>________________________________
> From: Markus Raab <us...@ma...>
>To: cpp...@li...
>Sent: Monday, April 1, 2013 4:14 PM
>Subject: [Cppcms-users] multithread safety in async application
>
>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?
>
You can not call async_flush_output(), but you can write to response().out()
the data would be buffered
>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().
>
No, you misunderstood the stuff. You can't access cppcms::http::context (and all its
related objects like response) from the threads other than event loop thread.
The lock would not help and for example some events (like on_peer_reset)
my be triggered by timers you have no control over.
What you need to do is to prepare a chunk and than pass it to the
asynchronous application thread (even loop) via post() callback.
What you propose is not safe.
>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?
>
Yes, also on_complete is always called with success or error. on_peer_reset
woks independently of sending sequence.
on_peer_reset is also not called on normal completion.
>> 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
>
>
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>
Artyom Beilis
--------------
CppCMS - C++ Web Framework: http://cppcms.com/
CppDB - C++ SQL Connectivity: http://cppcms.com/sql/cppdb/
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