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Callback Example inspired from proposed Boost.Async
///////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2016 Thomas Heller
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
///////////////////////////////////////////////////////////////////////////////
#include <hpx/hpx.hpp>
#include <hpx/hpx_main.hpp>
#include <hpx/include/threads.hpp>
#include <iostream>
struct manager
{
manager()
: executor(1)
{}
hpx::future<void> second()
{
// return the future once we are done.
return
// Start the task in the correct thread world
hpx::async(
executor,
[]()
{
std::cout << "Executing second long task...\n";
hpx::this_thread::sleep_for(std::chrono::milliseconds(1000));
}
// Once it is done, execute the continuation/callback in the
// same thread world. Instead of the executor, we could have used
// hpx::launch::sync to get the same effect
).then(executor,
[](hpx::future<void> f)
{
std::cout << "shutting down after second task is completed\n";
}
);
}
hpx::future<void> start()
{
// return the future once we are done.
return
// Start the task in the correct thread world
hpx::async(
executor,
[]()
{
std::cout << "Executing long task...\n";
hpx::this_thread::sleep_for(std::chrono::milliseconds(1000));
}
// Once it is done, execute the continuation/callback in the
// same thread world. Instead of the executor, we could have used
// hpx::launch::sync to get the same effect
).then(executor,
[this](hpx::future<void> f)
{
if (needs_second_task)
{
return second();
}
else
{
std::cout << "shutdown after first task\n";
return hpx::make_ready_future();
}
}
);
}
void cancel()
{
// fire&forget, cancel the manager in the corresponding thread world
hpx::apply(executor, [this](){ needs_second_task = false; });
}
// our thread world...
hpx::threads::executors::local_queue_executor executor;
bool needs_second_task = true;
};
int main()
{
std::cout << "example callback\n";
manager man;
auto fu = man.start();
// we changed our mind, cancel the manager right away
man.cancel();
// wait for shutdown
fu.get();
std::cout << "end example callback\n";
return 0;
}
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