[gRPC Exporter] gRPC channel is not properly closed

[XuanWang-Amos]

Describe your environment

N/A

What happened?

The gRPC channel is not being closed properly, preventing gRPC from shutting down cleanly.

Steps to Reproduce

Please refer to: grpc/grpc#38490 (comment)

Expected Result

gRPC cleanly shutting down.

Actual Result

gRPC not cleanly shutting down.

Additional context

In OTLPExporterMixin, gRPC channel was created directly and passed to _client:

opentelemetry-python/exporter/opentelemetry-exporter-otlp-proto-grpc/src/opentelemetry/exporter/otlp/proto/grpc/exporter.py

Lines 245 to 260 in a7fe4f8

	if insecure:
	self._client = self._stub(
	insecure_channel(self._endpoint, compression=compression)
	)
	else:
	credentials = _get_credentials(
	credentials,
	OTEL_EXPORTER_OTLP_CERTIFICATE,
	OTEL_EXPORTER_OTLP_CLIENT_KEY,
	OTEL_EXPORTER_OTLP_CLIENT_CERTIFICATE,
	)
	self._client = self._stub(
	secure_channel(
	self._endpoint, credentials, compression=compression
	)
	)

But the channel was not shutdown in shutdown method:

opentelemetry-python/exporter/opentelemetry-exporter-otlp-proto-grpc/src/opentelemetry/exporter/otlp/proto/grpc/exporter.py

Lines 356 to 363 in a7fe4f8

	def shutdown(self, timeout_millis: float = 30_000, **kwargs) -> None:
	if self._shutdown:
	logger.warning("Exporter already shutdown, ignoring call")
	return
	# wait for the last export if any
	self._export_lock.acquire(timeout=timeout_millis / 1e3)
	self._shutdown = True
	self._export_lock.release()

gRPC channel should be closed explicitly with context manager or by calling channel.close() method, example usage:
https://github.com/grpc/grpc/blob/822f9b15191840228d17dc0d305887374150150e/examples/python/helloworld/greeter_client.py#L25-L33

If not explicitly closed, the gRPC channel may prevent gRPC from shutting down cleanly, leading to issues like the one described in: grpc/grpc#38490

Would you like to implement a fix?

None

[xrmx]

I guess we a PR with the fix already #4370 😅