1SD_EVENT_ADD_CHILD(3)         sd_event_add_child         SD_EVENT_ADD_CHILD(3)
2
3
4

NAME

6       sd_event_add_child, sd_event_source_get_child_pid,
7       sd_event_child_handler_t - Add a child process state change event
8       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       typedef int (*sd_event_child_handler_t)(sd_event_source *s,
16                                               const siginfo_t *si,
17                                               void *userdata);
18
19       int sd_event_add_child(sd_event *event, sd_event_source **source,
20                              pid_t pid, int options,
21                              sd_event_child_handler_t handler,
22                              void *userdata);
23
24       int sd_event_source_get_child_pid(sd_event_source *source, pid_t *pid);
25

DESCRIPTION

27       sd_event_add_child() adds a new child process state change event source
28       to an event loop. The event loop object is specified in the event
29       parameter, the event source object is returned in the source parameter.
30       The pid parameter specifies the PID of the process to watch. The
31       handler must reference a function to call when the process changes
32       state. The handler function will be passed the userdata pointer, which
33       may be chosen freely by the caller. The handler also receives a pointer
34       to a siginfo_t structure containing information about the child process
35       event. The options parameter determines which state changes will be
36       watched for. It must contain an OR-ed mask of WEXITED (watch for the
37       child process terminating), WSTOPPED (watch for the child process being
38       stopped by a signal), and WCONTINUED (watch for the child process being
39       resumed by a signal). See waitid(2) for further information.
40
41       Only a single handler may be installed for a specific child process.
42       The handler is enabled for a single event (SD_EVENT_ONESHOT), but this
43       may be changed with sd_event_source_set_enabled(3). If the handler
44       function returns a negative error code, it will be disabled after the
45       invocation, even if the SD_EVENT_ON mode was requested before.
46
47       To destroy an event source object use sd_event_source_unref(3), but
48       note that the event source is only removed from the event loop when all
49       references to the event source are dropped. To make sure an event
50       source does not fire anymore, even when there's still a reference to it
51       kept, consider setting the event source to SD_EVENT_OFF with
52       sd_event_source_set_enabled(3).
53
54       If the second parameter of sd_event_add_child() is passed as NULL no
55       reference to the event source object is returned. In this case the
56       event source is considered "floating", and will be destroyed implicitly
57       when the event loop itself is destroyed.
58
59       Note that the handler function is invoked at a time where the child
60       process is not reaped yet (and thus still is exposed as a zombie
61       process by the kernel). However, the child will be reaped automatically
62       after the function returns. Child processes for which no child process
63       state change event sources are installed will not be reaped by the
64       event loop implementation.
65
66       If both a child process state change event source and a SIGCHLD signal
67       event source is installed in the same event loop, the configured event
68       source priorities decide which event source is dispatched first. If the
69       signal handler is processed first, it should leave the child processes
70       for which child process state change event sources are installed
71       unreaped.
72
73       sd_event_source_get_child_pid() retrieves the configured PID of a child
74       process state change event source created previously with
75       sd_event_add_child(). It takes the event source object as the source
76       parameter and a pointer to a pid_t variable to return the process ID
77       in.
78

RETURN VALUE

80       On success, these functions return 0 or a positive integer. On failure,
81       they return a negative errno-style error code.
82

ERRORS

84       Returned errors may indicate the following problems:
85
86       -ENOMEM
87           Not enough memory to allocate an object.
88
89       -EINVAL
90           An invalid argument has been passed. This includes specifying an
91           empty mask in options or a mask which contains values different
92           than a combination of WEXITED, WSTOPPED, and WCONTINUED.
93
94       -EBUSY
95           A handler is already installed for this child process.
96
97       -ESTALE
98           The event loop is already terminated.
99
100       -ECHILD
101           The event loop has been created in a different process.
102
103       -EDOM
104           The passed event source is not a child process event source.
105

NOTES

107       These APIs are implemented as a shared library, which can be compiled
108       and linked to with the libsystemd pkg-config(1) file.
109

SEE ALSO

111       systemd(1), sd-event(3), sd_event_new(3), sd_event_now(3),
112       sd_event_add_io(3), sd_event_add_time(3), sd_event_add_signal(3),
113       sd_event_add_inotify(3), sd_event_add_defer(3),
114       sd_event_source_set_enabled(3), sd_event_source_set_priority(3),
115       sd_event_source_set_userdata(3), sd_event_source_set_description(3),
116       waitid(2)
117
118
119
120systemd 239                                              SD_EVENT_ADD_CHILD(3)