8028564: Concurrent calls to CHM.put can fail to add the key/value to the map

[Paul Sandoz]

I have reviewed Doug's code, just need someone to quickly review the test code.

Paul.

On Dec 2, 2013, at 5:29 PM, Paul Sandoz <Paul.Sandoz at oracle.com> wrote:

> Hi,
> 
> http://cr.openjdk.java.net/~psandoz/tl/JDK-8028564-concurrent-resize/webrev/
> 
> This patch is contributed by Doug Lea and fixes two issues found in ConcurrentHashMap:
> 
>  1) A problem with concurrent resizes; and
> 
>  2) The skipping of elements when traversing through bins that are trees of entries.
> 
> Both of these issues can result in elements "disappearing" from the map, either because an update operation such as put failed, or because a contains operation failed to find the entry in the map.
> 
> Issue 1) was causing stream tests to fail intermittently on systems with many cores (24 to 32) (furthermore the CHM-based JDK test ToArray was also intermittently failing with less frequency). 
> 
> After some investigation the cause was distilled down to the use of ConcurrentHashMap in the F/J task used by Stream.forEachOrdered. 
> 
> Issue 2) was serendipitously reported on concurrentcy-interest just yesterday :-)
> 
> Both issues have test cases associated with them that have been tuned to reproduce on systems with low cores i.e. my MacBook!
> 
> Paul.