Multi-threaded Debugging

When debugging multi-threaded programs or Go goroutines, Krometrail exposes thread listing and selection so you can inspect any thread's state independently.

Listing Threads

CLI

krometrail threads

MCP: debug_threads

{ "session_id": "..." }

Returns all threads (or goroutines in Go), including:

• Thread/goroutine ID
• Name (if available)
• Current location (file:line:function)
• Status: stopped, running, or blocked

Example output for a Go program:

Threads (4):
  * 1  goroutine 1     main.processOrders   order.go:147    stopped (breakpoint)
    2  goroutine 6     net/http.serve       server.go:3086  running
    3  goroutine 7     runtime.gcBgMark     mgc.go:2431     running
    4  goroutine 8     main.backgroundJob   jobs.go:52      blocked (chan receive)

The * marks the currently selected thread.

Selecting a Thread

After listing threads, switch context to a specific thread:

CLI

krometrail threads --select 4

MCP: debug_threads

{ "session_id": "...", "select_thread_id": 4 }

Returns the viewport for the selected thread — source, locals, and call stack at that thread's current location.

Subsequent debug_step, debug_continue, and state inspection commands operate on the selected thread until you switch again.

Per-Thread Stepping

Once a thread is selected, all execution control commands apply to that thread:

# Select a thread
krometrail threads --select 4

# Step within that thread
krometrail step over

# The other threads remain in their current state

Language-Specific Notes

Python — threads correspond to OS threads created by threading.Thread. The GIL limits true parallelism, but the debugger shows all threads.

Node.js — single-threaded event loop. Worker threads (from worker_threads module) appear as separate threads when active.

Go — goroutines, not OS threads. Delve maps goroutines to the debug_threads concept. Goroutine count can be in the hundreds for typical Go programs; filter to stopped status to find interesting ones.

Java — OS threads. All threads created by the JVM (including GC threads) are listed. Filter by status or name to focus on application threads.

Rust — OS threads. Multi-threaded programs using std::thread::spawn expose each thread.

C/C++ — OS threads via GDB/lldb. Signal handling threads may appear.

Tips

• Filter by status — most threads are running or blocked in background work. Focus on stopped threads when a breakpoint fires.
• Goroutines vs. threads — Go programs may have dozens to thousands of goroutines. The debug_threads output limits to a reasonable count; use the filter parameter to narrow by name or status.
• Thread-local state — each thread has its own call stack and local variables. Switch threads with debug_threads to inspect state from a different execution context.