JUC 常用 4 大并发工具类 CountDownLatch、CyclicBarrier、Semaphore、ExChanger

/**
* Constructs a {@code CountDownLatch} initialized with the given count.
*
* @param count the number of times {@link #countDown} must be invoked
*        before threads can pass through {@link #await}
* @throws IllegalArgumentException if {@code count} is negative
*/
public CountDownLatch(int count) {
    if (count < 0) throw new IllegalArgumentException("count < 0");
    this.sync = new Sync(count);
}

/**
* Creates a new {@code CyclicBarrier} that will trip when the
* given number of parties (threads) are waiting upon it, and which
* will execute the given barrier action when the barrier is tripped,
* performed by the last thread entering the barrier.
*
* @param parties the number of threads that must invoke {@link #await}
*        before the barrier is tripped
* @param barrierAction the command to execute when the barrier is
*        tripped, or {@code null} if there is no action
* @throws IllegalArgumentException if {@code parties} is less than 1
*/
public CyclicBarrier(int parties, Runnable barrierAction) {
    if (parties <= 0) throw new IllegalArgumentException();
    this.parties = parties;
    this.count = parties;
    this.barrierCommand = barrierAction;
}
/**
* Creates a new {@code CyclicBarrier} that will trip when the
* given number of parties (threads) are waiting upon it, and
* does not perform a predefined action when the barrier is tripped.
*
* @param parties the number of threads that must invoke {@link #await}
*        before the barrier is tripped
* @throws IllegalArgumentException if {@code parties} is less than 1
*/
public CyclicBarrier(int parties) {
    this(parties, null);
}

/**
* Creates a {@code Semaphore} with the given number of
* permits and nonfair fairness setting.
*
* @param permits the initial number of permits available.
*        This value may be negative, in which case releases
*        must occur before any acquires will be granted.
*/
public Semaphore(int permits) {
    sync = new NonfairSync(permits);
}
/**
* Creates a {@code Semaphore} with the given number of
* permits and the given fairness setting.
*
* @param permits the initial number of permits available.
*        This value may be negative, in which case releases
*        must occur before any acquires will be granted.
* @param fair {@code true} if this semaphore will guarantee
*        first-in first-out granting of permits under contention,
*        else {@code false}
         参数fair表示是否是公平的，即等待时间越久的越先获取许可
*/
public Semaphore(int permits, boolean fair) {
    sync = fair ? new FairSync(permits) : new NonfairSync(permits);
}

/**
* Creates a new Exchanger.
*/
public Exchanger() {
    participant = new Participant();
}

/**
 * @description: 线程之间交换数据
 * @author: yh
 * @date: 2023/2/5
 */
public class UseExchange {
    private static final Exchanger<Set<String>> exchanger = new Exchanger<>();
    public static void main(String[] args) {
        new Thread(){
            @Override
            public void run() {
                Set<String> aSet = new HashSet<>();
                aSet.add("A");
                aSet.add("B");
                aSet.add("C");
                try {
                    Set<String> exchange = exchanger.exchange(aSet);
                    for (String s : exchange) {
                        System.out.println("aSet："+s);
                    }
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }.start();
        new Thread(){
            @Override
            public void run() {
                Set<String> bSet = new HashSet<>();
                bSet.add("1");
                bSet.add("2");
                bSet.add("3");
                try {
                    Set<String> exchange = exchanger.exchange(bSet);
                    for (String s : exchange) {
                        System.out.println("bSet："+s);
                    }
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }.start();
    }
}

bSet：A
aSet：1
bSet：B
aSet：2
bSet：C
aSet：3