Java多線程八

1 Lock與ReadWriteLock

1.1 Lock

<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">interface</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Lock</span> {</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> lock();
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> lockInterruptibly() <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throws</span> InterruptedException;
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> tryLock();
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">boolean</span> tryLock(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span> time, TimeUnit unit) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">throws</span> InterruptedException;
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> unlock();
    Condition newCondition();
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul>

  在Lock中聲明瞭四個方法來獲取鎖，那麼這四個方法有何區別呢？ 
  lock() 
  首先lock()方法是平常使用得最多的一個方法，就是用來獲取鎖。如果鎖已被其他線程獲取，則進行等待。 
  由於在前面講到如果採用Lock，必須主動去釋放鎖，並且在發生異常時，不會自動釋放鎖。因此一般來說，使用Lock必須在try{}catch{}塊中進行，並且將釋放鎖的操作放在finally塊中進行，以保證鎖一定被被釋放，防止死鎖的發生。通常使用Lock來進行同步的形式：

<code class="hljs r has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">Lock lock = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>;
lock.lock();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span>{
    //處理任務
}catch(Exception ex){

}finally{
    lock.unlock();   //釋放鎖
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul>

  tryLock()和tryLock(long time, TimeUnit unit) 
  tryLock()方法是有返回值的，它表示用來嘗試獲取鎖，如果獲取成功，則返回true，如果獲取失敗（即鎖已被其他線程獲取），則返回false，也就說這個方法無論如何都會立即返回。在拿不到鎖時不會一直在那等待。 
  tryLock(long time, TimeUnit unit)方法和tryLock()方法是類似的，只不過區別在於這個方法在拿不到鎖時會等待一定的時間，在時間期限之內如果還拿不到鎖，就返回false。如果如果一開始拿到鎖或者在等待期間內拿到了鎖，則返回true。 
  通過tryLock來獲取鎖的基本形式：

<code class="hljs r has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">Lock lock = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>(lock.tryLock()) {
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span>{
        //處理任務
    } catch(Exception ex){

    } finally {
        lock.unlock();   //釋放鎖
    } 
}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {
    //如果不能獲取鎖，則直接做其他事情
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li></ul>

  lockInterruptibly() 
  lockInterruptibly()方法比較特殊，當通過這個方法去獲取鎖時，如果線程正在等待獲取鎖，則這個線程能夠響應中斷，即中斷線程的等待狀態。也就使說，當兩個線程同時通過lock.lockInterruptibly()想獲取某個鎖時，假若此時線程A獲取到了鎖，而線程B只有在等待，那麼對線程B調用threadB.interrupt()方法能夠中斷線程B的等待過程。 
  由於lockInterruptibly()的聲明中拋出了異常，所以lock.lockInterruptibly()必須放在try塊中或者在調用lockInterruptibly()的方法外聲明拋出InterruptedException。

  lockInterruptibly()一般的使用形式：

<code class="hljs oxygene has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> void <span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">method</span><span class="hljs-params" style="color: rgb(102, 0, 102); box-sizing: border-box;">()</span> <span class="hljs-title" style="box-sizing: border-box;">throws</span> <span class="hljs-title" style="box-sizing: border-box;">InterruptedException</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">{
    lock.lockInterruptibly();
    try {  
     //.....
    }</span>
    <span class="hljs-title" style="box-sizing: border-box;">finally</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">{
        lock.unlock();
    }</span>  
}</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul>

  注意，當一個線程獲取了鎖之後，是不會被interrupt()方法中斷的。 
  因此當通過lockInterruptibly()方法獲取某個鎖時，如果不能獲取到，在進行等待的情況下，是可以響應中斷的。 
  而用synchronized修飾的話，當一個線程處於等待某個鎖的狀態，是無法被中斷的，只有一直等待下去。

1.2 Lock實現類ReentrantLock

  ReentrantLock，意思是“可重入鎖”，關於可重入鎖的概念在下一節講述。下面通過一些實例具體看一下如何使用ReentrantLock。 
  tryLock()

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> TrylockMethodTest {

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">main</span>(String[] args) {
        SharedDataService service = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> SharedDataService();

        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Thread(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Runnable() {

            @Override
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() {
                service.put(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"msg"</span>);
            }
        }).start();

        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Thread(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Runnable() {

            @Override
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() {
                service.put(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Message"</span>);
            }
        }).start();
    }

