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< h1 > tt< a class = "headerlink" href = "#tt" title = "永久链接至标题" > ¶< / a > < / h1 >
< blockquote >
< div > < p > 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< / p >
< / 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， < / p >
< div class = "section" id = "id1" >
< h2 > 使用参考< a class = "headerlink" href = "#id1" 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" > arthas-demo< / span > < / code > 。< / p >
< / div >
< div class = "section" id = "id2" >
< h3 > 记录调用< a class = "headerlink" href = "#id2" title = "永久链接至标题" > ¶< / a > < / h3 >
< 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-bash notranslate" > < div class = "highlight hljs" > < pre class = "bash" > $ tt -t demo.MathGame primeFactors
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 66 ms.
INDEX TIMESTAMP COST(ms) IS-RET IS-EXP OBJECT CLASS METHOD
-------------------------------------------------------------------------------------------------------------------------------------
1000 2018-12-04 11:15:38 1.096236 false true 0x4b67cf4d MathGame primeFactors
1001 2018-12-04 11:15:39 0.191848 false true 0x4b67cf4d MathGame primeFactors
1002 2018-12-04 11:15:40 0.069523 false true 0x4b67cf4d MathGame primeFactors
1003 2018-12-04 11:15:41 0.186073 false true 0x4b67cf4d MathGame primeFactors
1004 2018-12-04 11:15:42 17.76437 true false 0x4b67cf4d MathGame primeFactors< / pre > < / div >
< / div >
< ul >
< li > < p > 命令参数解析< / p >
< ul >
< li > < p > < 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 > 的 < code class = "docutils literal notranslate" > < span class = "pre" > print< / span > < / code > 方法的每次执行情况。< / p >
< / li >
< li > < p > < 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， < / p >
< / li >
< / ul >
< / li >
< li > < p > 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， ， ， < / 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 > ， ， ， < / 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 > 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 > < p > Arthas 似乎很难区分出重载的方法< / p > < / li >
< li > < p > 我只需要观察特定参数，但是 tt 却全部都给我记录了下来< / p > < / li >
< / ul >
< p > 条件表达式也是用 < code class = "docutils literal notranslate" > < span class = "pre" > < / 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 > 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.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 > 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==" 13989838402" < / span > < / code > < / p >
< / li >
< li > < p > 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，都使用了 < 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 = "id3" >
< h3 > 检索调用记录< a class = "headerlink" href = "#id3" title = "永久链接至标题" > ¶< / a > < / h3 >
< 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-bash notranslate" > < div class = "highlight hljs" > < pre class = "bash" > $ tt -l
INDEX TIMESTAMP COST(ms) IS-RET IS-EXP OBJECT CLASS METHOD
-------------------------------------------------------------------------------------------------------------------------------------
1000 2018-12-04 11:15:38 1.096236 false true 0x4b67cf4d MathGame primeFactors
1001 2018-12-04 11:15:39 0.191848 false true 0x4b67cf4d MathGame primeFactors
1002 2018-12-04 11:15:40 0.069523 false true 0x4b67cf4d MathGame primeFactors
1003 2018-12-04 11:15:41 0.186073 false true 0x4b67cf4d MathGame primeFactors
1004 2018-12-04 11:15:42 17.76437 true false 0x4b67cf4d MathGame primeFactors
9
1005 2018-12-04 11:15:43 0.4776 false true 0x4b67cf4d MathGame primeFactors
Affect(row-cnt:6) cost in 4 ms.< / pre > < / div >
< / div >
< p > 我需要筛选出 < code class = "docutils literal notranslate" > < span class = "pre" > primeFactors< / span > < / code > 方法的调用信息< / p >
< div class = "highlight-bash notranslate" > < div class = "highlight hljs" > < pre class = "bash" > $ tt -s ' method.name==" primeFactors" '
INDEX TIMESTAMP COST(ms) IS-RET IS-EXP OBJECT CLASS METHOD
-------------------------------------------------------------------------------------------------------------------------------------
1000 2018-12-04 11:15:38 1.096236 false true 0x4b67cf4d MathGame primeFactors
1001 2018-12-04 11:15:39 0.191848 false true 0x4b67cf4d MathGame primeFactors
1002 2018-12-04 11:15:40 0.069523 false true 0x4b67cf4d MathGame primeFactors
1003 2018-12-04 11:15:41 0.186073 false true 0x4b67cf4d MathGame primeFactors
1004 2018-12-04 11:15:42 17.76437 true false 0x4b67cf4d MathGame primeFactors
9
1005 2018-12-04 11:15:43 0.4776 false true 0x4b67cf4d MathGame primeFactors
Affect(row-cnt:6) cost in 607 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 = "id4" >
< h3 > 查看调用信息< a class = "headerlink" href = "#id4" title = "永久链接至标题" > ¶< / a > < / h3 >
< 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-bash notranslate" > < div class = "highlight hljs" > < pre class = "bash" > $ tt -i 1003
INDEX 1003
GMT-CREATE 2018-12-04 11:15:41
COST(ms) 0.186073
OBJECT 0x4b67cf4d
CLASS demo.MathGame
METHOD primeFactors
IS-RETURN false
IS-EXCEPTION true
PARAMETERS[0] @Integer[-564322413]
THROW-EXCEPTION java.lang.IllegalArgumentException: number is: -564322413, need > = 2
at demo.MathGame.primeFactors(MathGame.java:46)
at demo.MathGame.run(MathGame.java:24)
at demo.MathGame.main(MathGame.java:16)
Affect(row-cnt:1) cost in 11 ms.< / pre > < / div >
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< div class = "section" id = "id5" >
< h3 > 重做一次调用< a class = "headerlink" href = "#id5" title = "永久链接至标题" > ¶< / a > < / h3 >
< 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。通过 < code class = "docutils literal notranslate" > < span class = "pre" > --replay-times< / span > < / code > 指定
调用次数，通过 < code class = "docutils literal notranslate" > < span class = "pre" > --replay-interval< / span > < / code > 指定多次调用间隔(单位ms, 默认1000ms)< / p >
< div class = "highlight-bash notranslate" > < div class = "highlight hljs" > < pre class = "bash" > $ tt -i 1004 -p
RE-INDEX 1004
GMT-REPLAY 2018-12-04 11:26:00
OBJECT 0x4b67cf4d
CLASS demo.MathGame
METHOD primeFactors
PARAMETERS[0] @Integer[946738738]
IS-RETURN true
IS-EXCEPTION false
COST(ms) 0.186073
RETURN-OBJ @ArrayList[
@Integer[2],
@Integer[11],
@Integer[17],
@Integer[2531387],
]
Time fragment[1004] successfully replayed.
Affect(row-cnt:1) cost in 14 ms.< / pre > < / div >
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< 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 > 需要强调的点< / p >
< ol >
< li > < p > < 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 > < 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 >
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