加文件锁flock写入

 sprintf(wbuf,"sd=%d",ret);
     FILE* fp;
     fp = fopen("/tmp/testresult.txt","a+");
     flock(fp->_fileno,LOCK_EX);
     fwrite(wbuf,strlen(wbuf),1,fp);
     fwrite("\r\n",strlen("\r\n"),1,fp);
     fclose(fp);
     flock(fp->_fileno,LOCK_UN);