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rtc: fail fast instead of hanging when FFI is used across fork() #740

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rtc: fail fast instead of hanging when FFI is used across fork() #740

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16 changes: 15 additions & 1 deletion livekit-rtc/livekit/rtc/_ffi_client.py
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@devin-ai-integration devin-ai-integration Bot Jul 6, 2026

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🔍 Callback still uses auto-creating singleton property, inconsistent with dispose()

The ffi_event_callback at livekit-rtc/livekit/rtc/_ffi_client.py:194 still accesses FfiClient.instance (the auto-creating @classproperty), while FfiHandle.dispose() was deliberately changed to use FfiClient._instance (the raw class variable) to avoid auto-creation during shutdown or in forked children. In practice this is likely safe because native threads aren't inherited across fork(), so the callback shouldn't fire in a child process. However, for consistency with the fork-safety intent of this PR, it might be worth using FfiClient._instance here too (with a None guard).

(Refers to line 194)

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Original file line number Diff line number Diff line change
Expand Up @@ -83,7 +83,11 @@ def disposed(self) -> bool:
def dispose(self) -> None:
if self.handle != INVALID_HANDLE and not self._disposed:
self._disposed = True
assert FfiClient.instance._ffi_lib.livekit_ffi_drop_handle(ctypes.c_uint64(self.handle))
ffi = FfiClient._instance
if ffi is None or ffi._pid != os.getpid():
return
dropped = ffi._ffi_lib.livekit_ffi_drop_handle(ctypes.c_uint64(self.handle))
assert dropped
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def __repr__(self) -> str:
return f"FfiHandle({self.handle})"
Expand Down Expand Up @@ -218,6 +222,7 @@ def instance(cls) -> "FfiClient":
return cls._instance

def __init__(self) -> None:
self._pid = os.getpid()
self._lock = threading.RLock()
self._queue = FfiQueue[proto_ffi.FfiEvent]()

Expand Down Expand Up @@ -253,16 +258,25 @@ def __init__(self) -> None:
)

ffi_lib = self._ffi_lib
init_pid = self._pid

@atexit.register
def _dispose_lk_ffi() -> None:
if os.getpid() != init_pid:
return
ffi_lib.livekit_ffi_dispose()

@property
def queue(self) -> FfiQueue[proto_ffi.FfiEvent]:
return self._queue

def request(self, req: proto_ffi.FfiRequest) -> proto_ffi.FfiResponse:
if self._pid != os.getpid():
raise RuntimeError(
"livekit.rtc was used in a parent process before fork(); the native "
"runtime cannot be used across fork(). Do not create or connect a Room "
"(or use any livekit.rtc object) before forking child processes."
)
proto_data = req.SerializeToString()
proto_len = len(proto_data)
data = (ctypes.c_ubyte * proto_len)(*proto_data)
Expand Down
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