src/Yarn/BlockingCall.hpp

// Copyright 2019 The SwiftShader Authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//    http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include "WaitGroup.hpp"

#include <thread>
#include <type_traits>

namespace yarn {
namespace detail {

template <typename RETURN_TYPE>
class OnNewThread
{
public:
    template <typename F, typename ... Args>
    inline static RETURN_TYPE call(F&& f, Args&& ... args)
    {
        RETURN_TYPE result;
        WaitGroup wg(1);
        auto thread = std::thread([&]
        {
            defer(wg.done());
            result = f(args...);
        });
        wg.wait();
        thread.join();
        return result;
    }
};

template <>
class OnNewThread<void>
{
public:
    template <typename F, typename ... Args>
    inline static void call(F&& f, Args&& ... args)
    {
        WaitGroup wg(1);
        auto thread = std::thread([&]
        {
            defer(wg.done());
            f(args...);
        });
        wg.wait();
        thread.join()
    }
};

} // namespace detail

// blocking_call() calls the function F on a new thread, yielding this fiber
// to execute other tasks until F has returned.
//
// Example:
//
//  void runABlockingFunctionOnATask()
//  {
//      // Schedule a task that calls a blocking, non-yielding function.
//      yarn::schedule([=] {
//          // call_blocking_function() may block indefinitely.
//          // Ensure this call does not block other tasks from running.
//          auto result = yarn::blocking_call(call_blocking_function);
//          // call_blocking_function() has now returned.
//          // result holds the return value of the blocking function call.
//      });
//  }
template <typename F, typename ... Args>
auto inline blocking_call(F&& f, Args&& ... args) -> decltype(f(args...))
{
    return detail::OnNewThread<decltype(f(args...))>::call(std::forward<F>(f), std::forward<Args>(args)...);
}

} // namespace yarn