JAVA: 自己实现的锁

矫情吗；* 2023-07-24 08:47 21阅读 0赞

package action;
    
    import java.util.concurrent.ConcurrentLinkedQueue;
    import java.util.concurrent.locks.LockSupport;
    
    import sun.misc.Unsafe;
    
    public class MyLock {
    	private volatile  int state=0;
    
    	private static final long stateOffset;
    	private static final Unsafe unsafe=UnsafeFactory.getUnsafe();
    	private static ConcurrentLinkedQueue<Thread> waiters=new ConcurrentLinkedQueue<Thread>();
    	
    	
    	
    
    	public int getState() {
    		return state;
    	}
    
    	public void setState(int state) {
    		this.state = state;
    	}
    
    	
    
    	
    
    	public static long getStateoffset() {
    		return stateOffset;
    	}
    
    	static
    	{
    		try
    		{
    			stateOffset=unsafe.objectFieldOffset(MyLock.class.getDeclaredField("state"));
    			
    		}
    		catch(Exception ex)
    		{
    			System.out.println(ex.getMessage());
    			throw new Error();
    		}
    		
    	}
    	
    	public final  boolean compareAndSwapState(int expect,int update)
    	{
    		return unsafe.compareAndSwapInt(this, stateOffset,expect,update);
    	}
    	
    	public  boolean aquire() 
    	{
    		Thread current=Thread.currentThread();
    		int c=getState();
    		if(c==0)
    		{
    			if((waiters.size()==0||current==waiters.peek()))
    			{
    				if(compareAndSwapState(0,1))
    				{				
    				return true;
    				}
    				
    				else
    				{
    					return false;
    				}
    			}
    			
    			else
    			{
    				
    			}
    		}
    		
    		return false;
    		
    	}
    	
    	public void lock() 
    	{
    		if(aquire())
    		{
    			return;
    		}
    		
    		Thread current=Thread.currentThread();
    	
    		//System.out.println(Thread.currentThread()+":will enqueue "+waiters);
    		waiters.add(current);
    		//System.out.println(Thread.currentThread()+":finish enqueue "+waiters);
    		while(true)
    		{
    		
    			if((current==waiters.peek())&&aquire())
    				{
    				//System.out.println(Thread.currentThread()+":will dequeue "+waiters);
    				waiters.poll();
    				//System.out.println(Thread.currentThread()+":finish dequeue "+waiters);
    				return;
    				}
    			//System.out.println(Thread.currentThread()+":will park "+waiters);
    		LockSupport.park(current);
    		}
    			
    	}
    	
    	public void unlock()
    	{		
    		
    		while(!compareAndSwapState(1,0))
    		{
    			
    		}
    		
    			
    		Thread head=waiters.peek();
    		
    		if(head!=null)
    		{	
    			//System.out.println(Thread.currentThread()+":will awake "+head.getName());
    			LockSupport.unpark(head);	
    			//System.out.println(Thread.currentThread()+":finish awake "+head.getName());
    		}
    		else
    		{
    			
    		}
    		
    		
    	}
    
    }