1、synchronized直接修饰普通方法，会把整个实例锁住。如果是new两个实例，则互不干扰。

/**
* synchronized直接修饰普通方法，会把整个实例锁住。如果是new两个实例，则互不干扰。
*/
public class MyObject {

    //synchronized修饰为同步方法,如果先调用method1,则4秒后才会调用method2	
    private synchronized void method1(){
		try {
			System.out.println(Thread.currentThread().getName());
			Thread.sleep(4000);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
	

	//如果不用synchronized修饰,则可以直接异步调用,没有影响
	private void method2(){
		System.out.println(Thread.currentThread().getName());
	}

    public static void main(String[] args) {
		//创建一个对象，t1走完才会走t2.
		MyObject myObject=new MyObject();

        Thread t1=new Thread (new Runnable() {
			@Override
			public void run() {
				myObject.method1();
			}
		},"t1");
		Thread t2=new Thread (new Runnable() {
			@Override
			public void run() {
				myObject.method1();
			}
		},"t2");
		t1.start();
		t2.start();

        //创建两个对象，t3和t1\t2互不干扰。
        MyObject myObject02=new MyObject();
        Thread t3=new Thread (new Runnable() {
			@Override
			public void run() {
				myObject02.method1();
			}
		},"t2");
		t3.start();
	}
}

2、synchronized修饰的代码块传入this也属于对象锁。但能减小锁粒度，只同步代码块。对于对象锁（this），如果是同一个实例，就会锁住、按顺序访问，但是如果是不同实例，就可以同时访问。多例的是锁不住的。

//如下，m1和m2锁的不是一个对象，互不干扰。且只锁代码块。this是当前对象。
class ThisLock2 {
    private final Object LOCK = new Object();
    
    public void m2() {
        synchronized (LOCK) {
            try {
                System.out.println(Thread.currentThread());
                Thread.sleep(10_000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
    
    public void m1() {
        synchronized (this) {
            try {
                System.out.println(Thread.currentThread());
                Thread.sleep(10_000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

3、类锁相关

package my.mark.mybaibaoxiang.concurrent.jmmAndVolatile.lock;

/**
 * @author twotiger-wxm.
 * 验证对象锁和类锁互不干扰，类锁只是一个概念上的东西，并不是真实存在的。
 * 就相当于下方示例中，
 * testClassLock.duixiangLock();和TestClassLock.classLock();
 * 调用的是两个实例。
 * 每个类只有一个类锁，多线程调用同一个类锁是能锁住的。
 */
public class TestClassLock {

    public static synchronized void classLock(){
        int i=0;
        while (i++<500){
            System.out.println("类锁=="+i+Thread.currentThread().getName());
            /*try {
                Thread.sleep(500);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }*/
        }
    }

    public synchronized void duixiangLock(){
        int i=0;
        while (i++<500){
            System.out.println("对象锁=="+i+Thread.currentThread().getName());
            /*try {
                Thread.sleep(500);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }*/
        }
    }

    public static void main(String[] args) {
        TestClassLock testClassLock = new TestClassLock();
        Thread t1 = new Thread(new Runnable() {
            @Override
            public void run() {
                testClassLock.duixiangLock();
                //TestClassLock.classLock();//TODO 如果两个线程都用类锁，是能锁住的，执行完一个才会执行另一个。
            }
        },"t-duixiang");

        Thread t2 = new Thread(new Runnable() {
            @Override
            public void run() {
                TestClassLock.classLock();
            }
        },"t-class");
        t1.start();
        t2.start();
    }
}

package my.mark.mybaibaoxiang.concurrent.jmmAndVolatile.lock;

/**
 * @author twotiger-wxm.
 * 逃逸分析验证
 */
public class StackAllocTest {

    /**
     * 进行两种测试
     * 关闭逃逸分析，同时调大堆空间，避免堆内GC的发生，如果有GC信息将会被打印出来
     * VM运行参数：-Xmx4G -Xms4G -XX:-DoEscapeAnalysis -XX:+PrintGCDetails -XX:+HeapDumpOnOutOfMemoryError
     *
     * 开启逃逸分析
     * VM运行参数：-Xmx4G -Xms4G -XX:+DoEscapeAnalysis -XX:+PrintGCDetails -XX:+HeapDumpOnOutOfMemoryError
     *
     * 执行main方法后
     * jps 查看进程
     * jmap -histo 进程ID
     * 关闭逃逸分析的，显示有50万个实例。开启逃逸分析的只有八万多个。即开启逃逸分析很多对象没放堆。
     */

    public static void main(String[] args) {
        long start = System.currentTimeMillis();
        for (int i = 0; i < 500000; i++) {
            alloc();
        }
        long end = System.currentTimeMillis();
        //查看执行时间
        System.out.println("cost-time " + (end - start) + " ms");
        try {
            Thread.sleep(100000);
        } catch (InterruptedException e1) {
            e1.printStackTrace();
        }
    }


    private static TulingStudent alloc() {
        //Jit（即时编译just-in-time）编译时会对代码进行 逃逸分析
        //并不是所有对象存放在堆区，有的一部分存在线程栈空间
        TulingStudent student = new TulingStudent();
        return student;
    }

    static class TulingStudent {
        private String name;
        private int age;
    }
}

package my.mark.mybaibaoxiang.concurrent.jmmAndVolatile.lock.aqs;
/*
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

