Re: Information About A BlockingQueue

Robert Klemme <>
Wed, 25 Apr 2007 15:57:52 +0200
On 25.04.2007 15:47, Jason Cavett wrote:

I am currently in the process of using a BlockingQueue
(LinkedBlockingQueue, to be exact) to help with a producer/consumer
aspect of an application I'm developing. The user can continuously
add items to the queue for processing (and this does work). However,
I'm a little confused about how a BlockingQueue works.

When I add an item to the BlockingQueue, is the items copied into the
queue, or is it just a reference to the actual object?

The blocking queue holds on to objects in the queue like any other
collection does.

The reason I ask is because I notice that after adding 9 to 11 items
into the queue, the application slows considerably (despite the fact
that the "queue" stuff is running in a separate thread).

What is an "item"?

watching the output from the garbage collector, it appears as though I
have a memory leak. I attempted to use hprof to profile my
application to see where the memory leak is taking place, but I'm not

hprof is unlikely to help you with detecting memory leaks other than
finding excessive creation of instances. But to get a leak you must
also be holding on to those instances longer than intended which is
something you do not get from hprof IIRC. You might want to look at one
of the various profiler / memory analyzer tools around (JProbe,
OptimizeIt, Eclipse TPTP).

fully understanding the output of hprof. When my application lags
like this, it somewaht defeats the purpose of the use of the
BlockingQueue since I want users to be able to queue up files to

Can anybody clear up any possible issues or provide some insight with
the way BlockingQueue works and any possible memory issues I should be
keeping an eye out for (there isn't much information that I could find
from my own Google searches).

Here are some potential reasons for the slowdown:

  - your objects are large and you are tight on JVM memory so GC has to
kick in more often or your JVM starts swapping to disk

  - your processing is the slow bit (too much concurrency for example,
or it uses too much mem per processing instance)

There are probably more but without more detail we can't really tell.



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