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JIB: Java Instrumentation Buddy

JIB is a lightweight Java agent designed to seamlessly instrument functions in compiled Java applications at the bytecode level. Leveraging the power of Byte Buddy as its core, JIB offers efficient, lightweight, and application-level function instrumentation with minimal overhead.

Features

  • Non-intrusive bytecode manipulation
  • Configurable instrumentation targets
  • Flexible logging options
  • Method-level granularity for instrumentation
  • Seamless integration with existing Java applications
  • Compatible with Java 8 and above

Building

To build and install JIB, ensure you have Maven installed on your system. Then, execute the following command in the project root directory:

mvn clean install

This command compiles the source code, runs tests, and installs the artifact in your local Maven repository.

Creating a Deployable JAR

To use JIB as an agent attached to your Java application, you'll need to package it as a JAR file. Generate the JAR with this command:

mvn clean package

Upon successful execution, you'll find the jib.jar file in the /target directory, ready for deployment.

Usage

You can attach the agent to your Java application when executing it. Here is a sample structure for attaching the agent to your Java program.

# Running the program normally
java [OPTIONS] -jar <program commands>

# Attaching the agent to your program
java [OPTIONS] -javaagent:path/to/the/jib.jar=<config=configuration.yaml> -jar <program commands>

Agent Configuration

The agent configuration is specified in a YAML file. This file allows you to customize various aspects of the agent's behavior. Below are the available configuration options:

Logging

The logging section controls how the agent generates log files:

  • file: Specifies the path to the log file where the agent will write its output.

    • Default: app.log

  • addTimestampToFileNames: When set to true, adds a timestamp to the log file name.

    • Default: false

  • useHash: If true, the agent uses hashing for method signatures in the log file. This is useful for reducing the size of the log file when there are a large number of method logs with long signatures. The mapping of the hashes will be stored in a separate JSON file.

    • Default: false

  • optimizeTimestamp: When set to true, optimizes timestamp handling for improved performance. Basically, it removes the first 4 digits of the timestamp to reduce the log file size.

    • Default: false

Instrumentation

The instrumentation section defines which parts of your code the agent will instrument:

  • targetPackage: Specifies which package to instrument.

    • Default: * (all packages)

  • onlyCheckVisited: When set to true, the agent only instruments the entry of each function once. This is useful for checking code coverage.

    • Default: false

  • instrumentMainMethod: If true, the agent will instrument the main method of the main class.

    • Default: false

  • maxNumberOfInstrumentations: Sets a limit on the number of instrumentations to perform. Use -1 for unlimited.

    • Default: -1

  • targetMethods: Allows you to specify which methods to instrument or ignore. This section has two sub-sections:

    • instrument: A list of methods to instrument. If specified, only these methods will be instrumented.
      • Example: 
        instrument:
  - private static void com.example.MainClass.methodName(int a, java.lang.String b)
    • ignore: A list of methods to exclude from instrumentation. If specified, all methods except these will be instrumented.
      • Example: 
        ignore:
  - protected java.lang.String com.example.MainClass.ignoredMethodName(float a)

Misc

The misc section contains additional configuration options:

  • convertToJson: When set to true, converts the output logs to JSON format. This format is supported by visualization tools like Eclipse Trace Compass.
    • Default: false
Method Structure

When specifying methods in the instrument or ignore lists, use the following format:

[visibility] [static] return-type [declaring-class.]method-name(args)

Where:

  • [visibility] is one of (required):
    • public
    • protected
    • private
    • (empty for package-protected)
  • [static] is one of (required):
    • static
    • (empty for non-static)
  • return-type is the method's return type
    • it should be the fully qualified class name (e.g., java.lang.String or void) (required)
  • [declaring-class] is the fully qualified class name where the method is declared (optional)
  • method-name is the name of the method (required)
  • (args) are the method's parameters (required)

Examples:

private static void com.example.MainClass.methodName(int a, java.lang.String b)
protected java.lang.String ignoredMethodName(float a)
public java.util.List<java.lang.String> getNames()
void processData(byte[] data)

Note: You can specify either instrument or ignore, but not both since it doesn't make sense to instrument and ignore methods at the same time.

