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utils/logger/README.md

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+## summary ##
+-----------
+
+### log format ###
+```
+[time][level][thread_id][code location] log_content
+|   auto-generated(support config)    | | content |
+```
+
+### log example ###
+```
+[2022-10-21 09:47:36.835][Debug][7fff43722700][../nodes/vp_node.cpp:179] [screen_des_a] after meta flow, in_queue.size()==>12
+```
+
+### tips ###
+better to add important field using `[]` in log content `Manually`, such as `module`, `type`. below code add name of host node(module) and task(type) in log content.
+
+```
+VP_INFO(vp_utils::string_format("[%s] [record] save dir not exists, now creating save dir: `%s`", host_node_name, save_dir));
+```
+
+### log api ###
+
+#### log config ####
+```c++
+// log level
+VP_SET_LOG_LEVEL(_log_level);
+// log file dir
+VP_SET_LOG_DIR(_log_dir);
+// log kafka servers and topic
+VP_SET_LOG_KAFKA_SERVERS_AND_TOPIC(_kafka_servers_and_topic);
+
+// log to console or not
+VP_SET_LOG_TO_CONSOLE(_log_to_console);
+// log to file or not
+VP_SET_LOG_TO_FILE(_log_to_file);
+// log to kafka or not
+VP_SET_LOG_TO_KAFKA(_log_to_kafka);
+
+// include log level or not
+VP_SET_LOG_INCLUDE_LEVEL(_include_level);
+// include code location or not (where the log occurs)
+VP_SET_LOG_INCLUDE_CODE_LOCATION(_include_code_location);
+// include thread id or not (std::this_thread::get_id())
+VP_SET_LOG_INCLUDE_THREAD_ID(_include_thread_id);
+
+// warn if log cache in memory exceed this value
+VP_SET_LOG_CACHE_WARN_THRES(_log_cache_warn_threshold);
+```
+
+
+#### write log ####
+4 types of log
+```c++
+// error
+VP_ERROR(message);
+// warn
+VP_WARN(message);
+// info
+VP_INFO(message);
+// debug
+VP_DEBUG(message);
+```
+
+```c++
+// important! call at the begining of main()
+VP_LOGGER_INIT();
+```