import{_ as i,o as l,c as r,a as n,b as a,w as o,e as s,d as p,r as c}from"./app.5024572d.js";const u={},d=n("h1",{id:"watch",tabindex:"-1"},[n("a",{class:"header-anchor",href:"#watch","aria-hidden":"true"},"#"),s(" watch")],-1),m={href:"https://arthas.aliyun.com/doc/arthas-tutorials.html?language=en&id=command-watch",target:"_blank",rel:"noopener noreferrer"},k=n("code",null,"watch",-1),v=s(" online tutorial"),b=n("p",null,[s("Monitor methods in data aspect including "),n("code",null,"return values"),s(", "),n("code",null,"exceptions"),s(" and "),n("code",null,"parameters"),s(".")],-1),h=s("With the help of "),g={href:"https://commons.apache.org/proper/commons-ognl/index.html",target:"_blank",rel:"noopener noreferrer"},f=s("OGNL"),x=s(", you can easily check the details of variables when methods being invoked."),_=p('

Parameters & Options

There are four different scenarios for watch command, which makes it rather complicated.

Name	Specification
class-pattern	pattern for the class name
method-pattern	pattern for the method name
expression	expression to watch, default value `{params, target, returnObj}`
condition-expression	condition expression to filter
[b]	before method being invoked
[e]	when method encountering exceptions
[s]	when method exits normally
[f]	when method exits (either succeed or fail with exceptions)
[E]	turn on regex matching while the default is wildcard matching
[x:]	the depth to print the specified property with default value: 1, the max value is 4
`[m <arg>]`	Specify the max number of matched Classes, the default value is 50. Long format is `[maxMatch <arg>]`.

F.Y.I

any valid OGNL expression as "{params,returnObj}" supported
there are four watching points: -b, -e, -s and -f (the first three are off in default while -f on);
at the watching point, Arthas will use the expression to evaluate the variables and print them out;
in parameters and out parameters are different since they can be modified within the invoked methods; params stands for in parameters in -bwhile out parameters in other watching points;
there are no return values and exceptions when using -b.
In the result of the watch command, the location information will be printed. There are three possible values for location: AtEnter, AtExit, and AtExceptionExit. Corresponding to the method entry, the method returns normally, and the method throws an exception.

Advanced:

',6),y=s("Critical fields in "),w=n("em",null,"expression",-1),I={href:"https://github.com/alibaba/arthas/issues/71",target:"_blank",rel:"noopener noreferrer"},A=s("Special usages"),C={href:"https://commons.apache.org/dormant/commons-ognl/language-guide.html",target:"_blank",rel:"noopener noreferrer"},G=s("OGNL official guide"),j=n("h2",{id:"usage",tabindex:"-1"},[n("a",{class:"header-anchor",href:"#usage","aria-hidden":"true"},"#"),s(" Usage")],-1),M=n("h3",{id:"start-demo",tabindex:"-1"},[n("a",{class:"header-anchor",href:"#start-demo","aria-hidden":"true"},"#"),s(" Start Demo")],-1),L=s("Start "),E=n("code",null,"math-game",-1),O=s(" in "),F=s("Quick Start"),q=s("."),T=p(`

Check the `out parameters`, `this` and `return value`

TIP

The expression to watch, default value {params, target, returnObj}

$ watch demo.MathGame primeFactors -x 2
Press Q or Ctrl+C to abort.
Affect(class count: 1 , method count: 1) cost in 32 ms, listenerId: 5
method=demo.MathGame.primeFactors location=AtExceptionExit
ts=2021-08-31 15:22:57; [cost=0.220625ms] result=@ArrayList[
    @Object[][
        @Integer[-179173],
    ],
    @MathGame[
        random=@Random[java.util.Random@31cefde0],
        illegalArgumentCount=@Integer[44],
    ],
    null,
]
method=demo.MathGame.primeFactors location=AtExit
ts=2021-08-31 15:22:58; [cost=1.020982ms] result=@ArrayList[
    @Object[][
        @Integer[1],
    ],
    @MathGame[
        random=@Random[java.util.Random@31cefde0],
        illegalArgumentCount=@Integer[44],
    ],
    @ArrayList[
        @Integer[2],
        @Integer[2],
        @Integer[26947],
    ],
]

