Re: using ConcurrentHashMaps

From:

Vaibhav <consultvaibhav@gmail.com>

Newsgroups:

comp.lang.java.programmer

Date:

20 Apr 2007 08:40:24 -0700

Message-ID:

<1177083624.635825.190380@n59g2000hsh.googlegroups.com>

On Apr 20, 10:30 am, Robert Klemme <shortcut...@googlemail.com> wrote:

On 20.04.2007 17:17, Vaibhav wrote:

I have following code in my program. Is it possible to use a
ConcurrentHashMap in this scenario?

private Map mymap = Collections.synchronizedMap(new HashMap());

If you access your map only in synchronized blocks like below you do not
need a synchronizedMap.

I do have to access my map in other parts of the code, where I do not
need to synchronize.
It is not clear to me how the code should look if I use a
concurrentHashMap..
My question is that can I avoid synchronize block in this case if I
were using a concurrentHashMap.

public MyHandle getHandle(String id) {
        MyHandle handle = null;
        MyHandle tmpHandle;

        synchronized(mymap) {
            Iterator it = this.mymap.values().iterator();
            while(it.hasNext()) {
                tmpHandle = (MyHandle)it.next();
                if(id.equals(MyHandle.getId())) {
                    handle = tmpHandle;
                    break;
                }
            }
        //}

        return handle;
    }

Certainly you can use a ConcurrentHashMap but it would be more efficient
if you used the id as map key.

I unerstand the efficiency part when using id as key. Can you explain
how that will be thread safe?

Thanks for your help!