sd_event_new(3)

1SD_EVENT_NEW(3)                  sd_event_new                  SD_EVENT_NEW(3)
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3
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NAME

6       sd_event_new, sd_event_default, sd_event_ref, sd_event_unref,
7       sd_event_unrefp, sd_event_get_tid, sd_event - Acquire and release an
8       event loop object
9

SYNOPSIS

11       #include <systemd/sd-event.h>
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13       typedef struct sd_event sd_event;
14
15       int sd_event_new(sd_event **event);
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17       int sd_event_default(sd_event **event);
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19       sd_event *sd_event_ref(sd_event *event);
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21       sd_event *sd_event_unref(sd_event *event);
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23       void sd_event_unrefp(sd_event **event);
24
25       int sd_event_get_tid(sd_event *event, pid_t *tid);
26

DESCRIPTION

28       sd_event_new() allocates a new event loop object. The event loop object
29       is returned in the event parameter. After use, drop the returned
30       reference with sd_event_unref(). When the last reference is dropped,
31       the object is freed.
32
33       sd_event_default() acquires a reference to the default event loop
34       object of the calling thread, possibly allocating a new object if no
35       default event loop object has been allocated yet for the thread. After
36       use, drop the returned reference with sd_event_unref(). When the last
37       reference is dropped, the event loop is freed. If this function is
38       called while the object returned from a previous call from the same
39       thread is still referenced, the same object is returned again, but the
40       reference is increased by one. It is recommended to use this call
41       instead of sd_event_new() in order to share event loop objects between
42       various components that are dispatched in the same thread. All threads
43       have exactly either zero or one default event loop objects associated,
44       but never more.
45
46       After allocating an event loop object, add event sources to it with
47       sd_event_add_io(3), sd_event_add_time(3), sd_event_add_signal(3),
48       sd_event_add_child(3), sd_event_add_inotify(3), sd_event_add_defer(3),
49       sd_event_add_post(3) or sd_event_add_exit(3), and then execute the
50       event loop using sd_event_loop(3).
51
52       sd_event_ref() increases the reference count of the specified event
53       loop object by one.
54
55       sd_event_unref() decreases the reference count of the specified event
56       loop object by one. If the count hits zero, the object is freed. Note
57       that it is freed regardless of whether it is the default event loop
58       object for a thread or not. This means that allocating an event loop
59       with sd_event_default(), then releasing it, and then acquiring a new
60       one with sd_event_default() will result in two distinct objects. Note
61       that, in order to free an event loop object, all remaining event
62       sources of the event loop also need to be freed as each keeps a
63       reference to it.
64
65       sd_event_unrefp() is similar to sd_event_unref() but takes a pointer to
66       a pointer to an sd_event object. This call is useful in conjunction
67       with GCC's and LLVM's Clean-up Variable Attribute[1]. Note that this
68       function is defined as inline function. Use a declaration like the
69       following, in order to allocate an event loop object that is freed
70       automatically as the code block is left:
71
72           {
73                   __attribute__((cleanup(sd_event_unrefp))) sd_event *event = NULL;
74                   int r;
75                   ...
76                   r = sd_event_default(&event);
77                   if (r < 0)
78                           fprintf(stderr, "Failed to allocate event loop: %s\n", strerror(-r));
79                   ...
80           }
81
82       sd_event_ref(), sd_event_unref() and sd_event_unrefp() execute no
83       operation if the passed in event loop object is NULL.
84
85       sd_event_get_tid() retrieves the thread identifier ("TID") of the
86       thread the specified event loop object is associated with. This call is
87       only supported for event loops allocated with sd_event_default(), and
88       returns the identifier for the thread the event loop is the default
89       event loop of. See gettid(2) for more information on thread
90       identifiers.
91

RETURN VALUE

93       On success, sd_event_new(), sd_event_default() and sd_event_get_tid()
94       return 0 or a positive integer. On failure, they return a negative
95       errno-style error code.  sd_event_ref() always returns a pointer to the
96       event loop object passed in.  sd_event_unref() always returns NULL.
97
98   Errors
99       Returned errors may indicate the following problems:
100
101       -ENOMEM
102           Not enough memory to allocate the object.
103
104       -EMFILE
105           The maximum number of event loops has been allocated.
106
107       -ENXIO
108           sd_event_get_tid() was invoked on an event loop object that was not
109           allocated with sd_event_default().
110

NOTES

112       These APIs are implemented as a shared library, which can be compiled
113       and linked to with the libsystemd pkg-config(1) file.
114

NOTES

121        1. Clean-up Variable Attribute
122           https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html
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125
126systemd 248                                                    SD_EVENT_NEW(3)

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

NOTES

SEE ALSO

NOTES