text: /*
   * Copyright 2015 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 <functional>
  
  #include <boost/context/all.hpp>
  #include <boost/version.hpp>
  #include <folly/AtomicLinkedList.h>
  #include <folly/IntrusiveList.h>
  #include <folly/experimental/fibers/BoostContextCompatibility.h>
  
  namespace folly { namespace fibers {
  
  class Baton;
  class FiberManager;
  
  /**
   * @class Fiber
   * @brief Fiber object used by FiberManager to execute tasks.
   *
   * Each Fiber object can be executing at most one task at a time. In active
   * phase it is running the task function and keeps its context.
   * Fiber is also used to pass data to blocked task and thus unblock it.
   * Each Fiber may be associated with a single FiberManager.
   */
  class Fiber {
   public:
    /**
     * Sets data for the blocked task
     *
     * @param data this data will be returned by await() when task is resumed.
     */
    void setData(intptr_t data);
  
    Fiber(const Fiber&) = delete;
    Fiber& operator=(const Fiber&) = delete;
  
    ~Fiber();
   private:
    enum State {
      INVALID,                    /**< Does't have task function */
      NOT_STARTED,                /**< Has task function, not started */
      READY_TO_RUN,               /**< Was started, blocked, then unblocked */
      RUNNING,                    /**< Is running right now */
      AWAITING,                   /**< Is currently blocked */
      AWAITING_IMMEDIATE,         /**< Was preempted to run an immediate function,
                                       and will be resumed right away */
    };
  
    State state_{INVALID};        /**< current Fiber state */
  
    friend class Baton;
    friend class FiberManager;
  
    explicit Fiber(FiberManager& fiberManager);
  
    template <typename F>
    void setFunction(F&& func);
  
    template <typename F, typename G>
    void setFunctionFinally(F&& func, G&& finally);
  
    template <typename G>
    void setReadyFunction(G&& func);
  
    static void fiberFuncHelper(intptr_t fiber);
    void fiberFunc();
  
    /**
     * Switch out of fiber context into the main context,
     * performing necessary housekeeping for the new state.
     *
     * @param state New state, must not be RUNNING.
     *
     * @return The value passed back from the main context.
     */
    intptr_t preempt(State state);
  
    /**
     * Examines how much of the stack we used at this moment and
     * registers with the FiberManager (for monitoring).
     */
    void recordStackPosition();
  
    FiberManager& fiberManager_;  /**< Associated FiberManager */
    FContext fcontext_;           /**< current task execution context */
    intptr_t data_;               /**< Used to keep some data with the Fiber */
    std::function<void()> func_;  /**< task function */
    std::function<void()> readyFunc_; /**< function to be executed before jumping
                                           to this fiber */
  
    /**
     * Points to next fiber in remote ready list
     */
    folly::AtomicLinkedListHook<Fiber> nextRemoteReady_;
  
    static constexpr size_t kUserBufferSize = 256;
    std::aligned_storage<kUserBufferSize>::type userBuffer_;
  
    void* getUserBuffer();
  
    std::function<void()> resultFunc_;
    std::function<void()> finallyFunc_;
  
    folly::IntrusiveListHook listHook_; /**< list hook for different FiberManager
                                             queues */
    pid_t threadId_{0};
  };
  
  }}
  
  #include <folly/experimental/fibers/Fiber-inl.h>
  