問題描述：同一個物件，在多執行緒中進行操作，會出現記憶體可見性問題。

針對這種問題，我們做了一些應對措施

1. 加volatile， 結果發現沒有效果

2. 加lock

修改程式碼如下：

package feedback.common.lock;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
 * 所物件
 * Created by sff on 2018/5/8.
 */
public class FeedBackLock {
    private Lock lock = new ReentrantLock();
    private Condition done = lock.newCondition();
    private volatile AtomicBoolean finished = new AtomicBoolean(false);
    private volatile boolean success;
    private volatile Exception cause;

    public FeedBackLock(){
        success = false;
    }

    public void lock(long timeout) throws InterruptedException{
        lock.lock();
        try{
            if(!finished.get()){
                // 時間一到直接就過去了，不會拋異常的。
                done.await(timeout, TimeUnit.MILLISECONDS);
            }
        } catch (InterruptedException e) {
            throw e;
        } finally {
            lock.unlock();
        }
    }

    public void unLock() {
        lock.lock();
        try{
            this.success = cause == null;
            // 時間一到直接就過去了，不會拋異常的。
            done.signal();
            finished.set(true);
        } finally {
            lock.unlock();
        }
    }

    public boolean isSuccess() {
        lock.lock();
        try {
            return success;
        } finally {
            lock.unlock();
        }
    }

    public Exception getCause() {
        lock.lock();
        try {
            return cause != null ? cause : new TimeoutException("feedback timeout");
        } finally {
            lock.unlock();
        }
    }

    public void setCause(Exception cause) {
        this.cause = cause;
    }
}