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> class SharedDataService {
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> List<String> data = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ArrayList<String>();
        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 創建一個非公平的可重入鎖</span>
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> Lock <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">lock</span> = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ReentrantLock();

        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">put</span>(String msg) {
            <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/*
             * Acquires the lock only if it is free at the time of invocation.
             * 返回true說明獲取鎖成功
             */</span>
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">lock</span>.tryLock()) {
                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
                    System.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">out</span>.println(Thread.currentThread().getName()+<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"得到了鎖"</span>);
                    data.add(msg);
                    Thread.sleep(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1000</span>);
                    System.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">out</span>.println(Thread.currentThread().getName()+<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"存入數據"</span>+msg);
                } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (Exception e) {
                    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// TODO: handle exception</span>
                } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">finally</span> {
                    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">lock</span>.unlock();
                    System.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">out</span>.println(Thread.currentThread().getName()+<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"釋放了鎖"</span>);
                }
            } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {
                System.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">out</span>.println(Thread.currentThread().getName()+<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"獲取鎖失敗！"</span>);
            }
        }
    }
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li></ul>

  運行結果：

<code class="hljs mathematica has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">Thread</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>得到了鎖
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">Thread</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>獲取鎖失敗！
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">Thread</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>存入數據msg
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">Thread</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>釋放了鎖</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

  lockInterruptibly()

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> LockInterruptiblyMethodTest {

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">main</span>(String[] args) throws InterruptedException {
        SharedDataService service = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> SharedDataService();

        Thread thread0 = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Thread(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Runnable() {

            @Override
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() {
                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
                    service.put(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"msg"</span>);
                } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (InterruptedException e) {
                    e.printStackTrace();
                    System.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">out</span>.println(Thread.currentThread().getName()+<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"在等待獲取鎖時被中斷！"</span>);
                }
            }
        });
        thread0.start();

        Thread thread1 = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Thread(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Runnable() {

            @Override
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() {
                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
                    service.put(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Message"</span>);
                } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (InterruptedException e) {
                    e.printStackTrace();
                    System.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">out</span>.println(Thread.currentThread().getName()+<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"在等待獲取鎖時被中斷！"</span>);
                }
            }
        });
        thread1.start();

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 主線程中中斷thread1等待獲取鎖的阻塞狀態</span>
        Thread.sleep(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1000</span>);
        thread1.interrupt();
    }

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> class SharedDataService {
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> List<String> data = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ArrayList<String>();
        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 創建一個非公平的可重入鎖</span>
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> Lock <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">lock</span> = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ReentrantLock();

        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">put</span>(String msg) throws InterruptedException {
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">lock</span>.lockInterruptibly();
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
                System.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">out</span>.println(Thread.currentThread().getName()+<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"得到了鎖"</span>);
                data.add(msg);
                Thread.sleep(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4000</span>);
                System.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">out</span>.println(Thread.currentThread().getName()+<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"存入數據"</span>+msg);
            } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (Exception e) {
                <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// TODO: handle exception</span>
            } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">finally</span> {
                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">lock</span>.unlock();
                System.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">out</span>.println(Thread.currentThread().getName()+<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"釋放了鎖"</span>);
            }
        }
    }
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li></ul>

  運行結果： 
  

1.3 ReadWriteLock

<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">interface</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">ReadWriteLock</span> {</span>
    <span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**
     * 返回用於讀操作的鎖
     */</span>
    Lock readLock();

    <span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**
     * 返回用於寫操作的鎖
     */</span>
    Lock writeLock();
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li></ul>

  一個用來獲取讀鎖，一個用來獲取寫鎖。也就是說將文件的讀寫操作分開，分成2個鎖來分配給線程，從而使得多個線程可以同時進行讀操作。下面的ReentrantReadWriteLock實現了ReadWriteLock接口。

1.4 ReadWriteLock的實現類ReentrantReadWriteLock

  下面通過幾個例子來看一下ReentrantReadWriteLock具體用法：（主要看readLock和writeLock） 
  假如有多個線程要同時進行讀操作的話，先看一下synchronized達到的效果：（代碼比較簡單，省略了） 
         
  而採用ReadWriteLock的讀操作鎖如下：

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> ReadLockTest {

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">main</span>(String[] args) {
        SharedDataService service = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> SharedDataService();

        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Thread(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Runnable() {

            @Override
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() {
                service.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">get</span>();
            }
        }).start();

