[Asterisk-code-review] Add API for channel frame deferral. (asterisk[13])

[Mark Michelson]

Mark Michelson has uploaded a new change for review. ( https://gerrit.asterisk.org/4297 )

Change subject: Add API for channel frame deferral.
......................................................................

Add API for channel frame deferral.

There are several places in Asterisk that have duplicated logic
for deferring important frames until later.

This commit adds a couple of API calls to facilitate this automatically.

ast_channel_start_defer_frames(): Future reads of deferrable frames on
this channel will be deferred until later.

ast_channel_stop_defer_frames(): Any frames that have been deferred get
requeued onto the channel.

ASTERISK-26343

Change-Id: I3e1b87bc6796f222442fa6f7d1b6a4706fb33641
---
M include/asterisk/channel.h
M main/channel.c
M main/channel_internal_api.c
3 files changed, 85 insertions(+), 0 deletions(-)


  git pull ssh://gerrit.asterisk.org:29418/asterisk refs/changes/97/4297/1

diff --git a/include/asterisk/channel.h b/include/asterisk/channel.h
index a76e606..e2deee1 100644
--- a/include/asterisk/channel.h
+++ b/include/asterisk/channel.h
@@ -966,6 +966,11 @@
 	 * The channel is executing a subroutine or macro
 	 */
 	AST_FLAG_SUBROUTINE_EXEC = (1 << 27),
+	/*!
+	 * The channel is currently in an operation where
+	 * frames should be deferred.
+	 */
+	AST_FLAG_DEFER_FRAMES = (1 << 28),
 };
 
 /*! \brief ast_bridge_config flags */
@@ -4681,4 +4686,33 @@
  */
 enum ast_channel_error ast_channel_errno(void);
 
+/*!
+ * \brief Retrieve the deferred read queue.
+ */
+struct ast_readq_list *ast_channel_deferred_readq(struct ast_channel *chan);
+
+/*!
+ * \brief Start deferring deferrable frames on this channel
+ *
+ * Sometimes, a channel gets entered into a mode where a "main" application
+ * is tasked with servicing frames on the channel, but that application does
+ * not need to act on those frames. However, it would be imprudent to simply
+ * drop important frames. This function can be called so that important frames
+ * will be deferred, rather than placed in the channel frame queue as normal.
+ *
+ * \pre chan MUST be locked before calling
+ *
+ * \param chan The channel on which frames should be deferred
+ */
+void ast_channel_start_defer_frames(struct ast_channel *chan);
+
+/*!
+ * \brief Stop deferring deferrable frames on this channel
+ *
+ * When it is time to stop deferring frames on the channel, all deferred frames
+ * will be queued onto the channel's read queue so that the next servicer of
+ * the channel can handle those frames as necessary.
+ */
+void ast_channel_stop_defer_frames(struct ast_channel *chan);
+
 #endif /* _ASTERISK_CHANNEL_H */
diff --git a/main/channel.c b/main/channel.c
index 278104c..e85208b 100644
--- a/main/channel.c
+++ b/main/channel.c
@@ -1061,6 +1061,25 @@
 	return tmp;
 }
 
+void ast_channel_start_defer_frames(struct ast_channel *chan)
+{
+	ast_set_flag(ast_channel_flags(chan), AST_FLAG_DEFER_FRAMES);
+}
+
+void ast_channel_stop_defer_frames(struct ast_channel *chan)
+{
+	ast_clear_flag(ast_channel_flags(chan), AST_FLAG_DEFER_FRAMES);
+
+	/* Move the deferred frames onto the channel read queue, ahead of other queued frames */
+	ast_queue_frame_head(chan, AST_LIST_FIRST(ast_channel_deferred_readq(chan)));
+	/* ast_frfree will mosey down the list and free them all */
+	if (!AST_LIST_EMPTY(ast_channel_deferred_readq(chan))) {
+		ast_frfree(AST_LIST_FIRST(ast_channel_deferred_readq(chan)));
+	}
+	/* Reset the list to be empty */
+	AST_LIST_HEAD_INIT_NOLOCK(ast_channel_deferred_readq(chan));
+}
+
 static int __ast_queue_frame(struct ast_channel *chan, struct ast_frame *fin, int head, struct ast_frame *after)
 {
 	struct ast_frame *f;
@@ -3885,6 +3904,32 @@
 	if (!AST_LIST_EMPTY(ast_channel_readq(chan))) {
 		int skip_dtmf = should_skip_dtmf(chan);
 
+		if (ast_test_flag(ast_channel_flags(chan), AST_FLAG_DEFER_FRAMES)) {
+			AST_LIST_TRAVERSE_SAFE_BEGIN(ast_channel_readq(chan), f, frame_list) {
+				if (ast_is_deferrable_frame(f)) {
+					if (f->frametype == AST_FRAME_CONTROL && f->subclass.integer == AST_CONTROL_HANGUP) {
+						struct ast_frame *dup;
+
+						/* Hangup is a special case. We want to defer the frame, but we also do not
+						 * want to remove it from the frame queue. So rather than just moving the frame
+						 * over, we duplicate it and move the copy to the deferred readq.
+						 *
+						 * The reason for this? This way, whoever calls ast_read() will get a NULL return
+						 * immediately and can tell the channel has hung up and do what it needs to. Also,
+						 * when frame deferral finishes, then whoever calls ast_read() next will also get
+						 * the hangup.
+						 */
+						dup = ast_frdup(f);
+						AST_LIST_INSERT_TAIL(ast_channel_deferred_readq(chan), dup, frame_list);
+					} else {
+						AST_LIST_INSERT_TAIL(ast_channel_deferred_readq(chan), f, frame_list);
+						AST_LIST_REMOVE_CURRENT(frame_list);
+					}
+				}
+			}
+			AST_LIST_TRAVERSE_SAFE_END;
+		}
+
 		AST_LIST_TRAVERSE_SAFE_BEGIN(ast_channel_readq(chan), f, frame_list) {
 			/* We have to be picky about which frame we pull off of the readq because
 			 * there are cases where we want to leave DTMF frames on the queue until
diff --git a/main/channel_internal_api.c b/main/channel_internal_api.c
index 90f59d6..4bc770d 100644
--- a/main/channel_internal_api.c
+++ b/main/channel_internal_api.c
@@ -223,6 +223,7 @@
 	struct stasis_cp_single *topics;		/*!< Topic for all channel's events */
 	struct stasis_forward *endpoint_forward;	/*!< Subscription for event forwarding to endpoint's topic */
 	struct stasis_forward *endpoint_cache_forward; /*!< Subscription for cache updates to endpoint's topic */
+	struct ast_readq_list deferred_readq;
 };
 
 /*! \brief The monotonically increasing integer counter for channel uniqueids */
@@ -1698,3 +1699,8 @@
 
 	return *error_code;
 }
+
+struct ast_readq_list *ast_channel_deferred_readq(struct ast_channel *chan)
+{
+	return &chan->deferred_readq;
+}

-- 
To view, visit https://gerrit.asterisk.org/4297
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Gerrit-MessageType: newchange
Gerrit-Change-Id: I3e1b87bc6796f222442fa6f7d1b6a4706fb33641
Gerrit-PatchSet: 1
Gerrit-Project: asterisk
Gerrit-Branch: 13
Gerrit-Owner: Mark Michelson <mmichelson at digium.com>