update faq.md (#1660)

2024-04-21 10:21:39 +00:00 · 2021-01-11 15:47:07 +08:00
parent cc26b806d6
commit fac8dd5470
6 changed files with 141 additions and 5 deletions
@@ -37,7 +37,7 @@ No.
 No. But you can use some tricks to intercept the object with the `tt` command, or fetch it from a static method.


-#### How to filter method with the same name?
+##### How to filter method with the same name?

 You can used all variables in [fundamental fields in expressions](advice-class.md) for the condition express to filter method with the same name, you can use the number of parameters `params.length ==1`,parameter type `params[0] instanceof java.lang.Integer`,return value type `returnObj instanceof java.util.List` and so on in one or more combinations as condition express.

@@ -47,4 +47,17 @@ example [arthas-demo](quick-start.md)

 ```bash
 watch demo.MathGame primeFactors traceE '{params,returnObj,throwExp}' -v -n 5 -x 3 'params.length >0 && returnObj instanceof java.util.List'
-``` 
+``` 
+
+##### How to watch or trace constructor?
+
+```bash
+watch demo.MathGame <init> '{params,returnObj,throwExp}' -v -n 5 -x 3 '1==1'
+```
+
+
+##### java.lang.ClassFormatError: null, skywalking arthas compatible use
+
+When error log appear `java.lang.ClassFormatError: null`, it is usually modified by other bytecode tools that are not compatible with arthas modified bytecode.
+
+For example: use skywalking V8.1.0 below [cannot trace, watch classes enhanced by skywalking agent](https://github.com/alibaba/arthas/issues/1141), V8.1.0 or above is compatible, refer to skywalking configuration for more details. [skywalking compatible with other javaagent bytecode processing](https://github.com/apache/skywalking/blob/v8.1.0/docs/en/FAQ/Compatible-with-other-javaagent-bytecode-processing.md).
@@ -127,7 +127,7 @@ $ tt -i 1003
 Affect(row-cnt:1) cost in 11 ms.
 ```

-### Replay record
+#### Replay record

 Since Arthas stores the context of the call, you can even *replay* the method calling afterwards with extra option `-p` to replay the issue for advanced troubleshooting, option `--replay-times` 
 define the replay execution times, option  `--replay-interval` define the interval(unit in ms,with default value 1000) of replays   
@@ -152,13 +152,50 @@ Time fragment[1004] successfully replayed.
 Affect(row-cnt:1) cost in 14 ms.
 ```

+#### Watch express
+
+`-w, --watch-express` watch the time fragment by ognl express.
+
+* You can used all variables in [fundamental fields in expressions](advice-class.md) for the watch express。
+
+```bash
+[arthas@10718]$ tt -t demo.MathGame run -n 5 
+Press Q or Ctrl+C to abort.
+Affect(class count: 1 , method count: 1) cost in 56 ms, listenerId: 1
+ INDEX      TIMESTAMP                   COST(ms)     IS-RET     IS-EXP      OBJECT              CLASS                                     METHOD
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ 1000       2021-01-08 21:54:17         0.901091     true       false       0x7699a589          MathGame                                  run
+[arthas@10718]$ tt -w 'target.illegalArgumentCount'  -x 1 -i 1000
+@Integer[60]
+Affect(row-cnt:1) cost in 7 ms.
+```
+
+* Get a static field and calling a static method 
+
+```bash
+[arthas@10718]$ tt -t demo.MathGame run -n 5
+Press Q or Ctrl+C to abort.
+Affect(class count: 1 , method count: 1) cost in 56 ms, listenerId: 1
+ INDEX      TIMESTAMP                   COST(ms)     IS-RET     IS-EXP      OBJECT              CLASS                                     METHOD
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ 1000       2021-01-08 21:54:17         0.901091     true       false       0x7699a589          MathGame                                  run
+[arthas@10718]$ tt -w '@demo.MathGame@random.nextInt(100)'  -x 1 -i 1000
+@Integer[46]
+```
+
+Note that `com.taobao.arthas.core.advisor.Advice#getLoader` is used here, and that it is better to use the exact `classloader` [ognl](ognl.md).
+
+
+Advanced usage [get spring context to call the bean method](https://github.com/alibaba/arthas/issues/482)
+
+
 F.Y.I

 1. **Loss** of the `ThreadLocal`

    Arthas save params into an array, then invoke the method with the params again. The method execute in another thread, so the `ThreadLocal` **lost**.

-1. params may be modified
+2. params may be modified

    Arthas save params into an array, they are object references. The Objects may be modified by other code.

@@ -235,6 +235,23 @@ 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]
 ``` 

