kickoff() Is it thread safe？

[tianshangwuyun]

I want to know if this method is thread safe, and if the state in the flow is stored in memory and thread safe

[lakshit2234]

kickoff() is not thread-safe by default in CrewAI.

Here's why:

State storage: The flow state is stored in-memory as a Python object
on the Flow instance. If multiple threads share the same Flow instance
and call kickoff() simultaneously, they will read/write the same state
object — causing race conditions.

Safe approaches:

1. One instance per thread — create a separate Flow instance for
   each thread/request. This is the recommended pattern:

import threading
from crewai.flow.flow import Flow

def run_flow():
    flow = MyFlow()  # new instance per thread
    flow.kickoff()

threads = [threading.Thread(target=run_flow) for _ in range(5)]
for t in threads:
    t.start()

2. Use async instead — kickoff_async() with asyncio is safer
   for concurrent execution since each coroutine has its own execution context.

3. Avoid shared mutable state — if you must share a Flow instance,
   protect state mutations with threading.Lock().

Bottom line: treat each Flow instance as single-use and non-shared
across threads. Instantiate fresh per request/thread for safe concurrent usage.