'\" t
.TH "SD_BUS_SLOT_SET_DESTROY_CALLBACK" "3" "" "systemd 239" "sd_bus_slot_set_destroy_callback"
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.SH "NAME"
sd_bus_slot_set_destroy_callback, sd_bus_slot_get_destroy_callback, sd_bus_track_set_destroy_callback, sd_bus_track_get_destroy_callback, sd_bus_destroy_t \- Define the callback function for resource cleanup\&.
.SH "SYNOPSIS"
.sp
.ft B
.nf
#include <systemd/sd\-bus\&.h>
.fi
.ft
.HP \w'typedef\ int\ (*sd_bus_destroy_t)('u
.BI "typedef int (*sd_bus_destroy_t)(void\ *" "userdata" ");"
.HP \w'int\ sd_bus_slot_set_destroy_callback('u
.BI "int sd_bus_slot_set_destroy_callback(sd_bus_slot\ *" "slot" ", sd_bus_destroy_t\ " "callback" ");"
.HP \w'int\ sd_bus_slot_get_destroy_callback('u
.BI "int sd_bus_slot_get_destroy_callback(sd_bus_slot\ *" "slot" ", sd_bus_destroy_t\ *" "callback" ");"
.HP \w'int\ sd_bus_track_set_destroy_callback('u
.BI "int sd_bus_track_set_destroy_callback(sd_bus_track\ *" "track" ", sd_bus_destroy_t\ " "callback" ");"
.HP \w'int\ sd_bus_track_get_destroy_callback('u
.BI "int sd_bus_track_get_destroy_callback(sd_bus_track\ *" "track" ", sd_bus_destroy_t\ *" "callback" ");"
.SH "DESCRIPTION"
.PP
\fBsd_bus_slot_set_destroy_callback()\fR
sets
\fIcallback\fR
as the callback function to be called right before the bus slot object
\fIslot\fR
is deallocated\&. The
\fIuserdata\fR
pointer from the slot object will be passed as the
\fIuserdata\fR
parameter\&. This pointer can be set by an argument to the constructor functions, see
\fBsd_bus_add_match\fR(3), or directly, see
\fBsd_bus_slot_set_userdata\fR(3)\&. This callback function is called even if
\fIuserdata\fR
is
\fBNULL\fR\&. Note that this callback is invoked at a time where the bus slot object itself is already invalidated, and executing operations or taking new references to the bus slot object is not permissible\&.
.PP
\fBsd_bus_slot_get_destroy_callback()\fR
returns the current callback for
\fIslot\fR
in the
\fIcallback\fR
parameter\&.
.PP
\fBsd_bus_track_set_destroy_callback()\fR
and
\fBsd_bus_track_get_destroy_callback\fR
provide equivalent functionality for the
\fIuserdata\fR
pointer associated with bus peer tracking objects\&. For details about bus peer tracking objects, see
\fBsd_bus_track_new\fR(3)\&.
.SH "RETURN VALUE"
.PP
On success,
\fBsd_bus_slot_set_destroy_callback()\fR
and
\fBsd_bus_track_set_destroy_callback()\fR
return 0 or a positive integer\&. On failure, they return a negative errno\-style error code\&.
.PP
\fBsd_bus_slot_get_destroy_callback()\fR
and
\fBsd_bus_track_get_destroy_callback\fR
return positive if the destroy callback function is set, 0 if not\&. On failure, they return a negative errno\-style error code\&.
.SH "ERRORS"
.PP
Returned errors may indicate the following problems:
.PP
\fB\-EINVAL\fR
.RS 4
The
\fIslot\fR
or
\fItrack\fR
parameter is
\fBNULL\fR\&.
.RE
.SH "NOTES"
.PP
These APIs are implemented as a shared library, which can be compiled and linked to with the
\fBlibsystemd\fR\ \&\fBpkg-config\fR(1)
file\&.
.SH "SEE ALSO"
.PP
\fBsystemd\fR(1),
\fBsd-bus\fR(3),
\fBsd_bus_slot_set_floating\fR(3),
\fBsd_bus_add_match\fR(3),
\fBsd_bus_track_new\fR(3),
\fBsd_bus_slot_set_userdata\fR(3),
\fBsd_bus_track_set_userdata\fR(3)