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 <folly/ThreadLocal.h>
  #include <folly/io/async/EventBase.h>
  #include <wangle/concurrent/GlobalExecutor.h>
  
  namespace wangle {
  
  /*
   * IOObjectCache manages objects of type T that are dependent on an EventBase
   * provided by the global IOExecutor.
   *
   * Provide a factory that creates T objects given an EventBase, and get() will
   * lazily create T objects based on an EventBase from the global IOExecutor.
   * These are stored thread locally - for a given pair of event base and calling
   * thread there will only be one T object created.
   *
   * The primary use case is for managing objects that need to do async IO on an
   * event base (e.g. thrift clients) that can be used outside the IO thread
   * without much hassle. For instance, you could use this to manage Thrift
   * clients that are only ever called from within other threads without the
   * calling thread needing to know anything about the IO threads that the clients
   * will do their work on.
   */
  template <class T>
  class IOObjectCache {
   public:
    typedef std::function<std::shared_ptr<T>(folly::EventBase*)> TFactory;
  
    IOObjectCache() = default;
    explicit IOObjectCache(TFactory factory)
      : factory_(std::move(factory)) {}
  
    std::shared_ptr<T> get() {
      CHECK(factory_);
      auto eb = getIOExecutor()->getEventBase();
      CHECK(eb);
      auto it = cache_->find(eb);
      if (it == cache_->end()) {
        auto p = cache_->insert(std::make_pair(eb, factory_(eb)));
        it = p.first;
      }
      return it->second;
    };
  
    void setFactory(TFactory factory) {
      factory_ = std::move(factory);
    }
  
   private:
    folly::ThreadLocal<std::map<folly::EventBase*, std::shared_ptr<T>>> cache_;
    TFactory factory_;
  };
  
  } // namespace wangle
  