MultiFilePoller.h

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/*
 * Copyright 2004-present 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 <chrono>
#include <unordered_map>

#include <folly/Function.h>
#include <folly/SharedMutex.h>
#include <wangle/util/FilePoller.h>

namespace wangle {

class MultiFilePoller {
 public:
  using CallbackArg = std::unordered_map<std::string, std::string>;
  using Callback = folly::Function<void(const CallbackArg& newData) noexcept>;

  class CallbackId final {
   private:
    explicit CallbackId(size_t id) : id_(id) {
    }
    friend class MultiFilePoller;
    size_t id_;
  };

  explicit MultiFilePoller(std::chrono::milliseconds pollInterval);

  ~MultiFilePoller() = default;

  CallbackId registerFile(std::string path, Callback cb);

  CallbackId registerFiles(const std::vector<std::string>& paths, Callback cb);

  void cancelCallback(const CallbackId& cbId);

 private:
  void onFileUpdated(const std::string& triggeredPath);

  size_t getNextCallbackId();

  using StringReferences =
      std::vector<std::reference_wrapper<const std::string>>;

  struct CallbackDetail {
    CallbackDetail(StringReferences files, Callback cb)
        : files_(std::move(files)), cb_(std::move(cb)) {
    }
    StringReferences files_;
    Callback cb_;
  };

  // The following data structures are protected by the mutex.
  folly::SharedMutex rwlock_;
  size_t lastCallbackId_ = 0;
  std::unordered_map<std::string, std::vector<size_t>> pathsToCallbackIds_;
  std::unordered_map<size_t, CallbackDetail> idsToCallbacks_;

  // The following data structures are set by ctor only.
  wangle::FilePoller poller_;
};

} // namespace wangle