Re: WebSockets Thread Safety question
Martin Gainty wrote: use java.util.Collections.synchronizedList or even better use a ConcurrentLinkedQueue class (with offer()/peek()/poll() APIs), as I suspect you never need to access the middle elements in the ordered list directly, so why carry this extra java.util.List API baggage/bloat in respect of the implementation chosen for efficient concurrency. You can gain performance from being able to enqueue at one end and dequeue from the other end efficiently and as concurrently as possible. Useful for handing off data to a shared I/O worker thread but be careful to consider flow control and back pressure where the enqueuing code will be forced to block or generate an error when there are is already too many bytes of data in the queue. Adding in that kind of requirement makes things more tricky than ConcurrentLinkedQueue by itself can provide. Darryl - To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
WebSockets Thread Safety question
I have recently had problems with a simple WebSocket sample I'm developing.
Tomcat Version is 7.0.39.
When I use the syntax from the samples in the onTextMessage() method, I get
ConcurrentModificationException if I have more than one client sending data
to the server at the same time:
for(MyMessageInbound mmib: mmiList){
CharBuffer buffer = CharBuffer.wrap(cb);
mmib.myoutbound.writeTextMessage(buffer);
mmib.myoutbound.flush();
}
Changing it to the following works fine:
for(int i = 0; i mmib.size(); i++) {
MyMessageInbound mmib = mmiList.get(i);
CharBuffer buffer = CharBuffer.wrap(cb);
mmib.myoutbound.writeTextMessage(buffer);
mmib.myoutbound.flush();
}
However, this approach is not as efficient as to use an Iterator, unless I
clone the mmiList Collection to iterate over it...
About the mmiList object, why isn't it a Threadsafe Collection?
What's the recommended approach for this?
Regards
Re: WebSockets Thread Safety question
On 03/06/2013 08:45, Martin Schmiedel wrote: About the mmiList object, why isn't it a Threadsafe Collection? Where / how is that object declared? Mark - To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
Re: WebSockets Thread Safety question
When I use the syntax from the samples in the onTextMessage() method, I get
ConcurrentModificationException if I have more than one client sending data
to the server at the same time:
for(MyMessageInbound mmib: mmiList){
CharBuffer buffer = CharBuffer.wrap(cb);
mmib.myoutbound.writeTextMessage(buffer);
mmib.myoutbound.flush();
}
Changing it to the following works fine:
for(int i = 0; i mmib.size(); i++) {
MyMessageInbound mmib = mmiList.get(i);
CharBuffer buffer = CharBuffer.wrap(cb);
mmib.myoutbound.writeTextMessage(buffer);
mmib.myoutbound.flush();
}
However, this approach is not as efficient as to use an Iterator, unless I
clone the mmiList Collection to iterate over it...
Can you explain where is the in-efficiency?
Thanks
Chris
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RE: WebSockets Thread Safety question
/java/utiljavap Collections | grep synchronized
public static java.util.Collection synchronizedCollection(java.util.Collecti
on);
static java.util.Collection synchronizedCollection(java.util.Collection, jav
a.lang.Object);
public static java.util.Set synchronizedSet(java.util.Set);
static java.util.Set synchronizedSet(java.util.Set, java.lang.Object);
public static java.util.SortedSet synchronizedSortedSet(java.util.SortedSet)
;
public static java.util.List synchronizedList(java.util.List);
static java.util.List synchronizedList(java.util.List, java.lang.Object);
public static java.util.Map synchronizedMap(java.util.Map);
public static java.util.SortedMap synchronizedSortedMap(java.util.SortedMap)
;
use java.util.Collections.synchronizedList
Martin
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From: ch...@derham.me.uk
Date: Mon, 3 Jun 2013 07:42:01 -0300
Subject: Re: WebSockets Thread Safety question
To: users@tomcat.apache.org
When I use the syntax from the samples in the onTextMessage() method, I get
ConcurrentModificationException if I have more than one client sending data
to the server at the same time:
for(MyMessageInbound mmib: mmiList){
CharBuffer buffer = CharBuffer.wrap(cb);
mmib.myoutbound.writeTextMessage(buffer);
mmib.myoutbound.flush();
}
Changing it to the following works fine:
for(int i = 0; i mmib.size(); i++) {
MyMessageInbound mmib = mmiList.get(i);
CharBuffer buffer = CharBuffer.wrap(cb);
mmib.myoutbound.writeTextMessage(buffer);
mmib.myoutbound.flush();
}
However, this approach is not as efficient as to use an Iterator, unless I
clone the mmiList Collection to iterate over it...
Can you explain where is the in-efficiency?
Thanks
Chris
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Re: WebSockets Thread Safety question
-BEGIN PGP SIGNED MESSAGE-
Hash: SHA256
Chris,
On 6/3/13 6:42 AM, chris derham wrote:
When I use the syntax from the samples in the onTextMessage()
method, I get ConcurrentModificationException if I have more than
one client sending data to the server at the same time:
for(MyMessageInbound mmib: mmiList){ CharBuffer buffer =
CharBuffer.wrap(cb); mmib.myoutbound.writeTextMessage(buffer);
mmib.myoutbound.flush(); }
Changing it to the following works fine:
for(int i = 0; i mmib.size(); i++) { MyMessageInbound mmib =
mmiList.get(i); CharBuffer buffer = CharBuffer.wrap(cb);
mmib.myoutbound.writeTextMessage(buffer);
mmib.myoutbound.flush(); }
However, this approach is not as efficient as to use an Iterator,
unless I clone the mmiList Collection to iterate over it...
Can you explain where is the in-efficiency?
+1 -- the compiler generates pretty much identical bytecode in either
case.
I suppose having less actual code is a nice thing; I tend to agree
with that sentiment.
What I'd like to know is why there is a difference /at all/ in the two
code samples shown above.
- -chris
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