Multiplexing RabbitMQ message - rabbitmq

Question

For example i have 4 sources which publish meterics.
I would like to multiplex / merge all theses messages in one queue/exchange
--------+----+----+----+----+ -------+---------+----+---------+---------+
Source1 | M1 | M2 | M3 | | => Result | M1 | M4 | M2 | M3 | M6 | M5 | M7 |
Source2 | M4 | | | M5 |
Source3 | | | M6 | |
Source4 | | | | M7 |
For each queue:
* Read one message
* Publish message to the Result queue
Is there a "native" way to do this in RabbitMQ or should i write my own Consumer/Publisher ?
EDIT 1
Some example to clarify, let's say after some time I have
Processing "window"
+-+
Source1 |X|XXXXXXXXXXXXX
Source2 |Y|YYYYYYY
Source3 |Z|ZZZZZZZZZZ
Source4 |W|WW
+-+
And then later
Processing "window"
+-+
Source1 XXX|X|XXXXXXXXXX
Source2 YYY|Y|YYYY
Source3 ZZZ|Z|ZZZZZZZ
Source4 WWW| |
+-+
And then later
Processing "window"
+-+
Source1 XXXXXXXXX|X|XXXX
Source2 YYYYYYYY | |
Source3 ZZZZZZZZZ|Z|Z
Source4 WWW | |
+-+
The result consuming order will be:
X Y Z W X Y Z W X Y Z W X Y Z X Y Z X Y Z X Y Z X Y Z X Z X Z X Z X X X
X,Y,Z,W then
X,Y,Z,W then
X,Y,Z,W then
X,Y,Z
...
X,Z
...
This way, even if a source is "spamming" all other messages from other sources have a chance to be consumed.
For technical/financial reasons I need to consume only 1 message a time.
The consumer is way slower than the producers but the producers publish a lot but occasionaly.
If each source published to an exchange bound to the same queue, the result might be XXXXXXXXXXXXXX YYYYYYYY ZZZZZZZZZZZ WWW or
XXXXX Y XXXXX YYY XXX YYYY ZZZZZZZZZZZ WWW (depending on the publish rate of each source)

Answer 1

I think what you want can be achieved simply by running a single script that subscribes to all the queues.
The key requirement is to use a single application thread to handle all messages, regardless of which queue they arrive from. What that looks like will vary depending on what language and client library you're using - if you're using PHP, you'd have to really go out of your way not to be single-threaded, but maybe there are some client libraries that assume each callback is on a separate worker thread, and you'll need some shared resource for them to block on.
In terms of the actual RabbitMQ side of things, you will need to:
register a subscription for the server to push messages to you, with basic.consume; this is generally recommended over explicitly polling with basic.get anyway
use a single "channel" for all the basic.consume calls
use manual acknowledgements so that messages remain in the queue until your process has finished
set a per-queue prefetch limit of 1 with basic.qos
If you have 4 queues, A, B, C, and D, which have varying amounts of messages when you start the consumer:
When you first subscribe, the prefetch limit will mean that one message from each queue will be sent to the channel; call them A1, B1, C1, and D1
The client library will raise an asynchronous event in your application for each of these in turn
Your single worker thread will handle the first of these events, and start processing message A1
Until you manually acknowledge that message, no other messages can arrive
Once you acknowledge the first message (A1), a new message can be pre-fetched from that queue (A2)
Meanwhile, your worker thread will unblock and handle the next event which was already raised, for message B1
Only once you've processed the pending events for B1, C1, and D1 will the worker thread see the event for message A2
As long as the queues have messages waiting, they will be processed in a round-robin fashion. Even if all but one of the queues become empty, they will slot back into rotation as soon as a message arrives, because only one message from the busy queue will have been pre-fetched, the rest will just be waiting on the RabbitMQ server.