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<li class="toctree-l4"><a class="reference internal" href="#id3">观察函数调用入口的参数和返回值</a></li>
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<li class="toctree-l4"><a class="reference internal" href="#x">调整<code class="docutils literal notranslate"><span class="pre">-x</span></code>的值，观察具体的函数参数值</a></li>
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<li>watch</li>
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<div class="section" id="watch">
<h1>watch<a class="headerlink" href="#watch" title="永久链接至标题"></a></h1>
<p><a class="reference external" href="https://arthas.aliyun.com/doc/arthas-tutorials.html?language=cn&amp;id=command-watch"><code class="docutils literal notranslate"><span class="pre">watch</span></code>在线教程</a></p>
<blockquote>
<div><p>函数执行数据观测</p>
</div></blockquote>
<p>让你能方便的观察到指定函数的调用情况。能观察到的范围为：<code class="docutils literal notranslate"><span class="pre">返回值</span></code>、<code class="docutils literal notranslate"><span class="pre">抛出异常</span></code>、<code class="docutils literal notranslate"><span class="pre">入参</span></code>，通过编写 OGNL 表达式进行对应变量的查看。</p>
<div class="section" id="id1">
<h2>参数说明<a class="headerlink" href="#id1" title="永久链接至标题"></a></h2>
<p>watch 的参数比较多，主要是因为它能在 4 个不同的场景观察对象</p>
<table border="1" class="docutils">
<thead>
<tr>
<th align="right">参数名称</th>
<th align="left">参数说明</th>
</tr>
</thead>
<tbody>
<tr>
<td align="right"><em>class-pattern</em></td>
<td align="left">类名表达式匹配</td>
</tr>
<tr>
<td align="right"><em>method-pattern</em></td>
<td align="left">函数名表达式匹配</td>
</tr>
<tr>
<td align="right"><em>express</em></td>
<td align="left">观察表达式，默认值：<code>{params, target, returnObj}</code></td>
</tr>
<tr>
<td align="right"><em>condition-express</em></td>
<td align="left">条件表达式</td>
</tr>
<tr>
<td align="right">[b]</td>
<td align="left">在<strong>函数调用之前</strong>观察</td>
</tr>
<tr>
<td align="right">[e]</td>
<td align="left">在<strong>函数异常之后</strong>观察</td>
</tr>
<tr>
<td align="right">[s]</td>
<td align="left">在<strong>函数返回之后</strong>观察</td>
</tr>
<tr>
<td align="right">[f]</td>
<td align="left">在<strong>函数结束之后</strong>(正常返回和异常返回)观察</td>
</tr>
<tr>
<td align="right">[E]</td>
<td align="left">开启正则表达式匹配，默认为通配符匹配</td>
</tr>
<tr>
<td align="right">[x:]</td>
<td align="left">指定输出结果的属性遍历深度，默认为 1</td>
</tr>
</tbody>
</table><p>这里重点要说明的是观察表达式，观察表达式的构成主要由 ognl 表达式组成，所以你可以这样写<code class="docutils literal notranslate"><span class="pre">&quot;{params,returnObj}&quot;</span></code>，只要是一个合法的 ognl 表达式，都能被正常支持。</p>
<p>观察的维度也比较多，主要体现在参数 <code class="docutils literal notranslate"><span class="pre">advice</span></code> 的数据结构上。<code class="docutils literal notranslate"><span class="pre">Advice</span></code> 参数最主要是封装了通知节点的所有信息。请参考<a class="reference internal" href="advice-class.html"><span class="doc">表达式核心变量</span></a>中关于该节点的描述。</p>
<ul class="simple">
<li><p>特殊用法请参考：<a class="reference external" href="https://github.com/alibaba/arthas/issues/71">https://github.com/alibaba/arthas/issues/71</a></p></li>
<li><p>OGNL表达式官网：<a class="reference external" href="https://commons.apache.org/proper/commons-ognl/language-guide.html">https://commons.apache.org/proper/commons-ognl/language-guide.html</a></p></li>
</ul>
<p><strong>特别说明</strong>：</p>
<ul class="simple">
<li><p>watch 命令定义了4个观察事件点，即 <code class="docutils literal notranslate"><span class="pre">-b</span></code> 函数调用前，<code class="docutils literal notranslate"><span class="pre">-e</span></code> 函数异常后，<code class="docutils literal notranslate"><span class="pre">-s</span></code> 函数返回后，<code class="docutils literal notranslate"><span class="pre">-f</span></code> 函数结束后</p></li>
