pool.h

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/*
 * Copyright 2018-present Facebook, Inc.
 *
 * 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.
 */
#pragma once

#include <experimental/thread_pool> // @manual

#include <folly/experimental/pushmi/executor.h>
#include <folly/experimental/pushmi/time_single_sender.h>
#include <folly/experimental/pushmi/trampoline.h>

#if __cpp_deduction_guides >= 201703
#define MAKE(x) x MAKE_
#define MAKE_(...) \
  { __VA_ARGS__ }
#else
#define MAKE(x) make_##x
#endif

namespace folly {
namespace pushmi {

using std::experimental::static_thread_pool;
namespace execution = std::experimental::execution;

template <class Executor>
struct pool_executor {
  using properties = property_set<
      is_sender<>,
      is_executor<>,
      is_never_blocking<>,
      is_concurrent_sequence<>,
      is_single<>>;

  using e_t = Executor;
  e_t e;
  explicit pool_executor(e_t e) : e(std::move(e)) {}
  auto executor() {
    return *this;
  }
  PUSHMI_TEMPLATE(class Out)
  (requires Receiver<Out>)
  void submit(Out out) const {
    e.execute(
        [e = *this, out = std::move(out)]() mutable { set_value(out, e); });
  }
};

class pool {
  static_thread_pool p;

 public:
  inline explicit pool(std::size_t threads) : p(threads) {}

  inline auto executor() {
    auto exec = execution::require(
        p.executor(), execution::never_blocking, execution::oneway);
    return pool_executor<decltype(exec)>{exec};
  }

  inline void stop() {
    p.stop();
  }
  inline void wait() {
    p.wait();
  }
};

} // namespace pushmi
} // namespace folly