ReentrantLock实现生产者消费者和死锁

一、实现生产者消费者（线程交替执行）

Conditon中的await()对应Object的wait()，Condition中的signal()对应Object的notify()，Condition中的signalAll()对应Object的notifyAll()

condition.await()方法：使当前线程等待，直到收到信号或被中断。与此条件相关联的锁被原子释放。当前线程处于休眠状态，当其他一些线程为这个条件调用signalAll方法或signal方法时，当前线程被唤醒，然后重新获取与此条件相关联的锁

两个线程交替执行例子（同理生产者消费者也是这样交替执行）：

package com.yang.spbo.other.lock;

import java.util.concurrent.LinkedBlockingDeque;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;

/**
 * A,B两个线程交替执行
 * 〈功能详细描述〉
 *
 * @author 17090889
 * @see [相关类/方法]（可选）
 * @since [产品/模块版本] （可选）
 */
public class ConditionService {
    private ReentrantLock lock = new ReentrantLock();
    /**
     * 两个线程所以创建两个condition
     */
    private Condition A = lock.newCondition();
    private Condition B = lock.newCondition();

    private int number = 1;

    private boolean flag = false;

    private void executeA() {
        while (number < 100) {
            try {
                lock.lock();
                if (!flag) {
                    System.out.println("A等待");
                    A.await(); 
                }
                System.out.println("A " + number);
                number++;
                flag = false;
                System.out.println("B唤醒");
                B.signal();
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        }

    }

    private void executeB() {
        while (number < 100) {
            try {
                lock.lock();
                if (flag) {
                    System.out.println("B等待");
                    B.await();
                }
                System.out.println("B " + number);
                number++;
                flag = true;
                System.out.println("A唤醒");
                A.signal();
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        }

    }

    public static void main(String[] args) {
        final ConditionService cs = new ConditionService();
        ThreadPoolExecutor executor = new ThreadPoolExecutor(2, 5, 1, TimeUnit.MINUTES, new LinkedBlockingDeque<Runnable>(1000), new MyThreadFactory("conditionService"));

        executor.execute(new Runnable() {
            @Override
            public void run() {
                System.out.println(Thread.currentThread().getName());
                cs.executeA();
            }
        });
        executor.execute(new Runnable() {
            @Override
            public void run() {
                System.out.println(Thread.currentThread().getName());
                cs.executeB();
            }
        });
    }

    static class MyThreadFactory implements ThreadFactory {
        /**
         * 线程名字前缀
         */
        private String namePrefix;

        private AtomicInteger id = new AtomicInteger(1);

        public MyThreadFactory(String namePrefix) {
            this.namePrefix = namePrefix;
        }

        @Override
        public Thread newThread(Runnable r) {
            String threadName = namePrefix + "-worker-" + id.getAndIncrement();
            Thread thread;
            thread = new Thread(r, threadName);
            return thread;
        }
    }
}

运行结果：

conditionService-worker-1
A等待
conditionService-worker-2
B 1
A唤醒
B等待
A 2
B唤醒
A等待
B 3
A唤醒
B等待
A 4
B唤醒
A等待
B 5
A唤醒
B等待
A 6

二、死锁

什么是死锁？

　　死锁是指两个或多个事务在同一资源上相互占用，并请求锁定对方占用的资源（相互请求锁定对方已经锁定占用的资源），从而导致恶性循环等待的现象

　　如：两个线程都在锁内等待获取对方持有的锁。

　　如何避免死锁？

　　　　1）避免一个线程同时获取多个锁

　　　　2）避免一个线程在锁内同时占用多个资源，尽量保证每个锁只占用一个资源

　　　　3）尝试使用定时锁，使用lock.tryLock(timeout)来替代使用内部锁机制

　　　　4）对于数据库锁，加锁和解锁必须在同一个数据库连接里，否则会出现解锁失败的情况

ReentrantLock实现死锁：

/**
* ReentrantLock实现死锁
* 〈功能详细描述〉
*
* @author 17090889
* @see [相关类/方法]（可选）
* @since [产品/模块版本] （可选）
*/
public class DeadLockTest {
    private static ReentrantLock lock1 = new ReentrantLock();
    private static ReentrantLock lock2 = new ReentrantLock();

    public static void main(String[] args) {
        new Thread(new Runnable() {
            @Override
            public void run() {
                lock1.lock();
                try {
                    Thread.sleep(1000);
                    lock2.lock();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    lock1.unlock();
                }
            }
        }).start();
        new Thread(new Runnable() {
            @Override
            public void run() {
                lock2.lock();
                try {
                    Thread.sleep(1000);
                    lock1.lock();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    lock2.unlock();
                }

