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<div class="section" id="tt">
<span id="tt"></span><h1>tt<a class="headerlink" href="#tt" title="永久链接至标题"></a></h1>
<blockquote>
<div>方法执行数据的时空隧道,记录下指定方法每次调用的入参和返回信息,并能对这些不同的时间下调用进行观测</div></blockquote>
<p><code class="docutils literal notranslate"><span class="pre">watch</span></code> 虽然很方便和灵活,但需要提前想清楚观察表达式的拼写,这对排查问题而言要求太高,因为很多时候我们并不清楚问题出自于何方,只能靠蛛丝马迹进行猜测。</p>
<p>这个时候如果能记录下当时方法调用的所有入参和返回值、抛出的异常会对整个问题的思考与判断非常有帮助。</p>
<p>于是乎TimeTunnel 命令就诞生了。</p>
<div class="section" id="">
<span id="id1"></span><h2>记录方法的调用<a class="headerlink" href="#" title="永久链接至标题"></a></h2>
<ul>
<li><p class="first">基本用法</p>
<p>对于一个最基本的使用来说,就是记录下当前方法的每次调用环境现场。</p>
<div class="highlight-java notranslate"><div class="highlight"><pre><span></span><span class="n">$</span> <span class="n">tt</span> <span class="o">-</span><span class="n">t</span> <span class="o">-</span><span class="n">n</span> <span class="mi">3</span> <span class="o">*</span><span class="n">Test</span> <span class="n">print</span>
<span class="n">Press</span> <span class="n">Ctrl</span><span class="o">+</span><span class="n">D</span> <span class="n">or</span> <span class="n">Ctrl</span><span class="o">+</span><span class="n">X</span> <span class="n">to</span> <span class="n">abort</span><span class="o">.</span>
<span class="nf">Affect</span><span class="o">(</span><span class="n">class</span><span class="o">-</span><span class="n">cnt</span><span class="o">:</span><span class="mi">1</span> <span class="o">,</span> <span class="n">method</span><span class="o">-</span><span class="n">cnt</span><span class="o">:</span><span class="mi">1</span><span class="o">)</span> <span class="n">cost</span> <span class="n">in</span> <span class="mi">115</span> <span class="n">ms</span><span class="o">.</span>
<span class="o">+----------+----------------------+------------+----------+----------+-----------------+--------------------------------+--------------------------------+</span>
<span class="o">|</span> <span class="n">INDEX</span> <span class="o">|</span> <span class="n">TIMESTAMP</span> <span class="o">|</span> <span class="n">COST</span><span class="o">(</span><span class="n">ms</span><span class="o">)</span> <span class="o">|</span> <span class="n">IS</span><span class="o">-</span><span class="n">RET</span> <span class="o">|</span> <span class="n">IS</span><span class="o">-</span><span class="n">EXP</span> <span class="o">|</span> <span class="n">OBJECT</span> <span class="o">|</span> <span class="n">CLASS</span> <span class="o">|</span> <span class="n">METHOD</span> <span class="o">|</span>
<span class="o">+----------+----------------------+------------+----------+----------+-----------------+--------------------------------+--------------------------------+</span>
<span class="o">|</span> <span class="mi">1007</span> <span class="o">|</span> <span class="mi">2015</span><span class="o">-</span><span class="mo">07</span><span class="o">-</span><span class="mi">26</span> <span class="mi">12</span><span class="o">:</span><span class="mi">23</span><span class="o">:</span><span class="mi">21</span> <span class="o">|</span> <span class="mi">138</span> <span class="o">|</span> <span class="kc">true</span> <span class="o">|</span> <span class="kc">false</span> <span class="o">|</span> <span class="mh">0x42cc13a0</span> <span class="o">|</span> <span class="n">GaOgnlUtilsTest</span> <span class="o">|</span> <span class="n">print</span> <span class="o">|</span>
<span class="o">+----------+----------------------+------------+----------+----------+-----------------+--------------------------------+--------------------------------+</span>