        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Thread(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Runnable() {

            @Override
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() {
                service.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">get</span>();
            }
        }).start();
    }

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> class SharedDataService {
        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 創建一個讀寫鎖</span>
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> ReadWriteLock rwl = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ReentrantReadWriteLock();

        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">get</span>() {
            <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 獲取讀操作的鎖ReadLock</span>
            rwl.readLock().<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">lock</span>();
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
                System.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">out</span>.println(Thread.currentThread().getName()+<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"得到了鎖"</span>);
                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">6</span>; i++) {
                    Thread.sleep(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">500</span>);
                    System.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">out</span>.println(Thread.currentThread().getName()+<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"讀取數據"</span>);
                }
            } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span> (Exception e) {
                <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// TODO: handle exception</span>
            } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">finally</span> {
                rwl.readLock().unlock();<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 釋放ReadLock</span>
                System.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">out</span>.println(Thread.currentThread().getName()+<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"讀操作完畢釋放了鎖"</span>);
            }
        }
    }
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li></ul>

         
  說明採用讀寫鎖，thread0和thread1在同時進行讀操作。這樣就大大提升了讀操作的效率。 
  不過要注意的是：

  1. 如果有一個線程已經佔用了讀鎖，則此時其他線程如果要申請寫鎖，則申請寫鎖的線程會一直等待釋放讀鎖。 
  2. 如果有一個線程已經佔用了寫鎖，則此時其他線程如果申請寫鎖或者讀鎖，則申請的線程會一直等待釋放寫鎖。 
  在性能上來說，如果競爭資源不激烈，Lock和synchronized的性能是差不多的，而當競爭資源非常激烈時（即有大量線程同時競爭），此時Lock的性能要遠遠優於synchronized。所以說，在具體使用時要根據適當情況選擇。

1.5 利用讀寫鎖實現簡單的緩存系統

關於緩存系統： 
  緩存系統一般位於用戶和數據庫中間的一個環節，用戶直接訪問數據庫的時間是遠大於直接訪問內存，所以有了緩存區後用戶訪問數據時，先訪問緩存區，當緩存區有用戶需要的數據時直接拿走，當緩存區沒有這樣的數據，訪問數據庫並把訪問所得的數據放在緩存區，這樣當下一個需要這個數據的用戶就直接訪問內存即可得到。 
  JDK文檔中給出的Demo：

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> CashedDataDemo {

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">main</span>(String[] args) {

        CachedDataService cacheService = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> CachedDataService();
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>; i++) {
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Thread(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Runnable() {
                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">run</span>() {
                    cacheService.processCachedData();
                }
            }).start();
        }

    }

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> class CachedDataService {
        String data;
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">volatile</span> boolean cacheValid = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 緩存是否有效，即是否有數據</span>
        final ReentrantReadWriteLock rwl = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ReentrantReadWriteLock();

        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> processCachedData() {
            rwl.readLock().<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">lock</span>(); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 上讀鎖</span>
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!cacheValid) {
                <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* 在獲取寫鎖之前一定要先釋放讀鎖 */</span>
                rwl.readLock().unlock();
                <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* 其中一個線程獲得寫鎖 */</span>
                rwl.writeLock().<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">lock</span>();
                <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
                    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/*
                     * 注意此處需要再次檢查緩存的狀態，因爲其他的線程可能阻塞在獲取寫鎖的地方，
                     * 當實際寫緩存的線程寫完數據釋放寫鎖時，其他的線程仍然獲取到寫鎖，再此寫數據了。
                     */</span>
                    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!cacheValid) {
                        data = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"get new data!"</span>;
                        System.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">out</span>.println(Thread.currentThread().getName() + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"寫數據到緩存:"</span> + data);
                        Thread.sleep(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2000</span>);
                        cacheValid = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">true</span>; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 設置緩存狀態</span>
                    }
                } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">catch</span>(InterruptedException e) {

                }<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">finally</span> {
                    rwl.writeLock().unlock();
                }
                rwl.readLock().<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">lock</span>();
            }

            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
                System.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">out</span>.println(Thread.currentThread().getName() + <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"從緩存中獲取到數據:"</span> + data);
            } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">finally</span> {
                rwl.readLock().unlock();
            }
        }
    }
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li></ul>

  輸出： 
      

ReentrantReadWriteLocks can be used to improve concurrency in some uses of some kinds of Collections. This is typically worthwhile only when the collections are expected to be large, accessed by more reader threads than writer threads, and entail operations with overhead that outweighs synchronization overhead. For example, here is a class using a TreeMap that is expected to be large and concurrently accessed.