+#### Get a static field and calling a static method 
+
+```bash
+watch demo.MathGame * '{params,@demo.MathGame@random.nextInt(100)}' -v -n 1 -x 2
+[arthas@6527]$ watch demo.MathGame * '{params,@demo.MathGame@random.nextInt(100)}' -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],
+]
+```
+
+* Note that here you use `Thread.currentThread().getContextClassLoader()` to load, and it is better to use the exact `classloader` [ognl](ognl.md).
+

 #### Exclude the specified class

@@ -48,4 +48,18 @@ options json-format true

 ```bash
 watch demo.MathGame primeFactors traceE '{params,returnObj,throwExp}' -v -n 5 -x 3 'params.length >0 && returnObj instanceof java.util.List'
-``` 
+``` 
+
+##### 怎么watch、trace 构造函数 ？
+
+```bash
+watch demo.MathGame <init> '{params,returnObj,throwExp}' -v -n 5 -x 3 '1==1'
+```
+
+
+##### java.lang.ClassFormatError: null、skywalking arthas 兼容使用
+
+当出现这个错误日志`java.lang.ClassFormatError: null`,通常情况下都是被其他字节码工具修改过与arthas修改字节码不兼容。
+
+比如: 使用 skywalking V8.1.0 以下版本 [无法trace、watch 被skywalking agent 增强过的类](https://github.com/alibaba/arthas/issues/1141), V8.1.0 以上版本可以兼容使用,更多参考skywalking配置 [skywalking compatible with other javaagent bytecode processing](https://github.com/apache/skywalking/blob/v8.1.0/docs/en/FAQ/Compatible-with-other-javaagent-bytecode-processing.md)。
+
@@ -175,6 +175,44 @@ Affect(row-cnt:1) cost in 14 ms.

 你会发现结果虽然一样，但调用的路径发生了变化，由原来的程序发起变成了 Arthas 自己的内部线程发起的调用了。

+
+#### 观察表达式
+
+`-w, --watch-express` 观察时空隧道使用`ognl` 表达式
+
+* 使用[表达式核心变量](advice-class.md)中所有变量作为已知条件编写表达式。
+
+```bash
+[arthas@10718]$ tt -t demo.MathGame run -n 5
+Press Q or Ctrl+C to abort.
+Affect(class count: 1 , method count: 1) cost in 56 ms, listenerId: 1
+ INDEX      TIMESTAMP                   COST(ms)     IS-RET     IS-EXP      OBJECT              CLASS                                     METHOD
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ 1000       2021-01-08 21:54:17         0.901091     true       false       0x7699a589          MathGame                                  run
+[arthas@10718]$ tt -w 'target.illegalArgumentCount'  -x 1 -i 1000
+@Integer[60]
+Affect(row-cnt:1) cost in 7 ms.
+```
+
+* 获取类的静态字段、调用类的静态方法
+
+```bash
+[arthas@10718]$ tt -t demo.MathGame run -n 5
+Press Q or Ctrl+C to abort.
+Affect(class count: 1 , method count: 1) cost in 56 ms, listenerId: 1
+ INDEX      TIMESTAMP                   COST(ms)     IS-RET     IS-EXP      OBJECT              CLASS                                     METHOD
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ 1000       2021-01-08 21:54:17         0.901091     true       false       0x7699a589          MathGame                                  run
+[arthas@10718]$ tt -w '@demo.MathGame@random.nextInt(100)'  -x 1 -i 1000
+@Integer[46]
+```
+
+注意这里使用 `com.taobao.arthas.core.advisor.Advice#getLoader`加载,使用精确`classloader` [ognl](ognl.md)更好。
+
+
+高级用法 [获取spring context 调用bean 方法](https://github.com/alibaba/arthas/issues/482)
+
+
 - 需要强调的点

  1. **ThreadLocal 信息丢失**
@@ -235,6 +235,23 @@ 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]
 ``` 

+#### 获取类的静态字段、调用类的静态方法的例子
+
+```bash
+watch demo.MathGame * '{params,@demo.MathGame@random.nextInt(100)}' -v -n 1 -x 2
+[arthas@6527]$ watch demo.MathGame * '{params,@demo.MathGame@random.nextInt(100)}' -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],
+]
+```
+
+* 注意这里使用 `Thread.currentThread().getContextClassLoader()` 加载,使用精确`classloader` [ognl](ognl.md)更好。
+
 #### 排除掉指定的类

 > watch/trace/monitor/stack/tt 命令都支持 `--exclude-class-pattern` 参数