SD_BUS_GET_CURRENT_USERDATA(3)

💅 SD_BUS_GET_CURRENT_HANDLER(3) — the girlies' guide to peeking at your own callback

okay so this is section 3 of the manual, and yes bestie, we're talking about sd_bus_get_current_handler and its three icon besties. it's the one where sd-bus lets you look at what it's currently doing mid-callback. main character energy fr 💖

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✨ NAME ✨

sd_bus_get_current_handler, sd_bus_get_current_message, sd_bus_get_current_slot, sd_bus_get_current_userdata — the four functions that let you query info about the callback a bus object is currently running 🎀

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🌸 SYNOPSIS 🌸

#include <systemd/sd-bus.h>

typedef int (*sd_bus_message_handler_t)(sd_bus_message *m,
                                        void *userdata,
                                        sd_bus_error *ret_error);

sd_bus_message_handler_t sd_bus_get_current_handler(sd_bus *bus);

sd_bus_message* sd_bus_get_current_message(sd_bus *bus);

sd_bus_slot* sd_bus_get_current_slot(sd_bus *bus);

void* sd_bus_get_current_userdata(sd_bus *bus);

like, that typedef at the top? that's the actual callback shape, so you know what kind of function we're talking about here. slay ✨

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🦋 DESCRIPTION 🦋

okay so here's the vibe check: whenever sd-bus is about to invoke a user-supplied callback function, it quietly stores four little things — the current callback, the D-Bus message, the slot, and the userdata pointer. then it lets you come back and ask about them later 👑

the four functions that do the asking are, respectively:

• sd_bus_get_current_handler() — the current callback
• sd_bus_get_current_message() — the current D-Bus message
• sd_bus_get_current_slot() — the current slot
• sd_bus_get_current_userdata() — the current userdata pointer

and the catch (iykyk): if bus can't be resolved, or if execution does not reside in a user-supplied callback of bus, these functions return NULL. no callback, no info, no crumbs. 😭

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💀 RETURN VALUE 💀

• On success? these functions return the requested object. icon behavior 💅
• On failure? they return NULL. that's it, that's the whole mood.

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🧚 NOTES 🧚

• the functions described here are available as a shared library, which can be compiled against and linked to with the libsystemd pkg-config(1) file. standard, but important 💖
• all functions listed here are thread-agnostic, and only a single thread may operate on a given object at any given time. different threads may access the same object at different times. multiple independent objects may be used from different threads in parallel. so like, share the vibe, not the object, at the same time 🫶
• the code described here uses getenv(3), which is declared to be not multi-thread-safe. that means any code calling the functions described here must not call setenv(3) from a parallel thread. the recommendation is to only do calls to setenv() from an early phase of the program, when no other threads have been started. do it before the group chat gets loud, basically 🙈

ngl, that setenv(3) thing is a real one — please don't be cute about it. do your environment setup early, before threads spawn. periodt.

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⭐ HISTORY ⭐

sd_bus_get_current_handler(), sd_bus_get_current_message(), sd_bus_get_current_slot(), and sd_bus_get_current_userdata() were added in version 221. throwback era, honestly 🌈

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🌟 SEE ALSO 🌟

systemd(1), sd-bus(3)

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and that's the whole page, bestie — no notes, you ate 🍓

systemd 261.3 — that's the version, and this little page is filed under SD_BUS_GET...NT_HANDLER(3). mwah, go query some callbacks 💜✨🎀