[Cppcms-users] multithread safety in async application

[Markus R. <us...@ma...>]

Hi Artyom!

> Once you called async_flush_output you must wait for completion
> handler to be executed before you send more data.

Do you mean by "send more data" streaming to response().out() or do you mean 
calling async_flush_output again?

Is following sequence correct or did I misunderstood something?

publish thread 1    |publish thread 2    |async cppcms thread
mutex.lock()        |                    |
response().out()<<  |                    |
response().out()<<  |                    |
async_flush_output()|                    |
                    |                    |
                    |                    |in on_complete()
                    |                    |mutex.unlock()
                    |mutex.lock()        | 
                    |response().out()<<  |
                    |response().out()<<  |
                    |async_flush_output()|
                    |                    |
                    |                    |in on_peer_reset()
                    |                    |mutex.unlock()
stop sending        |stop sending        |

Is there a better sequence (that the threads can work more in parallel)?

So I need to have a mutex between:
- before calling response().out()
and:
- on_complete() or on_peer_reset().

Do I have a guarantee that either on_peer_reset() (callback of 
cppcms::http::context::async_flush_output) or on_complete() (callback of 
cppcms::http::context::async_on_peer_reset) is called in any case?

> For example "state" sse service does exactly the same it sends
> only latest data and if some was missed between async_flush_output
> and completion handler it would not be sent, but rather latest
> data should be.

Thank you for the examples, they are really great!


> About buffering,
> 
> when you work with async app. the write to response().out()
> just collects the data to the buffer, the I/O is performed
> uput async_flush_output request and than you can continue
> once you receive the notification.

Ok, good to know. See questions aboved about when exactly I am allowed to 
continue.

> So in general what you described is reasonable approach.

Thanks,
Markus Raab