Ensure cleanup when forked process ends (#785)

logfire/_internal/config.py

@@ -946,7 +946,7 @@ def fix_pid():  # pragma: no cover
                 set_meter_provider(self._meter_provider)
 
             @atexit.register
-            def _exit_open_spans():  # type: ignore[reportUnusedFunction]  # pragma: no cover
+            def exit_open_spans():  # pragma: no cover
                 # Ensure that all open spans are closed when the program exits.
                 # OTEL registers its own atexit callback in the tracer/meter providers to shut them down.
                 # Registering this callback here after the OTEL one means that this runs first.
@@ -961,6 +961,20 @@ def _exit_open_spans():  # type: ignore[reportUnusedFunction]  # pragma: no cove
                     # which would log a warning "Calling end() on an ended span."
                     span.end = lambda *_, **__: None  # type: ignore
 
+            # atexit isn't called in forked processes, patch os._exit to ensure cleanup.
+            # https://github.com/pydantic/logfire/issues/779
+            original_os_exit = os._exit
+
+            def patched_os_exit(code: int):  # pragma: no cover
+                try:
+                    exit_open_spans()
+                    self.force_flush()
+                except:  # noqa  # weird errors can happen during shutdown, ignore them *all* with a bare except
+                    pass
+                return original_os_exit(code)
+
+            os._exit = patched_os_exit
+
             self._initialized = True
 
             # set up context propagation for ThreadPoolExecutor and ProcessPoolExecutor