asio-users

[asio-users] Send / receive separately question

[Michael IV <exp...@gm...>]

Hi All. I have probably a stupid question to ask.But I am ASIO noob so
please bear  with me.

I have a server which sends some data in a loop constantly. But at the same
time,the server should also be able to receive a data from the client. The
data from the client arrives occasionally.What I did till now, was
activating send loop right after connection accept,then send the data
synchronously and receive the data synchronously right after send. But then
I found it degrades server's performance dramatically,because asio::read
blocks each time that there is nothing to receive (because the client is
not sending the data constantly). So  I want to separate asio::write from
asio::read routines.I found this answer to a similar problem:

https://stackoverflow.com/questions/33666662/boost-asio-networking-separate-send-and-receive

What I don't understand here is: if both send and receive async  methods
are being called always,how it doesn't cause to a stack overflow. I mean,
every time async read is called,but there is nothing to read yet, what
happens after the hood? Is this really the way to do what I asked? Thanks!

Re: [asio-users] Send / receive separately question

[Torsten R. <Torsten@Robitzki.de>]

Hi Michael,
	
> Am 23.10.2017 um 12:59 schrieb Michael IV <exp...@gm...>:
> 
> What I don't understand here is: if both send and receive async  methods are being called always,how it doesn't cause to a stack overflow. I mean, every time async read is called,but there is nothing to read yet, what happens after the hood? Is this really the way to do what I asked? Thanks!

asynchronous functions just queue the IO or timer and then return. If you have a single threaded server, the single thread of the server usually blocks in io_service::run(). You start your server by queuing a timeout. In the timeout handler, you queue a send and queue a next timeout. There are no recursive function calls. Even when you use lambdas and call the same function from the lambda. The lambda will be executed from the context of io_service::run(), not from from the function, where you defined the lambda.

kind regards,

Torsten

Re: [asio-users] Send / receive separately question

[Michael IV <exp...@gm...>]

Which means,I can call  async read and async write,chaining each of them
within their respective callbacks as suggested in SO answer, with no
worries?

On Mon, Oct 23, 2017 at 2:16 PM, Torsten Robitzki <To...@ro...>
wrote:

> Hi Michael,
>
> > Am 23.10.2017 um 12:59 schrieb Michael IV <exp...@gm...>:
> >
> > What I don't understand here is: if both send and receive async  methods
> are being called always,how it doesn't cause to a stack overflow. I mean,
> every time async read is called,but there is nothing to read yet, what
> happens after the hood? Is this really the way to do what I asked? Thanks!
>
> asynchronous functions just queue the IO or timer and then return. If you
> have a single threaded server, the single thread of the server usually
> blocks in io_service::run(). You start your server by queuing a timeout. In
> the timeout handler, you queue a send and queue a next timeout. There are
> no recursive function calls. Even when you use lambdas and call the same
> function from the lambda. The lambda will be executed from the context of
> io_service::run(), not from from the function, where you defined the lambda.
>
> kind regards,
>
> Torsten
>
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Re: [asio-users] Send / receive separately question

[Torsten R. <Torsten@Robitzki.de>]

> Am 23.10.2017 um 13:37 schrieb Michael IV <exp...@gm...>:
> 
> Which means,I can call  async read and async write,chaining each of them within their respective callbacks as suggested in SO answer, with no worries? 

Jep, when you queue a write, the callback will be called, when the data is written, when you queue a read, that callback is called when data is actually read. All those callbacks get called from within io_service::run().