linux how to use spdlog in multi-library？

[gakki2019]

Linux platform: There are several dynamic library(so), for example: libmy1.so, libmy2.so, ...
All of those libraries use spdlog to record loggers in console and same logger file.
I have read wiki (https://github.com/gabime/spdlog/wiki/How-to-use-spdlog-in-DLLs), but I am still confused how to implement.

libmy1.so, libmy2.so have no such API like "setup_logger" to setup sinks.
I put spdlog into a singleton class,

logger.hpp

class logger {
public:
    static spdlog::logger *get_instance() {
        static logger instance;
        return instance.m_logger.get();
    }

    void set_level(spdlog::level::level_enum lv);

private:
    logger() noexcept;
    logger(const logger &) = delete;
    logger &operator=(const logger &) = delete;

private:
    std::shared_ptr<spdlog::logger> m_logger;
};

logger.cpp

logger::logger() noexcept {
    auto console_sink = std::make_shared<spdlog::sinks::stdout_color_sink_mt>();
    console_sink->set_level(spdlog::level::trace);
    console_sink->set_pattern("[%Y-%m-%d %H:%M:%S.%e][%t][%l]%v");

    auto file_sink = std::make_shared<spdlog::sinks::rotating_file_sink_mt>("log/log.txt", 1024*1024, 5);
    file_sink->set_level(spdlog::level::trace);
    file_sink->set_pattern("[%Y-%m-%d %H:%M:%S.%e][%t][%l]%v");

    m_logger = std::make_shared<spdlog::logger>(spdlog::logger{"axcl_logger", {console_sink, file_sink}});
    spdlog::register_logger(m_logger);
    m_logger->set_level(spdlog::level::debug);
    m_logger->flush_on(spdlog::level::err);
}

Also provide macro in logger.hpp like：

#define MY_LOGGER logger::get_instance()
#define LOG_M_D(tag, fmt, ...)   MY_LOGGER ->log(spdlog::level::debug,    "[{}]: " fmt, tag, ##__VA_ARGS__)
#define LOG_M_I(tag, fmt, ...)     MY_LOGGER ->log(spdlog::level::info,        "[{}]: " fmt, tag, ##__VA_ARGS__)
#define LOG_M_W(tag, fmt, ...)   MY_LOGGER ->log(spdlog::level::warn,     "[{}]: " fmt, tag, ##__VA_ARGS__)

All libraries linked to logger.hpp, and logger.cpp, such as:

log
- logger.hpp
- logger.cpp

libmy1
- my1fun.cpp
- Makefile # gcc my1fun.cpp log/logger.cpp -shared -fPIC libmy1.so

libmy2
- my2func.cpp
- Makefile # gcc my2fun.cpp log/logger.cpp -shared -fPIC libmy2.so

Libraries print logger like：

#include "log/logger.hpp"
void function_in_my1_library() {
     LOG_M_I("tag", "hello {} in libmy1.so". "spdlog");
}

#include "log/logger.hpp"
void function_in_my2_library() {
     LOG_M_I("tag", "hello {}" in libmy2.so. "spdlog");
}

@tt4g could you help me? Thank you so much.

[tt4g]

I don't know what exactly you are having trouble doing.

At least as previously answered, function bodies with singleton variables should not be listed in header files: #3171 (reply in thread)
And template functions can be used in C++, but not in C (#3173).

[gakki2019]

Thanks for reply.
#3171 has fixed, there is no issue.
#3173 , yes, I have got your point.

In [wiki] (https://github.com/gabime/spdlog/wiki/How-to-use-spdlog-in-DLLs) shows how to use in DLLs, but it seems setup_logger API should be exported by the DLLs, which is not what I expected.

I’m still unsure how to use spdlog effectively across multiple libraries. Here's what I have done so far:
I provided a common logger.hpp and logger.cpp, which all the libraries compile and include to log into a single file.
Each library is compiled with the -fvisibility=hidden option to hide unnecessary symbols.
However, this approach led to a few issues:
1. Each library ends up with its own copy of the logger instance because the logger class is not marked with attribute((visibility("default"))).
2. It's difficult to change the log level for each library because each logger class has a own copy.
3. The logging performance appears to be slow. I’m not sure if this is related to I/O and I haven't tried spdlog's async mode to improve efficiency (I will do that)

To summarize:
There are several libraries on a Linux platform, and all of these libraries need to log into the same file using spdlog.
Could you guide me on how to implement this correctly? If there is a sample, I would greatly appreciate it.

[tt4g]

Did you use spdlog as a header-only library in each library? If so, each library will generate its own copy of spdlog.
If you want all libraries to share one spdlog, then spdlog must be built as a shared library.

[gakki2019]

Thanks to remind.
I did use spdlog as head-only.

Now I built spdlog to a shared libary by cmake: libspdlog.so, libspdlog.so1.14, libspdlog.so.1.14.1

All libraries have linked to libspdlog.so like (Makefile) :
CLIB += -L$(SPDLOG_LIB_PATH) -lspdlog

Then modify logger.cpp to add m_logger = spdlog::get("my_logger");

logger::logger() noexcept {
    m_logger = spdlog::get("my_logger");
    if (!m_logger) {
        printf("my_logger++++++++++++++++++++++++++++++++++++++++++++\n");
        auto console_sink = std::make_shared<spdlog::sinks::stdout_color_sink_mt>();
        console_sink->set_level(spdlog::level::trace);
        console_sink->set_pattern("[%Y-%m-%d %H:%M:%S.%e][%t][%L]%v");

        auto file_sink = std::make_shared<spdlog::sinks::rotating_file_sink_mt>("logs/axcl_logs.txt", 5 * 1024 * 1024, 5);
        file_sink->set_level(spdlog::level::trace);
        file_sink->set_pattern("[%Y-%m-%d %H:%M:%S.%e][%t][%L]%v");

        m_logger = std::make_shared<spdlog::logger>(spdlog::logger{"my_logger", {console_sink, file_sink}});
        spdlog::register_logger(m_logger);
        m_logger->set_level(spdlog::level::debug);
        m_logger->flush_on(spdlog::level::err);
    }
}

After launch program, each library will print "my_logger++++++++++++++++++++++++++++++++++++++++++++"

my_logger++++++++++++++++++++++++++++++++++++++++++++
my_logger++++++++++++++++++++++++++++++++++++++++++++
[2024-10-08 22:50:48.637][621][info][context manager][create_context][39]: context 1 is created, bind to thread 621
[2024-10-08 22:50:48.638][621][info][device manager][init][45]: device manager is initialized
[2024-10-08 22:50:48.638][623][info][device manager][listen][235]: +++
device id: 129
[2024-10-08 22:50:48.638][623][info][device manager][listen][246]: select +++
[2024-10-08 22:50:48.638][621][info][device][open][33]: 129 +++
my_logger++++++++++++++++++++++++++++++++++++++++++++

It seems spdlog registry not work in my code.

[tt4g]

This is because your library is still using header-only spdlog.
You must define the SPDLOG_COMPILED_LIB macro to use the shared library spdlog (duplicate #1470, #2494).