text: // Copyright 2021 The Dawn Authors
  //
  // 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.
  
  #ifndef SRC_DAWN_WIRE_CLIENT_REQUESTTRACKER_H_
  #define SRC_DAWN_WIRE_CLIENT_REQUESTTRACKER_H_
  
  #include <cstdint>
  #include <map>
  #include <utility>
  
  #include "dawn/common/Assert.h"
  #include "dawn/common/NonCopyable.h"
  
  namespace dawn::wire::client {
  
  class Device;
  class MemoryTransferService;
  
  template <typename Request>
  class RequestTracker : NonCopyable {
    public:
      ~RequestTracker() { ASSERT(mRequests.empty()); }
  
      uint64_t Add(Request&& request) {
          mSerial++;
          mRequests.emplace(mSerial, request);
          return mSerial;
      }
  
      bool Acquire(uint64_t serial, Request* request) {
          auto it = mRequests.find(serial);
          if (it == mRequests.end()) {
              return false;
          }
          *request = std::move(it->second);
          mRequests.erase(it);
          return true;
      }
  
      template <typename CloseFunc>
      void CloseAll(CloseFunc&& closeFunc) {
          // Call closeFunc on all requests while handling reentrancy where the callback of some
          // requests may add some additional requests. We guarantee all callbacks for requests
          // are called exactly onces, so keep closing new requests if the first batch added more.
          // It is fine to loop infinitely here if that's what the application makes use do.
          while (!mRequests.empty()) {
              // Move mRequests to a local variable so that further reentrant modifications of
              // mRequests don't invalidate the iterators.
              auto allRequests = std::move(mRequests);
              for (auto& [_, request] : allRequests) {
                  closeFunc(&request);
              }
          }
      }
  
      template <typename F>
      void ForAll(F&& f) {
          for (auto& [_, request] : mRequests) {
              f(&request);
          }
      }
  
    private:
      uint64_t mSerial;
      std::map<uint64_t, Request> mRequests;
  };
  
  }  // namespace dawn::wire::client
  
  #endif  // SRC_DAWN_WIRE_CLIENT_REQUESTTRACKER_H_
  