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Subject: Re: [Boost-users] [asio] Synchronous/Asynchronous pattern
From: Bill Somerville (bill_at_[hidden])
Date: 2009-03-10 07:03:15

Rutger ter Borg wrote:
> In an application we would like to support synchronous operations in the
> application layer, whereas operations below it are done with asynchronous
> operations. Callback handlers are not appropriate in this case,
> To make the example more clear, suppose you have a remote_vector which you
> would like to iterate through,
> remote_vector a(10);
> for( int i=0; i<10; ++i ) {
> std::cout << a[i] << std::endl;
> }
> here, a[i] will cause messages to be sent to retrieve the actual vector data
> before printing it. The network layer is hidden from the user.
> What is the best way to "emulate" synchronous behaviour with asio? The
> thread running this iteration should not block, but do other work (at the
> io_service?) until the requested results are received.

I don't really understand the requirement but I think it boils down to
whether the other work you want to do is coupled to the async network
i/o or not.

If it isn't then surely that can just be done in it's own thread and the
network i/o can simply be synchronous.

If it is then I would use a pair of condition variables to pass commands
and results between a "synchronous" layer to an "asynchronous" layer
which are just 2 separate threads. If there is no pending asynchronous
event to keep the io service alive then there are documented ways of
dealing with this using the io_service::work object.

> Many thanks,
> Kind regards,
> Rutger ter Borg


Bill Somerville

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