Re: [boost] [thread] Is there a non-blocking future-destructor?

Subject: Re: [boost] [thread] Is there a non-blocking future-destructor?
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2015-10-11 15:24:18

Le 11/10/15 20:43, Mikael Olenfalk a écrit :
> Hi,
>
> I have stumbled on a minor inconvenience when it comes to using
> boost::future. Below is a small example which first wraps an asio
> io_service as an Executor (see even further below) and then uses
> boost::async() to launch a simple task on the executor and tries to queue
> up a continuation using future::then(Ex, F):
>
>    1. the destructor of async_result does not block which is nice
Hmm, I believe that the in the develop branch tis should block.
>    2. the destructor of continuation_result does block which is a bit of an
> annoyance as this future I do not care about at all
>
> Is there a way to make the destructor not block?
>
> /M
The current implementation of feature is broken (at least respect to 
what the standard TS Concurrency says) as the future resulting from 
::then() should not blocks.

I have a branch 
(https://github.com/boostorg/thread/tree/feature/non_blocking_futures) 
that don't blocks on any future, but this will break async.
I have another branch that has copyable executors and non-blocking 
futures 
(https://github.com/boostorg/thread/tree/feature/make_executors_copyable).

Please, could you try on these branches and tell me how it works?

Vicente
>
>
>
> int main(int argc, char* argv[])
> {
>    boost::asio::io_service io_service;
>    asio_executor executor{ io_service };
>
>    auto async_result = boost::async(executor, []() { return 42; });
>    // hangs:
>    // async_result.then(executor, &g);
>
>    // does not hang:
>    auto continuation_result = async_result.then(executor,
> [](boost::future<int> r) {
>        cout << r.get() << endl;
>      });
>
>    cout << "start io_service" << endl;
>
>    io_service.run();
>
>    cout << "stop io_service" << endl;
>
>    return 0;
> }
>
>
> class asio_executor : public boost::executors::executor
> {
> public:
>    asio_executor(boost::asio::io_service &ios)
>      : _ios(ios)
>    {}
>
>    void close() override
>    {
>      _ios.stop();
>    }
>
>    bool closed() override
>    {
>      return _ios.stopped();
>    }
>
>    void submit(work&& w) override
>    {
>      // for some reason _ios.post(w); causes endless
>      // recursion and eventually a crash
>
>      _ios.post(std::move(w));
>    }
>
>    bool try_executing_one() override
>    {
>      return _ios.run_one() > 0;
>    }
>
> private:
>    boost::asio::io_service &_ios;
> };
>
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