sd_event_add_child, sd_event_source_get_child_pid — Add a child state change event source to an event loop
#include <systemd/sd-bus.h>
int sd_event_add_child( | sd_event *event, |
| sd_event_source **source, | |
| pid_t pid, | |
| int options, | |
| sd_event_child_handler_t handler, | |
void *userdata); |
typedef int (*sd_event_child_handler_t)( | sd_event_source *s, |
| const siginfo_t *si, | |
void *userdata); |
int sd_event_source_get_child_pid( | sd_event_source *source, |
pid_t *pid); |
sd_event_add_child() adds a new child
state change event source to an event loop object. The event loop
is specified in event, the event source is
returned in the source parameter. The
pid parameter specifies the process to
watch. The handler must reference a
function to call when the process changes state. The handler
function will be passed the userdata
pointer, which may be chosen freely by the caller. The handler
also receives a pointer to a const
siginfo_t structure containing the information about
the event. The options parameter determines
which state changes will be watched for. It must contain an OR-ed
mask of WEXITED (watch for the child
terminating), WSTOPPED (watch for the child
being stopped by a signal), and WCONTINUED
(watch for the child being resumed by a signal). See
waitid(2)
for further information.
Only a single handler may be installed for a specific
child. The handler is enabled
for a single event (SD_EVENT_ONESHOT),
but this may be
changed with
sd_event_source_set_enabled(3).
If the handler function returns a negative error code, it will be
disabled after the invocation, even if
SD_EVENT_ON mode is set.
sd_event_source_get_child_pid()
retrieves the configured pid of a child
state change event source created previously with
sd_event_add_child(). It takes the event
source object as the source parameter and a
pointer to pid_t to return the result in.
On success, these functions return 0 or a positive integer. On failure, they return a negative errno-style error code.
Returned errors may indicate the following problems:
-ENOMEM¶Not enough memory to allocate an object.
-EINVAL¶An invalid argument has been passed. This includes
specifying an empty mask in options or a mask
which contains values different than a combination of
WEXITED, WSTOPPED, and
WCONTINUED.
-EBUSY¶An handler is already installed for this child.
-ESTALE¶The event loop is already terminated.
-ECHILD¶The event loop has been created in a different process.
sd_event_add_child() and the other functions
described here are available as a shared library, which can be
compiled and linked to with the
libsystemd pkg-config(1)
file.