/*
 *
 *
 *
 *
 *
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

import java.util.Collection;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;

/**
 * A reentrant mutual exclusion {@link Lock} with the same basic
 * behavior and semantics as the implicit monitor lock accessed using
 * {@code synchronized} methods and statements, but with extended
 * capabilities.
 *
 * <p>A {@code ReentrantLock} is <em>owned</em> by the thread last
 * successfully locking, but not yet unlocking it. A thread invoking
 * {@code lock} will return, successfully acquiring the lock, when
 * the lock is not owned by another thread. The method will return
 * immediately if the current thread already owns the lock. This can
 * be checked using methods {@link #isHeldByCurrentThread}, and {@link
 * #getHoldCount}.
 *
 * <p>The constructor for this class accepts an optional
 * <em>fairness</em> parameter.  When set {@code true}, under
 * contention, locks favor granting access to the longest-waiting
 * thread.  Otherwise this lock does not guarantee any particular
 * access order.  Programs using fair locks accessed by many threads
 * may display lower overall throughput (i.e., are slower; often much
 * slower) than those using the default setting, but have smaller
 * variances in times to obtain locks and guarantee lack of
 * starvation. Note however, that fairness of locks does not guarantee
 * fairness of thread scheduling. Thus, one of many threads using a
 * fair lock may obtain it multiple times in succession while other
 * active threads are not progressing and not currently holding the
 * lock.
 * Also note that the untimed {@link #tryLock()} method does not
 * honor the fairness setting. It will succeed if the lock
 * is available even if other threads are waiting.
 *
 * <p>It is recommended practice to <em>always</em> immediately
 * follow a call to {@code lock} with a {@code try} block, most
 * typically in a before/after construction such as:
 *
 *  <pre> {@code
 * class X {
 *   private final ReentrantLock lock = new ReentrantLock();
 *   // ...
 *
 *   public void m() {
 *     lock.lock();  // block until condition holds
 *     try {
 *       // ... method body
 *     } finally {
 *       lock.unlock()
 *     }
 *   }
 * }}</pre>
 *
 * <p>In addition to implementing the {@link Lock} interface, this
 * class defines a number of {@code public} and {@code protected}
 * methods for inspecting the state of the lock.  Some of these
 * methods are only useful for instrumentation and monitoring.
 *
 * <p>Serialization of this class behaves in the same way as built-in
 * locks: a deserialized lock is in the unlocked state, regardless of
 * its state when serialized.
 *
 * <p>This lock supports a maximum of 2147483647 recursive locks by
 * the same thread. Attempts to exceed this limit result in
 * {@link Error} throws from locking methods.
 *
 * @since 1.5
 * @author Doug Lea
 * 悲观锁
 */
public class ReentrantLock implements Lock, java.io.Serializable {
    private static final long serialVersionUID = 7373984872572414699L;
    /**
     * 内部调用AQS的动作，都基于该成员属性实现
     */
    private final Sync sync;

    /**
     * ReentrantLock锁同步操作的基础类,继承自AQS框架.
     * 该类有两个继承类，1、NonfairSync 非公平锁，2、FairSync公平锁
     */
        abstract static class Sync extends AbstractQueuedSynchronizer {
        private static final long serialVersionUID = -5179523762034025860L;

        /**
         * 加锁的具体行为由子类实现
         */
        abstract void lock();

        /**
         * 尝试获取非公平锁
         */
        final boolean nonfairTryAcquire(int acquires) {
            //acquires = 1
            final Thread current = Thread.currentThread();
            int c = getState();
            /**
             * 不需要判断同步队列（CLH）中是否有排队等待线程
             * 判断state状态是否为0，不为0可以加锁
             */
            if (c == 0) {
                //unsafe操作，cas修改state状态
                if (compareAndSetState(0, acquires)) {
                    //独占状态锁持有者指向当前线程
                    setExclusiveOwnerThread(current);
                    return true;
                }
            }
            /**
             * state状态不为0，判断锁持有者是否是当前线程，
             * 如果是当前线程持有 则state+1
             */
            else if (current == getExclusiveOwnerThread()) {
                int nextc = c + acquires;
                if (nextc < 0) // overflow
                    throw new Error("Maximum lock count exceeded");
                setState(nextc);
                return true;
            }
            //加锁失败
            return false;
        }

