Re: ConcurrentArrayList

From:

Tom Anderson <twic@urchin.earth.li>

Newsgroups:

comp.lang.java.programmer

Date:

Fri, 24 Jul 2009 14:44:31 +0100

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<alpine.DEB.1.10.0907241443240.6464@urchin.earth.li>

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On Fri, 24 Jul 2009, Philipp wrote:

On Jul 24, 2:49?pm, "John B. Matthews" <nos...@nospam.invalid> wrote:

In article
<c52abccd-e618-4cc9-b48e-de95c07e9...@o15g2000yqm.googlegroups.com>,

?Philipp <djb...@gmail.com> wrote:

I can't find an implementation of a "ConcurrentArrayList", that is an
ArrayList which has the same concurrency ?properties as
ConcurrentHashMap has for HashMap:
- concurrent reads and writes with little contention
- safe interation while modification takess place (no
ConcurrentModificationException)

Is there such a thing?

Depending on your needs, you might look at these:

Yes thanks, I saw these

<http://java.sun.com/javase/6/docs/api/java/util/Collections.html
#synchronizedList(java.util.List)>

synchronizedList doesn't allow concurrent reads and writes. All access
is locked by a single mutex lock.

<http://www.j2ee.me/javase/6/docs/api/java/util/concurrent/
CopyOnWriteArrayList.html>

CopyOnWriteArrayList has very bad performance characteristics on
writes as the whole content gets copied on each insert.

My first request (concurrent) could be solved as simply as locking with
a ReadWriteLock instead of a mutex (although smarter solutions exist).
Regarding fail-safe Iterators, I'm a bit lost...

I don't think the arrayness of an ArrayList really admits an efficient
concurrent implementation. How would you handle inserts into the middle of
the list?

tom

--
Formal logical proofs, and therefore programs - formal logical proofs
that particular computations are possible, expressed in a formal system
called a programming language - are utterly meaningless. To write a
computer program you have to come to terms with this, to accept that
whatever you might want the program to mean, the machine will blindly
follow its meaningless rules and come to some meaningless conclusion. --
Dehnadi and Bornat
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