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Date: Tue, 31 May 2011 19:04:17 -1000
From: Jim Newsham <jnewsham@referentia.com>
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Subject: async send with preserved order
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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