perf: reduce framework overhead — lazy event bus, skip tracing when disabled (#5187)

* perf: reduce framework overhead for NVIDIA benchmarks

- Lazy initialize event bus thread pool and event loop on first emit()
  instead of at import time (~200ms savings)
- Skip trace listener registration (50+ handlers) when tracing disabled
- Skip trace prompt in non-interactive contexts (isatty check) to avoid
  20s timeout in CI/Docker/API servers
- Skip flush() when no events were emitted (avoids 30s timeout waste)
- Add _has_pending_events flag to track if any events were emitted
- Add _executor_initialized flag for lazy init double-checked locking

All existing behavior preserved when tracing IS enabled. No public APIs
changed - only conditional guards added.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* fix: address PR review comments — tracing override, executor init order, stdin guard, unused import

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* style: fix ruff formatting in trace_listener.py and utils.py

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
Co-authored-by: Iris Clawd <iris@crewai.com>
Co-authored-by: Greyson LaLonde <greyson.r.lalonde@gmail.com>

lib/crewai/src/crewai/events/event_bus.py

@@ -85,6 +85,8 @@ class CrewAIEventsBus:
     _shutting_down: bool
     _pending_futures: set[Future[Any]]
     _futures_lock: threading.Lock
+    _executor_initialized: bool
+    _has_pending_events: bool
 
     def __new__(cls) -> Self:
         """Create or return the singleton instance.
@@ -102,8 +104,9 @@ class CrewAIEventsBus:
     def _initialize(self) -> None:
         """Initialize the event bus internal state.
 
-        Creates handler dictionaries and starts a dedicated background
-        event loop for async handler execution.
+        Creates handler dictionaries. The thread pool executor and event loop
+        are lazily initialized on first emit() to avoid overhead when events
+        are never emitted.
         """
         self._shutting_down = False
         self._rwlock = RWLock()
@@ -115,19 +118,37 @@ class CrewAIEventsBus:
             type[BaseEvent], dict[Handler, list[Depends[Any]]]
         ] = {}
         self._execution_plan_cache: dict[type[BaseEvent], ExecutionPlan] = {}
-        self._sync_executor = ThreadPoolExecutor(
-            max_workers=10,
-            thread_name_prefix="CrewAISyncHandler",
-        )
         self._console = ConsoleFormatter()
+        # Lazy initialization flags - executor and loop created on first emit
+        self._executor_initialized = False
+        self._has_pending_events = False
 
-        self._loop = asyncio.new_event_loop()
-        self._loop_thread = threading.Thread(
-            target=self._run_loop,
-            name="CrewAIEventsLoop",
-            daemon=True,
-        )
-        self._loop_thread.start()
+    def _ensure_executor_initialized(self) -> None:
+        """Lazily initialize the thread pool executor and event loop.
+
+        Called on first emit() to avoid startup overhead when events are never used.
+        Thread-safe via double-checked locking.
+        """
+        if self._executor_initialized:
+            return
+
+        with self._instance_lock:
+            if self._executor_initialized:
+                return
+
+            self._sync_executor = ThreadPoolExecutor(
+                max_workers=10,
+                thread_name_prefix="CrewAISyncHandler",
+            )
+
+            self._loop = asyncio.new_event_loop()
+            self._loop_thread = threading.Thread(
+                target=self._run_loop,
+                name="CrewAIEventsLoop",
+                daemon=True,
+            )
+            self._loop_thread.start()
+            self._executor_initialized = True
 
     def _track_future(self, future: Future[Any]) -> Future[Any]:
         """Track a future and set up automatic cleanup when it completes.
@@ -431,6 +452,15 @@ class CrewAIEventsBus:
             sync_handlers = self._sync_handlers.get(event_type, frozenset())
             async_handlers = self._async_handlers.get(event_type, frozenset())
 
