HttpRequest#executeAsync leaks a thread on every call #2122

The executeAsync method of com.google.api.client.http.HttpRequest currently leaks a thread on every call; this means that multiple calls to the method will eventually exhaust all memory.

A quick inspection of the code for this method shows that it creates a new thread pool on every call, and never shuts the pool down.

Steps to replicate

This issue can be easily replicated in a unit test; for example, the following code (added in HttpRequestTest.java) will fail with an OutOfMemoryError due to an inability to create a new thread.

  @Test
  public void testThreadLeak() throws Exception {
    for (int i = 0; i < 1000000; i++) {
      RedirectTransport fakeTransport = new RedirectTransport();
      HttpRequest request =
              fakeTransport.createRequestFactory().buildGetRequest(new GenericUrl("http://gmail.com"));
      Future<HttpResponse> resp = request.executeAsync();
      resp.get();
    }
  }