Index · Directives systemd 256


sd_event_source_set_destroy_callback, sd_event_source_get_destroy_callback, sd_event_destroy_t — Define the callback function for resource cleanup


#include <systemd/sd-event.h>
typedef int (*sd_event_destroy_t)(void *userdata);
int sd_event_source_set_destroy_callback(sd_event_source *source,
 sd_event_destroy_t callback);
int sd_event_source_get_destroy_callback(sd_event_source *source,
 sd_event_destroy_t *callback);


sd_event_source_set_destroy_callback() sets callback as the callback function to be called right before the event source object source is deallocated. The userdata pointer from the event source object will be passed as the userdata parameter. This pointer can be set by an argument to the constructor functions, see sd_event_add_io(3), or directly, see sd_event_source_set_userdata(3). This callback function is called even if userdata is NULL. Note that this callback is invoked at a time where the event source object itself is already invalidated, and executing operations or taking new references to the event source object is not permissible.

sd_event_source_get_destroy_callback() returns the current callback for source in the callback parameter.

Return Value

On success, sd_event_source_set_destroy_callback() returns 0 or a positive integer. On failure, it returns a negative errno-style error code.

sd_event_source_get_destroy_callback() returns positive if the destroy callback function is set, 0 if not. On failure, returns a negative errno-style error code.


Returned errors may indicate the following problems:


The source parameter is NULL.


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

The code described here uses getenv(3), which is declared to be not multi-thread-safe. This means that the code calling the functions described here must not call setenv(3) from a parallel thread. It is recommended to only do calls to setenv() from an early phase of the program when no other threads have been started.


sd_event_destroy_t(), sd_event_source_set_destroy_callback(), and sd_event_source_get_destroy_callback() were added in version 239.

See Also

systemd(1), sd-event(3), sd_event_add_io(3), sd_event_add_time(3), sd_event_add_signal(3), sd_event_add_child(3), sd_event_add_inotify(3), sd_event_add_defer(3), sd_event_source_set_userdata(3)