Log Cache

[CTGUMARK]

After the program is started, the log size is 0. It will not be written to the log until the program is closed. Is there a cache mechanism? Will it be written to the log file only when it reaches a certain size? How to write in real time

[Barry-Xu-2018]

By default, if the environment variable RCL_LOGGING_SPDLOG_EXPERIMENTAL_OLD_FLUSHING_BEHAVIOR is not set, the default flush time is 5 seconds. Setting this environment variable uses the old default value, which maybe 3 seconds.

Currently, no interface is provided to specify flush time from the outside. So, you can only modify the code yourself.

Besides changing the flush time, you can also modify the flush_on() setting. Currently, error logs trigger an automatic flush. You can change it to spdlog::level::info so that info logs (and higher levels like warning and error) will trigger the flush action.

BTW, frequent file writing is generally not recommended.

rcl_logging/rcl_logging_spdlog/src/rcl_logging_spdlog.cpp

Lines 197 to 207 in 7529e87

	auto sink = std::make_unique<spdlog::sinks::basic_file_sink_mt>(name_buffer, false);
	g_root_logger = std::make_shared<spdlog::logger>("root", std::move(sink));
	if (!should_use_old_flushing_behavior) {
	// in this case we should do the new thing (until config files are supported)
	// which is to configure the logger to flush periodically and on
	// error level messages
	spdlog::flush_every(std::chrono::seconds(5));
	g_root_logger->flush_on(spdlog::level::err);
	} else {
	// the old behavior is to not configure the sink at all, so do nothing
	}

    auto sink = std::make_unique<spdlog::sinks::basic_file_sink_mt>(name_buffer, false);
    g_root_logger = std::make_shared<spdlog::logger>("root", std::move(sink));
    if (!should_use_old_flushing_behavior) {
      // in this case we should do the new thing (until config files are supported)
      // which is to configure the logger to flush periodically and on
      // error level messages
      spdlog::flush_every(std::chrono::seconds(5));
      g_root_logger->flush_on(spdlog::level::err);
    } else {
      // the old behavior is to not configure the sink at all, so do nothing
    }

[fujitatomoya]

@Barry-Xu-2018 @CTGUMARK i moved this issue to rcl_logging since this is the issue with this repository.