使用protobuf的生成器可以對proto文件進行解析后生成指定的目標語言代碼.隨著項目的不斷擴大, 協議修改變的非常頻繁, 因此每次重編變的異常耗時. 模仿C/C++編譯器的時間戳檢查生成機制,我給protobuf生成器添加了時間戳檢查功能. 下面說下原理:

此功能不是必須的, 可以通過命令行指定—timestampfile FILE 來指定要生成的proto文件對應的時間戳

每次運行解析器時, 解析器通過命令行獲取proto文件, 我們可以先讀取之前保存的時間戳, 然后與這個文件的當前修改時間進行對比

如果時間戳不相等,說明文件已經被修改, 需要重新生成.之后更新時間戳文件即可.

下面是在protobuf的protoc工程里添加的代碼:

command_line_interface.cc

void CommandLineInterface::ReadTimeStampFile( const string& timestampfile )
{
    FILE* f = fopen( timestampfile.c_str(), "rb" );

    if ( f == NULL )
        return;

    time_stamp_map_.clear( );

    while( !feof( f ) )
    {
        size_t read = 0;

        int strlen = 0;
        read = fread( &strlen, 1 , sizeof strlen,  f );

        if ( read == 0 )
            break;

        std::string filename;
        filename.resize( strlen );

        read = fread( (void*)filename.data(), 1, sizeof(char) * strlen, f );

        if ( read == 0 )
            break;


        __time64_t timestamp;
        read = fread( &timestamp, 1, sizeof(timestamp), f );

        if ( read == 0 )
            break;

        time_stamp_map_[filename] = timestamp;
    }

    fclose( f );
}

void CommandLineInterface::WriteTimeStampFile( const string& timestampfile )
{
    FILE* f = fopen( timestampfile.c_str(), "wb" );

    if ( f == NULL )
        return;

    for ( time_stamp_map::iterator it = time_stamp_map_.begin();
        it != time_stamp_map_.end();
        it++)
    {
        const std::string& filename = it->first;
        __time64_t timestamp = it->second;

        int strlen = filename.length();
        fwrite( &strlen, 1, sizeof(strlen), f );
        fwrite( (void*)filename.data(), 1, sizeof(char)*strlen, f );
        fwrite( &timestamp, 1, sizeof( timestamp ), f );
    }
    
    fclose( f );
}

bool CommandLineInterface::NeedGenerate( const std::string& filename )
{
    struct _stat buf;

    if ( _stat( filename.c_str(), &buf ) != 0 )
    {
        // file error
        return true;
    }

    time_stamp_map::iterator it = time_stamp_map_.find( filename );

    
    if ( it != time_stamp_map_.end() )
    {
        __time64_t& timestamp = it->second;

        if ( timestamp == buf.st_mtime )
            return false;
    }

    // don't hold the time stamp or time stamp not match, generate it!
    
    // save to map , then write time stamp
    time_stamp_map_[filename] = buf.st_mtime;

    return true;
}


void CommandLineInterface::CheckFileStamp( const string& timestampfile )
{
    
    ReadTimeStampFile( timestampfile );

    

    for (vector<string>::iterator it = input_files_.begin();
        it != input_files_.end();) {
        
        if ( !NeedGenerate( *it) )
        {
            it = input_files_.erase( it );
        }
        else
        {
            ++it;
        }
    }


    WriteTimeStampFile( timestampfile );
}

以上代碼為核心邏輯, 之后在int CommandLineInterface::Run(int argc, const char* const argv[]) 函數中添加代碼:

int CommandLineInterface::Run(int argc, const char* const argv[]) {
  Clear();
  if (!ParseArguments(argc, argv)) return 1;

  // Set up the source tree.
  DiskSourceTree source_tree;
  for (int i = 0; i < proto_path_.size(); i++) {
    source_tree.MapPath(proto_path_[i].first, proto_path_[i].second);
  }

  // Map input files to virtual paths if necessary.
  if (!inputs_are_proto_path_relative_) {
    if (!MakeInputsBeProtoPathRelative(&source_tree)) {
      return 1;
    }
  }

  // Allocate the Importer.
  ErrorPrinter error_collector(error_format_, &source_tree);
  Importer importer(&source_tree, &error_collector);

  vector<const FileDescriptor*> parsed_files;


  if ( time_stamp_filename_ != "" )
    CheckFileStamp( time_stamp_filename_ );

加黑部分為添加的代碼, 這里是檢查時間戳的入口

同時,我們還需要添加命令行解析開關, 這里在

bool CommandLineInterface::InterpretArgument(const string& name,
                                             const string& value) {

函數中,找到:

  } else if (name == "--error_format") {
    if (value == "gcc") {
      error_format_ = ERROR_FORMAT_GCC;
    } else if (value == "msvs") {
      error_format_ = ERROR_FORMAT_MSVS;
    } else {
      cerr << "Unknown error format: " << value << endl;
      return false;
    }

  } 
  else if ( name == "--timestampfile" ){
        time_stamp_filename_ = value;
  }
  else if (name == "--plugin") {
    if (plugin_prefix_.empty()) {
      cerr << "This compiler does not support plugins." << endl;
      return false;
    }

加黑部分為解析開關

之后在頭文件中添加聲明代碼:

  // Time stamp function
  void ReadTimeStampFile( const string& timestampfile );

  void WriteTimeStampFile( const string& timestampfile );

  bool NeedGenerate( const std::string& filename );

  void CheckFileStamp( const string& timestampfile );

  typedef std::map<std::string, __time64_t> time_stamp_map;    // proto file name as key, timestamp as value
  time_stamp_map time_stamp_map_;
  string time_stamp_filename_;

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