sd_bus_track_new(3) — Linux manual page


SD_BUS_TRACK_NEW(3)         sd_bus_track_new         SD_BUS_TRACK_NEW(3)

NAME         top

       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

SYNOPSIS         top

       #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);

DESCRIPTION         top

       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

       sd_bus_track_unref() destroys a reference to a bus peer tracking

       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[1]. Note that this function is defined as inline

       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

       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

RETURN VALUE         top

       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

       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().

       Returned errors may indicate the following problems:

           Bus peers have already been added to the bus peer tracking
           object and sd_bus_track_set_recursive() was called to change
           tracking mode.

           Specified parameter is invalid (NULL in case of output

           Memory allocation failed.

NOTES         top

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

       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

HISTORY         top

       sd_bus_track_new(), sd_bus_track_ref(), sd_bus_track_unref(),
       sd_bus_track_unrefp(), sd_bus_track_get_recursive(),
       sd_bus_track_set_recursive(), sd_bus_track_get_bus(),
       sd_bus_track_get_userdata(), and sd_bus_track_set_userdata() were
       added in version 232.

SEE ALSO         top

       systemd(1), sd-bus(3), sd_bus_track_add_name(3)

NOTES         top

        1. Clean-up Variable Attribute

COLOPHON         top

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systemd 257~devel                                    SD_BUS_TRACK_NEW(3)

Pages that refer to this page: sd-bus(3)sd_bus_slot_set_destroy_callback(3)sd_bus_track_add_name(3)systemd.directives(7)systemd.index(7)