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From Jim Newsham <>
Subject Re: async send with preserved order
Date Wed, 01 Jun 2011 21:22:31 GMT

Hi Claus,

Yeah I mentioned the single-threaded executor in my initial email, as 
the only way I know to make that work, and also pointed out the 
undesirable performance impact this approach has.  I would really like 
for all messages to be sent out in order without waiting for the result 
of each message before sending the next message.  For example:

Send 1; send 2; send 3; send 4; send 5.
Wait for response for 1, 2, 3, 4, 5 (using async callback).

Instead of:

Send 1; wait for response for 1.
Send 2; wait for response for 2.

My uninformed assessment is that this is not possible in Camel, since 
sending need to be synchronous/serial and receiving responses needs to 
be asynchronous yet these two operations form a single method call -- 
processor.process().  Does that sound right?  If so, this is more of an 
idealistic wish list item for camel 3 or camel 4. :)


On 6/1/2011 6:40 AM, Claus Ibsen wrote:
> Are you sure you want preserved order on the sender side?
> In essence to do that you may have to use a thread pool of 1, so the
> tasks are processed in sequence.
> I would assume the JDK in fact does grab the taks by order by default
> as the thread pool executor uses a queue for the tasks (FIFO).
> On the other hand if you want to process the responses in the same
> order as the tasks was submitted, then you can use a CompletionService
> for that.
> There is no out of the box in the JDK, so we created one in Camel as
> we needed it. See the org.apache.camel.util.concurrent package.
> On Wed, Jun 1, 2011 at 7:04 AM, Jim Newsham<>  wrote:
>> Is it possible to send asynchronously while preserving order?  For example:
>>       for (int i = 0; i<= COUNT; i++) {
>>         Object body = Integer.valueOf(i);
>>         producerTemplate.asyncCallbackRequestBody(URL, body, callback);
>>       }
>> Assuming that "URL" is a FIFO queue, is there some way for the recipient to
>> receive the messages in the order that the sender has sent them?  I think
>> the answer is no, since async calls just schedule a task on an executor, and
>> it's possible for the thread scheduler to choose/process send tasks out of
>> order. [*]
>> If that's correct, then *if order is important*, all sends must be
>> synchronous, and performance will suffer (transmission will be in serial
>> instead of in parallel, and any network latency will make matters worse
>> since InOut requires round-trip communication).  For this case, it really
>> would be useful to be able to async send and guarantee transmission order
>> (for JMS or whatever endpoint being used).
>> [*] One could set a single-threaded executor on the producer template.  The
>> call would be asynchronous and transmission in order, however the actual
>> send operations would still be in serial (each InOut message must be
>> completely processed before the next message is sent), so the performance
>> would still suffer.
>> Comments?
>> Jim

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