<span class="o">|</span> <span class="mi">1008</span> <span class="o">|</span> <span class="mi">2015</span><span class="o">-</span><span class="mo">07</span><span class="o">-</span><span class="mi">26</span> <span class="mi">12</span><span class="o">:</span><span class="mi">23</span><span class="o">:</span><span class="mi">22</span> <span class="o">|</span> <span class="mi">143</span> <span class="o">|</span> <span class="kc">true</span> <span class="o">|</span> <span class="kc">false</span> <span class="o">|</span> <span class="mh">0x42cc13a0</span> <span class="o">|</span> <span class="n">GaOgnlUtilsTest</span> <span class="o">|</span> <span class="n">print</span> <span class="o">|</span>
<span class="o">+----------+----------------------+------------+----------+----------+-----------------+--------------------------------+--------------------------------+</span>
<span class="o">|</span> <span class="mi">1009</span> <span class="o">|</span> <span class="mi">2015</span><span class="o">-</span><span class="mo">07</span><span class="o">-</span><span class="mi">26</span> <span class="mi">12</span><span class="o">:</span><span class="mi">23</span><span class="o">:</span><span class="mi">23</span> <span class="o">|</span> <span class="mi">130</span> <span class="o">|</span> <span class="kc">true</span> <span class="o">|</span> <span class="kc">false</span> <span class="o">|</span> <span class="mh">0x42cc13a0</span> <span class="o">|</span> <span class="n">GaOgnlUtilsTest</span> <span class="o">|</span> <span class="n">print</span> <span class="o">|</span>
<span class="o">+----------+----------------------+------------+----------+----------+-----------------+--------------------------------+--------------------------------+</span>
<span class="n">$</span>
</pre></div>
</div>
</li>
<li><p class="first">命令参数解析</p>
<ul>
<li><p class="first"><code class="docutils literal notranslate"><span class="pre">-t</span></code></p>
<p>tt 命令有很多个主参数,<code class="docutils literal notranslate"><span class="pre">-t</span></code> 就是其中之一。这个参数的表明希望记录下类 <code class="docutils literal notranslate"><span class="pre">*Test</span></code><code class="docutils literal notranslate"><span class="pre">print</span></code> 方法的每次执行情况。</p>
</li>
<li><p class="first"><code class="docutils literal notranslate"><span class="pre">-n</span> <span class="pre">3</span></code></p>
<p>当你执行一个调用量不高的方法时可能你还能有足够的时间用 <code class="docutils literal notranslate"><span class="pre">CTRL+C</span></code> 中断 tt 命令记录的过程,但如果遇到调用量非常大的方法,瞬间就能将你的 JVM 内存撑爆。</p>
<p>此时你可以通过 <code class="docutils literal notranslate"><span class="pre">-n</span></code> 参数指定你需要记录的次数,当达到记录次数时 Arthas 会主动中断tt命令的记录过程避免人工操作无法停止的情况。</p>
</li>
</ul>
</li>
<li><p class="first">表格字段说明</p>
</li>
</ul>
<table border="1" class="docutils">
<thead>
<tr>
<th>表格字段</th>
<th>字段解释</th>
</tr>
</thead>
<tbody>
<tr>
<td>INDEX</td>
<td>时间片段记录编号每一个编号代表着一次调用后续tt还有很多命令都是基于此编号指定记录操作非常重要。</td>
</tr>
<tr>
<td>TIMESTAMP</td>
<td>方法执行的本机时间,记录了这个时间片段所发生的本机时间</td>
</tr>
<tr>
<td>COST(ms)</td>
<td>方法执行的耗时</td>
</tr>
<tr>
<td>IS-RET</td>
<td>方法是否以正常返回的形式结束</td>
</tr>
<tr>
<td>IS-EXP</td>
<td>方法是否以抛异常的形式结束</td>
</tr>
<tr>
<td>OBJECT</td>
<td>执行对象的<code>hashCode()</code>注意曾经有人误认为是对象在JVM中的无力内存地址但很遗憾他不是。但他能帮助你简单的标记当前执行方法的类实体</td>
</tr>
<tr>
<td>CLASS</td>
<td>执行的类名</td>
</tr>
<tr>
<td>METHOD</td>
<td>执行的方法名</td>
</tr>
</tbody>
</table><ul>
<li><p class="first">条件表达式</p>
<p>不知道大家是否有在使用过程中遇到以下困惑</p>
<ul class="simple">
<li>Arthas 似乎很难区分出重载的方法</li>
<li>我只需要观察特定参数,但是 tt 却全部都给我记录了下来</li>
</ul>
<p>条件表达式也是用 <code class="docutils literal notranslate"><span class="pre">OGNL</span></code> 来编写,核心的判断对象依然是 <code class="docutils literal notranslate"><span class="pre">Advice</span></code> 对象。除了 <code class="docutils literal notranslate"><span class="pre">tt</span></code> 命令之外,<code class="docutils literal notranslate"><span class="pre">watch</span></code><code class="docutils literal notranslate"><span class="pre">trace</span></code><code class="docutils literal notranslate"><span class="pre">stack</span></code> 命令也都支持条件表达式。</p>
