|
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | NOTES | SEE ALSO | COLOPHON |
SD_EVENT_ADD_CHILD(3) sd_event_add_child SD_EVENT_ADD_CHILD(3)
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
#include <systemd/sd-event.h>
typedef struct sd_event_source sd_event_source;
typedef int (*sd_event_child_handler_t)(sd_event_source *s,
const siginfo_t *si,
void *userdata);
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);
int sd_event_source_get_child_pid(sd_event_source *source,
pid_t *pid);
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
event parameter, the event source object is returned in the source
parameter. The pid parameter specifies the PID of 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 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 terminating), 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 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 the SD_EVENT_ON mode was requested
before.
To destroy an event source object use sd_event_source_unref(3), 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 SD_EVENT_OFF with
sd_event_source_set_enabled(3).
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 implementation.
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.
sd_event_source_get_child_pid() 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
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
A handler is already installed for this child process.
-ESTALE
The event loop is already terminated.
-ECHILD
The event loop has been created in a different process.
-EDOM
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 libsystemd pkg-config(1) file.
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)
This page is part of the systemd (systemd system and service manager)
project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a bug
report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩. This
page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2017-07-05. If you dis‐
cover any rendering problems in this HTML version of the page, or you
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you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a mail
to man-pages@man7.org
systemd 234 SD_EVENT_ADD_CHILD(3)
Pages that refer to this page: sd-event(3), sd_event_add_defer(3), sd_event_add_io(3), sd_event_add_signal(3), sd_event_add_time(3), sd_event_new(3), sd_event_run(3), sd_event_set_watchdog(3), sd_event_source_get_event(3), sd_event_source_get_pending(3), sd_event_source_set_description(3), sd_event_source_set_enabled(3), sd_event_source_set_prepare(3), sd_event_source_set_priority(3), sd_event_source_set_userdata(3), sd_event_source_unref(3), systemd.directives(7), systemd.index(7)