* Add `vips_semaphore_down_timeout` to public API
In preparation for the next commit.
* threadset: stop idle threads after a regular timeout
In line with the previous behaviour of GLib's threadpool.
* threadset: fix a small memory leak
* threadset: ensure idle threads are freed on exit
GLib threads are spawned with `ref_count == 2`, this reference is
decreased during thread exit and associated resources are freed
during `g_thread_join()`. However, idle threads that are stopped
after a regular timeout are not joined. To fix this, decrease the
reference count during `vips_threadset_add()` and increase it just
before joining the thread with `g_thread_join()`.
See:
2d5d990c6a/glib/gthread.c (L522)2d5d990c6a/glib/gthread-posix.c (L1287)
* Deprecate `vips_g_thread_join()` in favor of `g_thread_join()`
* nit: remove extra semicolon
848a119faa