package thread;

import java.util.Random;

public class CmdRunnerSynchronized {

    public static boolean IS_RUNNING = false;

    private static final Object lock = new Object();

    public boolean start() {

        // 如果有任务在执行，直接返回
        if (IS_RUNNING) {
            System.out.println("--is running---"
                    + Thread.currentThread().getName());
            return false;
        }

        // sleep一会
        try {
            Thread.sleep(new Random().nextInt(2000));
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        synchronized (lock) {
            IS_RUNNING = true;
            System.out.println("--run start---"
                    + Thread.currentThread().getName());

            // sleep一会
            try {
                Thread.sleep(new Random().nextInt(2000));
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

            System.out.println("--run end---"
                    + Thread.currentThread().getName());
            IS_RUNNING = false;
        }

        return true;
    }

    public static void main(String[] args) {

        // 开10个线程
        for (int i = 0; i < 10; i++) {
            new Thread("Thread" + i) {
                public void run() {
                    try {
                        Thread.sleep(new Random().nextInt(1000));
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    CmdRunnerSynchronized run = new CmdRunnerSynchronized();
                    run.start();
                }
            }.start();
        }
    }
}

package thread;

import java.util.Random;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class CmdRunner {

    public static boolean IS_RUNNING = false;

    private static Lock scoreLock = new ReentrantLock();

    public boolean start() {

        if (scoreLock.tryLock()) {
            try {

                // sleep一会
                try {
                    Thread.sleep(new Random().nextInt(2000));
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

                IS_RUNNING = true;
                System.out.println("--run start---"
                        + Thread.currentThread().getName());

                // sleep一会
                try {
                    Thread.sleep(new Random().nextInt(2000));
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

                System.out.println("--run end---"
                        + Thread.currentThread().getName());
                IS_RUNNING = false;
                return true;
            } finally {
                scoreLock.unlock();
            }
        } else {
            System.out.println("--is running---"
                    + Thread.currentThread().getName());
            return false;
        }

    }

    public static void main(String[] args) {

        // 开10个线程
        for (int i = 0; i < 10; i++) {
            new Thread("Thread" + i) {
                public void run() {
                    try {
                        Thread.sleep(new Random().nextInt(1000));
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    CmdRunner run = new CmdRunner();
                    run.start();
                }
            }.start();
        }
    }
}