tt
==
Check the `parameters`, `return values` and `exceptions` of the methods at different times.
`watch` is a powerful command but due to its feasibility and complexity, it's quite hard to locate the issue effectively.
In such difficulties, `tt` comes into play.
With the help of `tt` (*TimeTunnel*), you can check the contexts of the methods at different times in execution history.
### Usage
#### Start Demo
Start `arthas-demo` in [Quick Start](quick-start.md).
#### Record method calls
```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
```
* `-t`
record the calling context of the method `demo.MathGame primeFactors`
* `-n 3`
limit the number of the records (avoid overflow for too many records; with `-n` option, Arthas can automatically stop recording once the records reach the specified limit)
* Property
|Name|Specification|
|---|---|
|INDEX|the index for each call based on time|
|TIMESTAMP|time to invoke the method|
|COST(ms)|time cost of the method call|
|IS-RET|whether method exits with normal return|
|IS-EXP|whether method failed with exceptions|
|OBJECT|`hashCode()` of the object invoking the method|
|CLASS|class name of the object invoking the method|
|METHOD|method being invoked|
* Condition expression
Tips:
1. `tt -t *Test print params.length==1` with different amounts of parameters;
2. `tt -t *Test print 'params[1] instanceof Integer'` with different types of parameters;
3. `tt -t *Test print params[0].mobile=="13989838402"` with specified parameter.
Advanced:
* [Critical fields in expression](advice-class.md)
* [Special usage](https://github.com/alibaba/arthas/issues/71)
* [OGNL official guide](https://commons.apache.org/proper/commons-ognl/language-guide.html)
#### List all records
```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.
```
#### Searching for records
```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.
```
Advanced:
* [Critical fields in expression](advice-class.md)
#### Check context of the call
Using `tt -i <index>` to check a specific calling details.
```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.
```
### 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
```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
RETURN-OBJ @ArrayList[
@Integer[2],
@Integer[11],
@Integer[17],
@Integer[2531387],
]
Time fragment[1004] successfully replayed.
Affect(row-cnt:1) cost in 14 ms.
```
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
Arthas save params into an array, they are object references. The Objects may be modified by other code.