        /**
         * 释放锁
         */
        protected final boolean tryRelease(int releases) {
            int c = getState() - releases;
            if (Thread.currentThread() != getExclusiveOwnerThread())
                throw new IllegalMonitorStateException();
            boolean free = false;
            if (c == 0) {
                free = true;
                setExclusiveOwnerThread(null);
            }
            setState(c);
            return free;
        }

        /**
         * 判断持有独占锁的线程是否是当前线程
         */
        protected final boolean isHeldExclusively() {
            return getExclusiveOwnerThread() == Thread.currentThread();
        }

        //返回条件对象
        final ConditionObject newCondition() {
            return new ConditionObject();
        }


        final Thread getOwner() {
            return getState() == 0 ? null : getExclusiveOwnerThread();
        }

        final int getHoldCount() {
            return isHeldExclusively() ? getState() : 0;
        }

        final boolean isLocked() {
            return getState() != 0;
        }

        /**
         * Reconstitutes the instance from a stream (that is, deserializes it).
         */
        private void readObject(java.io.ObjectInputStream s)
                throws java.io.IOException, ClassNotFoundException {
            s.defaultReadObject();
            setState(0); // reset to unlocked state
        }
    }

    /**
     * 非公平锁
     */
    static final class NonfairSync extends Sync {
        private static final long serialVersionUID = 7316153563782823691L;
        /**
         * 加锁行为
         */
        final void lock() {
            /**
             * 第一步：直接尝试加锁
             * 与公平锁实现的加锁行为一个最大的区别在于，此处不会去判断同步队列(CLH队列)中
             * 是否有排队等待加锁的节点，上来直接加锁（判断state是否为0,CAS修改state为1）
             * ，并将独占锁持有者 exclusiveOwnerThread 属性指向当前线程
             * 如果当前有人占用锁，再尝试去加一次锁
             */
            if (compareAndSetState(0, 1))
                setExclusiveOwnerThread(Thread.currentThread());
            else
                //AQS定义的方法,加锁
                acquire(1);
        }

        /**
         * 父类AbstractQueuedSynchronizer.acquire()中调用本方法
         */
        protected final boolean tryAcquire(int acquires) {
            return nonfairTryAcquire(acquires);
        }
    }

    /**
     * 公平锁
     */
    static final class FairSync extends Sync {
        private static final long serialVersionUID = -3000897897090466540L;

        final void lock() {
            acquire(1);
        }

        /**
         * 重写aqs中的方法逻辑
         * 尝试加锁，被AQS的acquire()方法调用
         */
        protected final boolean tryAcquire(int acquires) {
            final Thread current = Thread.currentThread();
            int c = getState();
            if (c == 0) {
                /**
                 * 与非公平锁中的区别，需要先判断队列当中是否有等待的节点
                 * 如果没有则可以尝试CAS获取锁
                 */
                if (!hasQueuedPredecessors() &&
                        compareAndSetState(0, acquires)) {
                    //独占线程指向当前线程
                    setExclusiveOwnerThread(current);
                    return true;
                }
            }
            else if (current == getExclusiveOwnerThread()) {
                int nextc = c + acquires;
                if (nextc < 0)
                    throw new Error("Maximum lock count exceeded");
                setState(nextc);
                return true;
            }
            return false;
        }
    }

    /**
     * 默认构造函数，创建非公平锁对象
     */
    public ReentrantLock() {
        sync = new NonfairSync();
    }

    /**
     * 根据要求创建公平锁或非公平锁
     */
    public ReentrantLock(boolean fair) {
        sync = fair ? new FairSync() : new NonfairSync();
    }

    /**
     * 加锁
     */
    public void lock() {
        sync.lock();
    }

    /**
     * 尝试获去取锁，获取失败被阻塞，线程被中断直接抛出异常
     */
    public void lockInterruptibly() throws InterruptedException {
        sync.acquireInterruptibly(1);
    }

    /**
     * 尝试加锁
     */
    public boolean tryLock() {
        return sync.nonfairTryAcquire(1);
    }

    /**
     * 指定等待时间内尝试加锁
     */
    public boolean tryLock(long timeout, TimeUnit unit)
            throws InterruptedException {
        return sync.tryAcquireNanos(1, unit.toNanos(timeout));
    }

    /**
     * 尝试去释放锁
     */
    public void unlock() {
        sync.release(1);
    }

