Request for review: Race conditions in java.nio.charset.Charset

[Ulf Zibis]

I.) Internal charset cache will be corrupted in theoretical race conditions:

Startpoint:
  cache1 --> Charset1
  cache2 --> Charset2

Scenario 1:
- Thread1 asks for Charset2 via Charset.forName("Charset2").
- If Thread1 is interrupted after code line: cache2 = cache1
  in method lookup2(String charsetName) we have:
  cache1 --> Charset1
  cache2 --> Charset1
> If now thread2 asks for Charset2, it can't find it in cache, so it invokes
  an expensive lookup via registered providers.

Scenario 2:
- Thread1 asks for Charset2.
- Thread1 is interupted before cache2 = cache1;
- If now thread2 asks for Charset2 we have after completing lookup2():
  cache1 --> Charset2
  cache2 --> Charset1
- Now thread1 resumes; after completing lookup2() we have:
  cache1 --> Charset2
  cache2 --> Charset2
> In the end we can see, that Charset1 is lost in cache.


II.) Endless loop, if VM's default charset (called by Charset.defaultCharset())
     needs to load mapping data via Class.getResourceAsStream():

- Invoking Class.getResourceAsStream(), again calls for Charset.defaultCharset(),
  so we are in endless loop.

Note: The error condition, described in
      http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6795536
      is fixed since Bug ID 6797688, but the endless loop, getting the default charset, remains.


See my patches here: https://bugs.openjdk.java.net/show_bug.cgi?id=100107


-Ulf