release_cb
# define EV_RELEASE_CB if (expect_false (release_cb)) release_cb (EV_A)
release_cb = release;
VAR (release_cb, void (*release_cb)(EV_P) EV_THROW)
#define release_cb ((loop)->release_cb)
vmci_wait_on_event(vmci_event *event, vmci_event_release_cb release_cb,
release_cb(client_data);
void vmci_wait_on_event(vmci_event *event, vmci_event_release_cb release_cb,
vmci_event_release_cb release_cb, void *client_data);