sd_event_unref(3)

1SD_EVENT_NEW(3)                  sd_event_new                  SD_EVENT_NEW(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;
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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);
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25       int sd_event_get_tid(sd_event *event, pid_t *tid);
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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.
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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.
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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) or sd_event_add_defer(3), and then execute the
49       event loop using sd_event_run(3).
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51       sd_event_ref() increases the reference count of the specified event
52       loop object by one.
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54       sd_event_unref() decreases the reference count of the specified event
55       loop object by one. If the count hits zero, the object is freed. Note
56       that it is freed regardless of whether it is the default event loop
57       object for a thread or not. This means that allocating an event loop
58       with sd_event_default(), then releasing it, and then acquiring a new
59       one with sd_event_default() will result in two distinct objects. Note
60       that, in order to free an event loop object, all remaining event
61       sources of the event loop also need to be freed as each keeps a
62       reference to it.
63
64       sd_event_unrefp() is similar to sd_event_unref() but takes a pointer to
65       a pointer to an sd_event object. This call is useful in conjunction
66       with GCC's and LLVM's Clean-up Variable Attribute[1]. Note that this
67       function is defined as inline function. Use a declaration like the
68       following, in order to allocate an event loop object that is freed
69       automatically as the code block is left:
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71           {
72                   __attribute__((cleanup(sd_event_unrefp)) sd_event *event = NULL;
73                   int r;
74                   ...
75                   r = sd_event_default(&event);
76                   if (r < 0)
77                           fprintf(stderr, "Failed to allocate event loop: %s\n", strerror(-r));
78                   ...
79           }
80
81       sd_event_ref(), sd_event_unref() and sd_event_unrefp() execute no
82       operation if the passed in event loop object is NULL.
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84       sd_event_get_tid() retrieves the thread identifier ("TID") of the
85       thread the specified event loop object is associated with. This call is
86       only supported for event loops allocated with sd_event_default(), and
87       returns the identifier for the thread the event loop is the default
88       event loop of. See gettid(2) for more information on thread
89       identifiers.
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RETURN VALUE

92       On success, sd_event_new(), sd_event_default() and sd_event_get_tid()
93       return 0 or a positive integer. On failure, they return a negative
94       errno-style error code.  sd_event_ref() always returns a pointer to the
95       event loop object passed in.  sd_event_unref() always returns NULL.
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ERRORS

98       Returned errors may indicate the following problems:
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100       -ENOMEM
101           Not enough memory to allocate the object.
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103       -EMFILE
104           The maximum number of event loops has been allocated.
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106       -ENXIO
107           sd_event_get_tid() was invoked on an event loop object that was not
108           allocated with sd_event_default().
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NOTES

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

120        1. Clean-up Variable Attribute
121           https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html
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125systemd 239                                                    SD_EVENT_NEW(3)