From e5f7e040dc911d2cea5edf1254057c140cdfff07 Mon Sep 17 00:00:00 2001
From: Wim Taymans <wtaymans@redhat.com>
Date: Wed, 16 Sep 2020 13:20:19 +0200
Subject: [PATCH] loop: simplify before and after events

Because the signal can't be removed from the callback we can
simply iterate backwards and then forwards.

The first added hook (the unlock/lock pair) is called last before
going into the poll and first when leaving. This executes all other
callbacks inside a locked situation. And removing them with the lock
is not going to cause problems.
---
 spa/include/spa/support/loop.h | 21 ++++++++++++++++++---
 spa/include/spa/utils/list.h   |  8 ++++++++
 spa/plugins/support/loop.c     | 15 ++-------------
 3 files changed, 28 insertions(+), 16 deletions(-)

diff --git a/spa/include/spa/support/loop.h b/spa/include/spa/support/loop.h
index 575dd2932..34ddaa89e 100644
--- a/spa/include/spa/support/loop.h
+++ b/spa/include/spa/support/loop.h
@@ -113,7 +113,9 @@ struct spa_loop_methods {
 #define spa_loop_invoke(l,...)		spa_loop_method(l,invoke,0,##__VA_ARGS__)
 
 
-/** Control hooks */
+/** Control hooks. These hooks can't be removed from their
+ *  callbacks and must be removed from a safe place (when the loop
+ *  is not running or when it is locked). */
 struct spa_loop_control_hooks {
 #define SPA_VERSION_LOOP_CONTROL_HOOKS	0
 	uint32_t version;
@@ -125,8 +127,21 @@ struct spa_loop_control_hooks {
 	void (*after) (void *data);
 };
 
-#define spa_loop_control_hook_before(l) spa_hook_list_call_simple(l, struct spa_loop_control_hooks, before, 0)
-#define spa_loop_control_hook_after(l) spa_hook_list_call_simple(l, struct spa_loop_control_hooks, after, 0)
+#define spa_loop_control_hook_before(l)							\
+({											\
+	struct spa_hook_list *_l = l;							\
+	struct spa_hook *_h;								\
+	spa_list_for_each_reverse(_h, &_l->list, link)					\
+		spa_callbacks_call(&_h->cb, struct spa_loop_control_hooks, before, 0);	\
+})
+
+#define spa_loop_control_hook_after(l)							\
+({											\
+	struct spa_hook_list *_l = l;							\
+	struct spa_hook *_h;								\
+	spa_list_for_each(_h, &_l->list, link)						\
+		spa_callbacks_call(&_h->cb, struct spa_loop_control_hooks, after, 0);	\
+})
 
 /**
  * Control an event loop
diff --git a/spa/include/spa/utils/list.h b/spa/include/spa/utils/list.h
index 8f0cce7c7..90917ea23 100644
--- a/spa/include/spa/utils/list.h
+++ b/spa/include/spa/utils/list.h
@@ -98,9 +98,17 @@ static inline void spa_list_remove(struct spa_list *elem)
 	     !spa_list_is_end(pos, head, member);			\
 	     pos = spa_list_next(pos, member))
 
+#define spa_list_for_each_prev(pos, head, curr, member)			\
+	for (pos = spa_list_last(curr, __typeof__(*pos), member);	\
+	     !spa_list_is_end(pos, head, member);			\
+	     pos = spa_list_prev(pos, member))
+
 #define spa_list_for_each(pos, head, member)				\
 	spa_list_for_each_next(pos, head, head, member)
 
+#define spa_list_for_each_reverse(pos, head, member)				\
+	spa_list_for_each_prev(pos, head, head, member)
+
 #define spa_list_for_each_safe_next(pos, tmp, head, curr, member)	\
 	for (pos = spa_list_first(curr, __typeof__(*pos), member);	\
 	     tmp = spa_list_next(pos, member),				\
diff --git a/spa/plugins/support/loop.c b/spa/plugins/support/loop.c
index 02c5675a6..f9c166531 100644
--- a/spa/plugins/support/loop.c
+++ b/spa/plugins/support/loop.c
@@ -278,24 +278,13 @@ static int loop_iterate(void *object, int timeout)
 	struct impl *impl = object;
 	struct spa_loop *loop = &impl->loop;
 	struct spa_poll_event ep[32];
-	struct spa_list save;
-	struct spa_hook *hook;
 	int i, nfds;
 
-	spa_list_init(&save);
-	spa_list_consume(hook, &impl->hooks_list.list, link) {
-		spa_list_remove(&hook->link);
-		spa_list_prepend(&save, &hook->link);
-		spa_callbacks_call(&hook->cb, struct spa_loop_control_hooks, before, 0);
-	}
+	spa_loop_control_hook_before(&impl->hooks_list);
 
 	nfds = spa_system_pollfd_wait(impl->system, impl->poll_fd, ep, SPA_N_ELEMENTS(ep), timeout);
 
-	spa_list_consume(hook, &save, link) {
-		spa_list_remove(&hook->link);
-		spa_list_append(&impl->hooks_list.list, &hook->link);
-		spa_callbacks_call(&hook->cb, struct spa_loop_control_hooks, after, 0);
-	}
+	spa_loop_control_hook_after(&impl->hooks_list);
 
 	if (SPA_UNLIKELY(nfds < 0))
 		return nfds;