Re: Concurrency question?

Knute Johnson <>
Sat, 31 Jan 2015 19:51:54 -0800
On 01/31/2015 12:42 PM, Eric Sosman wrote:

On 1/31/2015 2:20 PM, Volker Borchert wrote:

Knute Johnson wrote:

So I have a Map<Integer,String> [ ... ]

Do you see any holes in my logic? Any suggestions?


     That's fine if the consistency criterion involves only single
mappings. But if different mappings within the same Map must "agree"
(in some application-dependent sense), atomicity of individual updates
isn't good enough.

     Only Knute knows for sure ...

When I first saw Volker's suggestion I thought, no I can't iterate over
the map without some other synchronization but I looked into the
ConcurrentHashMap docs and found;

"Similarly, Iterators, Spliterators and Enumerations return elements
reflecting the state of the hash table at some point at or since the
creation of the iterator/enumeration. They do not throw
ConcurrentModificationException. However, iterators are designed to be
used by only one thread at a time."

As subtle as his suggestion was, I think he may be on to something. I'm
going to think about it some more but Volker may have the simplest solution.


Knute Johnson

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