Cleanup a bit

libvips/include/vips/internal.h

@@ -151,7 +151,6 @@ extern gboolean vips__cache_trace;
 void vips__thread_init(void);
 void vips__threadpool_init(void);
 void vips__threadpool_shutdown(void);
-int vips__thread_execute(const char *name, GFunc func, gpointer data);
 VIPS_API void vips__worker_lock(GMutex *mutex);
 
 void vips__cache_init(void);

libvips/iofuncs/threadset.c

@@ -138,7 +138,7 @@ vips_threadset_work(void *pointer)
 
 	/* Timed-out or exit has been requested, decrement number of threads.
 	 */
-	set->n_threads -= 1;
+	set->n_threads--;
 	gboolean signal_last = set->exit && set->n_threads == 0;
 	VIPS_DEBUG_MSG("vips_threadset_work: stopping %p (%d remaining)\n",
 		g_thread_self(), set->n_threads);
@@ -174,7 +174,7 @@ vips_threadset_add_thread(VipsThreadset *set)
 	 */
 	g_thread_unref(thread);
 
-	set->n_threads += 1;
+	set->n_threads++;
 	set->n_threads_highwater =
 		VIPS_MAX(set->n_threads_highwater, set->n_threads);
 
@@ -247,9 +247,14 @@ vips_threadset_run(VipsThreadset *set,
 
 	g_async_queue_lock(set->queue);
 
+	/* The queue length is calculated as the number of tasks in the queue
+	 * minus the number of waiting threads.
+	 */
+	const int queue_length = g_async_queue_length_unlocked(set->queue);
+
 	/* Create a new thread if there are no waiting threads in the queue.
 	 */
-	if (g_async_queue_length_unlocked(set->queue) >= 0)
+	if (queue_length >= 0)
 		if (vips_threadset_add_thread(set)) {
 			g_async_queue_unlock(set->queue);