Add documentation for jcmd support

docs/reference-manual/native-image/DebuggingAndDiagnostics.md

@@ -15,4 +15,5 @@ Native Image provides utilities for debugging and inspecting the produced binary
  - For an overview of static analysis results, see [Static Analysis Reports](StaticAnalysisReports.md)
  - For performance analysis, see [Linux Perf Profiler Support in Native Image](PerfProfiling.md)
  - For an overall insight regarding build phases and the contents of a native executable, use [Build Reports](BuildReport.md)
- - For native memory tracking, see [Native Memory Tracking (NMT)](NMT.md)
+ - For native memory tracking, see [Native Memory Tracking (NMT)](NMT.md)
+- See the [Java Diagnostic Command documentation](JCmd.md) for instructions on using `jcmd`.

docs/reference-manual/native-image/JCmd.md

@@ -0,0 +1,101 @@
+---
+layout: docs
+toc_group: debugging-and-diagnostics
+link_title: Java Diagnostic Command
+permalink: /reference-manual/native-image/debugging-and-diagnostics/jcmd/
+---
+
+# Java Diagnostic Command (jcmd) with Native Image
+
+Native Image now supports the Java Diagnostic Command (`jcmd`), enabling users to interact with native executables using the same `jcmd` tool they use for Java applications.
+This support complements existing Native Image monitoring features, including JDK Flight Recorder, heap dumps, and native memory tracking.
+
+## Enabling `jcmd` Support
+
+Support for `jcmd` is disabled by default and must be explicitly enabled at build time.
+
+To build a native executable with `jcmd` support, use the `--enable-monitoring=jcmd` option.
+```shell
+native-image --enable-monitoring=jcmd YourApplication
+```
+
+When enabling support for `jcmd`, you may also want to include additional monitoring features, such as JDK Flight Recorder or heap dumps.
+Including multiple monitoring features during the Native Image build process unlocks access to more diagnostic commands at runtime. For example:
+```shell
+native-image --enable-monitoring=jcmd,jfr,heapdump YourApplication
+```
+
+You may also want to include the `jvmstat` monitoring feature so your native executable can be discovered and listed with `jcmd -l` or `jcmd` with no arguments provided.
+```shell
+native-image --enable-monitoring=jcmd,jvmstat YourApplication
+```
+
+```shell
+jcmd -l
+1455557 YourApplication
+1455667 jdk.jcmd/sun.tools.jcmd.JCmd -l
+```
+
+To use `jcmd` at runtime, start your native executable as usual and obtain its process ID (PID).
+With the PID, you can use `jcmd` to connect to the running native application.
+For example, to list the available commands for a specific executable, run: `jcmd <pid> help`.
+```shell
+jcmd 388454 help
+
+388454:
+The following commands are available:
+GC.heap_dump
+GC.run
+JFR.start
+JFR.stop
+JFR.check
+JFR.dump
+Thread.dump_to_file
+Thread.print
+VM.command_line
+VM.native_memory
+VM.system_properties
+VM.uptime
+VM.version
+help
+
+For more information about a specific command use 'help <command>'.
+```
+
+## Supported Diagnostic Commands
+
+The following key-value pairs are supported:
+
+| Name                     | Included with `--enable-monitoring=`            | Description                                                                                         |
+|--------------------------|-------------------------------------------------|-----------------------------------------------------------------------------------------------------|
+| Compiler.dump_code_cache | Only available with Truffle runtime compilation | Print information about all compiled methods in the code cache.                                     |
+| GC.heap_dump             | heapdump                                        | Generate a HPROF format dump of the Java heap.                                                      |
+| GC.run                   | Always available                                | Call `java.lang.System.gc()`.                                                                       |
+| JFR.start                | jfr                                             | Starts a new JFR recording.                                                                         |
+| JFR.stop                 | jfr                                             | Stops a JFR recording.                                                                              |
+| JFR.check                | jfr                                             | Checks running JFR recording(s).                                                                    |
+| JFR.dump                 | jfr                                             | Copies contents of a JFR recording to file. Either the name or the recording id must be specified.  |
+| Thread.dump_to_file      | Always available                                | Dump threads, with stack traces, to a file in plain text or JSON format.                            |
+| Thread.print             | Always available                                | Print all threads with stacktraces.                                                                 |
+| VM.command_line          | Always available                                | Print the command line used to start this VM instance.                                              |
+| VM.native_memory         | nmt                                             | Print native memory usage.                                                                          |
+| VM.system_properties     | Always available                                | Print native memory usage                                                                           |
+| VM.uptime                | Always available                                | Print VM uptime.                                                                                    |
+| VM.version               | Always available                                | Print JVM version information.                                                                      | 
+| help                     | Always available                                | Display help information.                                                                           |
+
+## Performance
+
+Adding `jcmd` support to Native Image has minimal impact on performance when the application is idle.
+However, the performance impact varies significantly depending on the diagnostic commands used and how frequently they are invoked.
+For example, triggering multiple garbage collections will have a much greater overhead than dumping a single native memory tracking report.
+You can use `jcmd <pid> help <command>` to print the help information for a specific command which also lists its expected performance impact.
+
+## Limitations
+
+Currently, this feature is not available on Windows.
+
+### Further Reading
+
+- [Debugging and Diagnostics](DebuggingAndDiagnostics.md)
+- [Build and Run Native Executables with JFR](guides/build-and-run-native-executable-with-jfr.md)