Re: Collections and Decorators

From:

ankur <ankur.a.agarwal@gmail.com>

Newsgroups:

comp.lang.java.programmer

Date:

Sat, 14 Mar 2009 15:41:39 -0700 (PDT)

Message-ID:

<ea697087-2fbf-4158-9fa3-e71d9e93918b@p6g2000pre.googlegroups.com>

On Mar 14, 3:25 pm, ankur <ankur.a.agar...@gmail.com> wrote:

On Mar 14, 2:57 pm, Mark Space <marksp...@sbc.global.net> wrote:

ankur wrote:

for thread safety, rather than having to do instead

Collection sync_c = Collections.synchronizedCollection(c);

synchronized(sync_c) {

//do something on the collection sync_c

}

You don't. Once you do

Collection sync_c = Collections.synchronizedCollection(c);

// do something on the collection sync_c

You don't need to used "synchronized()" explicitly any more. The
collection itself does it for you.

Note if you have an operation that takes more than one call -- like
read-modify-write -- you still have to synchronize on the collection fo=

the entire operation.

Ok, so why doesn't this
Collection sync_c = Collections.synchronizedCollection(c);
take care of everything ? I mean even after I have sync_c why am I
still required to synchronize on the collection "for an operation that
takes more than one call -- like read-modify - execute". Using an
iterator is one example.

Is this due to some incomplete implementation ? I know I can look at
the source code but before I did that I wanted to ask this so as to
make sure I am not missing any subtle point.
-Ankur- Hide quoted text -

- Show quoted text -

In Collections.java this code snippet is present :

public Iterator<E> iterator() {
return c.iterator(); // Must be manually synched by user!
}

So, thats why Iterator operations need to manually synched. But my
question is why was this left unsynched in Java ? All other public
methods are synched on Object mutex in the static class

static class SynchronizedCollection<E>

--Ankur