    /**
     * 返回条件对象
     */
    public Condition newCondition() {
        return sync.newCondition();
    }

    /**
     * 返回当前线程持有的state状态数量
     */
    public int getHoldCount() {
        return sync.getHoldCount();
    }

    /**
     * 查询当前线程是否持有锁
     */
    public boolean isHeldByCurrentThread() {
        return sync.isHeldExclusively();
    }

    /**
     * 状态表示是否被Thread加锁持有
     */
    public boolean isLocked() {
        return sync.isLocked();
    }

    /**
     * 是否公平锁？是返回true 否则返回 false
     */
    public final boolean isFair() {
        return sync instanceof FairSync;
    }

    /**
     * Returns the thread that currently owns this lock, or
     * {@code null} if not owned. When this method is called by a
     * thread that is not the owner, the return value reflects a
     * best-effort approximation of current lock status. For example,
     * the owner may be momentarily {@code null} even if there are
     * threads trying to acquire the lock but have not yet done so.
     * This method is designed to facilitate construction of
     * subclasses that provide more extensive lock monitoring
     * facilities.
     *
     * @return the owner, or {@code null} if not owned
     */
    protected Thread getOwner() {
        return sync.getOwner();
    }

    /**
     * 判断队列当中是否有在等待获取锁的Thread节点
     */
    public final boolean hasQueuedThreads() {
        return sync.hasQueuedThreads();
    }

    /**
     * 当前线程是否在同步队列中等待
     */
    public final boolean hasQueuedThread(Thread thread) {
        return sync.isQueued(thread);
    }

    /**
     * Returns an estimate of the number of threads waiting to
     * acquire this lock.  The value is only an estimate because the number of
     * threads may change dynamically while this method traverses
     * internal data structures.  This method is designed for use in
     * monitoring of the system state, not for synchronization
     * control.
     *
     * @return the estimated number of threads waiting for this lock
     */
    public final int getQueueLength() {
        return sync.getQueueLength();
    }

    /**
     * 返回Thread集合，排队中的所有节点Thread会被返回
     */
    protected Collection<Thread> getQueuedThreads() {
        return sync.getQueuedThreads();
    }

    /**
     * 条件队列当中是否有正在等待的节点
     */
    public boolean hasWaiters(Condition condition) {
        if (condition == null)
            throw new NullPointerException();
        if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
            throw new IllegalArgumentException("not owner");
        return sync.hasWaiters((AbstractQueuedSynchronizer.ConditionObject)condition);
    }

    /**
     * Returns an estimate of the number of threads waiting on the
     * given condition associated with this lock. Note that because
     * timeouts and interrupts may occur at any time, the estimate
     * serves only as an upper bound on the actual number of waiters.
     * This method is designed for use in monitoring of the system
     * state, not for synchronization control.
     *
     * @param condition the condition
     * @return the estimated number of waiting threads
     * @throws IllegalMonitorStateException if this lock is not held
     * @throws IllegalArgumentException if the given condition is
     *         not associated with this lock
     * @throws NullPointerException if the condition is null
     */
    public int getWaitQueueLength(Condition condition) {
        if (condition == null)
            throw new NullPointerException();
        if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
            throw new IllegalArgumentException("not owner");
        return sync.getWaitQueueLength((AbstractQueuedSynchronizer.ConditionObject)condition);
    }

    /**
     * Returns a collection containing those threads that may be
     * waiting on the given condition associated with this lock.
     * Because the actual set of threads may change dynamically while
     * constructing this result, the returned collection is only a
     * best-effort estimate. The elements of the returned collection
     * are in no particular order.  This method is designed to
     * facilitate construction of subclasses that provide more
     * extensive condition monitoring facilities.
     *
     * @param condition the condition
     * @return the collection of threads
     * @throws IllegalMonitorStateException if this lock is not held
     * @throws IllegalArgumentException if the given condition is
     *         not associated with this lock
     * @throws NullPointerException if the condition is null
     */
    protected Collection<Thread> getWaitingThreads(Condition condition) {
        if (condition == null)
            throw new NullPointerException();
        if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
            throw new IllegalArgumentException("not owner");
        return sync.getWaitingThreads((AbstractQueuedSynchronizer.ConditionObject)condition);
    }

    /**
     * Returns a string identifying this lock, as well as its lock state.
     * The state, in brackets, includes either the String {@code "Unlocked"}
     * or the String {@code "Locked by"} followed by the
     * {@linkplain Thread#getName name} of the owning thread.
     *
     * @return a string identifying this lock, as well as its lock state
     */
    public String toString() {
        Thread o = sync.getOwner();
        return super.toString() + ((o == null) ?
                "[Unlocked]" :
                "[Locked by thread " + o.getName() + "]");
    }
}