一段测试代码

package com.java;

import java.lang.reflect.Field;

import sun.misc.Unsafe;

class SynTestClass {
	protected Thread mainThread;
	
	public SynTestClass(Thread mainThread) {
		this.mainThread = mainThread;
	}
	
	public void t() {
		System.out.println(Thread.currentThread().getName() + ": t");
		synchronized(mainThread) {
			mainThread.notify();
			System.out.println("notified");
		}
		try {
			Thread.sleep(24 * 60 * 60 * 1000);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
	
	public synchronized void tt() {
		System.out.println(Thread.currentThread().getName() + ": tt");
		synchronized(mainThread) {
			mainThread.notify();
			System.out.println("notified");
		}
		try {
			Thread.sleep(24 * 60 * 60 * 1000);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
}


class SynTestClass2 extends SynTestClass {
	
	public SynTestClass2(Thread mainThread) {
		super(mainThread);
	}
	
}

class ThreadTest1 extends Thread {
	private SynTestClass st;
	
	public ThreadTest1(SynTestClass st) {
		this.st = st;
	}
	
	public void run() {
		st.t();
	}
}

class ThreadTest11 extends Thread {
	private SynTestClass st;
	
	public ThreadTest11(SynTestClass st) {
		this.st = st;
	}
	
	public void run() {
		st.tt();
	}
}

class ThreadTest2 extends Thread {
	private SynTestClass2 st;
	
	public ThreadTest2(SynTestClass2 st) {
		this.st = st;
	}
	
	public void run() {
		st.t();
	}
}

class ThreadTest22 extends Thread {
	private SynTestClass2 st;
	
	public ThreadTest22(SynTestClass2 st) {
		this.st = st;
	}
	
	public void run() {
		st.tt();
	}
}

public class SynchronizedTest {

	public static Unsafe getUnsafe() throws Throwable {
		Class<?> unsafeClass = Unsafe.class;
		for (Field f : unsafeClass.getDeclaredFields()) {
			if ("theUnsafe".equals(f.getName())) {
				f.setAccessible(true);
				return (Unsafe) f.get(null);
			}
		}
		throw new IllegalAccessException("no declared field: theUnsafe");
	}
	
	public static void main(String[] args) {
		Thread mainThread = Thread.currentThread();
		
		SynTestClass2 st2 = new SynTestClass2(mainThread);
		
		Thread t = new ThreadTest2(st2);
//		Thread t = new ThreadTest22(st2);
		t.start();
		
		try {
			synchronized(mainThread) {
				mainThread.wait();
			}
		} catch (InterruptedException e) {
			System.out.println("Ok: it's expected, main thread continue to run...");
		}
		
		Unsafe unsafe = null;
		try {
			unsafe = SynchronizedTest.getUnsafe();
		} catch (Throwable e) {
			e.printStackTrace();
		}
		boolean ok = unsafe.tryMonitorEnter(st2);
		if (ok) {
			st2.t();
//			st2.tt();
			unsafe.monitorExit(st2);
		} else {
			System.out.println(Thread.currentThread().getName() + ": fail to enter monitor");
		}
	}
}