следить за сверстниками автобуса (track bus peers)
Имя (Name)
sd_bus_track_new, sd_bus_track_ref, sd_bus_track_unref,
sd_bus_track_unrefp, sd_bus_track_set_recursive,
sd_bus_track_get_recursive, sd_bus_track_get_bus,
sd_bus_track_get_userdata, sd_bus_track_set_userdata - Track bus
peers
Синопсис (Synopsis)
#include <systemd/sd-bus.h>
int sd_bus_track_new(sd_bus* bus, sd_bus_track** ret,
sd_bus_track_handler_t handler,
void* userdata);
sd_bus_track *sd_bus_track_ref(sd_bus_track *t);
sd_bus_track *sd_bus_track_unref(sd_bus_track *t);
void sd_bus_track_unrefp(sd_bus_track **t);
int sd_bus_track_get_recursive(sd_bus_track *t);
int sd_bus_track_set_recursive(sd_bus_track *t, int b);
sd_bus* sd_bus_track_get_bus(sd_bus_track *t);
void* sd_bus_track_get_userdata(sd_bus_track *t);
void* sd_bus_track_set_userdata(sd_bus_track *t, void *userdata);
Описание (Description)
sd_bus_track_new() creates a new bus peer tracking object. The
object is allocated for the specified bus, and returned in the
*ret parameter. After use, the object should be freed again by
dropping the acquired reference with sd_bus_track_unref() (see
below). A bus peer tracking object may be used to keep track of
peers on a specific IPC bus, for cases where peers are making use
of one or more local objects, in order to control the lifecycle
of the local objects and ensure they stay around as long as the
peers needing them are around, and unreferenced (and possibly
destroyed) as soon as all relevant peers have vanished. Each bus
peer tracking object may be used to track zero, one or more peers
add a time. References to specific bus peers are added via
sd_bus_track_add_name(3) or sd_bus_track_add_sender(). They may
be dropped again via sd_bus_track_remove_name() and
sd_bus_track_remove_sender(). Alternatively, references on peers
are removed automatically when they disconnect from the bus. If
non-NULL the handler may specify a function that is invoked
whenever the last reference is dropped, regardless whether the
reference is dropped explicitly via sd_bus_track_remove_name() or
implicitly because the peer disconnected from the bus. The final
argument userdata may be used to attach a generic user data
pointer to the object. This pointer is passed to the handler
callback when it is invoked.
sd_bus_track_ref() creates a new reference to a bus peer tracking
object. This object will not be destroyed until
sd_bus_track_unref() has been called as many times plus once
more. Once the reference count has dropped to zero, the specified
object cannot be used anymore, further calls to
sd_bus_track_ref() or sd_bus_track_unref() on the same object are
illegal.
sd_bus_track_unref() destroys a reference to a bus peer tracking
object.
sd_bus_track_unrefp() is similar to sd_bus_track_unref() but
takes a pointer to a pointer to an sd_bus_track object. This call
is useful in conjunction with GCC's and LLVM's Clean-up Variable
Attribute
sd_bus_track_ref(), sd_bus_track_unref() and
sd_bus_track_unrefp() execute no operation if the passed in bus
peer tracking object is NULL.
Bus peer tracking objects may exist in two modes: by default they
operate in non-recursive mode, but may optionally be switched
into recursive mode. If operating in the default non-recursive
mode a peer is either tracked or not tracked. In this mode
invoking sd_bus_track_add_name() multiple times in a row for the
same peer is fully equivalent to calling it just once, as the
call adds the peer to the set of tracked peers if necessary, and
executes no operation if the peer is already being tracked. A
single invocation of sd_bus_track_remove_name() removes the
reference on the peer again, regardless how many times
sd_bus_track_add_name() was called before. If operating in
recursive mode, the number of times sd_bus_track_add_name() is
invoked for the same peer name is counted and
sd_bus_track_remove_name() must be called the same number of
times before the peer is not tracked anymore, with the exception
when the tracked peer vanishes from the bus, in which case the
count is irrelevant and the tracking of the specific peer is
immediately removed. sd_bus_track_get_recursive() may be used to
determine whether the bus peer tracking object is operating in
recursive mode. sd_bus_track_set_recursive() may be used to
enable or disable recursive mode. By default a bus peer tracking
object operates in non-recursive mode, and
sd_bus_track_get_recursive() for a newly allocated object hence
returns a value equal to zero. Use sd_bus_track_set_recursive()
to enable recursive mode, right after allocation. It takes a
boolean argument to enable or disable recursive mode. Note that
tracking objects for which sd_bus_track_add_name() was already
invoked at least once (and which hence track already one or more
peers) may not be switched from recursive to non-recursive mode
anymore.
sd_bus_track_get_bus() returns the bus object the bus peer
tracking object belongs to. It returns the bus object initially
passed to sd_bus_track_new() when the object was allocated.
sd_bus_track_get_userdata() returns the generic user data pointer
set on the bus peer tracking object at the time of creation using
sd_bus_track_new() or at a later time, using
sd_bus_track_set_userdata().
Возвращаемое значение (Return value)
On success, sd_bus_track_new() and sd_bus_track_set_recursive()
return 0 or a positive integer. On failure, they return a
negative errno-style error code.
sd_bus_track_ref() always returns the argument.
sd_bus_track_unref() always returns NULL.
sd_bus_track_get_recursive() returns 0 if non-recursive mode is
selected (default), and greater than 0 if recursive mode is
selected. On failure a negative errno-style error code is
returned.
sd_bus_track_get_bus() returns the bus object associated to the
bus peer tracking object.
sd_bus_track_get_userdata() returns the generic user data pointer
associated with the bus peer tracking object.
sd_bus_track_set_userdata() returns the previous user data
pointer set.
The sd_bus_track_new() function creates a new object and the
caller owns the sole reference. When not needed anymore, this
reference should be destroyed with sd_bus_track_unref().
Errors
Returned errors may indicate the following problems:
-EBUSY
Bus peers have already been added to the bus peer tracking
object and sd_bus_track_set_recursive() was called to change
tracking mode.
-EINVAL
Specified parameter is invalid (NULL in case of output
parameters).
-ENOMEM
Memory allocation failed.
Примечание (Note)
These APIs are implemented as a shared library, which can be
compiled and linked to with the libsystemd pkg-config(1) file.
Смотри также (See also)
systemd(1), sd-bus(3) sd_bus_track_add_name(3)
Примечание (Note)
1. Clean-up Variable Attribute
https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html