In the above result, the method is executed twice, the first result is location=AtExceptionExit, indicating that the method throws an exception, so returnObj is null
In the second result is location=AtExit, indicating that the method returns normally, so you can see that the result of returnObj is an ArrayList

Specify the max number of matched Classes

$ watch demo.MathGame primeFactors -m 1
Press Q or Ctrl+C to abort.
Affect(class count: 1 , method count: 1) cost in 302 ms, listenerId: 3
method=demo.MathGame.primeFactors location=AtExceptionExit
ts=2022-12-25 19:58:41; [cost=0.222419ms] result=@ArrayList[
    @Object[][isEmpty=false;size=1],
    @MathGame[demo.MathGame@3bf400],
    null,
]
method=demo.MathGame.primeFactors location=AtExceptionExit
ts=2022-12-25 19:58:51; [cost=0.046928ms] result=@ArrayList[
    @Object[][isEmpty=false;size=1],
    @MathGame[demo.MathGame@3bf400],
    null,
]

Check `in parameters`

$ watch demo.MathGame primeFactors "{params,returnObj}" -x 2 -b
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 50 ms.
ts=2018-12-03 19:23:23; [cost=0.0353ms] result=@ArrayList[
    @Object[][
        @Integer[-1077465243],
    ],
    null,
]

Compared to the previous check:

return value is null since it's -b.

Check before and after at the same time

$ watch demo.MathGame primeFactors "{params,target,returnObj}" -x 2 -b -s -n 2
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 46 ms.
ts=2018-12-03 19:29:54; [cost=0.01696ms] result=@ArrayList[
    @Object[][
        @Integer[1],
    ],
    @MathGame[
        random=@Random[java.util.Random@522b408a],
        illegalArgumentCount=@Integer[13038],
    ],
    null,
]
ts=2018-12-03 19:29:54; [cost=4.277392ms] result=@ArrayList[
    @Object[][
        @Integer[1],
    ],
    @MathGame[
        random=@Random[java.util.Random@522b408a],
        illegalArgumentCount=@Integer[13038],
    ],
    @ArrayList[
        @Integer[2],
        @Integer[2],
        @Integer[2],
        @Integer[5],
        @Integer[5],
        @Integer[73],
        @Integer[241],
        @Integer[439],
    ],
]

F.Y.I

-n 2: threshold of execution times is 2.
the first block of output is the before watching point;
*the order of the output determined by the *watching* order itself (nothing to do with the order of the options -b -s).

Use `-x` to check more details

$ watch demo.MathGame primeFactors "{params,target}" -x 3
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 58 ms.
ts=2018-12-03 19:34:19; [cost=0.587833ms] result=@ArrayList[
    @Object[][
        @Integer[1],
    ],
    @MathGame[
        random=@Random[
            serialVersionUID=@Long[3905348978240129619],
            seed=@AtomicLong[3133719055989],
            multiplier=@Long[25214903917],
            addend=@Long[11],
            mask=@Long[281474976710655],
            DOUBLE_UNIT=@Double[1.1102230246251565E-16],
            BadBound=@String[bound must be positive],
            BadRange=@String[bound must be greater than origin],
            BadSize=@String[size must be non-negative],
            seedUniquifier=@AtomicLong[-3282039941672302964],
            nextNextGaussian=@Double[0.0],
            haveNextNextGaussian=@Boolean[false],
            serialPersistentFields=@ObjectStreamField[][isEmpty=false;size=3],
            unsafe=@Unsafe[sun.misc.Unsafe@2eaa1027],
            seedOffset=@Long[24],
        ],
        illegalArgumentCount=@Integer[13159],
    ],
]

-x: Expand level of object (1 by default)
The max value of -x is 4, to prevent the expansion result taking up too much memory. Users can specify the field in the ognl expression.

