Thanks Brian,
Looking at our implementation code, DGC uses an Executor called
ThreadPool, it's javadoc states:
/**
* ThreadPool is a simple thread pool implementation of the Executor
* interface.
*
* A new task is always given to an idle thread, if one is available;
* otherwise, a new thread is always created. There is no minimum
* warm thread count, nor is there a maximum thread count (tasks are
* never queued unless there are sufficient idle threads to execute
* them).
*
* New threads are created as daemon threads in the thread group that
* was passed to the ThreadPool instance's constructor. Each thread's
* name is the prefix NewThreadAction.NAME_PREFIX followed by the name
* of the task it is currently executing, or "Idle" if it is currently
* idle.
ThreadPool predates Java 5, it looks like we can fix this by using an
Executor from Java 5, we can look at limiting the number of threads
created based on available CPU's and a scaling factor and place the
tasks in a BlockingQueue, so if the queue is filled, it blocks.
Can you report the issue as a Bug on Jira for me, I'll fix this before
the next release.
Regards,
Peter.
Peter Firmstone wrote:
Hi Peter,
I was wondering if you had any thoughts on this post from Bryan on
River users?
Hope you don't mind me asking ;)
Best Regards,
Peter Firmstone.
------------------------------------------------------------------------
Subject:
Re: DGC threads issue
From:
Tom Hobbs <tvho...@googlemail.com>
Date:
Thu, 12 Jan 2012 20:45:01 +0000
To:
u...@river.apache.org, dev@river.apache.org
To:
u...@river.apache.org, dev@river.apache.org
Hi Bryan,
Sorry that no one got back to you about this. I'm afraid that I don't
know the answer to your question, I've copied the dev list into this
email in case someone who monitors that list (but not this one) has
any ideas.
Best regards,
Tom
On Thu, Jan 12, 2012 at 2:29 PM, Bryan Thompson <br...@systap.com> wrote:
Just to follow up on this thread myself. I modified the pattern to return a "thick"
future rather than a proxy for the future. This caused the RMI call to wait on the server until
the future was done and then sent back the outcome. This "fixed" the DGC memory/thread
leak by reducing the number of exported proxies drammatically.
In terms of best practices, is distributed DGC simply not useful for exported
objects with short life spans? Can it only be used with proxies for relatively
long lived services?
Thanks,
Bryan
-----Original Message-----
From: Bryan Thompson
Sent: Tuesday, January 03, 2012 12:06 PM
To: u...@river.apache.org
Subject: DGC threads issue
Hello,
Background:
I am seeing what would appear to be one DGC thread allocated
per exported object. This is using River 2.2 and Sun JDK
1.6.0_17. Relevant configuration parameters are below.
I am observing problems with the DGC threads not being
retired on a timely basis. The exported objects are proxies
for Futures which are being executed on the service. The
code pattern is such that the proxied Future goes out of
lexical scope quite quickly. E.g.,
rmiCallReturningProxyForFuture().get().
Under a modest load, a large number of such Futures are
exported which results in a large number of long lived DGC
threads. This turns into a problem for the JVM due to the
stack allocation per thread. Presumably this is not good for
other reasons as well (e.g., scheduling).
I have tried to override the leaseValue and checkInterval
defaults per the configuration options below. I suspect that
the lease interval is somehow not being obeyed, which is
presumably a problem on my end. However, I can verify that
the configuration values are in fact showing up in
System.getProperties() for at least some of the JVMs involved
(the one which drives the workload and the one that I am
monitoring with the large number of DGC lease threads).
Some questions:
Is this one-thread-per-exported proxy the expected behavior
when DGC is requested for the exported object?
The DGC lease checker threads appear to expire ~14 - 15
minutes after I terminate the process which was originating
the RMI requests. This is close the sum of the default
leaseValue (10m) and checkInterval (5m) parameters, but maybe
there is some other timeout which is controlling this? If
this is the sum of those parameters, why would the DGC lease
threads live until the sum of those values? I thought that
the lease would expire after the leaseValue (10m default).
Can the issue I am observing be caused by a low heap pressure
on the JVM to which the RMI proxies were exported? If it
fails to GC those proxies, even though they are reachable,
could that cause DGC to continue to retain those proxies on
the JVM which exported them?
Is there any way to configure DGC to use a thread pool or to
have the leases managed by a single thread?
Is it possible that there is an interaction with the useNIO option?
Relevant options that I am using include:
-Dcom.sun.jini.jeri.tcp.useNIO=true
-Djava.rmi.dgc.leaseValue=30000
-Dsun.rmi.dgc.checkInterval=15000
-Dsun.rmi.transport.tcp.connectionPool=true
Thanks in advance,
Bryan
