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From "Henry Saputra (JIRA)" <j...@apache.org>
Subject [jira] Created: (CLK-636) Replace EDU.oswego.cs.dl.util.concurrent.ConcurrentReaderHashMap with java.util.concurrent.ConcurrentHashMap
Date Tue, 02 Mar 2010 10:17:27 GMT
Replace EDU.oswego.cs.dl.util.concurrent.ConcurrentReaderHashMap with java.util.concurrent.ConcurrentHashMap
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                 Key: CLK-636
                 URL: https://issues.apache.org/jira/browse/CLK-636
             Project: Click
          Issue Type: Improvement
          Components: core
    Affects Versions: 2.2.0
            Reporter: Henry Saputra


Since Click required Java SDK 1.5 or later, we could leverage the java.util.concurrent.ConcurrentHashMap
class to replace EDU.oswego.cs.dl.util.concurrent.ConcurrentReaderHashMap class so reducing
the Click runtime dependency.

In my opinion here are some good reasons why:
1. The ConcurrentHashMap class in Java SDK is more efficient since it utilizes internal hash
classes to support better granularity and concurrency compare to simple syncrhonized on the
instance like in DU.oswego.cs.dl.util.concurrent.ConcurrentReaderHashMap.
2. Looking at the use case ConcurrentReaderHashMap in Click, it used to cache the OGNL expression
(please correct me if I am wrong). This scenario does not need exclusive lock on update which
is the intended/ preferred use case for ConcurrentReaderHashMap. If there is a miss on OGNL
expression on a name in the cache, it will cerate one and put it to the map if no other thread
has not. So it will still perform as well as or better locking entire table. However, if we
do need exclusive lock on update, we can simulate ConcurrentReaderHashMap with ConcurrentHashMap
by setting concurrencyLevel to one.
3. The ConcurrentHashMap support generic which is part of task being done to move Click code
to Java generics.
4. Looks like the EDU.oswego.cs.dl.util.concurrent.ConcurrentReaderHashMap class is created
by Doug Lea before contributions to java.util.concurrent packages in Java 1.5 SDK so the code
may no longer optimized.

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