NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | NOTES | SEE ALSO | COLOPHON

SD_EVENT_ADD_CHILD(3)        sd_event_add_child        SD_EVENT_ADD_CHILD(3)

NAME         top

       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

SYNOPSIS         top

       #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);

DESCRIPTION         top

       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.

RETURN VALUE         top

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

ERRORS         top

       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.

NOTES         top

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

SEE ALSO         top

       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)

COLOPHON         top

       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 2017-03-13.  If you dis‐
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       COLOPHON (which is not part of the original manual page), send a mail
       to man-pages@man7.org

systemd 233                                            SD_EVENT_ADD_CHILD(3)