<li><p>4个观察事件点 <code class="docutils literal notranslate"><span class="pre">-b</span></code>、<code class="docutils literal notranslate"><span class="pre">-e</span></code>、<code class="docutils literal notranslate"><span class="pre">-s</span></code> 默认关闭，<code class="docutils literal notranslate"><span class="pre">-f</span></code> 默认打开，当指定观察点被打开后，在相应事件点会对观察表达式进行求值并输出</p></li>
<li><p>这里要注意<code class="docutils literal notranslate"><span class="pre">函数入参</span></code>和<code class="docutils literal notranslate"><span class="pre">函数出参</span></code>的区别，有可能在中间被修改导致前后不一致，除了 <code class="docutils literal notranslate"><span class="pre">-b</span></code> 事件点 <code class="docutils literal notranslate"><span class="pre">params</span></code> 代表函数入参外，其余事件都代表函数出参</p></li>
<li><p>当使用 <code class="docutils literal notranslate"><span class="pre">-b</span></code> 时，由于观察事件点是在函数调用前，此时返回值或异常均不存在</p></li>
<li><p>在watch命令的结果里，会打印出<code class="docutils literal notranslate"><span class="pre">location</span></code>信息。<code class="docutils literal notranslate"><span class="pre">location</span></code>有三种可能值：<code class="docutils literal notranslate"><span class="pre">AtEnter</span></code>，<code class="docutils literal notranslate"><span class="pre">AtExit</span></code>，<code class="docutils literal notranslate"><span class="pre">AtExceptionExit</span></code>。对应函数入口，函数正常return，函数抛出异常。</p></li>
</ul>
</div>
<div class="section" id="id2">
<h2>使用参考<a class="headerlink" href="#id2" title="永久链接至标题"></a></h2>
<div class="section" id="demo">
<h3>启动 Demo<a class="headerlink" href="#demo" title="永久链接至标题"></a></h3>
<p>启动<a class="reference internal" href="quick-start.html"><span class="doc">快速入门</span></a>里的<code class="docutils literal notranslate"><span class="pre">math-game</span></code>。</p>
</div>
<div class="section" id="this">
<h3>观察函数调用返回时的参数、this对象和返回值<a class="headerlink" href="#this" title="永久链接至标题"></a></h3>
<blockquote>
<div><p>观察表达式，默认值是<code class="docutils literal notranslate"><span class="pre">{params,</span> <span class="pre">target,</span> <span class="pre">returnObj}</span></code></p>
</div></blockquote>
<div class="highlight-bash notranslate"><div class="highlight hljs"><pre class="bash">$ watch demo.MathGame primeFactors -x 2
Press Q or Ctrl+C to abort.
Affect(class count: 1 , method count: 1) cost in 32 ms, listenerId: 5
method=demo.MathGame.primeFactors location=AtExceptionExit
ts=2021-08-31 15:22:57; [cost=0.220625ms] result=@ArrayList[
@Object[][
@Integer[-179173],
],
@MathGame[
random=@Random[java.util.Random@31cefde0],
illegalArgumentCount=@Integer[44],
],
null,
]
method=demo.MathGame.primeFactors location=AtExit
ts=2021-08-31 15:22:58; [cost=1.020982ms] result=@ArrayList[
@Object[][
@Integer[1],
],
@MathGame[
random=@Random[java.util.Random@31cefde0],
illegalArgumentCount=@Integer[44],
],
@ArrayList[
@Integer[2],
@Integer[2],
@Integer[26947],
],
]</pre></div>
</div>
<ul class="simple">
<li><p>上面的结果里，说明函数被执行了两次，第一次结果是<code class="docutils literal notranslate"><span class="pre">location=AtExceptionExit</span></code>，说明函数抛出异常了，因此<code class="docutils literal notranslate"><span class="pre">returnObj</span></code>是null</p></li>
<li><p>在第二次结果里是<code class="docutils literal notranslate"><span class="pre">location=AtExit</span></code>，说明函数正常返回，因此可以看到<code class="docutils literal notranslate"><span class="pre">returnObj</span></code>结果是一个ArrayList</p></li>
</ul>
</div>
<div class="section" id="id3">
<h3>观察函数调用入口的参数和返回值<a class="headerlink" href="#id3" title="永久链接至标题"></a></h3>
<div class="highlight-bash notranslate"><div class="highlight hljs"><pre class="bash">$ watch demo.MathGame primeFactors &quot;{params,returnObj}&quot; -x 2 -b
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 50 ms.
