text: /*
   * Copyright 2016 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 <thread>
  #include <typeinfo>
  
  #include <folly/AtomicIntrusiveLinkedList.h>
  #include <folly/CPortability.h>
  #include <folly/Function.h>
  #include <folly/IntrusiveList.h>
  #include <folly/Portability.h>
  #include <folly/fibers/BoostContextCompatibility.h>
  #include <folly/io/async/Request.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();
  
    /**
     * Retrieve this fiber's base stack and stack size.
     *
     * @return This fiber's stack pointer and stack size.
     */
    std::pair<void*, size_t> getStack() const {
      void* const stack =
          std::min<void*>(fcontext_.stackLimit(), fcontext_.stackBase());
      const size_t size = std::abs(
          reinterpret_cast<intptr_t>(fcontext_.stackBase()) -
          reinterpret_cast<intptr_t>(fcontext_.stackLimit()));
      return {stack, size};
    }
  
   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 */
      YIELDED, /**< The fiber yielded execution voluntarily */
    };
  
    State state_{INVALID}; /**< current Fiber state */
  
    friend class Baton;
    friend class FiberManager;
  
    explicit Fiber(FiberManager& fiberManager);
  
    void init(bool recordStackUsed);
  
    template <typename F>
    void setFunction(F&& func);
  
    template <typename F, typename G>
    void setFunctionFinally(F&& func, G&& finally);
  
    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::shared_ptr<RequestContext> rcontext_; /**< current RequestContext */
    folly::Function<void()> func_; /**< task function */
    bool recordStackUsed_{false};
    bool stackFilledWithMagic_{false};
  
    /**
     * Points to next fiber in remote ready list
     */
    folly::AtomicIntrusiveLinkedListHook<Fiber> nextRemoteReady_;
  
    static constexpr size_t kUserBufferSize = 256;
    std::aligned_storage<kUserBufferSize>::type userBuffer_;
  
    void* getUserBuffer();
  
    folly::Function<void()> resultFunc_;
    folly::Function<void()> finallyFunc_;
  
    class LocalData {
     public:
      LocalData() {}
      LocalData(const LocalData& other);
      LocalData& operator=(const LocalData& other);
  
      template <typename T>
      T& get() {
        if (data_) {
          assert(*dataType_ == typeid(T));
          return *reinterpret_cast<T*>(data_);
        }
        return getSlow<T>();
      }
  
      void reset();
  
      // private:
      template <typename T>
      FOLLY_NOINLINE T& getSlow();
  
      static void* allocateHeapBuffer(size_t size);
      static void freeHeapBuffer(void* buffer);
  
      template <typename T>
      static void dataCopyConstructor(void*, const void*);
      template <typename T>
      static void dataBufferDestructor(void*);
      template <typename T>
      static void dataHeapDestructor(void*);
  
      static constexpr size_t kBufferSize = 128;
      std::aligned_storage<kBufferSize>::type buffer_;
      size_t dataSize_;
  
      const std::type_info* dataType_;
      void (*dataDestructor_)(void*);
      void (*dataCopyConstructor_)(void*, const void*);
      void* data_{nullptr};
    };
  
    LocalData localData_;
  
    folly::IntrusiveListHook listHook_; /**< list hook for different FiberManager
                                             queues */
    folly::IntrusiveListHook globalListHook_; /**< list hook for global list */
    std::thread::id threadId_{};
  
  #ifdef FOLLY_SANITIZE_ADDRESS
    void* asanFakeStack_{nullptr};
    const void* asanMainStackBase_{nullptr};
    size_t asanMainStackSize_{0};
  #endif
  };
  }
  }
  
  #include <folly/fibers/Fiber-inl.h>
  