Man pages matching name gearman_worker_set_log_fn in section 3:

gearman_worker_set_log_fn.3.en	debian 10 / libgearman-dev
gearman_worker_set_log_fn.3.en	debian 11 / libgearman-dev
gearman_worker_set_log_fn.3.en	debian 12 / libgearman-dev