sd_event_source_set_userdata, sd_event_source_get_userdata - Set or retrieve user data pointer of event sources
void* sd_event_source_set_userdata(sd_event_source *source, void *userdata);
void* sd_event_source_get_userdata(sd_event_source *source);
sd_event_source_set_userdata() may be used to set an arbitrary user data pointer for the event source object specified as source. The user data pointer is usually specified when creating an event source object with calls such as sd_event_add_io(3) or sd_event_add_time(3), and may be updated with this call. The user data pointer is also passed to all handler callback functions associated with the event source. The userdata parameter specifies the new user data pointer to set, the function returns the previous user data pointer. Note that NULL is a valid user data pointer.
sd_event_source_get_userdata() may be used to query the current user data pointer assigned to the event source object source.
On success, sd_event_source_set_userdata() and sd_event_source_get_userdata() return the previously set user data pointer. On failure, they return 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.