Using grpc as client in webflux - spring-webflux

Question

Our team's project is a product that accepts requests and then forwards them to processing business machines. We use Springboot's webflux as a framework and use gRPC in it as a client to send requests to business machines.
Its process is as follows:
User <-> Webflux <-> gRPC <-> The machine that actually handle the business
We were drawn to the asynchronous non-blocking nature of webflux and gRPC. gRPC uses streaming.
The controller and service we wrote are roughly as follows:
#PostMapping(”xxxx“)
pulbic Mono<String> mac() {
final COmpletableFuture<String> future = new CompletableFuture<>();
final StreamObserver<MacMessage> request = gRPCService.getStub.mac(new StreamObserver<>() {
String mac;
#Override
public void onNext(MacMessage value) {
mac = Base64.encode(value.getMac.toByteArray());
}
#Override
public void onError(Throwable t) {
future.completeExceptionally(t);
}
#Override
public void onCompleted() {
future.complete(mac);
}
});
request.onNext(MacMessage.newBuilder().setxxxx....build());
request.onCompleted();
return Mono.fromFuture(future);
}
In addition, when I tried the Mono API recently, I found another way of writing, which does not require the use of CompletableFuture, and the effect is similar:
#PostMapping(”xxxx“)
pulbic Mono<String> mac() {
return Mono.create(monoSink -> {
final StreamObserver<MacMessage> request = gRPCService.getStub.mac(new StreamObserver<>() {
String mac;
#Override
public void onNext(MacMessage value) {
mac = Base64.encode(value.getMac.toByteArray());
}
#Override
public void onError(Throwable t) {
monoSink.error(t);
}
#Override
public void onCompleted() {
monoSink.success(mac);
}
});
request.onNext(MacMessage.newBuilder().setxxxx....build());
request.onCompleted();
});
}
I would like to know whether the above writing methods have met the requirements of asynchronous non-blocking, and if not, how should they be used?
The reason for this doubt is that (taking the above code as an example) we found that if we only use printing to consume the response value in gRPC StreamObserver#onNext, the performance is much higher than the above two writing methods, and the performance of the above two writing methods is similar . This makes me wonder, is there such a big difference in the performance of printing the consumption response value and returning the response value?