On 21/03/17 21:32, Edward Burns wrote:
> Hello Volunteers,
>
> Background
> ==========
>
> This old issues is in our list of low hanging fruit so I thought I'd try
> to resolve it. The reporter factually points out that the current
> specification for Servlet#init() says nothing about "visibility" as
> discussed in section 17.4.5 of the JLS. The reporter requests we say
> something here.
>
> Consider this code:
>
> public class MyServlet extends Servlet {
> ServletConfig config = null;
>
> public void init(ServletConfig config) {
> this.config = config;
> }
>
> public void doGet() {
> // do something with config.
> }
> }
>
> Lots of code out there does this, but the fact that it works is a bit
> sketchy.
>
> This issue is asking for clarification of the safety of doing the above.
> We have three options, none of them very appealing.
>
> Option WONTFIX:
>
> We simply punt on this issue and mark it as WONTFIX.
>
> Option ServletAuthor:
>
> I propose we take the easy way out here and add the following text to
> Servlet#init():
>
> Note that containers are not obligated to invoke the Servlet#init()
> method on the same thread that may be used for any subsequent
> invocations of request handling methods on the same Servlet. Therefore,
> care must be taken to ensure the proper visibility expectations are
> maintained. The results are unspecified if these measures are not taken.
>
> And the following sentence after the sentence in 2.3.3.1. New text in
> **.
>
> 2.3.3.1 Multithreading Issues
>
> A servlet container may send concurrent requests through the service
> method of the servlet. To handle the requests, the Servlet Developer
> must make adequate provisions for concurrent processing with multiple
> threads in the service method. **The Servlet Developer must also make
> adequate provisions for the visibility, in the service() method of
> data passed to Servlet.init(), per the Java Memory Model.**
>
> Option Container:
>
> We modify the spec to require the container to ensure the visibility
> requirements are met.
>
> I propose we take the easy way out here and add the following text to
> Servlet#init():
>
> Containers must ensure that the ServletConfig object passed to
> Servlet.init() is visible, per the Java Memory Model, to the service
> method (and any convenience methods thereof).
>
> ACTION: Please weigh in on this by close of business Friday 24 March
> 2017. In the absence of any discussion, we'll go with option
> ServletAuthor.
I prefer Option Container. This is the behaviour users tend to assume
and it is going to be less work (overall) to fix this in a handful of
containers than in every Servlet.
Mark