多线程开发-ReentrantLock 可重复锁详解

多线程开发 ReentrantLock 可重复锁详解

 

1. Condition  await  条件变量阻塞
2. Condition  signal 条件变量唤醒
3. ReentrantLock lock 获得锁
4. ReentrantLock unlock 释放锁
5. lockInterruptibly  作用:持有锁的线程长期不释放的时候，正在等待的线程可以选择放弃等待
6. new ReentrantLock(); 默认是非公平锁
7. new ReentrantLock(false); 公平锁
8. tryLock  多选一， 当A获得锁的时候，B探测到A获得锁后就不会再去获取锁了
9. tryLock(n,m)  前提:m:TimeUnit.SECONDS ,逻辑:跟tryLock一样，区别:但等待n秒后再去检测
10. isHeldByCurrentThread  查询当前线程是否保持此锁

---

• 1、Condition  await  条件变量阻塞
• 2、Condition  signal 条件变量唤醒
• 3、ReentrantLock lock 获得锁
• 4、ReentrantLock unlock 释放锁

 

例子说明:

package yzy_test.com.test;

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
import com.alibaba.fastjson.JSON;

class ConditionDemo {

   private ReentrantLock lock     = new ReentrantLock();
   //条件变量1
   private Condition     take     = lock.newCondition();
   //条件变量2
   private Condition     put      = lock.newCondition();
   //阻塞队列(先进先出)
   private BlockingQueue queue    = new ArrayBlockingQueue<>(10000);
   // 队列的最大容量
   private int           capacity = 5;
   // 初始值
   private int           i        = 1;
  //往队列里面插入数据
   public void put() {
       lock.lock(); //获得锁
       System.out.println(String.format("【put】i=%d 获取锁!!!", i));
       try {
           //使用while的目的:它醒了之后你得用while循环让它再去判断一次条件
           while (queue.size() == capacity) {
               System.out.println(String.format("【put】插入 %d 时队列满，执行put.await！队列值：【%s】", i,JSON.toJSONString(queue.toArray())));
               put.await();//条件阻塞
           }
           queue.put(i);
           System.out.println(String.format("【put】插入 %d 到队列", i));
           i++;
           // 读操作唤醒
           take.signal(); //条件唤醒
       } catch (Exception e) {
       } finally {
           System.out.println(String.format("【put】i=%d 释放锁!!!", i - 1));
           lock.unlock(); //释放锁 一般放在finally里
       }
   }
   /**
          * 从队列读数据
    */
   public void take() {
       lock.lock();  //获取锁
       System.out.println("【take】获取锁！");
       int data = 0;
       try {
           //使用while的目的:它醒了之后你得用while循环让它再去判断一次条件
           while (queue.size() == 0) {
               System.out.println("【take】执行take.await！");
               take.await();//条件阻塞
           }
           data = (int) queue.take();
           System.out.println(String.format("【take】从队列读取值 %d ,队列值：【%s】", data, JSON.toJSONString(queue.toArray())));
           // 写操作唤醒
           put.signal();//条件唤醒
       } catch (Exception e) {
       } finally {
           System.out.println(String.format("【take】i=%d 释放锁!!!", data));
           lock.unlock(); //释放锁 一般放在finally
       }
   }
}
public class ConditionTest {
	  // 写任务
    static class WriteTask implements Runnable {
        private ConditionDemo condition;
        public WriteTask(ConditionDemo condition){
            this.condition = condition;
        }
        @Override
        public void run() {
                condition.put();
        }
    }
    // 读任务
    static class ReadTask implements Runnable {
        private ConditionDemo condition;
        public ReadTask(ConditionDemo condition){
            this.condition = condition;
        }
        public void run() {
                condition.take();
        }
    }
    public static void main(String[] args) throws InterruptedException {
        ConditionDemo condition = new ConditionDemo();
        //类似于一个线程池的功能
        for (int i = 0; i < 20; i++) {
            new Thread(new WriteTask(condition)).start();;     
           }
        for (int i = 0; i < 20; i++) {
            new Thread(new ReadTask(condition)).start();;
           } 
    }
}

效果:

