+ Coroutine *co = NULL;
+
+ if (CONFIG_COROUTINE_POOL) {
+ co = QSLIST_FIRST(&alloc_pool);
+ if (!co) {
+ if (release_pool_size > POOL_BATCH_SIZE) {
+ /* Slow path; a good place to register the destructor, too. */
+ if (!coroutine_pool_cleanup_notifier.notify) {
+ coroutine_pool_cleanup_notifier.notify = coroutine_pool_cleanup;
+ qemu_thread_atexit_add(&coroutine_pool_cleanup_notifier);
+ }
+
+ /* This is not exact; there could be a little skew between
+ * release_pool_size and the actual size of release_pool. But
+ * it is just a heuristic, it does not need to be perfect.
+ */
+ alloc_pool_size = atomic_xchg(&release_pool_size, 0);
+ QSLIST_MOVE_ATOMIC(&alloc_pool, &release_pool);
+ co = QSLIST_FIRST(&alloc_pool);
+ }
+ }
+ if (co) {
+ QSLIST_REMOVE_HEAD(&alloc_pool, pool_next);
+ alloc_pool_size--;
+ }
+ }
+
+ if (!co) {
+ co = qemu_coroutine_new();
+ }
+