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> class RWDictionary {
   <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> final Map m = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> TreeMap();
   <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> final ReentrantReadWriteLock rwl = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ReentrantReadWriteLock();
   <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> final Lock r = rwl.readLock();
   <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> final Lock w = rwl.writeLock();

   <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> Data <span class="hljs-title" style="box-sizing: border-box;">get</span>(String key) {
     r.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">lock</span>();
     <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> m.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">get</span>(key); }
     <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">finally</span> { r.unlock(); }
   }
   <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> String[] <span class="hljs-title" style="box-sizing: border-box;">allKeys</span>() {
     r.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">lock</span>();
     <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> m.keySet().toArray(); }
     <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">finally</span> { r.unlock(); }
   }
   <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> Data <span class="hljs-title" style="box-sizing: border-box;">put</span>(String key, Data <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">value</span>) {
     w.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">lock</span>();
     <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> { <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> m.put(key, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">value</span>); }
     <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">finally</span> { w.unlock(); }
   }
   <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">clear</span>() {
     w.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">lock</span>();
     <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> { m.clear(); }
     <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">finally</span> { w.unlock(); }
   }
 }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li></ul>

2 Condition

  Condition可以替代傳統的線程間通信，用await()替換wait()，用signal()替換notify()，用signalAll()替換notifyAll()。傳統線程的通信方式，Condition都可以實現。

  注意，Condition是被綁定到Lock上的，要創建一個Lock的Condition必須用newCondition()方法。Condition的強大之處在於它可以爲多個線程間建立不同的Condition。

  看JDK文檔中的一個例子：假定有一個綁定的緩衝區，它支持 put 和 take 方法。如果試圖在空的緩衝區上執行 take 操作，則在某一個項變得可用之前，線程將一直阻塞；如果試圖在滿的緩衝區上執行 put 操作，則在有空間變得可用之前，線程將一直阻塞。我們喜歡在單獨的等待 set 中保存put 線程和take 線程，這樣就可以在緩衝區中的項或空間變得可用時利用最佳規劃，一次只通知一個線程。可以使用兩個Condition 實例來做到這一點。

——其實就是java.util.concurrent.ArrayBlockingQueue的功能

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">class BoundedBuffer {
   final Lock <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">lock</span> = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ReentrantLock();          <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//鎖對象</span>
   final Condition notFull  = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">lock</span>.newCondition(); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//緩衝區未滿，寫數據</span>
   final Condition notEmpty = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">lock</span>.newCondition(); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//緩衝區非空，讀數據</span>

   final Object[] items = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Object[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span>];<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//緩存隊列</span>
   <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> putptr;  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//寫索引</span>
   <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> takeptr; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//讀索引</span>
   <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> count;   <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//隊列中數據數目</span>

   <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//寫</span>
   <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">put</span>(Object x) throws InterruptedException {
     <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">lock</span>.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">lock</span>(); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//鎖定</span>
     <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
       <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 如果隊列滿，則阻塞<寫線程></span>
       <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">while</span> (count == items.length) {
         notFull.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">await</span>(); 
       }
       <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 寫入隊列，並更新寫索引</span>
       items[putptr] = x; 
       <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (++putptr == items.length) putptr = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; 
       ++count;

       <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 喚醒<讀線程></span>
       notEmpty.signal(); 
     } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">finally</span> { 
       <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">lock</span>.unlock();<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//解除鎖定 </span>
     } 
   }

   <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//讀 </span>
   <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> Object <span class="hljs-title" style="box-sizing: border-box;">take</span>() throws InterruptedException { 
     <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">lock</span>.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">lock</span>(); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//鎖定 </span>
     <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">try</span> {
       <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 如果隊列空，則阻塞<讀線程></span>
       <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">while</span> (count == <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) {
          notEmpty.<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">await</span>();
       }

       <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//讀取隊列，並更新讀索引</span>
       Object x = items[takeptr]; 
       <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (++takeptr == items.length) takeptr = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
       --count;

       <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 喚醒<寫線程></span>
       notFull.signal(); 
       <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> x; 
     } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">finally</span> { 
       <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">lock</span>.unlock();<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//解除鎖定 </span>
     } 
   } 
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li></li></ul>