Re: [asio-users] Use multiple UDP sockets bound to same local server port

[Alejandro S. <al...@al...>]

You don't need multiple io_services. You can either:

a) Run many threads from the same io_service, each thread calling
io_service::run() as per HTTP Server example 3,

b) Use one thread to read UDP data and implement your own
producer/consumer scheme using good ol' pool of threads.


On Tue, Sep 4, 2012 at 1:31 AM, Gheorghe Marinca
<ghe...@gm...> wrote:
> Well in case of tcp you have connections and when you accept communication
> with a client happens on a newly created client server socket. In case of
> udp that is a shared socket instance I cannot concurrently use same socket
> for multiple send receive with multiple clients. So I would said that
> decently that can affect scalability if I don't use multiple ioservice
> threads as was suggested at some point.
>
> On Sep 4, 2012 6:48 AM, "Yuri Timenkov" <yu...@ti...> wrote:
>>
>> 2 sockets open with the same port (with reuse port/address option) may
>> receive only broad/multicast packets. Unicast packet will be delivered to
>> only one (usually last opened) socket.
>>
>> There is no such thing as "connection" for UDP. When you "connect" your
>> udp socket you just set up a filter or default send_to address. But from
>> network perspective you still have a single open port. You can receive and
>> send packets from/to any address.
>>
>> I think you also misunderstand what receive_from does. The endpoint
>> parameter is *output-only*. ASIO puts origin of received packet there and
>> doesn't use it for input.
>>
>> As it was said many times in this list you should store this address/port
>> combination in your own, user-space "session" and send response there later
>> (when you receive your data) using async_send_to.
>>
>> I really don't understand why are you so concerned about scalability? Have
>> you done any measurements? Web servers have only 1 socket open (on 80 port)
>> and at the same time can handle lots of requests each second. It's not
>> sockets you should worry about.
>> How multiple sockets help you? In rough approximation you still have
>> single network interface, single packets queue in OS kernel. Even if you
>> send data to "different" sockets then packets still have to be put into
>> single queue. If your handler is I/O-bound you should make it async to scale
>> well.
>>
>> Regards,
>> Yuri
>>
>> On Tue, Sep 4, 2012 at 12:50 AM, Gheorghe Marinca
>> <ghe...@gm...> wrote:
>>>
>>> Thanks for prompt replay Jeff. I see that normal UDP API could use option
>>> "reuse port" but ASIO only has
>>>
>>> boost::asio::socket_base::reuse_address
>>>
>>>
>>> The problem with the approach mentioned by you is that in this case on
>>> multiple clients requests (and time needed on each one for processing) I
>>> cannot simultaneously "async_receive_from" (for reading more requests),
>>>
>>>
>>>
>>> and "async_send_to" (for sending back responses as they are available).
>>> How I am going to have scalability ?
>>>
>>> Best regards
>>> -Ghita
>>>
>>>
>>> On Mon, Sep 3, 2012 at 11:34 PM, Jeff Koftinoff <je...@jd...>
>>> wrote:
>>>>
>>>> Hello Ghita
>>>>
>>>> You are not to use different sockets for this purpose.
>>>>
>>>> You are not to use bind for sending to a client.
>>>>
>>>> You are to use send_to() with the existing server socket. One of the
>>>> parameters of send_to() is the address of the client you are sending to.
>>>>
>>>> Remember that if you are using async_send_to() you can not call it again
>>>> on the same socket until the first async_send_to() was signalled as
>>>> completed.
>>>>
>>>> Regards,
>>>> Jeff
>>>>
>>>> On 2012-09-03, at 1:29 PM, Gheorghe Marinca <ghe...@gm...>
>>>> wrote:
>>>>
>>>> Hy.
>>>>
>>>> I've been looking for some days for a resolution to this.
>>>> Is it possible to bind multiple sockets to same UDP server port ? If I
>>>> use :
>>>>
>>>> socket(ioService,
>>>> boost::asio::ip::udp::endpoint(boost::asio::ip::udp::v4(), port))
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> and if I try to create another socket on same port (used for sending
>>>> datagrams from same server port *but* to different clients endpoint) I get
>>>> bind errors (asio throws exception)
>>>> Is there a way to do this ? This must be a common use case, sending
>>>> datagrams to multiple clients using same server port...
>>>>
>>>> Thanks
>>>> -Ghita
>>>>
>>>>
>>>>
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>>>
>>>
>>>
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>>
>>
>>
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>
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-- 
Alejandro Santos