Hi Eric,
Its Stefano not Stephano ;)
Comments inside...
Am Samstag, 24. Dezember 2011 schrieb Eric Charles<[email protected]>:
Hi Stephano, Thx for the inputs. I'm fine to have volatile fields and to
use them is synchronized blocks when needed, and out-of synchronized blocks
when possible.
I still have to find the few hours to better understand the usage and
context.
Maybe you can give me a hint about about the 2 user threads?
Is there a test case that ensures the class is thread-safe (or sould I
ask 'is it feasible to have a test for this')?
Check Out the AbstractProtocolTransportTest..
How did you came to the conclusion it was not thread-safe: pure code
review, or exceptions/abnormal behavior in an operational deployment?
I noticed that the Responses were written out of order at a paid Project .
That was why I was starting to investigate..
I believe the beauty resides in the easy-understanding. For example, if
this class is designed to be used by only 2 threads, it should come out for
the reader from javadoc, method, fields... namings.
As this is more a internal thing I would Not mention it.
Thx,
Eric
Bye,
Norman
On 24/12/11 12:19, Stefano Bagnara wrote:
2011/12/24 Eric Charles<[email protected]>:
Hi Stephano,
Opening the discussion to learn more :)
- Why are you considering that 2 threads is a criteria to use standard
synchronization rather than some atomic fields.
It is a criteria to not use the ConcurrentLinkedQueue that is a
structure thought to handle many concurrent threads and is overkill
for 2 threads.
- I can understand you replace a concurrent by a non-concurrent queue.
However, you now have a blocking queue. Is there an impact due to this
blocking aspect?
I think the answer is no. That's why I did that.
Remember we have 2 threads and they do 2 different things, they simply
block each other when they add or remove from the queue.
- You defined isAsync as volatile and sometimes encapsulate access to
isAsync in a synchronized block, sometime not. Why using 2 different
thread-safety strategies in this class?
Because some times it needed sincronization, other times I felt it was
not needed (the access to the volatile doesn't need synchronization. I
just synchronize to ensure that the change to the list happens
together with the change in the volatile var).
If you can find a better solution you're welcome to provide one. It
took a couple of hours to reach a working solution.
The previous one was not thread safe at this line:
------
if (listenerAdded == false) {
write.set(false);
-----
It could happen another thread already added a new item to the queue
but skipped to process it because write was true. So we ended up with
an item in the queue never written.
I don't like too much my solution and I felt it a bit hackish, but
that was my best solution for my limited time, so if you can provide a
more elegant solution while still being thread safe, I'm more than
happy :-)
Stefano
Thx,
Eric
On 21/12/11 15:47, [email protected] wrote:
Author: bago
Date: Wed Dec 21 14:47:25 2011
New Revision: 1221748
URL: http://svn.apache.org/viewvc?rev=1221748&view=rev
Log:
An attempt to refactor AbstractProtocolTransport to be thread safe. I
moved back to standard synchronization as we only have max 2 threads
competing for the queue so it doesn't make sense to use a non blocking
queue. Norman, please overview, and feel free to revert if you don't like
the solution (i thought it was better to simply commit instead of opening
a
JIRA to show you this).
Modified:
james/protocols/trunk/api/src/main/java/org/apache/james/protocols/api/AbstractProtocolTransport.java
Modified:
james/protocols/trunk/api/src/main/java/org/apache/james/protocols/api/AbstractProtocolTransport.java
URL:
http://svn.apache.org/viewvc/james/protocols/trunk/api/src/main/java/org/apache/james/protocols/api/AbstractProtocolTransport.java?rev=1221748&r1=1221747&r2=1221748&view=diff
==============================================================================
---
james/protocols/trunk/api/src/main/java/org/apache/james/protocols/api/AbstractProtocolTransport.java
(original)
+++
james/protocols/trunk/api/src/main/java/org/apache/james/protocols/api/AbstractProtocolTransport.java
Wed Dec 21 14:47:25 2011
@@ -22,9 +22,8 @@ package org.apache.james.protocols.api;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.util.List;
-import java.util.concurrent.ConcurrentLinkedQueue;
-import java.util.concurrent.atomic.AtomicBool