ts=2018-12-03 19:23:23; [cost=0.0353ms] result=@ArrayList[
@Object[][
@Integer[-1077465243],
],
null,
]</pre></div>
</div>
<ul class="simple">
<li><p>对比前一个例子，返回值为空（事件点为函数执行前，因此获取不到返回值）</p></li>
</ul>
</div>
<div class="section" id="id4">
<h3>同时观察函数调用前和函数返回后<a class="headerlink" href="#id4" title="永久链接至标题"></a></h3>
<div class="highlight-bash notranslate"><div class="highlight hljs"><pre class="bash">$ watch demo.MathGame primeFactors &quot;{params,target,returnObj}&quot; -x 2 -b -s -n 2
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 46 ms.
ts=2018-12-03 19:29:54; [cost=0.01696ms] result=@ArrayList[
@Object[][
@Integer[1],
],
@MathGame[
random=@Random[java.util.Random@522b408a],
illegalArgumentCount=@Integer[13038],
],
null,
]
ts=2018-12-03 19:29:54; [cost=4.277392ms] result=@ArrayList[
@Object[][
@Integer[1],
],
@MathGame[
random=@Random[java.util.Random@522b408a],
illegalArgumentCount=@Integer[13038],
],
@ArrayList[
@Integer[2],
@Integer[2],
@Integer[2],
@Integer[5],
@Integer[5],
@Integer[73],
@Integer[241],
@Integer[439],
],
]</pre></div>
</div>
<ul class="simple">
<li><p>参数里<code class="docutils literal notranslate"><span class="pre">-n</span> <span class="pre">2</span></code>，表示只执行两次</p></li>
<li><p>这里输出结果中，第一次输出的是函数调用前的观察表达式的结果，第二次输出的是函数返回后的表达式的结果</p></li>
<li><p>结果的输出顺序和事件发生的先后顺序一致，和命令中 <code class="docutils literal notranslate"><span class="pre">-s</span> <span class="pre">-b</span></code> 的顺序无关</p></li>
</ul>
</div>
<div class="section" id="x">
<h3>调整<code class="docutils literal notranslate"><span class="pre">-x</span></code>的值，观察具体的函数参数值<a class="headerlink" href="#x" title="永久链接至标题"></a></h3>
<div class="highlight-bash notranslate"><div class="highlight hljs"><pre class="bash">$ watch demo.MathGame primeFactors &quot;{params,target}&quot; -x 3
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 58 ms.
ts=2018-12-03 19:34:19; [cost=0.587833ms] result=@ArrayList[
@Object[][
@Integer[1],
],
@MathGame[
random=@Random[
serialVersionUID=@Long[3905348978240129619],
seed=@AtomicLong[3133719055989],
multiplier=@Long[25214903917],
addend=@Long[11],
mask=@Long[281474976710655],
DOUBLE_UNIT=@Double[1.1102230246251565E-16],
BadBound=@String[bound must be positive],
BadRange=@String[bound must be greater than origin],
BadSize=@String[size must be non-negative],
seedUniquifier=@AtomicLong[-3282039941672302964],
nextNextGaussian=@Double[0.0],
haveNextNextGaussian=@Boolean[false],
serialPersistentFields=@ObjectStreamField[][isEmpty=false;size=3],
unsafe=@Unsafe[sun.misc.Unsafe@2eaa1027],
seedOffset=@Long[24],
],
illegalArgumentCount=@Integer[13159],
],
]</pre></div>
</div>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">-x</span></code>表示遍历深度，可以调整来打印具体的参数和结果内容，默认值是1。</p></li>
</ul>
</div>
<div class="section" id="id5">
<h3>条件表达式的例子<a class="headerlink" href="#id5" title="永久链接至标题"></a></h3>
<div class="highlight-bash notranslate"><div class="highlight hljs"><pre class="bash">$ watch demo.MathGame primeFactors &quot;{params[0],target}&quot; &quot;params[0]&lt;0&quot;
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 68 ms.
