使用Protocol Buffers的GzipOutputStream和GzipInputStream的简单工作示例

Question

经过几天试验协议缓冲区后,我试图压缩文件.使用Python,这很简单,并且不需要使用流.

由于我们的大部分代码都是用C++编写的,我想用同一种语言压缩/解压缩文件.我已经尝试过boost gzip库,但无法使其工作(不压缩):

int writeEventCollection(HEP::MyProtoBufClass* protobuf, std::string filename, unsigned int compressionLevel) {
            ofstream file(filename.c_str(), ios_base::out | ios_base::binary);
            filtering_streambuf<output> out;
            out.push(gzip_compressor(compressionLevel));
            out.push(file);
            if (!protobuf->SerializeToOstream(&file)) {//serialising to wrong stream I asume
                    cerr << "Failed to write ProtoBuf." << endl;
                    return -1;
            }
            return 0;
    }

我搜索了使用GzipOutputStream和GzipInputStream与协议缓冲区但没有找到工作示例的示例.

正如您现在可能已经注意到的那样,我最初是一个初学者,并且非常感谢http://code.google.com/apis/protocolbuffers/docs/cpptutorial.html中的完整工作示例 (我有我的地址_本,如何将它保存在gziped文件中？)

先感谢您.

编辑:工作实例.

示例1在StackOverflow上的答案之后

int writeEventCollection(shared_ptr<HEP::EventCollection> eCollection, 
std::string filename, unsigned int compressionLevel) { 
filtering_ostream out; 
out.push(gzip_compressor(compressionLevel)); 
out.push(file_sink(filename, ios_base::out | ios_base::binary)); 
if (!eCollection->SerializeToOstream(&out)) { 
                cerr << "Failed to write event collection." << endl; 
                return -1; 
} 

return 0; 
} 

示例2在Google的Protobuf讨论组上回答以下问题:

int writeEventCollection2(shared_ptr<HEP::EventCollection> 
eCollection, std::string filename, 
                        unsigned int compressionLevel) { 
using namespace google::protobuf::io; 
int filedescriptor = open(filename.c_str(), O_WRONLY | O_CREAT | O_TRUNC, 
                S_IREAD | S_IWRITE); 
if (filedescriptor == -1) { 
                        throw "open failed on output file"; 
                } 
google::protobuf::io::FileOutputStream file_stream(filedescriptor); 
GzipOutputStream::Options options; 
options.format = GzipOutputStream::GZIP; 
options.compression_level = compressionLevel; 
google::protobuf::io::GzipOutputStream gzip_stream(&file_stream, 
options); 
if (!eCollection->SerializeToZeroCopyStream(&gzip_stream)) { 
     cerr << "Failed to write event collection." << endl; 
     return -1; 
     } 
close(filedescriptor); 
return 0; 
} 

关于性能的一些评论(阅读当前格式和编写ProtoBuf 11146文件):示例1:

real    13m1.185s 
user    11m18.500s 
sys     0m13.430s 
CPU usage: 65-70% 
Size of test sample: 4.2 GB (uncompressed 7.7 GB, our current compressed format: 7.7 GB)

例2:

real    12m37.061s 
user    10m55.460s 
sys     0m11.900s 
CPU usage: 90-100% 
Size of test sample: 3.9 GB

似乎Google的方法更有效地使用CPU,稍微快一点(虽然我希望它在准确度范围内)并且使用相同的压缩设置产生约7%的小数据集.

Answer 1

您的假设是正确的：您发布的代码不起作用，因为您直接写入ofstream而不是通过filtering_streambuf. 为了使这项工作有效，您可以使用filtering_ostream：

ofstream file(filename.c_str(), ios_base::out | ios_base::binary); 
filtering_ostream out; 
out.push(gzip_compressor(compressionLevel)); 
out.push(file);

if (!protobuf->SerializeToOstream(&out)) {
    // ... etc.
}

或者更简洁地使用file_sink：

filtering_ostream out; 
out.push(gzip_compressor(compressionLevel)); 
out.push(file_sink(filename, ios_base::out | ios_base::binary));

if (!protobuf->SerializeToOstream(&out)) {
    // ... etc.
}

我希望这有帮助！