</li>
<li><p class="first">解决方法重载</p>
<p><code class="docutils literal notranslate"><span class="pre">tt</span> <span class="pre">-t</span> <span class="pre">*Test</span> <span class="pre">print</span> <span class="pre">params[0].length==1</span></code></p>
<p>通过制定参数个数的形式解决不同的方法签名,如果参数个数一样,你还可以这样写</p>
<p><code class="docutils literal notranslate"><span class="pre">tt</span> <span class="pre">-t</span> <span class="pre">*Test</span> <span class="pre">print</span> <span class="pre">'params[1]</span> <span class="pre">instanceof</span> <span class="pre">Integer'</span></code></p>
</li>
<li><p class="first">解决指定参数</p>
<p><code class="docutils literal notranslate"><span class="pre">tt</span> <span class="pre">-t</span> <span class="pre">*Test</span> <span class="pre">print</span> <span class="pre">params[0].mobile==&quot;13989838402&quot;</span></code></p>
</li>
<li><p class="first">构成条件表达式的 <code class="docutils literal notranslate"><span class="pre">Advice</span></code> 对象</p>
<p>前边看到了很多条件表达式中,都适用了 <code class="docutils literal notranslate"><span class="pre">params[0]</span></code>,有关这个变量的介绍,请参考<a class="reference internal" href="advice-class.html"><span class="doc">表达式核心变量</span></a></p>
</li>
</ul>
</div>
<div class="section" id="">
<span id="id2"></span><h2>检索调用记录<a class="headerlink" href="#" title="永久链接至标题"></a></h2>
<p>当你用 <code class="docutils literal notranslate"><span class="pre">tt</span></code> 记录了一大片的时间片段之后,你希望能从中筛选出自己需要的时间片段,这个时候你就需要对现有记录进行检索。</p>
<p>假设我们有这些记录</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>$ tt -l
+----------+----------------------+------------+----------+----------+-----------------+--------------------------------+--------------------------------+
| INDEX | TIMESTAMP | COST(ms) | IS-RET | IS-EXP | OBJECT | CLASS | METHOD |
+----------+----------------------+------------+----------+----------+-----------------+--------------------------------+--------------------------------+
| 1000 | 2015-07-26 01:16:27 | 130 | true | false | 0x42cc13a0 | GaOgnlUtilsTest | print |
+----------+----------------------+------------+----------+----------+-----------------+--------------------------------+--------------------------------+
| 1001 | 2015-07-26 01:16:27 | 0 | false | true | 0x42cc13a0 | GaOgnlUtilsTest | printAddress |
+----------+----------------------+------------+----------+----------+-----------------+--------------------------------+--------------------------------+
| 1002 | 2015-07-26 01:16:28 | 119 | true | false | 0x42cc13a0 | GaOgnlUtilsTest | print |
+----------+----------------------+------------+----------+----------+-----------------+--------------------------------+--------------------------------+
| 1003 | 2015-07-26 01:16:28 | 0 | false | true | 0x42cc13a0 | GaOgnlUtilsTest | printAddress |
+----------+----------------------+------------+----------+----------+-----------------+--------------------------------+--------------------------------+
| 1004 | 2015-07-26 12:21:56 | 130 | true | false | 0x42cc13a0 | GaOgnlUtilsTest | print |
+----------+----------------------+------------+----------+----------+-----------------+--------------------------------+--------------------------------+
| 1005 | 2015-07-26 12:21:57 | 138 | true | false | 0x42cc13a0 | GaOgnlUtilsTest | print |
+----------+----------------------+------------+----------+----------+-----------------+--------------------------------+--------------------------------+
| 1006 | 2015-07-26 12:21:58 | 130 | true | false | 0x42cc13a0 | GaOgnlUtilsTest | print |
+----------+----------------------+------------+----------+----------+-----------------+--------------------------------+--------------------------------+
Affect(row-cnt:7) cost in 2 ms.
