hadoop/hadoop-hdfs-project/hadoop-hdfs-native-client/src/main/native/libhdfspp/lib/common/util.h

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 LIB_COMMON_UTIL_H_
#define LIB_COMMON_UTIL_H_

#include "hdfspp/status.h"
#include "common/logging.h"

#include <mutex>
#include <string>

#include <asio/error_code.hpp>
#include <openssl/rand.h>
#include <google/protobuf/io/coded_stream.h>


namespace google {
  namespace protobuf {
    class MessageLite;
  }
}

namespace hdfs {

// typedefs based on code that's repeated everywhere
typedef std::lock_guard<std::mutex> mutex_guard;


Status ToStatus(const ::asio::error_code &ec);

// Determine size of buffer that needs to be allocated in order to serialize msg
// in delimited format
int DelimitedPBMessageSize(const ::google::protobuf::MessageLite *msg);

// Construct msg from the input held in the CodedInputStream
// return false on failure, otherwise return true
bool ReadDelimitedPBMessage(::google::protobuf::io::CodedInputStream *in,
                            ::google::protobuf::MessageLite *msg);

// Serialize msg into a delimited form (java protobuf compatible)
// err, if not null, will be set to false on failure
std::string SerializeDelimitedProtobufMessage(const ::google::protobuf::MessageLite *msg,
                                              bool *err);

std::string Base64Encode(const std::string &src);

// Return a new high-entropy client name
std::string GetRandomClientName();

// Returns true if _someone_ is holding the lock (not necessarily this thread,
// but a std::mutex doesn't track which thread is holding the lock)
template<class T>
bool lock_held(T & mutex) {
  bool result = !mutex.try_lock();
  if (!result)
    mutex.unlock();
  return result;
}

// Shutdown and close a socket safely; will check if the socket is open and
// catch anything thrown by asio.
// Returns a string containing error message on failure, otherwise an empty string.
std::string SafeDisconnect(asio::ip::tcp::socket *sock);


// The following helper function is used for classes that look like the following:
//
// template <typename socket_like_object>
// class ObjectThatHoldsSocket {
//   socket_like_object sock_;
//   void DoSomethingWithAsioTcpSocket();
// }
//
// The trick here is that ObjectThatHoldsSocket may be templated on a mock socket
// in mock tests.  If you have a method that explicitly needs to call some asio
// method unrelated to the mock test you need a way of making sure socket_like_object
// is, in fact, an asio::ip::tcp::socket.  Otherwise the mocks need to implement
// lots of no-op boilerplate.  This will return the value of the input param if
// it's a asio socket, and nullptr if it's anything else.

template <typename sock_t>
inline asio::ip::tcp::socket *get_asio_socket_ptr(sock_t *s) {
  (void)s;
  return nullptr;
}
template<>
inline asio::ip::tcp::socket *get_asio_socket_ptr<asio::ip::tcp::socket>
                                            (asio::ip::tcp::socket *s) {
  return s;
}

//Check if the high bit is set
bool IsHighBitSet(uint64_t num);


// Provide a way to do an atomic swap on a callback.
// SetCallback, AtomicSwapCallback, and GetCallback can only be called once each.
// AtomicSwapCallback and GetCallback must only be called after SetCallback.
//
// We can't throw on error, and since the callback is templated it's tricky to
// generate generic dummy callbacks.  Complain loudly in the log and get good
// test coverage.  It shouldn't be too hard to avoid invalid states.
template <typename CallbackType>
class SwappableCallbackHolder {
 private:
  std::mutex state_lock_;
  CallbackType callback_;
  bool callback_set_      = false;
  bool callback_swapped_  = false;
  bool callback_accessed_ = false;
 public:
  bool IsCallbackSet() {
    mutex_guard swap_lock(state_lock_);
    return callback_set_;
  }

  bool IsCallbackAccessed() {
    mutex_guard swap_lock(state_lock_);
    return callback_accessed_;
  }

  bool SetCallback(const CallbackType& callback) {
    mutex_guard swap_lock(state_lock_);
    if(callback_set_ || callback_swapped_ || callback_accessed_) {
      LOG_ERROR(kAsyncRuntime, << "SetCallback violates access invariants.")
      return false;
    }
    callback_ = callback;
    callback_set_ = true;
    return true;
  }

  CallbackType AtomicSwapCallback(const CallbackType& replacement, bool& swapped) {
    mutex_guard swap_lock(state_lock_);
    if(!callback_set_ || callback_swapped_) {
      LOG_ERROR(kAsyncRuntime, << "AtomicSwapCallback violates access invariants.")
      swapped = false;
    } else if (callback_accessed_) {
      // Common case where callback has been invoked but caller may not know
      LOG_DEBUG(kAsyncRuntime, << "AtomicSwapCallback called after callback has been accessed");
      return callback_;
    }

    CallbackType old = callback_;
    callback_ = replacement;
    callback_swapped_ = true;
    swapped = true;
    return old;
  }
  CallbackType GetCallback() {
    mutex_guard swap_lock(state_lock_);
    if(!callback_set_ || callback_accessed_) {
      LOG_ERROR(kAsyncRuntime, << "GetCallback violates access invariants.")
    }
    callback_accessed_ = true;
    return callback_;
  }
};


}

#endif