学习Java并发编程之前你不得不知道的那点事

package com.lizba.p1;
/**
 * <p>
 *      测试并发执行和串行的速度
 * </p>
 *
 * @Author: Liziba
 * @Date: 2021/6/2 23:40
 */
public class ConcurrencyTest {
    /** 执行次数 */
    private static final long count = 10000;
    public static void main(String[] args) throws InterruptedException {
        concurrency();
        serial();
    }
    /**
     * 并发执行
     * @throws InterruptedException
     */
    private static void concurrency() throws InterruptedException {
        long start = System.currentTimeMillis();
        Thread thread = new Thread(new Runnable() {
            public void run() {
                int a = 0;
                for (long i = 0; i < count; i++) {
                    a +=5;
                }
            }
        });
        thread.start();
        int b = 0;
        for (long i = 0; i < count; i++) {
            b--;
        }
        thread.join();
        long time = System.currentTimeMillis() - start;
        System.out.println("concurrency :" + time + "ms, b=" + b);
    }
    /**
     * 串行执行
     */
    private static void serial() {
        long start = System.currentTimeMillis();
        int a = 0;
        for (long i = 0; i < count; i++) {
            a += 5;
        }
        int b = 0;
        for (long i = 0; i < count; i++) {
            b--;
        }
        long time = System.currentTimeMillis() - start;
        System.out.println("serial :" + time + "ms, b=" + b);
    }
}

package com.lizba.p1;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
/**
 * <p>
 *      线程池Dump测试 -- 代码只是示例
 * </p>
 *
 * @Author: Liziba
 * @Date: 2021/6/4 23:26
 */
public class ThreadPoolDumpTest {
    public static void main(String[] args) {
        // 创建固定大小的线程池
        ExecutorService fixedThreadPool = Executors.newFixedThreadPool(300);
        // 初始化线程池中的线程
        for (int i = 0; i < 300; i++) {
            fixedThreadPool.execute(getThread(i));
        }
        while (true) {
            try {
                Thread.sleep(5000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("测试！");
        }
    }
    /**
     * 创建线程
     * @param i
     * @return
     */
    private static Runnable getThread(final int i) {
        return new Runnable() {
            public void run() {
                try {
                    Thread.sleep(50);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(i);
            }
        };
    }
}

"pool-1-thread-300" #311 prio=5 os_prio=0 tid=0x000000002fe46800 nid=0x4880 waiting on condition [0x0000000033cfe000]
   java.lang.Thread.State: WAITING (parking)
  at sun.misc.Unsafe.park(Native Method)
  - parking to wait for  <0x000000077b098178> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
  at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
  at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
  at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
  at java.lang.Thread.run(Thread.java:748)
   Locked ownable synchronizers:
  - None

package com.lizba.p1;
/**
 * <p>
 *      死锁示例代码
 * </p>
 *
 * @Author: Liziba
 * @Date: 2021/6/5 0:37
 */
public class DeadLockDemo {
    private static final String A = "A";
    private static final String B = "B";
    /**
     * t1\t2互相持有锁
     */
    private void deadLock() {
        Thread t1 = new Thread(new Runnable() {
            public void run() {
                // 持有锁A
                synchronized (A) {
                    try {
                        Thread.currentThread().sleep(2000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    // 持有锁B
                    synchronized (B) {
                        System.out.println("hold Lock B");
                    }
                }
            }
        });
        Thread t2 = new Thread(new Runnable() {
            public void run() {
                // 持有锁B
                synchronized (B) {
                    try {
                        Thread.currentThread().sleep(2000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    // 持有锁A
                    synchronized (A) {
                        System.out.println("hold Lock A");
                    }
                }
            }
        });
        t1.start();
        t2.start();
    }
    public static void main(String[] args) {
        new DeadLockDemo().deadLock();
    }
}

"Thread-1" #13 prio=5 os_prio=0 tid=0x000000001e011000 nid=0x5318 waiting for monitor entry [0x000000001fcef000]
   java.lang.Thread.State: BLOCKED (on object monitor)
  at com.lizba.p1.DeadLockDemo$2.run(DeadLockDemo.java:50)
  - waiting to lock <0x000000076b042000> (a java.lang.String)
  - locked <0x000000076b042030> (a java.lang.String)
  at java.lang.Thread.run(Thread.java:748)
   Locked ownable synchronizers:
  - None
"Thread-0" #12 prio=5 os_prio=0 tid=0x000000001e00f800 nid=0x4b38 waiting for monitor entry [0x000000001fbef000]
   java.lang.Thread.State: BLOCKED (on object monitor)
  at com.lizba.p1.DeadLockDemo$1.run(DeadLockDemo.java:33)
  - waiting to lock <0x000000076b042030> (a java.lang.String)
  - locked <0x000000076b042000> (a java.lang.String)
  at java.lang.Thread.run(Thread.java:748)
   Locked ownable synchronizers:
  - None