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From: Knute Johnson <eternal@knutejohnson.com>
Newsgroups: comp.lang.java.programmer
Subject: Re: Concurrency question?
Date: Sat, 31 Jan 2015 19:51:54 -0800
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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?
>>
>> java.util.concurrent.ConcurrentHashMap<K,V>
>
>      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