for_each_2.cpp

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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.
 */
#include <algorithm>
#include <cassert>
#include <iostream>
#include <vector>

#include <folly/experimental/pushmi/examples/for_each.h>
#include <folly/experimental/pushmi/examples/pool.h>

using namespace folly::pushmi::aliases;

template <class Executor, class Allocator = std::allocator<char>>
auto naive_executor_bulk_target(Executor e, Allocator a = Allocator{}) {
  return [e, a](
             auto init,
             auto selector,
             auto input,
             auto&& func,
             auto sb,
             auto se,
             auto out) {
    using RS = decltype(selector);
    using F = std::conditional_t<
        std::is_lvalue_reference<decltype(func)>::value,
        decltype(func),
        typename std::remove_reference<decltype(func)>::type>;
    using Out = decltype(out);
    try {
      typename std::allocator_traits<Allocator>::template rebind_alloc<char>
          allocState(a);
      auto shared_state = std::allocate_shared<std::tuple<
          std::exception_ptr, // first exception
          Out, // destination
          RS, // selector
          F, // func
          std::atomic<decltype(init(input))>, // accumulation
          std::atomic<std::size_t>, // pending
          std::atomic<std::size_t> // exception count (protects assignment to
                                   // first exception)
          >>(
          allocState,
          std::exception_ptr{},
          std::move(out),
          std::move(selector),
          (decltype(func)&&)func,
          init(std::move(input)),
          1,
          0);
      e | op::submit([e, sb, se, shared_state](auto) {
        auto stepDone = [](auto shared_state) {
          // pending
          if (--std::get<5>(*shared_state) == 0) {
            // first exception
            if (std::get<0>(*shared_state)) {
              mi::set_error(
                  std::get<1>(*shared_state), std::get<0>(*shared_state));
              return;
            }
            try {
              // selector(accumulation)
              auto result = std::get<2>(*shared_state)(
                  std::move(std::get<4>(*shared_state).load()));
              mi::set_value(std::get<1>(*shared_state), std::move(result));
            } catch (...) {
              mi::set_error(
                  std::get<1>(*shared_state), std::current_exception());
            }
          }
        };
        for (decltype(sb) idx{sb}; idx != se;
             ++idx, ++std::get<5>(*shared_state)) {
          e | op::submit([shared_state, idx, stepDone](auto ex) {
            try {
              // this indicates to me that bulk is not the right abstraction
              auto old = std::get<4>(*shared_state).load();
              auto step = old;
              do {
                step = old;
                // func(accumulation, idx)
                std::get<3> (*shared_state)(step, idx);
              } while (!std::get<4>(*shared_state)
                            .compare_exchange_strong(old, step));
            } catch (...) {
              // exception count
              if (std::get<6>(*shared_state)++ == 0) {
                // store first exception
                std::get<0>(*shared_state) = std::current_exception();
              } // else eat the exception
            }
            stepDone(shared_state);
          });
        }
        stepDone(shared_state);
      });
    } catch (...) {
      e |
          op::submit([out = std::move(out), ep = std::current_exception()](
                         auto) mutable { mi::set_error(out, ep); });
    }
  };
}

int main() {
  mi::pool p{std::max(1u, std::thread::hardware_concurrency())};

  std::vector<int> vec(10);

  mi::for_each(
      naive_executor_bulk_target(p.executor()),
      vec.begin(),
      vec.end(),
      [](int& x) { x = 42; });

  assert(
      std::count(vec.begin(), vec.end(), 42) == static_cast<int>(vec.size()));

  std::cout << "OK" << std::endl;

  p.stop();
  p.wait();
}