PMEMOBJ_LOG_USE_DEFAULT_FUNCTION(3)

💖 pmemobj_log_set_function() — set the logging function 💖

okay bestie, welcome to the PMDK Programmer's Manual ✨ this one's all about picking who gets to hear the library's gossip (aka the logging messages). no cap, it's a short one, so let's go 🫶

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✨ SYNOPSIS ✨

#include <libpmemobj.h>

typedef void pmemobj_log_function(
    enum pmemobj_log_level level,
    const char *file_name,
    unsigned line_no,
    const char *function_name,
    const char *message);

int pmemobj_log_set_function(pmemobj_log_function *log_function);

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🌸 DESCRIPTION 🌸

pmemobj_log_set_function() is literally your way of choosing which function receives every single logging message the library generates. iconic, right?

So log_function can be one of two things:

• PMEMOBJ_LOG_USE_DEFAULT_FUNCTION — the default logging function, built right into the library, no effort required 💅
• a pointer to a user-defined function — for when you want main character energy and handle the logs yourself 👑

The parameters your user-defined log function gets handed are as follows, bestie:

• level — the log level of the message (peep pmemobj_log_set_threshold(3) for the available log levels) 👀
• file_name — the name of the source file where the message is coming from. it could be set to NULL, and in that case neither line_no nor function_name are provided. so don't come for them, they just aren't there 🙈
• line_no — the source file line where the message is coming from
• function_name — the function name where the message is coming from
• message — the message string, the actual tea ☕

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🎀 THE DEFAULT LOGGING FUNCTION 🎀

The library ships with a default logging function that writes messages to syslog(3) and to stderr(3). it's enabled during library initialization (she's already awake when you get there 💅) and you can bring her back anytime using PMEMOBJ_LOG_USE_DEFAULT_FUNCTION as the log_function argument.

Here's the deets on her behaviour, fr fr:

• she sinks all the logging messages into syslog(3) unconditionally — no questions asked
• additionally, she sinks a logging message into stderr(3) if its logging level is not less severe than the value indicated by the PMEMOBJ_LOG_THRESHOLD_AUX threshold, and it is not of level PMEMOBJ_LOG_LEVEL_HARK

⚠️ heads up: the PMEMOBJ_LOG_THRESHOLD threshold's value applies to the default logging function. pls read the notes below, they matter 👇

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⭐ RETURN VALUE ⭐

pmemobj_log_set_function() returns 0 on success ✨ or returns a non-zero value and sets errno on failure 😭. and on failure, the logging function remains unchanged — no half-done glow-ups here.

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💀 ERRORS 💀

pmemobj_log_set_function() can set the following errno values on fail:

• EAGAIN — multiple threads attempted to change the logging function concurrently. a retry may fix the problem. this error is not expected when the function is called from just one thread at a time. so like, one at a time, bestie, we are not doing chaos today 🫶

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🦋 NOTE 🦋

The logging messages of level less severe than indicated by the PMEMOBJ_LOG_THRESHOLD threshold's value won't make it to the logging function — and no, it does not matter whether the logging function is the default logging function or user-provided. them's the rules 💅

The user-defined function must be thread-safe. periodt 🔥

The library will call your user-defined function before returning from pmemobj_log_set_function() to deliver basic information about the library:

• “src version: 2.y.z”
• “compiled with support for shutdown state”
• “compiled with libndctl 63+”

like, she's introducing herself before you two even properly start talking. obsessed 🌸

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🌈 SEE ALSO 🌈

pmemobj_log_get_threshold(3), pmemobj_log_set_threshold(3).

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and that's the whole page, bestie!! 🎉 this was served fresh from the PMDK programmer's manual, dated 2025-07-24 — so go forth, set your logging function, and slay 💖✨🎀🦋👑