sd_event_add_child, sd_event_source_get_child_pid, sd_event_child_handler_t — Add a child process state change event source to an event loop
typedef struct sd_event_source sd_event_source;
|const siginfo_t *si,|
sd_event_add_child() adds a new child
process state change event source to an event loop. The event loop
object is specified in the
the event source object is returned in the
source parameter. The
pid parameter specifies the PID of the
process to watch. The
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
siginfo_t structure containing
information about the child process 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 process
WSTOPPED (watch for the child
process being stopped by a signal), and
WCONTINUED (watch for the child process being
resumed by a signal). See waitid(2)
for further information.
Only a single handler may be installed for a specific
child process. The handler is enabled for a single event
SD_EVENT_ONESHOT), but this may be changed
If the handler function returns a negative error code, it will be
disabled after the invocation, even if the
SD_EVENT_ON mode was requested before.
To destroy an event source object use
but note that the event source is only removed from the event loop
when all references to the event source are dropped. To make sure
an event source does not fire anymore, even when there's still a
reference to it kept, consider setting the event source to
If the second parameter of
sd_event_add_child() is passed as NULL no
reference to the event source object is returned. In this case the
event source is considered "floating", and will be destroyed
implicitly when the event loop itself is destroyed.
Note that the
handler function is
invoked at a time where the child process is not reaped yet (and
thus still is exposed as a zombie process by the kernel). However,
the child will be reaped automatically after the function
returns. Child processes for which no child process state change
event sources are installed will not be reaped by the event loop
If both a child process state change event source and a
SIGCHLD signal event source is installed in
the same event loop, the configured event source priorities decide
which event source is dispatched first. If the signal handler is
processed first, it should leave the child processes for which
child process state change event sources are installed unreaped.
retrieves the configured PID of a child process 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 a pid_t variable to return the process ID
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:
Not enough memory to allocate an object.
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
A handler is already installed for this child process.
The event loop is already terminated.
The event loop has been created in a different process.
The passed event source is not a child process event source.
These APIs are implemented as a shared
library, which can be compiled and linked to with the
systemd(1), sd-event(3), sd_event_new(3), sd_event_now(3), sd_event_add_io(3), sd_event_add_time(3), sd_event_add_signal(3), sd_event_add_defer(3), sd_event_source_set_enabled(3), sd_event_source_set_priority(3), sd_event_source_set_userdata(3), sd_event_source_set_description(3), waitid(2)