text: /*
   * Copyright (c) Facebook, Inc. and its affiliates.
   *
   * 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 <memory>
  
  #include <folly/Executor.h>
  #include <folly/executors/IOExecutor.h>
  
  namespace folly {
  
  namespace detail {
  std::shared_ptr<Executor> tryGetImmutableCPUPtr();
  bool isDefaultExecutor(Executor*);
  } // namespace detail
  
  /**
   * Return the global executor.
   * The global executor is a CPU thread pool and is immutable.
   *
   * May return an invalid KeepAlive on shutdown.
   */
  folly::Executor::KeepAlive<> getGlobalCPUExecutor();
  
  /**
   * Return the global IO executor.
   * The global executor is an IO thread pool and is immutable.
   *
   * May return an invalid KeepAlive on shutdown.
   */
  folly::Executor::KeepAlive<> getGlobalIOExecutor();
  
  /**
   * Retrieve the global Executor. If there is none, a default InlineExecutor
   * will be constructed and returned. This is named CPUExecutor to distinguish
   * it from IOExecutor below and to hint that it's intended for CPU-bound tasks.
   *
   * Can return nullptr on shutdown.
   */
  std::shared_ptr<folly::Executor> getCPUExecutor();
  
  /**
   * Set an Executor to be the global Executor which will be returned by
   * subsequent calls to getCPUExecutor().
   */
  void setCPUExecutor(std::weak_ptr<folly::Executor> executor);
  
  /**
   * Set the CPU executor to the immutable default returned by
   * getGlobalCPUExecutor.
   */
  void setCPUExecutorToGlobalCPUExecutor();
  
  /**
   * Retrieve the global IOExecutor. If there is none, a default
   * IOThreadPoolExecutor will be constructed and returned.
   *
   * IOExecutors differ from Executors in that they drive and provide access to
   * one or more EventBases.
   *
   * Can return nullptr on shutdown.
   */
  std::shared_ptr<IOExecutor> getIOExecutor();
  
  /**
   * Set an IOExecutor to be the global IOExecutor which will be returned by
   * subsequent calls to getIOExecutor().
   */
  void setIOExecutor(std::weak_ptr<IOExecutor> executor);
  
  /**
   * Retrieve an event base from the global IOExecutor
   *
   * NOTE: This is not shutdown-safe, the returned pointer may be
   * invalid during shutdown.
   */
  folly::EventBase* getEventBase();
  
  } // namespace folly
  