From: Edward Burns <edward.burns_at_oracle.com>
Date: Tue, 21 Mar 2017 14:32:14 -0700

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.

Thanks,

Ed

-- 
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