Incorrect validation of DST in java.util.SimpleTimeZone

[Venkateswara R Chintala]

Hi,

In a multi-threaded environment, when java.util.SimpleTimeZone object is 
used to create a default timezone, there can be a race condition between 
the methods java.util.Timezone.getDefault() and 
java.util.Timezone.getDefaultRef() which can result in inconsistency of 
cache that is used to validate a particular time/date in DST.

When a thread is cloning a default timezone object (SimpleTimeZone) and 
at the same time if a different thread modifies the time/year values, 
then the cache values (cacheYear, cacheStart, cacheEnd) can become 
inconsistent which leads to incorrect DST determination.

We considered two approaches to fix the issue.

1)Synchronize access to cloning default timezone object when cache is 
being modified.

2)Invalidate the cache while returning the clone.

We preferred the second option as synchronization is more expensive.

We have attached the patch and jtreg testcase. Please review.

-- 
Regards
-Venkat