1SD_BUS_TRACK_NEW(3) sd_bus_track_new SD_BUS_TRACK_NEW(3)
2
6 sd_bus_track_new, sd_bus_track_ref, sd_bus_track_unref,
7 sd_bus_track_unrefp, sd_bus_track_set_recursive,
8 sd_bus_track_get_recursive, sd_bus_track_get_bus,
9 sd_bus_track_get_userdata, sd_bus_track_set_userdata - Track bus peers
10
12 #include <systemd/sd-bus.h>
13 int sd_bus_track_new(sd_bus* bus, sd_bus_track** ret,
15 sd_bus_track_handler_t handler, void* userdata);
16 sd_bus_track *sd_bus_track_ref(sd_bus_track *t);
18 sd_bus_track *sd_bus_track_unref(sd_bus_track *t);
20 void sd_bus_track_unrefp(sd_bus_track **t);
22 int sd_bus_track_get_recursive(sd_bus_track *t);
24 int sd_bus_track_set_recursive(sd_bus_track *t, int b);
26 sd_bus* sd_bus_track_get_bus(sd_bus_track *t);
28 void* sd_bus_track_get_userdata(sd_bus_track *t);
30 void* sd_bus_track_set_userdata(sd_bus_track *t, void *userdata);
32
34 sd_bus_track_new() creates a new bus peer tracking object. The object
35 is allocated for the specified bus, and returned in the *ret parameter.
36 After use, the object should be freed again by dropping the acquired
37 reference with sd_bus_track_unref() (see below). A bus peer tracking
38 object may be used to keep track of peers on a specific IPC bus, for
39 cases where peers are making use of one or more local objects, in order
40 to control the lifecycle of the local objects and ensure they stay
41 around as long as the peers needing them are around, and unreferenced
42 (and possibly destroyed) as soon as all relevant peers have vanished.
43 Each bus peer tracking object may be used to track zero, one or more
44 peers add a time. References to specific bus peers are added via
45 sd_bus_track_add_name(3) or sd_bus_track_add_sender(). They may be
46 dropped again via sd_bus_track_remove_name() and
47 sd_bus_track_remove_sender(). Alternatively, references on peers are
48 removed automatically when they disconnect from the bus. If non-NULL
49 the handler may specify a function that is invoked whenever the last
50 reference is dropped, regardless whether the reference is dropped
51 explicitly via sd_bus_track_remove_name() or implicitly because the
52 peer disconnected from the bus. The final argument userdata may be used
53 to attach a generic user data pointer to the object. This pointer is
54 passed to the handler callback when it is invoked.
55 sd_bus_track_ref() creates a new reference to a bus peer tracking
57 object. This object will not be destroyed until sd_bus_track_unref()
58 has been called as many times plus once more. Once the reference count
59 has dropped to zero, the specified object cannot be used anymore,
60 further calls to sd_bus_track_ref() or sd_bus_track_unref() on the same
61 object are illegal.
62 sd_bus_track_unref() destroys a reference to a bus peer tracking
64 object.
65 sd_bus_track_unrefp() is similar to sd_bus_track_unref() but takes a
67 pointer to a pointer to an sd_bus_track object. This call is useful in
68 conjunction with GCC's and LLVM's Clean-up Variable Attribute[1]. Note
69 that this function is defined as inline function.
70 sd_bus_track_ref(), sd_bus_track_unref() and sd_bus_track_unrefp()
72 execute no operation if the passed in bus peer tracking object is NULL.
73 Bus peer tracking objects may exist in two modes: by default they
75 operate in non-recursive mode, but may optionally be switched into
76 recursive mode. If operating in the default non-recursive mode a peer
77 is either tracked or not tracked. In this mode invoking
78 sd_bus_track_add_name() multiple times in a row for the same peer is
79 fully equivalent to calling it just once, as the call adds the peer to
80 the set of tracked peers if necessary, and executes no operation if the
81 peer is already being tracked. A single invocation of
82 sd_bus_track_remove_name() removes the reference on the peer again,
83 regardless how many times sd_bus_track_add_name() was called before. If
84 operating in recursive mode, the number of times
85 sd_bus_track_add_name() is invoked for the same peer name is counted
86 and sd_bus_track_remove_name() must be called the same number of times
87 before the peer is not tracked anymore, with the exception when the
88 tracked peer vanishes from the bus, in which case the count is
89 irrelevant and the tracking of the specific peer is immediately
90 removed. sd_bus_track_get_recursive() may be used to determine whether
91 the bus peer tracking object is operating in recursive mode.
92 sd_bus_track_set_recursive() may be used to enable or disable recursive
93 mode. By default a bus peer tracking object operates in non-recursive
94 mode, and sd_bus_track_get_recursive() for a newly allocated object
95 hence returns a value equal to zero. Use sd_bus_track_set_recursive()
96 to enable recursive mode, right after allocation. It takes a boolean
97 argument to enable or disable recursive mode. Note that tracking
98 objects for which sd_bus_track_add_name() was already invoked at least
99 once (and which hence track already one or more peers) may not be
100 switched from recursive to non-recursive mode anymore.
101 sd_bus_track_get_bus() returns the bus object the bus peer tracking
103 object belongs to. It returns the bus object initially passed to
104 sd_bus_track_new() when the object was allocated.
105 sd_bus_track_get_userdata() returns the generic user data pointer set
107 on the bus peer tracking object at the time of creation using
108 sd_bus_track_new() or at a later time, using
109 sd_bus_track_set_userdata().
110
112 On success, sd_bus_track_new() and sd_bus_track_set_recursive() return
113 0 or a positive integer. On failure, they return a negative errno-style
114 error code.
115 sd_bus_track_ref() always returns the argument.
117 sd_bus_track_unref() always returns NULL.
119 sd_bus_track_get_recursive() returns 0 if non-recursive mode is
121 selected (default), and greater than 0 if recursive mode is selected.
122 On failure a negative errno-style error code is returned.
123 sd_bus_track_get_bus() returns the bus object associated to the bus
125 peer tracking object.
126 sd_bus_track_get_userdata() returns the generic user data pointer
128 associated with the bus peer tracking object.
129 sd_bus_track_set_userdata() returns the previous user data pointer set.
130
132 The sd_bus_track_new() function creates a new object and the caller
133 owns the sole reference. When not needed anymore, this reference should
134 be destroyed with sd_bus_track_unref().
135 Errors
137 Returned errors may indicate the following problems:
138 -EBUSY
140 Bus peers have already been added to the bus peer tracking object
141 and sd_bus_track_set_recursive() was called to change tracking
142 mode.
143 -EINVAL
145 Specified parameter is invalid (NULL in case of output parameters).
146 -ENOMEM
148 Memory allocation failed.
149
151 Functions described here are available as a shared library, which can
152 be compiled against and linked to with the libsystemd pkg-config(1)
153 file.
154 The code described here uses getenv(3), which is declared to be not
156 multi-thread-safe. This means that the code calling the functions
157 described here must not call setenv(3) from a parallel thread. It is
158 recommended to only do calls to setenv() from an early phase of the
159 program when no other threads have been started.
160
162 systemd(1), sd-bus(3) sd_bus_track_add_name(3)
163
165 1. Clean-up Variable Attribute
166 https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html
167systemd 254 SD_BUS_TRACK_NEW(3)