sd_event_add_signal(3)

1SD_EVENT_ADD_SIGNAL(3)        sd_event_add_signal       SD_EVENT_ADD_SIGNAL(3)
2
3
4

NAME

6       sd_event_add_signal, sd_event_source_get_signal,
7       sd_event_signal_handler_t, SD_EVENT_SIGNAL_PROCMASK - Add a UNIX
8       process signal event source to an event loop
9

SYNOPSIS

11       #include <systemd/sd-event.h>
12
13       typedef struct sd_event_source sd_event_source;
14
15       SD_EVENT_SIGNAL_PROCMASK
16
17       typedef int (*sd_event_signal_handler_t)(sd_event_source *s,
18                                                const struct signalfd_siginfo *si,
19                                                void *userdata);
20
21       int sd_event_add_signal(sd_event *event, sd_event_source **source,
22                               int signal, sd_event_signal_handler_t handler,
23                               void *userdata);
24
25       int sd_event_source_get_signal(sd_event_source *source);
26

DESCRIPTION

28       sd_event_add_signal() adds a new UNIX process signal event source to an
29       event loop. The event loop object is specified in the event parameter,
30       and the event source object is returned in the source parameter. The
31       signal parameter specifies the numeric signal to be handled (see
32       signal(7)).
33
34       The handler parameter is a function to call when the signal is received
35       or NULL. The handler function will be passed the userdata pointer,
36       which may be chosen freely by the caller. The handler also receives a
37       pointer to a signalfd_siginfo structure containing information about
38       the received signal. See signalfd(2) for further information. The
39       handler may return negative to signal an error (see below), other
40       return values are ignored. If handler is NULL, a default handler that
41       calls sd_event_exit(3) will be used.
42
43       Only a single handler may be installed for a specific signal. The
44       signal must be blocked in all threads before this function is called
45       (using sigprocmask(2) or pthread_sigmask(3)). For convenience, if the
46       special flag SD_EVENT_SIGNAL_PROCMASK is ORed into the specified signal
47       the signal will be automatically masked as necessary, for the calling
48       thread. Note that this only works reliably if the signal is already
49       masked in all other threads of the process, or if there are no other
50       threads at the moment of invocation.
51
52       By default, the event source is enabled permanently (SD_EVENT_ON), but
53       this may be changed with sd_event_source_set_enabled(3). If the handler
54       function returns a negative error code, it will either be disabled
55       after the invocation, even if the SD_EVENT_ON mode was requested
56       before, or it will cause the loop to terminate, see
57       sd_event_source_set_exit_on_failure(3).
58
59       To destroy an event source object use sd_event_source_unref(3), but
60       note that the event source is only removed from the event loop when all
61       references to the event source are dropped. To make sure an event
62       source does not fire anymore, even if it is still referenced, disable
63       the event source using sd_event_source_set_enabled(3) with
64       SD_EVENT_OFF.
65
66       If the second parameter of sd_event_add_signal() is NULL no reference
67       to the event source object is returned. In this case the event source
68       is considered "floating", and will be destroyed implicitly when the
69       event loop itself is destroyed.
70
71       If the handler parameter to sd_event_add_signal() is NULL, and the
72       event source fires, this will be considered a request to exit the event
73       loop. In this case, the userdata parameter, cast to an integer, is
74       passed as the exit code parameter to sd_event_exit(3).
75
76       sd_event_source_get_signal() returns the configured signal number of an
77       event source created previously with sd_event_add_signal(). It takes
78       the event source object as the source parameter.
79

RETURN VALUE

81       On success, these functions return 0 or a positive integer. On failure,
82       they return a negative errno-style error code.
83
84   Errors
85       Returned errors may indicate the following problems:
86
87       -ENOMEM
88           Not enough memory to allocate an object.
89
90       -EINVAL
91           An invalid argument has been passed.
92
93       -EBUSY
94           A handler is already installed for this signal or the signal was
95           not blocked previously.
96
97       -ESTALE
98           The event loop is already terminated.
99
100       -ECHILD
101           The event loop has been created in a different process, library or
102           module instance.
103
104       -EDOM
105           The passed event source is not a signal event source.
106

NOTES

108       Functions described here are available as a shared library, which can
109       be compiled against and linked to with the libsystemd pkg-config(1)
110       file.
111
112       The code described here uses getenv(3), which is declared to be not
113       multi-thread-safe. This means that the code calling the functions
114       described here must not call setenv(3) from a parallel thread. It is
115       recommended to only do calls to setenv() from an early phase of the
116       program when no other threads have been started.
117

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

NOTES

SEE ALSO