Why does spdlog::register_logger() throw an exception?

[wolf-chesty]

Hey,

For my application I need to be able to dynamically change the logging directory. Looking at the code I've noticed that the function spdlog::set_default_logger() can be invoked multiple times and will replace the default logger being used by spdlog in a manner that is thread safe.

spdlog::register_logger() doesn't behave the same way. The way spdlog works currently actually requires that we invoke 'spdlog::drop()` before replacing the logging target. Like so:

spdlog::drop("logger_name");
// Accessing the log sink here can crash the application
spdlog::register_logger(new_logger);

We aren't able to replace a non-default logging sink, only the default logger can be replaced in a thread-safe manner. Is there a reason for this?

Thanks,

[tt4g]

Loggers with the same name cannot be registered in spdlog's logger registry.
You must use spdlog::drop() to delete loggers with the same name.

The reason why spdlog::set_default_logger() automatically replaces loggers is so that there is no moment when a logger accessed by the global logging API, such as spdlog::info(), is disabled.

You are using an API that is not designed to replace sinks.
Instead of replacing loggers, use dist_sink, which supports sink replacement: https://github.com/gabime/spdlog/wiki/4.-Sinks

You can use spdlog::sinks::dist_sink_mt and call spdlog::dist_sink::set_sinks() to replace sinks.

spdlog/include/spdlog/sinks/dist_sink.h

Lines 42 to 45 in e593f66

	void set_sinks(std::vector<std::shared_ptr<sink>> sinks) {
	std::lock_guard<Mutex> lock(base_sink<Mutex>::mutex_);
	sinks_ = std::move(sinks);
	}