---

• 5、lockInterruptibly  作用:持有锁的线程长期不释放的时候，正在等待的线程可以选择放弃等待
• 6、new ReentrantLock(); 默认是非公平锁
• 7、new ReentrantLock(false); 公平锁

 

例子说明:

package yzy_test.com.test;

import java.util.concurrent.locks.ReentrantLock;
/**
 * lockInterruptibly() 作用:持有锁的线程长期不释放的时候，正在等待的线程可以选择放弃等待
 * 创建一个非公平锁，默认是非公平锁
 * Lock lock = new ReentrantLock();
 * Lock lock = new ReentrantLock(false);
 * */
class LockTest{
	//非公平锁
	 final ReentrantLock lock     = new ReentrantLock();
     static Boolean flag_one = false;
     static Boolean flag_two = false;
     static Boolean flag_three = false;

     Thread test_one = new Thread(new Runnable() {
		public void run() {
			 try {
	    		 lock.lock();
				 long startTime = System.currentTimeMillis();
        		 System.out.println(Thread.currentThread().getName()+"开始执行:");
	    		 while(!flag_one) {	  
    	    		 long endTime = System.currentTimeMillis();
    	    		 //3秒自动中断，防止死锁设计
	    			 if((endTime-startTime)/1000 == 3) {
	        			 flag_one = true;
	        			 System.out.println(Thread.currentThread().getName()+"执行结束，线程中断失败耗时"+((endTime-startTime)/1000)+"秒自动中断");
	        			 return;
	        		 }
	        	 } 
	    		 long endTime = System.currentTimeMillis();
	   			 System.out.println(Thread.currentThread().getName()+"执行结束，线程中断成功耗时"+((endTime-startTime)/1000)+"秒");

	    	 }finally {
				lock.unlock();
			}			
		}
	});
     Thread test_two = new Thread(new Runnable() {
		public void run() {
			 try {
	    		 lock.lock();
				 long startTime = System.currentTimeMillis();
				 System.out.println(Thread.currentThread().getName()+"开始执行:");
	    		 while(!flag_two) {
	    			 try {
	    				 Thread.sleep(200);
	    	    		 long endTime = System.currentTimeMillis();
	    	    		 //3秒自动中断，防止死锁设计
	    				 if((endTime-startTime)/1000 == 3) {
	    					 flag_two = true;
		        			 System.out.println(Thread.currentThread().getName()+"执行结束，线程中断失败，线程中断耗时"+((endTime-startTime)/1000)+"秒自动中断");
		        			 return;
		        		 }
	    			 }catch(Exception e) {
	    				 flag_two = true;
	    			 }
	        		
	        	 } 
	    		 long endTime = System.currentTimeMillis();
	   			 System.out.println(Thread.currentThread().getName()+"执行结束，线程中断成功耗时"+((endTime-startTime)/1000)+"秒");	    	 
	   			 }finally {
				lock.unlock();
			}			
		}
	});
     Thread test_three = new Thread(new Runnable() {
		public void run() {
			 try {
	    		 lock.lock();
				 long startTime = System.currentTimeMillis();
        		 System.out.println(Thread.currentThread().getName()+"开始执行:");
	    		 while(!flag_three) {
	    			 //配合 线程interrupt()使用，抛出异常，中断线程
		    		 lock.lockInterruptibly();
    	    		 long endTime = System.currentTimeMillis();
    	    		 //3秒自动中断，防止死锁设计
	        		 if((endTime-startTime)/1000 == 3) {
	        			 flag_three = true;
	        			 System.out.println(Thread.currentThread().getName()+"执行结束，线程中断失败耗时"+((endTime-startTime)/1000)+"秒自动中断");
	        			 return;
	        		 }
	        	 } 
	    		 long endTime = System.currentTimeMillis();
	   			 System.out.println(Thread.currentThread().getName()+"执行结束，线程中断成功耗时"+((endTime-startTime)/1000)+"秒");	    	

			} catch(Exception e){
				e.printStackTrace();
				flag_three = true;
			}finally {
				lock.unlock();
			}			
		}
	});
    
