1SD_BUS_SLOT_SET_USERDATA(3)sd_bus_slot_set_userdataSD_BUS_SLOT_SET_USERDATA(3)
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NAME

6       sd_bus_slot_set_userdata, sd_bus_slot_get_userdata - Set and query the
7       value in the "userdata" field
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SYNOPSIS

10       #include <systemd/sd-bus.h>
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12       void* sd_bus_slot_set_userdata(sd_bus_slot* slot, void* userdata);
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14       void* sd_bus_slot_get_userdata(sd_bus_slot* slot);
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DESCRIPTION

17       The userdata pointer allows data to be passed between the point where a
18       callback is registered, for example when a filter is added using
19       sd_bus_add_filter(3) or an asynchronous function call is made using
20       sd_bus_call_async(3), and the point where the callback is called,
21       without having any global state. The pointer has type void* and is not
22       used by the sd-bus functions in any way, except to pass to the callback
23       function.
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25       Usually, the userdata field is set when the slot object is initially
26       registered.  sd_bus_slot_set_userdata() may be used to change it later
27       for the bus slot object slot. Previous value of the field is returned.
28       The argument and returned value may be NULL. It will be passed as the
29       userdata argument to the callback function attached to the slot.
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31       sd_bus_slot_set_userdata() gets the value of the userdata field in the
32       bus slot object slot.
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RETURN VALUE

35       On success, these functions return the value of the userdata field
36       before the function call. If the slot object is NULL, NULL will be
37       returned to signify an error, but this is not distinguishable from the
38       userdata field value being NULL.
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NOTES

41       Functions described here are available as a shared library, which can
42       be compiled against and linked to with the libsystemd pkg-config(1)
43       file.
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45       The code described here uses getenv(3), which is declared to be not
46       multi-thread-safe. This means that the code calling the functions
47       described here must not call setenv(3) from a parallel thread. It is
48       recommended to only do calls to setenv() from an early phase of the
49       program when no other threads have been started.
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SEE ALSO

52       systemd(1), sd-bus(3), sd_bus_slot_set_destroy_callback(3),
53       sd_bus_add_match(3), sd_bus_slot_get_current_userdata(3)
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57systemd 254                                        SD_BUS_SLOT_SET_USERDATA(3)
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