupport

1、基本介绍

1. LockSupport 是 Java 并发包中的一个工具类，提供了线程阻塞和唤醒的基础功能，它是构建高级同步工具的基石（例如，AQS）

2. LockSupport 的底层是使用 Unsafe 类来实现的

2、基本使用

1. 基本使用

Thread t1 = new Thread(() -> {
    System.out.println(Thread.currentThread().getName() + "：进入");
    LockSupport.park();
    System.out.println(Thread.currentThread().getName() + "：被唤醒");
}, "t1");
t1.start();

try {
    TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
    e.printStackTrace();
}

new Thread(() -> {
    System.out.println(Thread.currentThread().getName() + "：唤醒 " + t1.getName());
    LockSupport.unpark(t1);
}, "t2").start();

# 输出结果

t1：进入
t2：唤醒 t1
t1：被唤醒

2. 先唤醒后阻塞（许可证的预先授予）

Thread t1 = new Thread(() -> {
    try {
        TimeUnit.SECONDS.sleep(2);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }

    System.out.println(Thread.currentThread().getName() + "：进入");
    LockSupport.park();
    System.out.println(Thread.currentThread().getName() + "：被唤醒");
}, "t1");
t1.start();

try {
    TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
    e.printStackTrace();
}

new Thread(() -> {
    System.out.println(Thread.currentThread().getName() + "：唤醒 " + t1.getName());
    LockSupport.unpark(t1);
}, "t2").start();

# 输出结果

t2：唤醒 t1
t1：进入
t1：被唤醒

3. 超时阻塞

Thread t1 = new Thread(() -> {
    System.out.println(Thread.currentThread().getName() + "：进入");
    LockSupport.parkNanos(TimeUnit.SECONDS.toNanos(5));
    System.out.println(Thread.currentThread().getName() + "：被唤醒");
}, "t1");
t1.start();

try {
    TimeUnit.SECONDS.sleep(10);
} catch (InterruptedException e) {
    e.printStackTrace();
}

new Thread(() -> {
    System.out.println(Thread.currentThread().getName() + "：唤醒 " + t1.getName());
    LockSupport.unpark(t1);
}, "t2").start();

# 输出结果

t1：进入
t1：被唤醒
t2：唤醒 t1

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("HH:mm:ss");

Thread t1 = new Thread(() -> {
    System.out.println(Thread.currentThread().getName() + "：进入" + " [" + formatter.format(LocalDateTime.now()) + "]");
    LockSupport.parkNanos(TimeUnit.SECONDS.toNanos(5));
    System.out.println(Thread.currentThread().getName() + "：被唤醒" + " [" + formatter.format(LocalDateTime.now()) + "]");
    LockSupport.parkNanos(TimeUnit.SECONDS.toNanos(10));
    System.out.println(Thread.currentThread().getName() + "：再次被唤醒" + " [" + formatter.format(LocalDateTime.now()) + "]");
}, "t1");
t1.start();

try {
    TimeUnit.SECONDS.sleep(10);
} catch (InterruptedException e) {
    e.printStackTrace();
}

new Thread(() -> {
    System.out.println(Thread.currentThread().getName() + "：唤醒 " + t1.getName() + " [" + formatter.format(LocalDateTime.now()) + "]");
    LockSupport.unpark(t1);
}, "t2").start();

# 输出结果

t1：进入 [15:24:14]
t1：被唤醒 [15:24:19]
t2：唤醒 t1 [15:24:24]
t1：再次被唤醒 [15:24:24]