为什么在多线程中解析谷歌协议缓冲区的消息时速度很慢?

I try to parse many Google protocol buffer messages from a binary file generated by calling SerializeToString. I first load all Bytes into a heap memory by calling new function. I also have two arrays to store the Bytes begin address of a message in the heap memory and the Bytes count of the message. Then I begin to parse message by calling ParseFromString.I want to quicken the procedure by using multi-thread. In each thread, I pass the start index and end index of address array and Byte count array.I try to parse many Google protocol buffer mess