ts=2018-12-03 19:36:04; [cost=0.530255ms] result=@ArrayList[
@Integer[-18178089],
@MathGame[demo.MathGame@41cf53f9],
]</pre></div>
</div>
<ul class="simple">
<li><p>只有满足条件的调用，才会有响应。</p></li>
</ul>
</div>
<div class="section" id="id6">
<h3>观察异常信息的例子<a class="headerlink" href="#id6" title="永久链接至标题"></a></h3>
<div class="highlight-bash notranslate"><div class="highlight hljs"><pre class="bash">$ watch demo.MathGame primeFactors &quot;{params[0],throwExp}&quot; -e -x 2
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 62 ms.
ts=2018-12-03 19:38:00; [cost=1.414993ms] result=@ArrayList[
@Integer[-1120397038],
java.lang.IllegalArgumentException: number is: -1120397038, need &gt;= 2
at demo.MathGame.primeFactors(MathGame.java:46)
at demo.MathGame.run(MathGame.java:24)
at demo.MathGame.main(MathGame.java:16)
,
]</pre></div>
</div>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">-e</span></code>表示抛出异常时才触发</p></li>
<li><p>express中，表示异常信息的变量是<code class="docutils literal notranslate"><span class="pre">throwExp</span></code></p></li>
</ul>
</div>
<div class="section" id="id7">
<h3>按照耗时进行过滤<a class="headerlink" href="#id7" title="永久链接至标题"></a></h3>
<div class="highlight-bash notranslate"><div class="highlight hljs"><pre class="bash">$ watch demo.MathGame primeFactors &#x27;{params, returnObj}&#x27; &#x27;#cost&gt;200&#x27; -x 2
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 66 ms.
ts=2018-12-03 19:40:28; [cost=2112.168897ms] result=@ArrayList[
@Object[][
@Integer[1],
],
@ArrayList[
@Integer[5],
@Integer[428379493],
],
]</pre></div>
</div>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">#cost&gt;200</span></code>(单位是<code class="docutils literal notranslate"><span class="pre">ms</span></code>)表示只有当耗时大于200ms时才会输出，过滤掉执行时间小于200ms的调用</p></li>
</ul>
</div>
<div class="section" id="id8">
<h3>观察当前对象中的属性<a class="headerlink" href="#id8" title="永久链接至标题"></a></h3>
<p>如果想查看函数运行前后，当前对象中的属性，可以使用<code class="docutils literal notranslate"><span class="pre">target</span></code>关键字，代表当前对象</p>
<div class="highlight-bash notranslate"><div class="highlight hljs"><pre class="bash">$ watch demo.MathGame primeFactors &#x27;target&#x27;
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 52 ms.
ts=2018-12-03 19:41:52; [cost=0.477882ms] result=@MathGame[
random=@Random[java.util.Random@522b408a],
illegalArgumentCount=@Integer[13355],
]</pre></div>
</div>
<p>然后使用<code class="docutils literal notranslate"><span class="pre">target.field_name</span></code>访问当前对象的某个属性</p>
<div class="highlight-bash notranslate"><div class="highlight hljs"><pre class="bash">$ watch demo.MathGame primeFactors &#x27;target.illegalArgumentCount&#x27;
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 67 ms.
ts=2018-12-03 20:04:34; [cost=131.303498ms] result=@Integer[8]
ts=2018-12-03 20:04:35; [cost=0.961441ms] result=@Integer[8]</pre></div>
</div>
</div>
<div class="section" id="id9">
<h3>获取类的静态字段、调用类的静态函数的例子<a class="headerlink" href="#id9" title="永久链接至标题"></a></h3>
<div class="highlight-bash notranslate"><div class="highlight hljs"><pre class="bash">watch demo.MathGame * &#x27;{params,@demo.MathGame@random.nextInt(100)}&#x27; -v -n 1 -x 2
[arthas@6527]$ watch demo.MathGame * &#x27;{params,@demo.MathGame@random.nextInt(100)}&#x27; -n 1 -x 2
Press Q or Ctrl+C to abort.
