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 illegal.

       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 function.

       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

       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

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 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


       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         top

       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

           Specified parameter is invalid (NULL in case of output

           Memory allocation failed.

NOTES         top

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

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 233                                              SD_BUS_TRACK_NEW(3)