sd_event_add_defer

Index · Directives · Python · libudev · gudev systemd 220

## Name

sd_event_add_defer, sd_event_add_post, sd_event_add_exit — Add static event sources to an event loop

## Synopsis

    #include <systemd/sd-bus.h>

`int sd_event_add_defer(` | sd_event *event,
| sd_event_source **source,
| sd_event_handler_t handler,
| void *userdata`)`;

`int sd_event_add_post(` | sd_event *event,
| sd_event_source **source,
| sd_event_handler_t handler,
| void *userdata`)`;

`int sd_event_add_exit(` | sd_event *event,
| sd_event_source **source,
| sd_event_handler_t handler,
| void *userdata`)`;

`typedef int (*sd_event_handler_t)(` | sd_event_source *s,
| void *userdata`)`;

## Description

Those three functions add new event sources to an event loop object. The event loop is specified in `event`, the event source is returned in the `source` parameter. The event sources are enabled statically and will "fire" when the event loop is run and the conditions described below are met. The handler function will be passed the `userdata` pointer, which may be chosen freely by the caller.

`sd_event_add_defer()` adds a new event source that will "fire" the next time the event loop is run. By default, the handler will be called once (`SD_EVENT_ONESHOT`).

`sd_event_add_post()` adds a new event source that will "fire" if any event handlers are invoked whenever the event loop is run. By default, the source is enabled permanently (`SD_EVENT_ON`).

`sd_event_add_exit()` adds a new event source that will "fire" when the event loop is terminated with `sd_event_exit()`.

The sd_event_source_set_enabled(3) function may be used to enable the event source permanently (`SD_EVENT_ON`) or to make it fire just once (`SD_EVENT_ONESHOT`). If the handler function returns a negative error code, it will be disabled after the invocation, even if `SD_EVENT_ON` mode is set.

## Return Value

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

## Errors

Returned errors may indicate the following problems:

`-ENOMEM`

  Not enough memory to allocate an object.

`-EINVAL`

  An invalid argument has been passed.

`-ESTALE`

  The event loop is already terminated.

`-ECHILD`

  The event loop has been created in a different process.

## Notes

Functions described here are available as a shared library, which can be compiled and linked to with the `libsystemd` pkg-config(1) file.

## See Also

systemd(1), sd-event(3), sd_event_new(3), sd_event_add_time(3), sd_event_add_signal(3), sd_event_add_child(3), sd_event_source_set_enabled(3)