Re: [Cppcms-users] Synchronous app calls io_service.post() and blocks itself

[Artyom B. <art...@ya...>]

>
> Such hand made "cache" seems to be unable to fit my case. I
> need to use
> booster::aio::io_service as a synchronizer, like a mutex, to
> 
> *sequentially* execute cppdb operations and manipulate
> in-memory data.
 
One VERY important point to alarm you.

There is ONE even loop that handles LOTS of operations:
incoming connections, uploads, transfers, request parsing,
etc.

It MUST not be blocked. As it basically blocks the entire CppCMS
service from doing its job.

If you call some heavy query to cppdb FROM the event loop
or async app. You'll block the entire application.

It is bad idea to abuse the even loop for such a purpose.
Any operations in the async application or event loop must
be as fast as possible and what is important -  never block.

If you run for example an SQL query that access the disk
you may delay your entire cppcms application up to 6ms
required for a physical disk to seek to the non-cached data.

If you need to perform blocking/heavy operation by the async-app,
inside event loop - post it to the thread pool and get the
results "posted" back.

If you want some "job queue" for sequential execution you'll probably want to
create some additional execution queue,

you may create your own booster::aio::io_service and run it in its own thread
that would act like a dispatch queue (although it is most likely overkill)

Or write your own simple job queue (which is quite a textbook tasks)

Artyom