arthas/arthas-tutorials-en/command/tt/tt.md

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 command comes into play.

With the help of tt{{}} (TimeTunnel), you can check the contexts of the methods at different times in execution history.

Usage

Record method calls

tt -t demo.MathGame primeFactors{{execute T2}}

Press Q{{exec interrupt}} or Ctrl+C{{exec interrupt}} to abort

• -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
• Special usage
• OGNL official guide

List all records

tt -l{{execute T2}}

Searching for records

tt -s 'method.name=="primeFactors"'{{execute T2}}

Advanced:

• Critical fields in expression

Check context of the call

tt -i 1003{{execute T2}}

Using tt -i <index>{{}} to check a specific calling details.

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

tt -i 1004 -p{{execute T2}}

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.

2. params may be modified

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