Affect(class count: 1 , method count: 5) cost in 34 ms, listenerId: 3
ts=2021-01-05 21:35:20; [cost=0.173966ms] result=@ArrayList[
@Object[][
@Integer[-138282],
],
@Integer[89],
]</pre></div>
</div>
<ul class="simple">
<li><p>注意这里使用 <code class="docutils literal notranslate"><span class="pre">Thread.currentThread().getContextClassLoader()</span></code> 加载,使用精确<code class="docutils literal notranslate"><span class="pre">classloader</span></code> <a class="reference internal" href="ognl.html"><span class="doc">ognl</span></a>更好。</p></li>
</ul>
</div>
<div class="section" id="id10">
<h3>排除掉指定的类<a class="headerlink" href="#id10" title="永久链接至标题"></a></h3>
<blockquote>
<div><p>watch/trace/monitor/stack/tt 命令都支持 <code class="docutils literal notranslate"><span class="pre">--exclude-class-pattern</span></code> 参数</p>
</div></blockquote>
<p>使用 <code class="docutils literal notranslate"><span class="pre">--exclude-class-pattern</span></code> 参数可以排除掉指定的类，比如：</p>
<div class="highlight-bash notranslate"><div class="highlight hljs"><pre class="bash">watch javax.servlet.Filter * --exclude-class-pattern com.demo.TestFilter</pre></div>
</div>
</div>
<div class="section" id="id11">
<h3>不匹配子类<a class="headerlink" href="#id11" title="永久链接至标题"></a></h3>
<p>默认情况下 watch/trace/monitor/stack/tt 命令都会匹配子类。如果想不匹配，可以通过全局参数关掉。</p>
<div class="highlight-bash notranslate"><div class="highlight hljs"><pre class="bash">options disable-sub-class true</pre></div>
</div>
</div>
<div class="section" id="v">
<h3>使用 -v 参数打印更多信息<a class="headerlink" href="#v" title="永久链接至标题"></a></h3>
<blockquote>
<div><p>watch/trace/monitor/stack/tt 命令都支持 <code class="docutils literal notranslate"><span class="pre">-v</span></code> 参数</p>
</div></blockquote>
<p>当命令执行之后，没有输出结果。有两种可能：</p>
<ol class="simple">
<li><p>匹配到的函数没有被执行</p></li>
<li><p>条件表达式结果是 false</p></li>
</ol>
<p>但用户区分不出是哪种情况。</p>
<p>使用 <code class="docutils literal notranslate"><span class="pre">-v</span></code>选项，则会打印<code class="docutils literal notranslate"><span class="pre">Condition</span> <span class="pre">express</span></code>的具体值和执行结果，方便确认。</p>
<p>比如：</p>
<div class="highlight-default notranslate"><pre class="literal-block">$ watch -v -x 2 demo.MathGame print &#x27;params&#x27; &#x27;params[0] &gt; 100000&#x27;
Press Q or Ctrl+C to abort.
Affect(class count: 1 , method count: 1) cost in 29 ms, listenerId: 11
Condition express: params[0] &gt; 100000 , result: false
Condition express: params[0] &gt; 100000 , result: false
Condition express: params[0] &gt; 100000 , result: true
ts=2020-12-02 22:38:56; [cost=0.060843ms] result=@Object[][
@Integer[200033],
@ArrayList[
@Integer[200033],
],
]
Condition express: params[0] &gt; 100000 , result: true
ts=2020-12-02 22:38:57; [cost=0.052877ms] result=@Object[][
@Integer[123047],
@ArrayList[
@Integer[29],
@Integer[4243],
],
]</pre>
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