Use condition expressions to locate specific call

$ watch demo.MathGame primeFactors "{params[0],target}" "params[0]<0"
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 68 ms.
ts=2018-12-03 19:36:04; [cost=0.530255ms] result=@ArrayList[
    @Integer[-18178089],
    @MathGame[demo.MathGame@41cf53f9],
]

Check `exceptions`

$ watch demo.MathGame primeFactors "{params[0],throwExp}" -e -x 2
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 62 ms.
ts=2018-12-03 19:38:00; [cost=1.414993ms] result=@ArrayList[
    @Integer[-1120397038],
    java.lang.IllegalArgumentException: number is: -1120397038, need >= 2
	at demo.MathGame.primeFactors(MathGame.java:46)
	at demo.MathGame.run(MathGame.java:24)
	at demo.MathGame.main(MathGame.java:16)
,
]

-e\b: Trigger when an exception is thrown
throwExp: the exception object

Filter by time cost

$ watch demo.MathGame primeFactors '{params, returnObj}' '#cost>200' -x 2
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 66 ms.
ts=2018-12-03 19:40:28; [cost=2112.168897ms] result=@ArrayList[
    @Object[][
        @Integer[1],
    ],
    @ArrayList[
        @Integer[5],
        @Integer[428379493],
    ],
]

#cost>200 (ms) filter out all invokings that take less than 200ms.

Check the field of the target object

target is the this object in java.

$ watch demo.MathGame primeFactors 'target'
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 52 ms.
ts=2018-12-03 19:41:52; [cost=0.477882ms] result=@MathGame[
    random=@Random[java.util.Random@522b408a],
    illegalArgumentCount=@Integer[13355],
]

target.field_name: the field of the current object.

$ watch demo.MathGame primeFactors 'target.illegalArgumentCount'
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 67 ms.
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

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],
]

`,32),P=s("Note that here you use "),R=n("code",null,"Thread.currentThread().getContextClassLoader()",-1),N=s(" to load, and it is better to use the exact "),S=n("code",null,"classloader",-1),U=s(),$=s("ognl"),B=s("."),D=p(`

Exclude the specified class

TIP

The watch/trace/monitor/stack/tt commands all support the --exclude-class-pattern parameter

Use the --exclude-class-pattern parameter to exclude the specified class, for example:

watch javax.servlet.Filter * --exclude-class-pattern com.demo.TestFilter

Does not match subclass

By default, the watch/trace/monitor/stack/tt commands will match subclass. If you don't want to match, you can turn it off.

options disable-sub-class true

Use the -v parameter to print more information

The watch/trace/monitor/stack/tt commands all support the -v parameter.

When the command is executed, there is no output result. There are two possibilities:

The matched function is not executed
The result of the conditional expression is false

But the user cannot tell which situation is.

Using the -v option, the specific value and execution result of Condition express will be printed for easy confirmation.

such as:

$ watch -v -x 2 demo.MathGame print 'params' 'params[0] > 100000'
Press Q or Ctrl+C to abort.
Affect(class count: 1 , method count: 1) cost in 29 ms, listenerId: 11
Condition express: params[0] > 100000 , result: false
Condition express: params[0] > 100000 , result: false
Condition express: params[0] > 100000 , result: true
ts=2020-12-02 22:38:56; [cost=0.060843ms] result=@Object[][
    @Integer[1],
    @ArrayList[
        @Integer[200033],
    ],
]
Condition express: params[0] > 100000 , result: true
ts=2020-12-02 22:38:57; [cost=0.052877ms] result=@Object[][
    @Integer[1],
    @ArrayList[
        @Integer[29],
        @Integer[4243],
    ],
]

`,15);function z(Q,V){const e=c("ExternalLinkIcon"),t=c("RouterLink");return l(),r("div",null,[d,n("p",null,[n("a",m,[k,v,a(e)])]),b,n("p",null,[h,n("a",g,[f,a(e)]),x]),_,n("ul",null,[n("li",null,[a(t,{to:"/en/doc/advice-class.html"},{default:o(()=>[y,w]),_:1})]),n("li",null,[n("a",I,[A,a(e)])]),n("li",null,[n("a",C,[G,a(e)])])]),j,M,n("p",null,[L,E,O,a(t,{to:"/en/doc/quick-start.html"},{default:o(()=>[F]),_:1}),q]),T,n("ul",null,[n("li",null,[P,R,N,S,U,a(t,{to:"/en/doc/ognl.html"},{default:o(()=>[$]),_:1}),B])]),D])}const Y=i(u,[["render",z],["__file","watch.html.vue"]]);export{Y as default};

# Parameters & Options

# Check the out parameters, this and return value

# Specify the max number of matched Classes

# Check in parameters

# Check before and after at the same time

# Use -x to check more details

# Use condition expressions to locate specific call

# Check exceptions

# Filter by time cost

# Check the field of the target object

# Get a static field and calling a static method

# Exclude the specified class

# Does not match subclass

# Use the -v parameter to print more information