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// Copyright 2019 The Marl Authors.
//
// 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.
#ifndef marl_blocking_call_h
#define marl_blocking_call_h
#include "defer.h"
#include "waitgroup.h"
#include <thread>
#include <type_traits>
#include <utility>
namespace marl {
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(
[&](Args&&... args) {
defer(wg.done());
result = f(std::forward<Args>(args)...);
},
std::forward<Args>(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(
[&](Args&&... args) {
defer(wg.done());
f(std::forward<Args>(args)...);
},
std::forward<Args>(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 marl
#endif // marl_blocking_call_h