Here's an example of a complete configuration file:

logging:
  file: app.log
  addTimestampToFileNames: true
  useHash: true
  optimizeTimestamp: true

instrumentation:
  targetPackage: com.example
  onlyCheckVisited: false
  instrumentMainMethod: true
  maxNumberOfInstrumentations: 1000
  targetMethods:
    instrument:
      - private static void com.example.MainClass.methodName(int a, java.lang.String b)

misc:
  convertToJson: true

Example

Let's consider a simple Java program with the following structure:

package com.example.pkg;

import java.util.HashMap;

public class Main {
    public static void main(String[] args) {
        firstMethod();

        Main main = new Main();
        main.secondMethod();
        main.thirdMethod(1, 2);
        main.fourthMethod();
        fifthMethod(new HashMap<String, Integer>(), "key");
    }

    private static void firstMethod() {
        System.out.println("First Method");
    }

    String secondMethod() {
        return "Second Method";
    }

    public int thirdMethod(int a, int b) {
        return a + b;
    }

    protected Another fourthMethod() {
        return new Another();
    }

    private static void fifthMethod(HashMap<String, Integer> map, String key) {
        if (map.containsKey(key)) {
            System.out.println("Key exists");
        } else {
            System.out.println("Key does not exist");
        }

        return;
    }
}

Full Instrumentation

Suppose we want to instrument the program to log the entry and exit of each method. We can create a YAML configuration file to specify the methods to instrument and the logging options. For now, let's just instrument all the methods in the com.example.pkg package and log the output to a file.

Configuration File

logging:
    file: app.log

instrumentation:
    targetPackage: com.example.pkg

After the instrumentation, the agent will store all the logs in a single file (i.e., app.log). Each line shows a function entry or exit along with the S/E (start or end) time and the function's signature.

[TIME_NANO_SECONDS] S|E FUNCTION_SIGNATURE

[1724605175635717866] S public static void com.example.pkg.Main.main(java.lang.String[])
[1724605175637779321] S private static void com.example.pkg.Main.firstMethod()
[1724605175637903541] E private static void com.example.pkg.Main.firstMethod()
[1724605175637944911] S java.lang.String com.example.pkg.Main.secondMethod()
[1724605175637971154] E java.lang.String com.example.pkg.Main.secondMethod()
[1724605175637995449] S public int com.example.pkg.Main.thirdMethod(int,int)
[1724605175638028792] E public int com.example.pkg.Main.thirdMethod(int,int)
[1724605175638069161] S protected com.example.pkg.Another com.example.pkg.Main.fourthMethod()
[1724605175640295270] E protected com.example.pkg.Another com.example.pkg.Main.fourthMethod()
[1724605175640359832] S private static void com.example.pkg.Main.fifthMethod(java.util.HashMap,java.lang.String)
[1724605175640388900] E private static void com.example.pkg.Main.fifthMethod(java.util.HashMap,java.lang.String)
[1724605175640410797] E public static void com.example.pkg.Main.main(java.lang.String[])

Partial Instrumentation

Now, we may specify the methods to instrument or ignore in the configuration file. For instance, we can instrument only the main method and the thirdMethod in the Main class:

Configuration File

logging:
    file: app.log

instrumentation:
    targetPackage: com.example.pkg
    instrumentMainMethod: true
    targetMethods:
        instrument:
            - public int com.example.pkg.Main.thirdMethod(int a, int b)

After running the program with this configuration, the log file will only contain entries for the main and thirdMethod functions.

[1724605175635717866] S public static void com.example.pkg.Main.main(java.lang.String[])
[1724605175637995449] S public int com.example.pkg.Main.thirdMethod(int,int)
[1724605175638028792] E public int com.example.pkg.Main.thirdMethod(int,int)
[1724605175640410797] E public static void com.example.pkg.Main.main(java.lang.String[])

Use Hashing for Method Signatures

If you want to use hashing for method signatures in the log file, you can enable the useHash option in the configuration file. This option is useful when there are a large number of method logs with long signatures.

