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 ` 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.