$
</pre></div>
</div>
<p>我需要筛选出 <code class="docutils literal notranslate"><span class="pre">printAddress</span></code> 方法的调用信息</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>$ tt -s method.name==&quot;printAddress&quot;
+----------+----------------------+------------+----------+----------+-----------------+--------------------------------+--------------------------------+
| INDEX | TIMESTAMP | COST(ms) | IS-RET | IS-EXP | OBJECT | CLASS | METHOD |
+----------+----------------------+------------+----------+----------+-----------------+--------------------------------+--------------------------------+
| 1001 | 2015-07-26 01:16:27 | 0 | false | true | 0x42cc13a0 | GaOgnlUtilsTest | printAddress |
+----------+----------------------+------------+----------+----------+-----------------+--------------------------------+--------------------------------+
| 1003 | 2015-07-26 01:16:28 | 0 | false | true | 0x42cc13a0 | GaOgnlUtilsTest | printAddress |
+----------+----------------------+------------+----------+----------+-----------------+--------------------------------+--------------------------------+
Affect(row-cnt:2) cost in 55 ms.
$
</pre></div>
</div>
<p>你需要一个 <code class="docutils literal notranslate"><span class="pre">-s</span></code> 参数。<span style="color:red;">同样的,搜索表达式的核心对象依旧是 <code class="docutils literal notranslate"><span class="pre">Advice</span></code> 对象。</span></p>
</div>
<div class="section" id="">
<span id="id3"></span><h2>查看调用信息<a class="headerlink" href="#" title="永久链接至标题"></a></h2>
<p>对于具体一个时间片的信息而言,你可以通过 <code class="docutils literal notranslate"><span class="pre">-i</span></code> 参数后边跟着对应的 <code class="docutils literal notranslate"><span class="pre">INDEX</span></code> 编号查看到他的详细信息。</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>$
$ tt -i 1003
+-----------------+------------------------------------------------------------------------------------------------------+
| INDEX | 1003 |
+-----------------+------------------------------------------------------------------------------------------------------+
| GMT-CREATE | 2015-07-26 01:16:28 |
+-----------------+------------------------------------------------------------------------------------------------------+
| COST(ms) | 0 |
+-----------------+------------------------------------------------------------------------------------------------------+
| OBJECT | 0x42cc13a0 |
+-----------------+------------------------------------------------------------------------------------------------------+
| CLASS | GaOgnlUtilsTest |
+-----------------+------------------------------------------------------------------------------------------------------+
| METHOD | printAddress |
+-----------------+------------------------------------------------------------------------------------------------------+
| IS-RETURN | false |
+-----------------+------------------------------------------------------------------------------------------------------+
| IS-EXCEPTION | true |
+-----------------+------------------------------------------------------------------------------------------------------+
| PARAMETERS[0] | Address@53448f87 |
+-----------------+------------------------------------------------------------------------------------------------------+
| THROW-EXCEPTION | java.lang.RuntimeException: test |
| | at GaOgnlUtilsTest.printAddress(Unknown Source) |
| | at GaOgnlUtilsTest.&lt;init&gt;(Unknown Source) |
| | at GaOgnlUtilsTest.main(Unknown Source) |
+-----------------+------------------------------------------------------------------------------------------------------+
Affect(row-cnt:1) cost in 1 ms.