Configuration File

logging:
    file: app.log
    useHash: true

instrumentation:
    targetPackage: com.example.pkg

After running the program with this configuration, the log file will contain hashed method signatures instead of the full method signatures. The mapping of the hashes will be stored in a separate JSON file.

  • Log file:

    [1724685951931233870] S A
[1724685951933340359] S B
[1724685951933525189] E B
[1724685951933581572] S C
[1724685951933615793] E C
[1724685951933641228] S D
[1724685951933668752] E D
[1724685951933730567] S E
[1724685951936219996] E E
[1724685951936283964] S F
[1724685951936315634] E F
[1724685951936338337] E A

  • Log metadata (.json)

    {
    "start_time": 1724685951888001220,
    "end_time": 1724685951936780901,
    "method_signature_hash": {
        "public int com.example.pkg.Main.thirdMethod(int,int)": "D",
        "java.lang.String com.example.pkg.Main.secondMethod()": "C",
        "protected com.example.pkg.Another com.example.pkg.Main.fourthMethod()": "E",
        "public static void com.example.pkg.Main.main(java.lang.String[])": "A",
        "private static void com.example.pkg.Main.firstMethod()": "B",
        "private static void com.example.pkg.Main.fifthMethod(java.util.HashMap,java.lang.String)": "F"
    }
}

Analysis

There are several ways to analyze the logs generated by the agent. One common approach is to use visualization tools like Eclipse Trace Compass™ to gain insights into the program's execution flow and performance characteristics. You can also write custom scripts to parse and analyze the logs based on your specific requirements.

Analysis with Trace Compass

Background: Eclipse Trace Compass™ is an open source application to solve performance and reliability issues by reading and analyzing logs or traces of a system. Its goal is to provide views, graphs, metrics, and more to help extract useful information from traces, in a way that is more user-friendly and informative than huge text dumps.

If you want to import the collected instrumentation logs in Trace Compass, you can use the convertToJson option in the configuration file to convert the output logs to JSON format.

JSON Output Example:

[
    {
        "ts": 1724686484544229.333,
        "ph": "B",
        "name": "public static void com.example.pkg.Main.main(java.lang.String[])"
    },
    {
        "ts": 1724686484546125.563,
        "ph": "B",
        "name": "private static void com.example.pkg.Main.firstMethod()"
    },
    {
        "ts": 1724686484546247.763,
        "ph": "E",
        "name": "private static void com.example.pkg.Main.firstMethod()"
    },
    {
        "ts": 1724686484546282.093,
        "ph": "B",
        "name": "java.lang.String com.example.pkg.Main.secondMethod()"
    },
    {
        "ts": 1724686484546306.258,
        "ph": "E",
        "name": "java.lang.String com.example.pkg.Main.secondMethod()"
    },
    {
        "ts": 1724686484546331.966,
        "ph": "B",
        "name": "public int com.example.pkg.Main.thirdMethod(int,int)"
    },
    {
        "ts": 1724686484546356.608,
        "ph": "E",
        "name": "public int com.example.pkg.Main.thirdMethod(int,int)"
    },
    {
        "ts": 1724686484546380.330,
        "ph": "B",
        "name": "protected com.example.pkg.Another com.example.pkg.Main.fourthMethod()"
    },
    {
        "ts": 1724686484548543.913,
        "ph": "E",
        "name": "protected com.example.pkg.Another com.example.pkg.Main.fourthMethod()"
    },
    {
        "ts": 1724686484548604.858,
        "ph": "B",
        "name": "private static void com.example.pkg.Main.fifthMethod(java.util.HashMap,java.lang.String)"
    },
    {
        "ts": 1724686484548632.518,
        "ph": "E",
        "name": "private static void com.example.pkg.Main.fifthMethod(java.util.HashMap,java.lang.String)"
    },
    {
        "ts": 1724686484548654.718,
        "ph": "E",
        "name": "public static void com.example.pkg.Main.main(java.lang.String[])"
    }
]

Then, you may import the trace file in Trace Compass. Below is a sample visualization of our trace file (i.e., Flame Chart)

jib_flame_chart

You can see this video tutorial on Youtube to see how to import the generated json file in Trace Compass.