# Working With Fork Process Models

The `BatchSpanProcessor` is not fork-safe and doesn’t work well with application servers (Gunicorn, uWSGI) which are based on the pre-fork web server model. The `BatchSpanProcessor` spawns a thread to run in the background to export spans to the telemetry backend. During the fork, the child process inherits the lock which is held by the parent process and deadlock occurs. We can use fork hooks to get around this limitation of the span processor.

Please see http://bugs.python.org/issue6721 for the problems about Python locks in (multi)threaded context with fork.

The source code for the examples with Flask app are available here.

## Gunicorn post_fork hook

    from opentelemetry import trace
    from opentelemetry.exporter.otlp.proto.grpc.trace_exporter import OTLPSpanExporter
    from opentelemetry.sdk.resources import Resource
    from opentelemetry.sdk.trace import TracerProvider
    from opentelemetry.sdk.trace.export import BatchSpanProcessor

    def post_fork(server, worker):
        server.log.info("Worker spawned (pid: %s)", worker.pid)

        resource = Resource.create(attributes={
            "service.name": "api-service"
        })

        trace.set_tracer_provider(TracerProvider(resource=resource))
        span_processor = BatchSpanProcessor(
            OTLPSpanExporter(endpoint="http://localhost:4317")
        )
        trace.get_tracer_provider().add_span_processor(span_processor)

## uWSGI postfork decorator

    from uwsgidecorators import postfork

    from opentelemetry import trace
    from opentelemetry.exporter.otlp.proto.grpc.trace_exporter import OTLPSpanExporter
    from opentelemetry.sdk.resources import Resource
    from opentelemetry.sdk.trace import TracerProvider
    from opentelemetry.sdk.trace.export import BatchSpanProcessor

    @postfork
    def init_tracing():
        resource = Resource.create(attributes={
            "service.name": "api-service"
        })

        trace.set_tracer_provider(TracerProvider(resource=resource))
        span_processor = BatchSpanProcessor(
            OTLPSpanExporter(endpoint="http://localhost:4317")
        )
        trace.get_tracer_provider().add_span_processor(span_processor)