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fix: resolve _ENV_LOCK deadlock that blocks chat after first message

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The v0.39.0 security sprint introduced _ENV_LOCK to protect env var
mutations in the streaming path. The implementation held the lock for
the entire agent run (potentially minutes), then tried to re-acquire
it in the finally block — a guaranteed deadlock on any non-reentrant
threading.Lock().

Result: first message completes (done event fires before finally hits),
but the lock is never released. Every subsequent chat/start POST blocks
forever waiting for that lock.

Fix: narrow the lock scope to just the env mutation. Set the vars inside
the with block, then let the lock release before the agent starts. The
finally block re-acquires cleanly since it no longer re-enters an
already-held lock.

No logic change — only the critical section boundary moves.
This commit is contained in:
Nathan Esquenazi
2026-04-08 14:22:39 +00:00
parent 9e9fcb09d2
commit 4422a87de9
1 changed files with 14 additions and 11 deletions
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25
api/streaming.py
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@@ -107,6 +107,9 @@ def _run_agent_streaming(session_id, msg_text, model, workspace, stream_id, atta
HERMES_HOME=_profile_home,
)
# Still set process-level env as fallback for tools that bypass thread-local
# Acquire lock only for the env mutation, then release before the agent runs.
# The finally block re-acquires to restore — keeping critical sections short
# and preventing a deadlock where the restore would re-enter the same lock.
with _ENV_LOCK:
old_cwd = os.environ.get('TERMINAL_CWD')
old_exec_ask = os.environ.get('HERMES_EXEC_ASK')
@@ -117,8 +120,8 @@ def _run_agent_streaming(session_id, msg_text, model, workspace, stream_id, atta
os.environ['HERMES_SESSION_KEY'] = session_id
if _profile_home:
os.environ['HERMES_HOME'] = _profile_home
try:
# Lock released — agent runs without holding it
try:
def on_token(text):
if text is None:
return # end-of-stream sentinel
@@ -378,16 +381,16 @@ def _run_agent_streaming(session_id, msg_text, model, workspace, stream_id, atta
usage['threshold_tokens'] = getattr(_cc, 'threshold_tokens', 0) or 0
usage['last_prompt_tokens'] = getattr(_cc, 'last_prompt_tokens', 0) or 0
put('done', {'session': s.compact() | {'messages': s.messages, 'tool_calls': tool_calls}, 'usage': usage})
finally:
finally:
with _ENV_LOCK:
if old_cwd is None: os.environ.pop('TERMINAL_CWD', None)
else: os.environ['TERMINAL_CWD'] = old_cwd
if old_exec_ask is None: os.environ.pop('HERMES_EXEC_ASK', None)
else: os.environ['HERMES_EXEC_ASK'] = old_exec_ask
if old_session_key is None: os.environ.pop('HERMES_SESSION_KEY', None)
else: os.environ['HERMES_SESSION_KEY'] = old_session_key
if old_hermes_home is None: os.environ.pop('HERMES_HOME', None)
else: os.environ['HERMES_HOME'] = old_hermes_home
if old_cwd is None: os.environ.pop('TERMINAL_CWD', None)
else: os.environ['TERMINAL_CWD'] = old_cwd
if old_exec_ask is None: os.environ.pop('HERMES_EXEC_ASK', None)
else: os.environ['HERMES_EXEC_ASK'] = old_exec_ask
if old_session_key is None: os.environ.pop('HERMES_SESSION_KEY', None)
else: os.environ['HERMES_SESSION_KEY'] = old_session_key
if old_hermes_home is None: os.environ.pop('HERMES_HOME', None)
else: os.environ['HERMES_HOME'] = old_hermes_home
except Exception as e:
print('[webui] stream error:\n' + traceback.format_exc(), flush=True)