            }
        }).start();
    }
}

分析过程:

c:\Program Files\Java\jdk1.7.0_79\bin>jps
7996 Main
3960 Jps
8396 Launcher
5568 Launcher
1204
8212 Bootstrap
396 ProfilerServer

8036 DeadLockTest

2.c:\Program Files\Java\jdk1.7.0_79\bin>jstack 8036

Found one Java-level deadlock:
=============================
"Thread-1":
waiting for ownable synchronizer 0x00000007d5e6f5c0, (a java.util.concurrent.l
ocks.ReentrantLock$NonfairSync),
which is held by "Thread-0"
"Thread-0":
waiting for ownable synchronizer 0x00000007d5e6f5f0, (a java.util.concurrent.l
ocks.ReentrantLock$NonfairSync),
which is held by "Thread-1"

Java stack information for the threads listed above:
===================================================
"Thread-1":
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for <0x00000007d5e6f5c0> (a java.util.concurrent.lock
s.ReentrantLock$NonfairSync)
        at java.util.concurrent.locks.LockSupport.park(LockSupport.java:186)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInt
errupt(AbstractQueuedSynchronizer.java:834)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(A
bstractQueuedSynchronizer.java:867)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(Abstrac
tQueuedSynchronizer.java:1197)
        at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLo
ck.java:214)
        at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:290)

        at deadLock.DeadLockTest$2.run(DeadLockTest.java:38)
        at java.lang.Thread.run(Thread.java:745)
"Thread-0":
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for <0x00000007d5e6f5f0> (a java.util.concurrent.lock
s.ReentrantLock$NonfairSync)
        at java.util.concurrent.locks.LockSupport.park(LockSupport.java:186)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInt
errupt(AbstractQueuedSynchronizer.java:834)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(A
bstractQueuedSynchronizer.java:867)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(Abstrac
tQueuedSynchronizer.java:1197)

at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLo

ck.java:214)

at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:290)

at deadLock.DeadLockTest$1.run(DeadLockTest.java:24)

at java.lang.Thread.run(Thread.java:745)

Found 1 deadlock.

补充：

synchronized实现死锁:

/**
* synchronized实现死锁
* 〈功能详细描述〉
*
* @author 17090889
* @see [相关类/方法]（可选）
* @since [产品/模块版本] （可选）
*/
public class DeadLockTest2 {
    private static Object obj1 = new Object();
    private static Object obj2 = new Object();

    public static void main(String[] args) {
        new Thread(new Runnable() {
            @Override
            public void run() {
                synchronized (obj1) {
                    System.out.println("thead1 get lock1");
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    synchronized (obj2) {
                        System.out.println("thead1 get lock2");
                    }
                    System.out.println("thread1 end");
                }
            }
        }, "thead1").start();
        new Thread(new Runnable() {
            @Override
            public void run() {
                synchronized (obj2) {
                    System.out.println("thead2 get lock2");
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    synchronized (obj1) {
                        System.out.println("thead2 get lock1");
                    }
                    System.out.println("thread2 end");
                }
            }
        }, "thead2").start();
    }
}

Found one Java-level deadlock:
=============================
"thead2":
waiting to lock monitor 0x000000000b15a7c8 (object 0x00000007d5e6f290, a java.
lang.Object),
which is held by "thead1"
"thead1":
waiting to lock monitor 0x000000000b1593d8 (object 0x00000007d5e6f2a0, a java.
lang.Object),
which is held by "thead2"

Java stack information for the threads listed above:
===================================================
"thead2":
        at deadLock.DeadLockTest2$2.run(DeadLockTest2.java:44)
        - waiting to lock <0x00000007d5e6f290> (a java.lang.Object)
        - locked <0x00000007d5e6f2a0> (a java.lang.Object)
        at java.lang.Thread.run(Thread.java:745)
"thead1":
        at deadLock.DeadLockTest2$1.run(DeadLockTest2.java:27)
        - waiting to lock <0x00000007d5e6f2a0> (a java.lang.Object)
        - locked <0x00000007d5e6f290> (a java.lang.Object)
        at java.lang.Thread.run(Thread.java:745)

Found 1 deadlock.

END.

posted @ 2021-01-16 23:47 杨岂阅读(604) 评论(0) 编辑收藏举报

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ReentrantLock实现生产者消费者和死锁

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