$
</pre></div>
</div>
</div>
<div class="section" id="">
<span id="id4"></span><h2>重做一次调用<a class="headerlink" href="#" title="永久链接至标题"></a></h2>
<p>当你稍稍做了一些调整之后,你可能需要前端系统重新触发一次你的调用,此时得求爷爷告奶奶的需要前端配合联调的同学再次发起一次调用。而有些场景下,这个调用不是这么好触发的。</p>
<p><code class="docutils literal notranslate"><span class="pre">tt</span></code> 命令由于保存了当时调用的所有现场信息,所以我们可以自己主动对一个 <code class="docutils literal notranslate"><span class="pre">INDEX</span></code> 编号的时间片自主发起一次调用,从而解放你的沟通成本。此时你需要 <code class="docutils literal notranslate"><span class="pre">-p</span></code> 参数。</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>$ tt -i 1003 -p
+-----------------+---------------------------------------------------------------------------------------------------------+
| RE-INDEX | 1003 |
+-----------------+---------------------------------------------------------------------------------------------------------+
| GMT-REPLAY | 2015-07-26 17:29:51 |
+-----------------+---------------------------------------------------------------------------------------------------------+
| OBJECT | 0x42cc13a0 |
+-----------------+---------------------------------------------------------------------------------------------------------+
| CLASS | GaOgnlUtilsTest |
+-----------------+---------------------------------------------------------------------------------------------------------+
| METHOD | printAddress |
+-----------------+---------------------------------------------------------------------------------------------------------+
| PARAMETERS[0] | Address@53448f87 |
+-----------------+---------------------------------------------------------------------------------------------------------+
| IS-RETURN | false |
+-----------------+---------------------------------------------------------------------------------------------------------+
| IS-EXCEPTION | true |
+-----------------+---------------------------------------------------------------------------------------------------------+
| THROW-EXCEPTION | java.lang.RuntimeException: test |
| | at GaOgnlUtilsTest.printAddress(GaOgnlUtilsTest.java:78) |
| | at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) |
| | at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) |
| | at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) |
| | at java.lang.reflect.Method.invoke(Method.java:483) |
| | at com.github.ompc.Arthas.util.GaMethod.invoke(GaMethod.java:81) |
| | at com.github.ompc.Arthas.command.TimeTunnelCommand$6.action(TimeTunnelCommand.java:592) |
| | at com.github.ompc.Arthas.server.DefaultCommandHandler.execute(DefaultCommandHandler.java:175) |
| | at com.github.ompc.Arthas.server.DefaultCommandHandler.executeCommand(DefaultCommandHandler.java:83) |
| | at com.github.ompc.Arthas.server.GaServer$4.run(GaServer.java:329) |
| | at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) |
| | at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) |
| | at java.lang.Thread.run(Thread.java:745) |
+-----------------+---------------------------------------------------------------------------------------------------------+
replay time fragment[1003] success.
Affect(row-cnt:1) cost in 3 ms.
$
</pre></div>
</div>
<p>你会发现结果虽然一样,但调用的路径发生了变化,有原来的程序发起变成了 Arthas 自己的内部线程发起的调用了。</p>
<ul>
<li><p class="first">需要强调的点</p>
<ol>
<li><p class="first"><strong>ThreadLocal 信息丢失</strong></p>
<p>很多框架偷偷的将一些环境变量信息塞到了发起调用线程的 ThreadLocal 中,由于调用线程发生了变化,这些 ThreadLocal 线程信息无法通过 Arthas 保存,所以这些信息将会丢失。</p>
<p>一些常见的 CASE 比如:鹰眼的 TraceId 等。</p>
</li>
<li><p class="first"><strong>引用的对象</strong></p>
<p>需要强调的是,<code class="docutils literal notranslate"><span class="pre">tt</span></code> 命令是将当前环境的对象引用保存起来,但仅仅也只能保存一个引用而已。如果方法内部对入参进行了变更,或者返回的对象经过了后续的处理,那么在 <code class="docutils literal notranslate"><span class="pre">tt</span></code> 查看的时候将无法看到当时最准确的值。这也是为什么 <code class="docutils literal notranslate"><span class="pre">watch</span></code> 命令存在的意义。</p>
</li>
</ol>
</li>
</ul>
</div>
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