Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.java.programmer > #3760

Re: Concurrent bidirectional one-to-many map?

Show all headers | View raw

Sebastian wrote:
>schrieb markspace:
>> Sebastian wrote:
>>> Does anyone know of a concurrent bidirectional one-to-many
>>> map implementation?
>>>
>>> By bidirectional I mean that I can lookup keys by values, by

You want Apache Commons Collections, BidiMap, perhaps.

>>> one-to-many I mean that the value end of the map is a list or
>>> set, and by concurrent I mean that I do not need to synchronize
>>> externally and get performance comparable to that of
>>> java.util.concurrent.ConcurrentHashMap in both directions.
>>>
>>> If this beast doesn't exist, how would I go about inventing it?
>>> I must say that I am by no means any sort of concurrency guru...

>> Can you just put both keys and values in as the key? Something like:
>>
>> Map<Key,Key> myMap =...

> Thanks for the idea. I do not yet see how to deal with the
> one-to-many aspect of my problem.
>
> To give an example, I'm trying to solve a problem like this:
> Associate tasks with workspaces, where a workspace may hold many
> tasks,but a task may be associate with at most one workspace.
>
> Idea:
>
>    private ConcurrentMap<Item, Workspace> wsMap =
>      new ConcurrentHashMap<Item, Workspace>();
>
>    public boolean isAssigned( Item item ) {
>      return wsMap.containsKey( item );
>    }
>
>    public void assign( Item item, Workspace ws ) {
>      wsMap.putIfAbsent( item, ws );
>      if( !ws.equals( wsMap.get( item) ) ) {
>        throw new NotAssignableException();
>      }
>    }
>
>
> Now I want to be able to close a workspace, releasing all tasks
> to be assignable again to other workspaces.
>
>   public void closeWorkspace( Workspace ws ) {
>      // how do this efficiently? iterate over all
>      // entries (holding a write lock) and remove it
>      // when the value equals ws?
>  }

You're closing workspaces, so presumably you're at the end of some sort of 
session.  How efficient does this have to be?  What else is using this 
'Workspace' instance at the same time?  If something else is trying to access 
the same 'Workspace' instance at the same time, isn't that already too bad 
because you're closing the 'Workspace'?  SO - just hold the lock (one you use 
explicitly and for all operations on the same instance) until the method is done.

You use the work "efficiently" as if it means anything here, but you have not 
thought about that meaning in context.  On the face of it, it looks like you 
need nothing at all to do with "efficiency".

I'm not so sure that 'ConcurrentMap' is the way to go here.  You need to use 
explicit locks based on what I see here.

-- 
Lew
Honi soit qui mal y pense.
http://upload.wikimedia.org/wikipedia/commons/c/cf/Friz.jpg

Back to comp.lang.java.programmer | Previous | Next — Previous in thread | Next in thread | Find similar

Thread

Concurrent bidirectional one-to-many map? Sebastian <sebastian@undisclosed.invalid> - 2011-05-06 22:07 +0200
  Re: Concurrent bidirectional one-to-many map? markspace <-@.> - 2011-05-06 13:45 -0700
    Re: Concurrent bidirectional one-to-many map? Sebastian <sebastian@undisclosed.invalid> - 2011-05-07 11:43 +0200
      Re: Concurrent bidirectional one-to-many map? Lew <noone@lewscanon.com> - 2011-05-07 07:59 -0400
        Re: Concurrent bidirectional one-to-many map? Lew <noone@lewscanon.com> - 2011-05-07 12:49 -0400
          Re: Concurrent bidirectional one-to-many map? Sebastian <sebastian@undisclosed.invalid> - 2011-05-07 21:34 +0200
      Re: Concurrent bidirectional one-to-many map? Patricia Shanahan <pats@acm.org> - 2011-05-07 06:40 -0700
        Re: Concurrent bidirectional one-to-many map? Tom Anderson <twic@urchin.earth.li> - 2011-05-08 04:51 +0100
          Re: Concurrent bidirectional one-to-many map? Robert Klemme <shortcutter@googlemail.com> - 2011-05-09 06:43 -0700
            Re: Concurrent bidirectional one-to-many map? Tom Anderson <twic@urchin.earth.li> - 2011-05-09 18:28 +0100
              Re: Concurrent bidirectional one-to-many map? Sebastian <sebastian@undisclosed.invalid> - 2011-05-09 22:57 +0200
                Re: Concurrent bidirectional one-to-many map? Lew <noone@lewscanon.com> - 2011-05-09 18:36 -0400
                Re: Concurrent bidirectional one-to-many map? Tom Anderson <twic@urchin.earth.li> - 2011-05-10 08:34 +0100
                Re: Concurrent bidirectional one-to-many map? Sebastian <sebastian@undisclosed.invalid> - 2011-05-11 10:09 +0200
                Re: Concurrent bidirectional one-to-many map? Sebastian <sebastian@undisclosed.invalid> - 2011-05-11 10:51 +0200
                Re: Concurrent bidirectional one-to-many map? Robert Klemme <shortcutter@googlemail.com> - 2011-05-11 04:55 -0700
                Re: Concurrent bidirectional one-to-many map? Lew <noone@lewscanon.com> - 2011-05-11 09:00 -0400
                Re: Concurrent bidirectional one-to-many map? Sebastian <sebastian@undisclosed.invalid> - 2011-05-11 20:47 +0200
      Re: Concurrent bidirectional one-to-many map? markspace <-@.> - 2011-05-07 09:35 -0700
      Re: Concurrent bidirectional one-to-many map? Michal Kleczek <kleku75@gmail.com> - 2011-05-09 16:42 +0200
  Re: Concurrent bidirectional one-to-many map? Roedy Green <see_website@mindprod.com.invalid> - 2011-05-07 03:46 -0700

csiph-web