folly::observer::ObserverCreator< Observable, Traits > Class Template Reference

#include <Observable.h>

Public Types
using	T = typename Traits::element_type

Public Member Functions
template<typename... Args>
	ObserverCreator (Args &&...args)
Observer< T >	getObserver ()&&

Private Types
using	Context = detail::ObserverCreatorContext< Observable, Traits >

Private Attributes
std::shared_ptr< Context >	context_

Detailed Description

template<typename Observable, typename Traits = ObservableTraits<Observable>>
class folly::observer::ObserverCreator< Observable, Traits >

Definition at line 48 of file Observable.h.

Member Typedef Documentation

template<typename Observable, typename Traits = ObservableTraits<Observable>>

using folly::observer::ObserverCreator< Observable, Traits >::Context = detail::ObserverCreatorContext<Observable, Traits>

private

Definition at line 58 of file Observable.h.

template<typename Observable, typename Traits = ObservableTraits<Observable>>

using folly::observer::ObserverCreator< Observable, Traits >::T = typename Traits::element_type

Definition at line 50 of file Observable.h.

Constructor & Destructor Documentation

template<typename Observable , typename Traits >

template<typename... Args>

folly::observer::ObserverCreator< Observable, Traits >::ObserverCreator ( Args &&...  args )

explicit

Definition at line 98 of file Observable-inl.h.

    : context_(std::make_shared<Context>(std::forward<Args>(args)...)) {}

Member Function Documentation

template<typename Observable , typename Traits >

Observer< typename ObserverCreator< Observable, Traits >::T > folly::observer::ObserverCreator< Observable, Traits >::getObserver

(

)

Definition at line 103 of file Observable-inl.h.

References context, folly::observer::ObserverCreator< Observable, Traits >::context_, folly::observer::detail::ObserverCreatorContext< Observable, Traits >::get(), folly::observer::makeObserver(), and folly::gen::move.

                                                    {
  // This master shared_ptr allows grabbing derived weak_ptrs, pointing to the
  // the same Context object, but using a separate reference count. Master
  // shared_ptr destructor then blocks until all shared_ptrs obtained from
  // derived weak_ptrs are released.
  class ContextMasterPointer {
   public:
    explicit ContextMasterPointer(std::shared_ptr<Context> context)
        : contextMaster_(std::move(context)),
          context_(
              contextMaster_.get(),
              [destroyBaton = destroyBaton_](Context*) {
                destroyBaton->post();
              }) {}
    ~ContextMasterPointer() {
      if (context_) {
        context_.reset();
        destroyBaton_->wait();
      }
    }
    ContextMasterPointer(const ContextMasterPointer&) = delete;
    ContextMasterPointer(ContextMasterPointer&&) = default;
    ContextMasterPointer& operator=(const ContextMasterPointer&) = delete;
    ContextMasterPointer& operator=(ContextMasterPointer&&) = default;

    Context* operator->() const {
      return contextMaster_.get();
    }

    std::weak_ptr<Context> get_weak() {
      return context_;
    }

   private:
    std::shared_ptr<folly::Baton<>> destroyBaton_{
        std::make_shared<folly::Baton<>>()};
    std::shared_ptr<Context> contextMaster_;
    std::shared_ptr<Context> context_;
  };
  // We want to make sure that Context can only be destroyed when Core is
  // destroyed. So we have to avoid the situation when subscribe callback is
  // locking Context shared_ptr and remains the last to release it.
  // We solve this by having Core hold the master shared_ptr and subscription
  // callback gets derived weak_ptr.
  ContextMasterPointer contextMaster(context_);
  auto contextWeak = contextMaster.get_weak();
  auto observer = makeObserver(
      [context = std::move(contextMaster)]() { return context->get(); });

  context_->setCore(observer.core_);
  context_->subscribe([contextWeak = std::move(contextWeak)] {
    if (auto context = contextWeak.lock()) {
      context->update();
    }
  });

  // Do an extra update in case observable was updated between observer creation
  // and setting updates callback.
  context_->update();
  context_.reset();

  return observer;
}

Member Data Documentation

template<typename Observable, typename Traits = ObservableTraits<Observable>>

std::shared_ptr<Context> folly::observer::ObserverCreator< Observable, Traits >::context_

private

Definition at line 60 of file Observable.h.

Referenced by folly::observer::ObserverCreator< Observable, Traits >::getObserver().

---

The documentation for this class was generated from the following files:

• proxygen/folly/folly/experimental/observer/Observable.h
• proxygen/folly/folly/experimental/observer/Observable-inl.h