使用StampedLock替代ReentrantReadWriteLock

悲观读(写的机会很少)

package com.dwz.stampedLock;

import java.util.ArrayList;
import java.util.List;
import java.util.Optional;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.StampedLock;
import java.util.stream.Collectors;

/**
 *     悲观读(写的机会很少)
 *    100 threads
 *    99  threads need read lock
 *    1    threads need write lock
 *    可以使用StampedLock替代ReentrantReadWriteLock
 */
public class StampedLockExample {
    private final static StampedLock lock = new StampedLock();
    
    private final static List<Long> DATA = new ArrayList<>();
    
    private static void read() {
        long stamped = -1;
        try {
            stamped = lock.readLock();
            Optional.of(DATA.stream().map(String::valueOf).collect(Collectors.joining("#", "R-", "")))
                    .ifPresent(System.out::println);
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlockRead(stamped);
        }
    }
    
    private static void write() {
        long stamped = -1;
        try {
            stamped = lock.writeLock();
            DATA.add(System.currentTimeMillis());
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlockWrite(stamped);
        }
    }
    
    public static void main(String[] args) {
        final ExecutorService executor = Executors.newFixedThreadPool(10);
        Runnable readTask = () -> {
            for(;;) {
                read();
            }
        };
        
        Runnable writeTask = () -> {
            for(;;) {
                write();
            }
        };
        
        executor.submit(readTask);
        executor.submit(readTask);
        executor.submit(readTask);
        executor.submit(readTask);
        executor.submit(readTask);
        executor.submit(readTask);
        executor.submit(readTask);
        executor.submit(readTask);
        executor.submit(readTask);
        executor.submit(writeTask);
    }
}

改进

package com.dwz.stampedLock;

import java.util.ArrayList;
import java.util.List;
import java.util.Optional;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.StampedLock;
import java.util.stream.Collectors;
/**
 *    乐观读（写的机会相对增多）
 */
public class StampedLockExample2 {
    private final static StampedLock lock = new StampedLock();
    
    private final static List<Long> DATA = new ArrayList<>();
    
    private static void read() {
        long stamp = lock.tryOptimisticRead();
        if(lock.validate(stamp)) {//验证在该时间锁是否还持有
            try {
                stamp = lock.readLock();
                Optional.of(DATA.stream().map(String::valueOf).collect(Collectors.joining("#", "R-", "")))
                        .ifPresent(System.out::println);
                TimeUnit.SECONDS.sleep(1);
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                lock.unlockRead(stamp);
            }
        }
    }
    
    private static void write() {
        long stamped = -1;
        try {
            stamped = lock.writeLock();
            DATA.add(System.currentTimeMillis());
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlockWrite(stamped);
        }
    }
    
    public static void main(String[] args) {
        final ExecutorService executor = Executors.newFixedThreadPool(10);
        Runnable readTask = () -> {
            for(;;) {
                read();
            }
        };
        
        Runnable writeTask = () -> {
            for(;;) {
                write();
            }
        };
        
        executor.submit(readTask);
        executor.submit(readTask);
        executor.submit(readTask);
        executor.submit(readTask);
        executor.submit(readTask);
        executor.submit(readTask);
        executor.submit(readTask);
        executor.submit(readTask);
        executor.submit(readTask);
        executor.submit(writeTask);
    }
}