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 <folly/futures/Promise.h>
  #include <folly/Portability.h>
  
  namespace folly {
  
  /*
   * SharedPromise provides the same interface as Promise, but you can extract
   * multiple Futures from it, i.e. you can call getFuture() as many times as
   * you'd like. When the SharedPromise is fulfilled, all of the Futures will be
   * called back. Calls to getFuture() after the SharedPromise is fulfilled return
   * a completed Future. If you find yourself constructing collections of Promises
   * and fulfilling them simultaneously with the same value, consider this
   * utility instead. Likewise, if you find yourself in need of setting multiple
   * callbacks on the same Future (which is indefinitely unsupported), consider
   * refactoring to use SharedPromise to "split" the Future.
   */
  template <class T>
  class SharedPromise {
  public:
    SharedPromise() = default;
    ~SharedPromise() = default;
  
    // not copyable
    SharedPromise(SharedPromise const&) = delete;
    SharedPromise& operator=(SharedPromise const&) = delete;
  
    // movable
    SharedPromise(SharedPromise<T>&&) noexcept;
    SharedPromise& operator=(SharedPromise<T>&&) noexcept;
  
    /**
     * Provide a way to split a Future<T>. Note that while the Futures from
     * `getFuture()' depend on the completion of the parameter Future they do not
     * inherit any other properties such as Executor's passed to `via' etc.
     */
    explicit SharedPromise(Future<T>);
  
    /**
     * Return a Future tied to the shared core state. Unlike Promise::getFuture,
     * this can be called an unlimited number of times per SharedPromise.
     */
    Future<T> getFuture();
  
    /** Return the number of Futures associated with this SharedPromise */
    size_t size();
  
    /** Fulfill the SharedPromise with an exception_wrapper */
    void setException(exception_wrapper ew);
  
    /** Fulfill the SharedPromise with an exception_ptr, e.g.
      try {
        ...
      } catch (...) {
        p.setException(std::current_exception());
      }
      */
    FOLLY_DEPRECATED("use setException(exception_wrapper)")
    void setException(std::exception_ptr const&);
  
    /** Fulfill the SharedPromise with an exception type E, which can be passed to
      std::make_exception_ptr(). Useful for originating exceptions. If you
      caught an exception the exception_wrapper form is more appropriate.
      */
    template <class E>
    typename std::enable_if<std::is_base_of<std::exception, E>::value>::type
    setException(E const&);
  
    /// Set an interrupt handler to handle interrupts. See the documentation for
    /// Future::raise(). Your handler can do whatever it wants, but if you
    /// bother to set one then you probably will want to fulfill the SharedPromise with
    /// an exception (or special value) indicating how the interrupt was
    /// handled.
    void setInterruptHandler(std::function<void(exception_wrapper const&)>);
  
    /// Sugar to fulfill this SharedPromise<Unit>
    template <class B = T>
    typename std::enable_if<std::is_same<Unit, B>::value, void>::type
    setValue() {
      setTry(Try<T>(T()));
    }
  
    /** Set the value (use perfect forwarding for both move and copy) */
    template <class M>
    void setValue(M&& value);
  
    void setTry(Try<T>&& t);
  
    /** Fulfill this SharedPromise with the result of a function that takes no
      arguments and returns something implicitly convertible to T.
      Captures exceptions. e.g.
  
      p.setWith([] { do something that may throw; return a T; });
    */
    template <class F>
    void setWith(F&& func);
  
    bool isFulfilled();
  
  private:
    std::mutex mutex_;
    size_t size_{0};
    bool hasValue_{false};
    Try<T> try_;
    std::vector<Promise<T>> promises_;
    std::function<void(exception_wrapper const&)> interruptHandler_;
  };
  
  }
  
  #include <folly/futures/Future.h>
  #include <folly/futures/SharedPromise-inl.h>
  