Request for review: Race conditions in java.nio.charset.Charset (original) (raw)

Ulf Zibis Ulf.Zibis at gmx.de
Tue Oct 6 22:09:15 UTC 2009

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.

-Ulf