Disruptor预备知识

最新推荐文章于 2025-09-13 09:06:35 发布

iteye_7017

最新推荐文章于 2025-09-13 09:06:35 发布

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分类专栏： java并发框架-Disruptor3.2 文章标签： java

本文链接：https://blog.youkuaiyun.com/iteye_7017/article/details/82673815

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本文介绍了Java中并发编程的基础知识，包括使用Unsafe类进行内存直接操作的方法、Condition接口的用法、计算以2为底的对数的两种方式、获取数组元素偏移量和大小的技巧、AtomicReferenceFieldUpdater类的应用、Arrays.copyOf()方法的使用及可变参数的介绍。

1.sun.misc.Unsafe 示例

package com.java.magic.part4.exception;

import java.lang.reflect.Field;

import sun.misc.Unsafe;

class Target{
	
	int intParam = 3;
	
	long longParam;
	
	String strParam;
	
	String strParam1;
}

public class UnsafeTest {
	
	private static Unsafe unsafe;
	
	static{
		try {
			//通过反射获取theUnsafe
			Field field = Unsafe.class.getDeclaredField("theUnsafe");
			field.setAccessible(true);
			unsafe = (Unsafe)field.get(null);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
	
	public static void main(String[] args) throws Exception {
		
		Class clazz = Target.class;
		Field[] fields = clazz.getDeclaredFields();
		System.out.println("fieldNameeeee:fieldOffset");
		for(Field f : fields){
			//获取属性偏移量，可以通过这个偏移量给属性设值
			System.out.println(f.getName()+" : "+unsafe.objectFieldOffset(f));
		}
		System.out.println("--------------------------------");
		Target target = new Target();
		Field intParam = clazz.getDeclaredField("intParam");
		int a = (Integer) intParam.get(target);
		System.out.println("intParam原始值："+a);
		long intParamOffset = unsafe.objectFieldOffset(intParam);
		System.out.println("intParam实例变量偏移量："+intParamOffset);
		//intParam实例变量偏移量是offset 原始值是3，我们要改成10
		System.out.println(unsafe.compareAndSwapInt(target, intParamOffset, 3, 10));
		System.out.println("intParam改变之后的值："+target.intParam);
		
		System.out.println("--------------------------------");
		//这个时候已经改为10了,所以会返回false  
        System.out.println(unsafe.compareAndSwapInt(target, intParamOffset, 3, 10)); 
        
        System.out.println("--------------------------------");
        Field strParam = clazz.getDeclaredField("strParam");
        String str = (String) strParam.get(target);
        System.out.println("strParam原始值："+str);
        long strParamOffset = unsafe.objectFieldOffset(strParam);
        System.out.println("strParam实例变量的偏移量是："+strParamOffset);
        System.out.println(unsafe.compareAndSwapObject(target, strParamOffset, null, "5")); 
		System.out.println("strParam改变之后的值："+target.strParam);
		
		
	}
	

}

2.java.util.concurrent.locks.Condition

package com.java.magic.part4.exception;

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

class NumberWrapper{
	
	public int value = 1;
}

public class ConditionTest {
	
	public static void main(String[] args) {
		
		//初始化可重入锁
		final Lock lock = new ReentrantLock();
		
		//第一个条件当屏幕上输出到3
		final Condition reachThreeCondition = lock.newCondition();
		
		//第二个条件当屏幕上输出到6
		final Condition reachSixCondition = lock.newCondition();
		
		//NumberWrapper只是为了封装一个数字，一边可以将数字对象共享
		final NumberWrapper num = new NumberWrapper();
		
