'\" t
.TH "SD_BUS_NEW" "3" "" "systemd 256.7" "sd_bus_new"
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.nh
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.\" * MAIN CONTENT STARTS HERE *
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.SH "NAME"
sd_bus_new, sd_bus_ref, sd_bus_unref, sd_bus_unrefp, sd_bus_close_unref, sd_bus_close_unrefp, sd_bus_flush_close_unref, sd_bus_flush_close_unrefp \- Create a new bus object and create or destroy references to it
.SH "SYNOPSIS"
.sp
.ft B
.nf
#include <systemd/sd\-bus\&.h>
.fi
.ft
.HP \w'int\ sd_bus_new('u
.BI "int sd_bus_new(sd_bus\ **" "bus" ");"
.HP \w'sd_bus\ *sd_bus_ref('u
.BI "sd_bus *sd_bus_ref(sd_bus\ *" "bus" ");"
.HP \w'sd_bus\ *sd_bus_unref('u
.BI "sd_bus *sd_bus_unref(sd_bus\ *" "bus" ");"
.HP \w'sd_bus\ *sd_bus_close_unref('u
.BI "sd_bus *sd_bus_close_unref(sd_bus\ *" "bus" ");"
.HP \w'sd_bus\ *sd_bus_flush_close_unref('u
.BI "sd_bus *sd_bus_flush_close_unref(sd_bus\ *" "bus" ");"
.HP \w'void\ sd_bus_unrefp('u
.BI "void sd_bus_unrefp(sd_bus\ **" "busp" ");"
.HP \w'void\ sd_bus_close_unrefp('u
.BI "void sd_bus_close_unrefp(sd_bus\ **" "busp" ");"
.HP \w'void\ sd_bus_flush_close_unrefp('u
.BI "void sd_bus_flush_close_unrefp(sd_bus\ **" "busp" ");"
.SH "DESCRIPTION"
.PP
\fBsd_bus_new()\fR
creates a new bus object\&. This object is reference\-counted, and will be destroyed when all references are gone\&. Initially, the caller of this function owns the sole reference and the bus object will not be connected to any bus\&. To connect it to a bus, make sure to set an address with
\fBsd_bus_set_address\fR(3)
or a related call, and then start the connection with
\fBsd_bus_start\fR(3)\&.
.PP
In most cases, it is better to use
\fBsd_bus_default_user\fR(3),
\fBsd_bus_default_system\fR(3)
or related calls instead of the more low\-level
\fBsd_bus_new()\fR
and
\fBsd_bus_start()\fR\&. The higher\-level functions not only allocate a bus object but also start the connection to a well\-known bus in a single function call\&.
.PP
\fBsd_bus_ref()\fR
increases the reference counter of
\fIbus\fR
by one\&.
.PP
\fBsd_bus_unref()\fR
decreases the reference counter of
\fIbus\fR
by one\&. Once the reference count has dropped to zero,
\fIbus\fR
is destroyed and cannot be used anymore, so further calls to
\fBsd_bus_ref()\fR
or
\fBsd_bus_unref()\fR
are illegal\&.
.PP
\fBsd_bus_unrefp()\fR
is similar to
\fBsd_bus_unref()\fR
but takes a pointer to a pointer to an
\fBsd_bus\fR
object\&. This call is useful in conjunction with GCC\*(Aqs and LLVM\*(Aqs
\m[blue]\fBClean\-up Variable Attribute\fR\m[]\&\s-2\u[1]\d\s+2\&. Note that this function is defined as an inline function\&. Use a declaration like the following, in order to allocate a bus object that is freed automatically as the code block is left:
.sp
.if n \{\
.RS 4
.\}
.nf
{
  __attribute__((cleanup(sd_bus_unrefp))) sd_bus *bus = NULL;
  int r;
  \&...
  r = sd_bus_default(&bus);
  if (r < 0) {
    errno = \-r;
    fprintf(stderr, "Failed to allocate bus: %m\en");
  }
  \&...
}
.fi
.if n \{\
.RE
.\}
.PP
\fBsd_bus_ref()\fR
and
\fBsd_bus_unref()\fR
execute no operation if the argument is
\fBNULL\fR\&.
\fBsd_bus_unrefp()\fR
will first dereference its argument, which must not be
\fBNULL\fR, and will execute no operation if
\fIthat\fR
is
\fBNULL\fR\&.
.PP
\fBsd_bus_close_unref()\fR
is similar to
\fBsd_bus_unref()\fR, but first executes
\fBsd_bus_close\fR(3), ensuring that the connection is terminated before the reference to the connection is dropped and possibly the object freed\&.
.PP
\fBsd_bus_flush_close_unref()\fR
is similar to
\fBsd_bus_unref()\fR, but first executes
\fBsd_bus_flush\fR(3)
as well as
\fBsd_bus_close\fR(3), ensuring that any pending messages are synchronously flushed out before the reference to the connection is dropped and possibly the object freed\&. This call is particularly useful immediately before exiting from a program as it ensures that any pending outgoing messages are written out, and unprocessed but queued incoming messages released before the connection is terminated and released\&.
.PP
\fBsd_bus_close_unrefp()\fR
is similar to
\fBsd_bus_close_unref()\fR, but may be used in GCC\*(Aqs and LLVM\*(Aqs Clean\-up Variable Attribute, see above\&. Similarly,
\fBsd_bus_flush_close_unrefp()\fR
is similar to
\fBsd_bus_flush_close_unref()\fR\&.
.SH "RETURN VALUE"
.PP
On success,
\fBsd_bus_new()\fR
returns 0 or a positive integer\&. On failure, it returns a negative errno\-style error code\&.
.PP
\fBsd_bus_ref()\fR
always returns the argument\&.
.PP
\fBsd_bus_unref()\fR
and
\fBsd_bus_flush_close_unref()\fR
always return
\fBNULL\fR\&.
.SS "Errors"
.PP
Returned errors may indicate the following problems:
.PP
\fB\-ENOMEM\fR
.RS 4
Memory allocation failed\&.
.RE
.SH "NOTES"
.PP
Functions described here are available as a shared library, which can be compiled against and linked to with the
\fBlibsystemd\fR\ \&\fBpkg-config\fR(1)
file\&.
.PP
The code described here uses
\fBgetenv\fR(3), which is declared to be not multi\-thread\-safe\&. This means that the code calling the functions described here must not call
\fBsetenv\fR(3)
from a parallel thread\&. It is recommended to only do calls to
\fBsetenv()\fR
from an early phase of the program when no other threads have been started\&.
.SH "HISTORY"
.PP
\fBsd_bus_new()\fR,
\fBsd_bus_ref()\fR, and
\fBsd_bus_unref()\fR
were added in version 209\&.
.PP
\fBsd_bus_unrefp()\fR
was added in version 229\&.
.PP
\fBsd_bus_flush_close_unref()\fR
and
\fBsd_bus_flush_close_unrefp()\fR
were added in version 240\&.
.PP
\fBsd_bus_close_unref()\fR
and
\fBsd_bus_close_unrefp()\fR
were added in version 241\&.
.SH "SEE ALSO"
.PP
\fBsystemd\fR(1), \fBsd-bus\fR(3), \fBsd_bus_default_user\fR(3), \fBsd_bus_default_system\fR(3), \fBsd_bus_open_user\fR(3), \fBsd_bus_open_system\fR(3), \fBsd_bus_close\fR(3)
.SH "NOTES"
.IP " 1." 4
Clean-up Variable Attribute
.RS 4
\%https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html
.RE