Re: [Boost-users] [boost::asio] Wait for multiple async_read()'s

Subject: Re: [Boost-users] [boost::asio] Wait for multiple async_read()'s
From: Maarten de Vries (maarten_at_[hidden])
Date: 2017-01-21 07:24:45

Hey,

On 21 January 2017 at 13:09, Adam Zegelin <adam_at_[hidden]> wrote:

> Hi,
>
>
> Another alternative I can think of is that the function that schedules
> all the async_writes knows ahead-of-time the number of reads that need
> to be completed. Each async_read() handler would put its results into
> a shared list and then, if the list's size is equal to the expected
> number of results, fires the "completion" handler. While easy enough
> to implement, this seems fraught with issues. If there is more than
> one thread calling io_service.run(), then access to the shared list
> has to be synchronised. Also, it doesn't seem very generic — I have a
> number of places where this write n, read n, execute (or is it map,
> reduce?) pattern needs to happen, and I'd prefer a solution that was
> write one, worked everywhere.
>

​I would definitely go with this approach​. It's by far the simplest and to
me it seems to match an asynchronous philosophy pretty well.

You can use an io_service::strand [1] to synchronize access to the shared
list easily without explicit locking. For best performance you should
probably keep the handler running in the strand as short as possible and
keep the parts of the read handler that don't access shared state outside
of the strand.

[1]
http://www.boost.org/doc/libs/1_63_0/doc/html/boost_asio/reference.html#boost_asio.reference.io_service__strand

​Hope ​this helps,

-- Maarten