}
public class ReentrantLockTest {
  public static void main(String[] args) throws InterruptedException {
	  LockTest test = new LockTest();
	  //ReentrantLock lock 无try/catch执行
	  test.test_one.start();
	  test.test_one.setName("线程A：ReentrantLock lock 无try/catch执行");
	  Thread.sleep(2000);
	  test.test_one.interrupt();
	//ReentrantLock lock 有try/catch执行
	  test.test_two.start();
	  test.test_two.setName("线程B：ReentrantLock lock try/catch执行");
	  Thread.sleep(2000);
	  test.test_two.interrupt();
	//ReentrantLock lockInterruptibly try/catch执行 
	 
	  test.test_three.start();
	  test.test_three.setName("线程C：ReentrantLock lockInterruptibly try/catch执行");
	  Thread.sleep(2000);
	  test.test_three.interrupt();
  }
}

效果:

---

• 8、tryLock  多选一， 当A获得锁的时候，B探测到A获得锁后就不会再去获取锁了
• 9、tryLock(n,m)  前提:m:TimeUnit.SECONDS ,逻辑:跟tryLock一样，区别:但等待n秒后再去检测
• 10、isHeldByCurrentThread  查询当前线程是否保持此锁

 

例子说明:

package yzy_test.com.test;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReentrantLock;
/**
 * tryLock 多选一， 当A获得锁的时候，B探测到A获得锁后就不会再去获取锁了
 * tryLock(n,m)  前提:m:TimeUnit.SECONDS ,逻辑:跟tryLock一样，区别:但等待n秒后再去检测
 * isHeldByCurrentThread  查询当前线程是否保持此锁
 * */
public class RunTryLockTest {

	 private long time ;
	 public RunTryLockTest(long time) {
		 this.time = time;
	 }
	 public ReentrantLock lock = new ReentrantLock();
	    public void TryLockTest(){
	        try {
	            if (lock.tryLock()){
	                System.out.println(Thread.currentThread().getName()+"--获得锁");
	            } else {
	                System.out.println(Thread.currentThread().getName()+"--没有获得锁");
	            }
	        } finally {
	            if (lock.isHeldByCurrentThread()){
	                lock.unlock();
	            }
	        }
	    }
	 
	    public void TryLockTestTime(){
        	long startTime = System.currentTimeMillis();
	        try {
	        	//等待3秒后再去探寻是否有其他线程保持锁
	            if(lock.tryLock(3, TimeUnit.SECONDS)) {
	            	Thread.sleep(time);
	                System.out.println(Thread.currentThread().getName()+"--开始获得锁");
	            } else {
	                System.out.println(Thread.currentThread().getName()+"--没有获得锁");
	            }
	        } catch (Exception e) {
	            e.printStackTrace();
	        } finally {
	        	//查询当前线程是否保持此锁
	            if (lock.isHeldByCurrentThread()){
	                lock.unlock();
		    		 long endTime = System.currentTimeMillis();
	                System.out.println(Thread.currentThread().getName()+"释放锁耗时："+((endTime-startTime)));
	            }
	        }
	    }
	   
	   public static void main(String[] args) throws InterruptedException {
		   final long time = 4000;
		   final RunTryLockTest test = new RunTryLockTest(time);
		   Runnable tryLockTest = new Runnable() {			
			@Override
			public void run() {
				test.TryLockTest();				
			}
		   };
		   Runnable tryLockTestTime = new Runnable() {			
				@Override
				public void run() {
					test.TryLockTestTime();				
				}
		   };
		   Thread t1 = new Thread(tryLockTest);
		   t1.setName("tryLock 例子1");
		   Thread t2 = new Thread(tryLockTest);
		   t2.setName("tryLock 例子2");
		   Thread t3 = new Thread(tryLockTestTime);
		   t3.setName("tryLockTime 例子1");
		   Thread t4 = new Thread(tryLockTestTime);
		   t4.setName("tryLockTime 例子2【添加时长"+time+"】");
		   //同步执行测试:
		   //执行tryLock
		   t1.start();
		   t2.start();
		   t1.join();
		   t2.join();

		   //执行 tryLockTime
		   t3.start();
		   t4.start();
		   t3.join();
		   t4.join();
	   }
}

效果:

本文地址：https://blog.csdn.net/weixin_38316697/article/details/107334049