		//初始化A线程，这个线程输出123， 789
		Thread threadA = new Thread(new Runnable() {
			
			@Override
			public void run() {
		        //reachThreeCondition.signal(); 这个东西需要放到lock.lock()和lock.unlock()之间使用
				lock.lock();
				try{
					while(num.value <= 3){
						System.out.println(Thread.currentThread().getName()+" : "+(num.value++));
					}
					reachThreeCondition.signal();//唤醒由reachThreeCondition.await()造成阻塞的线程
				} finally{
					lock.unlock();
				}
				
				
				lock.lock();
				try {
					if(num.value < 6){
						reachSixCondition.await();//阻塞当前线程,直到reachSixCondition.signal()唤醒当前线程
					}
				} catch (InterruptedException e) {
					e.printStackTrace();
				} finally{
					lock.unlock();
				}
				
				while(num.value <= 9){
					System.out.println(Thread.currentThread().getName()+" : "+(num.value++));
				}
				
			}
		});
		
		//初始化B线程，这个线程输出456
		Thread threadB = new Thread(new Runnable() {
			
			@Override
			public void run() {
			    lock.lock();
			    try{
			    	 if(num.value < 3){
						 reachThreeCondition.await();//阻塞当前线程,直到reachThreeCondition.signal()唤醒当前线程
		             }
			    } catch(Exception e){
			    	
			    } finally{
			    	lock.unlock();
			    }

			    lock.lock();
			    try{
			    	while(num.value <= 6){
						System.out.println(Thread.currentThread().getName()+" : "+(num.value++));
					}
			    	reachSixCondition.signal();//唤醒由reachSixCondition.await()造成阻塞的线程
			    } finally{
			    	lock.unlock();
			    }
			    
				
			}
		});
		
		//
		threadA.start();
		threadB.start();
		
		
	}

}

3.求以2为低N的对数

方法1(推荐)

	public static int log2(int i)
    {
        int r = 0;
        while ((i >>= 1) != 0)
        {
            ++r;
        }
        return r;
    }

方法2

Math.log(N)/Math.log(2)

4.获取long类型的数组中首个元素的偏移量和每个元素的所占内存空间大小

public static void unsafeTest() throws Exception{
	     Unsafe unsafe = getUnsafe();
	     
	     //获取long类型的数组中首个元素的偏移量
	     int offset = unsafe.arrayBaseOffset(long[].class);
	     //获取long类型的数组中为每个元素分配的内存空间大小
	     int scale = unsafe.arrayIndexScale(long[].class);
	     System.out.println("offset:"+offset+", scale:"+scale);
	     
	     long[] buffer = new long[10];
	     //unsafe
	     unsafe.putOrderedLong(buffer, offset+	16, 1003l);
	     
	     
	     System.out.println(buffer[2]);
	     
	     
	    
	}

5.AtomicReferenceFieldUpdater类

package com.java.magic.part4.exception;

import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;


import sun.misc.Unsafe;

public class Test {
	
	protected volatile String[] names = new String[0];

	/**
	 * 参考：http://huangyunbin.iteye.com/blog/1944153
	 * AtomicReferenceFieldUpdater<AbstractSequencer, Sequence[]> SEQUENCE_UPDATER =
		        AtomicReferenceFieldUpdater.newUpdater(AbstractSequencer.class, Sequence[].class, "gatingSequences");
	 */
	public static void AtomicReferenceFieldUpdaterTest() throws Exception{
		
		AtomicReferenceFieldUpdater<Test, String[]> updater = AtomicReferenceFieldUpdater.newUpdater(Test.class, String[].class, "names");
		
		Test test = new Test();
	    System.out.println(test.names);
		System.out.println(updater.get(test)); //获取对象里面的成员变量，说明获取的是Test中的names
	}
}

6.Arrays.copyOf() 方法

	public static void arraysCopyOf(){
		
		String[] names = {"高伟刚","高红成","高显兵"};
		System.out.println("names length:"+names.length);
		String[] newnames = Arrays.copyOf(names, 5);
		System.out.println("newnames length:"+newnames.length);
		for(int i =0 ; i< newnames.length; i++){
			System.out.println(newnames[i]);
		}
	}

7.jdk5新特性：可变参数

/*
	 * 如果传的是数组的话，那么names的长度是数据的大小
	 */
	public static void paramTest(String... names){
		
		System.out.println(names.length);
	}