Query on using Collection object in Multithreading

All,
I have a query on multithreading, I have a collection object-eg. HashMap which needs to be shared
among threads, I my have 3 options
1st option is to synchronize the method which does some manipulation on the collection object,
2nd option is to hold a lock on that object like
synchronized(object){
//do some work
3rd option - to make use of class ConcurrentHashMap available in java.util.concurrent package; which claims to be
Thread safe but also says the following in the API - They do not throw ConcurrentModificationException. However,
iterators are designed to be used by only one thread at a time
My queston is - how do I choose between these 3?
I know the decison needs to be taken by keeping performance issue in mind and also the number of times the values in HashMap will be updated by the threads. Can some one explain to me when/under what circumstances do I use options 1 || 2 || 3

My application has actually gone live now - after doing some load/performance testing
and comming to the conclusion that performance is satisfactory [I am designing a SMS gateway
that receives/buffers/stores/sends SMS]
Initially I used Hashmap and a LinkedList to store objects in memory and I had a mixture
of places where some times I made the entire method that modifies the LinkedList & hashmap
synchronized and some places where I held a lock on the object alone (I wasnt too sure which to use where)
Then upon movin to 1.5 I rechanged the the data structure to use ConcurrentLinkedQueue & ConcurrenthashMap.
But i have places where I still hold synchronized locks over those objects (which i think is unnecessary and removing the locks may improve the performance)
So can i come to the conclusion that classes in java.util.concurrent are all threadsafe and we can stop holding locks on the objects and let java take care of itself [or should I still hold a lock when doing structural modification] [though the APi states that a oncurrentmodificationexception will not be thrown & iterators are designed to be used by only one thread at a time]

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Andreas Thiel wrote:
Hi,
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Andreas
Stephen Kim
[email protected]
SolarMetric, Inc.
http://www.solarmetric.com

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Regarding your problem you can do one of the following tasks:
1- easily to tuning on your view object, I mean in the tuning page of the view you can set that only return 1 record or 2-3 record fetch not all the record.
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2- you can order by the timestamp descending and in the where clause only set the rownum<2 (will return the last record) you can also set rownum<5 and get the 4 last record etc.
3-editing the view query in the expert mode is not advised at all because of many consequences that you will face.
4- maybe it is not bat that you add a readonly view for the table you mentioned and every time you unpdate the entity just re-execute the read-only view.( this method maybe is good maybe is not it depends on your business logic)
Regards.
Edited by: Amir Khanof on Sep 3, 2010 11:11 PM

Query on using Collection object in Multithreading

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