Groups > comp.lang.java.programmer > #30976

Re: Concurrency question?

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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

Thread

Concurrency question? Knute Johnson <nospam@rabbitbrush.frazmtn.com> - 2015-01-31 10:34 -0800
  Re: Concurrency question? Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-01-31 14:04 -0500
    Re: Concurrency question? Knute Johnson <nospam@rabbitbrush.frazmtn.com> - 2015-01-31 11:23 -0800
  Re: Concurrency question? Arne Vajhøj <arne@vajhoej.dk> - 2015-01-31 14:12 -0500
    Re: Concurrency question? Knute Johnson <nospam@rabbitbrush.frazmtn.com> - 2015-01-31 11:33 -0800
  Re: Concurrency question? v_borchert@despammed.com (Volker Borchert) - 2015-01-31 19:20 +0000
    Re: Concurrency question? Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-01-31 15:42 -0500
      Re: Concurrency question? Knute Johnson <eternal@knutejohnson.com> - 2015-01-31 19:51 -0800
        Re: Concurrency question? Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-02-01 09:24 -0500
  Re: Concurrency question? Kevin McMurtrie <mcmurtrie@pixelmemory.us> - 2015-01-31 22:59 -0800
    Re: Concurrency question? Arne Vajhøj <arne@vajhoej.dk> - 2015-02-01 12:55 -0500
      Re: Concurrency question? Silvio <silvio@internet.com> - 2015-02-01 22:19 +0100
      Re: Concurrency question? Kevin McMurtrie <mcmurtrie@pixelmemory.us> - 2015-02-06 22:29 -0800
        Re: Concurrency question? Knute Johnson <eternal@knutejohnson.com> - 2015-02-07 10:14 -0800
        Re: Concurrency question? Robert Klemme <shortcutter@googlemail.com> - 2015-02-08 19:33 +0100
  Re: Concurrency question? olupot douglas <olupotd3@gmail.com> - 2015-02-07 01:06 -0800
  Re: Concurrency question? Haddock <ffm2002@web.de> - 2015-02-16 06:32 -0800

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