fix: double start bug

[paul-nechifor]

Problem

In certain tests (test_dimos_skills) lcm.start could be called twice.

Solution

Make LCMService.start idempotent.

[greptile-apps]

Greptile Summary

This PR makes LCMService.start() idempotent by adding a dedicated _start_lock and an early-return guard (if self._thread is not None and self._thread.is_alive(): return). The stop() method is also brought under _start_lock and now explicitly sets self._thread = None after joining, enabling the guard to distinguish a stopped thread from a running one.

• _start_lock is correctly initialized in __init__, __setstate__, and excluded from __getstate__ — the full lifecycle is covered.
• stop() now sets self._thread = None only on the non-self-join path; when the LCM thread calls stop() on itself, the thread reference is left set but the is_alive() check in start() still allows a future restart, so behavior is correct in both paths.
• The test is updated to assert service._thread is None (matching the new cleanup) rather than not service._thread.is_alive().

Confidence Score: 5/5

Safe to merge — the change is narrowly scoped to making start() idempotent and does not alter any message-handling or subscription logic.

The lock is correctly initialized in all three state-management paths (init, setstate, getstate), the early-return guard is sound, and stop() reliably nulls the thread reference on the join path. No existing behavior is changed for the normal start-then-stop lifecycle.

No files require special attention.

Important Files Changed

Filename	Overview
dimos/protocol/service/lcmservice.py	Adds _start_lock to make start() idempotent and brings stop() under the same lock; thread reference is now nulled after join for clean state.
dimos/protocol/service/test_lcmservice.py	Single assertion updated to match new stop() behavior (thread set to None rather than just dead).

Sequence Diagram

%%{init: {'theme': 'neutral'}}%%
sequenceDiagram
    participant Caller
    participant LCMService
    participant _start_lock
    participant LCMThread

    Note over Caller,LCMThread: Idempotent start() - second call is a no-op

    Caller->>LCMService: start()
    LCMService->>_start_lock: acquire
    LCMService->>LCMService: _thread alive? No
    LCMService->>LCMThread: create and start thread
    LCMThread-->>LCMService: _loop_running.set()
    LCMService->>_start_lock: release

    Caller->>LCMService: start() again
    LCMService->>_start_lock: acquire
    LCMService->>LCMService: _thread alive? Yes - return
    LCMService->>_start_lock: release

    Caller->>LCMService: stop()
    LCMService->>_start_lock: acquire
    LCMService->>LCMThread: _stop_event.set()
    LCMService->>LCMThread: join(timeout)
    LCMThread-->>LCMService: thread exits
    LCMService->>LCMService: "_thread = None"
    LCMService->>_start_lock: release

Loading

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sequenceDiagram
    participant Caller
    participant LCMService
    participant _start_lock
    participant LCMThread

    Note over Caller,LCMThread: Idempotent start() - second call is a no-op

    Caller->>LCMService: start()
    LCMService->>_start_lock: acquire
    LCMService->>LCMService: _thread alive? No
    LCMService->>LCMThread: create and start thread
    LCMThread-->>LCMService: _loop_running.set()
    LCMService->>_start_lock: release

    Caller->>LCMService: start() again
    LCMService->>_start_lock: acquire
    LCMService->>LCMService: _thread alive? Yes - return
    LCMService->>_start_lock: release

    Caller->>LCMService: stop()
    LCMService->>_start_lock: acquire
    LCMService->>LCMThread: _stop_event.set()
    LCMService->>LCMThread: join(timeout)
    LCMThread-->>LCMService: thread exits
    LCMService->>LCMService: "_thread = None"
    LCMService->>_start_lock: release

Loading

_{Reviews (4): Last reviewed commit: "fix: double start bug" | Re-trigger Greptile}

[codecov]

Codecov Report

❌ Patch coverage is 76.19048% with 10 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
dimos/protocol/service/lcmservice.py	75.60%	5 Missing and 5 partials ⚠️

@@            Coverage Diff             @@
##             main    #2589      +/-   ##
==========================================
+ Coverage   69.61%   70.88%   +1.27%     
==========================================
  Files         878      866      -12     
  Lines       79326    77251    -2075     
  Branches     7126     6867     -259     
==========================================
- Hits        55220    54759     -461     
+ Misses      22301    20691    -1610     
+ Partials     1805     1801       -4     

Flag	Coverage Δ
OS-ubuntu-24.04-arm	62.99% <71.42%> (+<0.01%)	⬆️
OS-ubuntu-latest	65.82% <71.42%> (-0.01%)	⬇️
Py-3.10	65.82% <71.42%> (+<0.01%)	⬆️
Py-3.11	65.82% <71.42%> (+<0.01%)	⬆️
Py-3.12	65.82% <71.42%> (-0.01%)	⬇️
Py-3.13	65.82% <71.42%> (+<0.01%)	⬆️
Py-3.14	65.83% <71.42%> (-0.01%)	⬇️
Py-3.14t	65.82% <71.42%> (-0.01%)	⬇️
SelfHosted-Large	30.11% <45.23%> (+0.01%)	⬆️
SelfHosted-Linux	37.80% <42.85%> (+<0.01%)	⬆️
SelfHosted-macOS	36.59% <42.85%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
dimos/protocol/service/test_lcmservice.py	100.00% <100.00%> (ø)
dimos/protocol/service/lcmservice.py	88.18% <75.60%> (-3.34%)	⬇️

... and 13 files with indirect coverage changes

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