jni-jattach

JVM Dynamic Attach library

Is a jni implementation of the apangin/jattach utility

The utility to send commands to remote JVM via Dynamic Attach mechanism.

All-in-one jmap + jstack + jcmd + jinfo functionality in a single tiny program.
No installed JDK required, works with just JRE.

This is the lightweight native version of HotSpot Attach API
https://docs.oracle.com/javase/8/docs/jdk/api/attach/spec/

Usage

int responseCode = Jattach.exec(pid, command, option1, option2, option3, buffer);

Where buffer - DirectByteBuffer in which the response will be written, if null, the result will be written to standard stdout. Use ByteBuffer.allocateDirect(bufferSize).

Supported commands:

• load : load agent library
• properties : print system properties
• agentProperties : print agent properties
• datadump : show heap and thread summary. Issue: the result of this command is written to standard stdout, even if buffer is not null
• threaddump : dump all stack traces (like jstack)
• dumpheap : dump heap (like jmap)
• inspectheap : heap histogram (like jmap -histo)
• setflag : modify manageable VM flag
• printflag : print VM flag
• jcmd : execute jcmd command

Examples

Load JVMTI agent

int responseCode = Jattach.exec(pid, "load", "path to jvmti agent", "true" | "false", "[options]", buffer);

Where true means that the path is absolute, false - the path is relative, options are passed to the agent.

Load jar agent

int responseCode = Jattach.exec(pid, "load", "instrument", "false", "agentJar.jar", null);

Get properties of runnning jvm

ByteBuffer buffer = ByteBuffer.allocateDirect(8192);
int responseCode = Jattach.exec(pid, "properties", null, null, null, buffer);

Terminal usage

$ java -jar jattach.jar <pid> <command> [options] [--buffersize <size>]