sd_bus_new - Man Page

#include <systemd/sd-bus​.h>

int sd_bus_new(sd_bus **bus);

sd_bus *sd_bus_ref(sd_bus *bus);

sd_bus *sd_bus_unref(sd_bus *bus);

sd_bus *sd_bus_close_unref(sd_bus *bus);

sd_bus *sd_bus_flush_close_unref(sd_bus *bus);

void sd_bus_unrefp(sd_bus **busp);

void sd_bus_close_unrefp(sd_bus **busp);

void sd_bus_flush_close_unrefp(sd_bus **busp);

sd_bus_new() 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 sd_bus_set_address(3) or a related call, and then start the connection with sd_bus_start(3)​.

In most cases, it is better to use sd_bus_default_user(3), sd_bus_default_system(3) or related calls instead of the more low-level sd_bus_new() and sd_bus_start()​. 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​.

sd_bus_ref() increases the reference counter of bus by one​.

sd_bus_unref() decreases the reference counter of bus by one​. Once the reference count has dropped to zero, bus is destroyed and cannot be used anymore, so further calls to sd_bus_ref() or sd_bus_unref() are illegal​.

sd_bus_unrefp() is similar to sd_bus_unref() but takes a pointer to a pointer to an sd_bus object​. This call is useful in conjunction with GCC's and LLVM's Clean-up Variable Attribute​^[1]​. 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:

{
  __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\n");
  }
  ​...
}

sd_bus_ref() and sd_bus_unref() execute no operation if the argument is NULL​. sd_bus_unrefp() will first dereference its argument, which must not be NULL, and will execute no operation if that is NULL​.

sd_bus_close_unref() is similar to sd_bus_unref(), but first executes sd_bus_close(3), ensuring that the connection is terminated before the reference to the connection is dropped and possibly the object freed​.

sd_bus_flush_close_unref() is similar to sd_bus_unref(), but first executes sd_bus_flush(3) as well as sd_bus_close(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​.

sd_bus_close_unrefp() is similar to sd_bus_close_unref(), but may be used in GCC's and LLVM's Clean-up Variable Attribute, see above​. Similarly, sd_bus_flush_close_unrefp() is similar to sd_bus_flush_close_unref()​.

On success, sd_bus_new() returns 0 or a positive integer​. On failure, it returns a negative errno-style error code​.

sd_bus_ref() always returns the argument​.

sd_bus_unref() and sd_bus_flush_close_unref() always return NULL​.

Functions described here are available as a shared library, which can be compiled against and linked to with the libsystemd ​pkg-config(1) file​.

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​.

The code described here uses getenv(3), which is declared to be not multi-thread-safe​. This means that the code calling the functions described here must not call setenv(3) from a parallel thread​. It is recommended to only do calls to setenv() from an early phase of the program when no other threads have been started​.

sd_bus_new(), sd_bus_ref(), and sd_bus_unref() were added in version 209​.

sd_bus_unrefp() was added in version 229​.

sd_bus_flush_close_unref() and sd_bus_flush_close_unrefp() were added in version 240​.

sd_bus_close_unref() and sd_bus_close_unrefp() were added in version 241​.

systemd(1), sd-bus(3), sd_bus_default_user(3), sd_bus_default_system(3), sd_bus_open_user(3), sd_bus_open_system(3), sd_bus_close(3)

1.

Clean-up Variable Attribute
https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html

sd-bus(3), sd_bus_close(3), sd_bus_default(3), sd_bus_message_get_cookie(3), sd_bus_message_get_monotonic_usec(3), sd_bus_message_new(3), sd_bus_message_set_destination(3), sd_bus_request_name(3), sd_bus_set_address(3), sd_bus_slot_ref(3), systemd.directives(7), systemd.index(7).

The man pages sd_bus_close_unref(3), sd_bus_close_unrefp(3), sd_bus_flush_close_unref(3), sd_bus_flush_close_unrefp(3), sd_bus_ref(3), sd_bus_unref(3) and sd_bus_unrefp(3) are aliases of sd_bus_new(3).