Debug adapter disconnects (EOF) during long-running computation

[dorbittonn]

Environment

• dap v0.4.1
• debugpy 1.8.18
• Python 3.11.9
• Linux 6.8.0-106-generic x86_64

Description

When a breakpoint takes a long time to reach (program doing heavy computation for minutes), the debug adapter disconnects with EOF. The program itself continues running fine — only the debug adapter connection is lost.

Steps to reproduce

# slow_app.py
import time
import hashlib

def expensive_work():
    results = []
    for i in range(120):  # ~2 minutes of computation
        data = str(i).encode()
        for _ in range(200_000):
            data = hashlib.sha256(data).digest()
        results.append(data)
        print(f"cycle {i}/120", flush=True)
    return results  # breakpoint target

if __name__ == "__main__":
    result = expensive_work()
    print(f"Done, got {len(result)} results")

Two failure modes observed:

Mode 1: dap debug --break (single command)

dap debug slow_app.py --break slow_app.py:14 --session repro
# After ~60s:
# Error: reading response: read length: read unix @->~/.dap-cli/repro.sock: i/o timeout

Mode 2: --stop-on-entry + continue

dap debug slow_app.py --stop-on-entry --session repro
# Returns immediately, stopped at entry ✓

dap continue --break slow_app.py:14 --session repro
# After ~60s:
# Error: debug adapter disconnected unexpectedly: EOF

Expected behavior

dap continue blocks until the breakpoint is hit (however long that takes) and returns the auto-context.

Actual behavior

The debug adapter connection drops after ~60 seconds of continuous computation, even though the program is still running correctly.

Real-world context

This was discovered while trying to debug a PyQt6 app doing GPU inference (torch + CUDA) on 6 video streams. The program needs ~5 minutes of processing to reach the breakpoint at cycle 95. The same program runs perfectly without dap.

Possible cause

There may be a hardcoded timeout in the daemon ↔ adapter communication that doesn't account for long periods without DAP protocol messages (the program is computing, not hitting breakpoints or producing debug events).