title: Spring Webflux / Reactor release calling thread
body: <p>So I understand that under the hood Spring WebFlux and Reactor uses netty for nio, now I would like to release the calling thread to free up the resources in order to handle more requests. Is the below simple code releasing the calling thread? </p>
  
  <pre><code>@GetMapping("/foo")
  public Mono&lt;Void&gt; bar() {
  
    someService.veryLongSyncOperation();
  
    return Mono.empty();
  }
  </code></pre>
  
  <p>I did not wrap the service call in a Flux/Mono, I just want to first verify that the calling thread is released while the service does its long work. Is this enough to achieve calling thread release? If so is there a way to test this? </p>
  
  <p>I was thinking that the framework sees the return type and that's enough for it to know that it must release the calling thread.</p>