+        # Skip executor initialization if no handlers exist for this event
+        if not sync_handlers and not async_handlers:
+            return None
+
+        # Lazily initialize executor and event loop only when handlers exist
+        self._ensure_executor_initialized()
+        # Track that we have pending events for flush optimization
+        self._has_pending_events = True
+
         if has_dependencies:
             return self._track_future(
                 asyncio.run_coroutine_threadsafe(
@@ -474,6 +504,10 @@ class CrewAIEventsBus:
         Returns:
             True if all handlers completed, False if timeout occurred.
         """
+        # Skip flush entirely if no events were ever emitted
+        if not self._has_pending_events:
+            return True
+
         with self._futures_lock:
             futures_to_wait = list(self._pending_futures)
 
@@ -629,6 +663,9 @@ class CrewAIEventsBus:
 
         with self._rwlock.w_locked():
             self._shutting_down = True
+            # Check if executor was ever initialized (lazy init optimization)
+            if not self._executor_initialized:
+                return
             loop = getattr(self, "_loop", None)
 
         if loop is None or loop.is_closed():

lib/crewai/src/crewai/events/listeners/tracing/trace_listener.py

@@ -17,7 +17,10 @@ from crewai.events.listeners.tracing.first_time_trace_handler import (
 from crewai.events.listeners.tracing.trace_batch_manager import TraceBatchManager
 from crewai.events.listeners.tracing.types import TraceEvent
 from crewai.events.listeners.tracing.utils import (
+    is_tracing_enabled_in_context,
     safe_serialize_to_dict,
+    should_auto_collect_first_time_traces,
+    should_enable_tracing,
 )
 from crewai.events.types.a2a_events import (
     A2AAgentCardFetchedEvent,
@@ -198,6 +201,17 @@ class TraceCollectionListener(BaseEventListener):
         if self._listeners_setup:
             return
 
+        # Skip registration entirely if tracing is disabled and not first-time user
+        # This avoids overhead of 50+ handler registrations when tracing won't be used
+        # Also check is_tracing_enabled_in_context() so per-run overrides (Crew(tracing=True)) still work
+        if (
+            not should_enable_tracing()
+            and not is_tracing_enabled_in_context()
+            and not should_auto_collect_first_time_traces()
+        ):
+            self._listeners_setup = True
+            return
+
         self._register_env_event_handlers(crewai_event_bus)
         self._register_flow_event_handlers(crewai_event_bus)
         self._register_context_event_handlers(crewai_event_bus)

lib/crewai/src/crewai/events/listeners/tracing/utils.py

@@ -481,6 +481,26 @@ def should_auto_collect_first_time_traces() -> bool:
     return is_first_execution()
 
 
+def _is_interactive_terminal() -> bool:
+    """Check if stdin is an interactive terminal.
+
+    Returns False in non-interactive contexts (CI, API servers, Docker, etc.)
+    to avoid blocking on prompts that no one can respond to.
+    """
+    import sys
+
+    try:
+        stdin = getattr(sys, "stdin", None)
+        if stdin is None:
+            return False
+        isatty = getattr(stdin, "isatty", None)
+        if not callable(isatty):
+            return False
+        return bool(isatty())
+    except Exception:
+        return False
+
+
 def prompt_user_for_trace_viewing(timeout_seconds: int = 20) -> bool:
     """
     Prompt user if they want to see their traces with timeout.
@@ -492,6 +512,11 @@ def prompt_user_for_trace_viewing(timeout_seconds: int = 20) -> bool:
     if should_suppress_tracing_messages():
         return False
 
+    # Skip prompt in non-interactive contexts (CI, API servers, Docker, etc.)
+    # This avoids blocking for 20 seconds when no one can respond
+    if not _is_interactive_terminal():
+        return False
+
     try:
         import threading
 

lib/crewai/tests/tracing/test_tracing.py

@@ -793,6 +793,10 @@ class TestTraceListenerSetup:
                 "crewai.events.listeners.tracing.utils._is_test_environment",
                 return_value=False,
             ),
+            patch(
+                "crewai.events.listeners.tracing.utils._is_interactive_terminal",
+                return_value=True,
+            ),
             patch("threading.Thread") as mock_thread,
         ):
             from crewai.events.listeners.tracing.utils import (