From: Andre Noll <maan@systemlinux.org>
Date: Sat, 19 Sep 2009 08:21:48 +0000 (+0200)
Subject: fecdec: Defer decoding until the first slice of the second group arrives.
X-Git-Tag: v0.3.5~1^2~3
X-Git-Url: http://git.tuebingen.mpg.de/?p=paraslash.git;a=commitdiff_plain;h=faeabd31b4bea5c097acff4738a0626e3c84f1d9

fecdec: Defer decoding until the first slice of the second group arrives.

Otherwise, this could lead to buffer underruns in the decoding application
in case slices are missed. So introdce group_completion_status which tracks
whether we already have received the first group sucessfully and are waiting
for the first slice of the next group.
---

diff --git a/fecdec_filter.c b/fecdec_filter.c
index a3cba9bb..74e1b4f5 100644
--- a/fecdec_filter.c
+++ b/fecdec_filter.c
@@ -4,7 +4,7 @@
  * Licensed under the GPL v2. For licencing details see COPYING.
  */
 
-/** \file fecdec_filter.c A filter fec-decodes an audio stream. */
+/** \file fecdec_filter.c A filter that fec-decodes an audio stream. */
 
 #include <dirent.h>
 #include "para.h"
@@ -70,6 +70,20 @@ struct fecdec_group {
 	unsigned char **data;
 };
 
+/**
+ * The fecdec filter defers decoding of the first group until the first slice
+ * of the next group was received. This avoids buffer underruns in subsequent
+ * filters of the filter chain.
+ */
+enum group_completion_status {
+	/** No complete group received so far. */
+	GCS_NO_COMPLETE_GROUP,
+	/** First group received, but not yet decoded. */
+	GCS_FIRST_GROUP_COMPLETE,
+	/** At least one complete group decoded. */
+	GCS_FIRST_GROUP_DECODED,
+};
+
 /**
  * Data private to the fecdec filter.
  */
@@ -80,6 +94,10 @@ struct private_fecdec_data {
 	struct fecdec_group groups[NUM_FEC_GROUPS];
 	/** Whether an audio file header was already received. */
 	int have_header;
+	/** See \ref group_completion_status. */
+	unsigned completion_status;
+	/** Points to the first received group. */
+	struct fecdec_group *first_complete_group;
 };
 
 /** Iterate over all fecdec groups. */
@@ -153,6 +171,13 @@ static struct fecdec_group *try_to_free_group(struct private_fecdec_data *pfd)
 	FOR_EACH_FECDEC_GROUP(fg, pfd) {
 		if (!group_complete(fg))
 			continue;
+		/*
+		 * Don't clear the first complete group if it has not yet been
+		 * decoded.
+		 */
+		if (pfd->completion_status == GCS_FIRST_GROUP_COMPLETE
+				&& pfd->first_complete_group == fg)
+			continue;
 		clear_group(fg);
 		return fg;
 	}
@@ -171,6 +196,8 @@ static struct fecdec_group *free_oldest_group(struct private_fecdec_data *pfd)
 		PARA_WARNING_LOG("Clearing incomplete group %d "
 			"(contains %d slices)\n", oldest->h.group_num,
 			oldest->num_received_slices);
+	assert(pfd->completion_status != GCS_FIRST_GROUP_COMPLETE
+		|| oldest != pfd->first_complete_group);
 	clear_group(oldest);
 	return oldest;
 }
@@ -211,8 +238,8 @@ static int add_slice(char *buf, struct fecdec_group *fg)
 	int r, slice_num;
 
 	if (group_complete(fg)) {
-		PARA_DEBUG_LOG("group complete, ignoring slice %d\n",
-			fg->h.slice_num);
+		PARA_DEBUG_LOG("group %d complete, ignoring slice %d\n",
+			fg->h.group_num, fg->h.slice_num);
 		fg->num_received_slices++;
 		return 0;
 	}
@@ -267,7 +294,7 @@ static int decode_group(struct fecdec_group *fg, struct filter_node *fn)
 		PARA_INFO_LOG("dropping unusable group %d\n", fg->h.group_num);
 		return 0;
 	}
-	PARA_DEBUG_LOG("decoding group %d %d slices\n", fg->h.group_num,
+	PARA_DEBUG_LOG("decoding group %d (%d slices)\n", fg->h.group_num,
 		fg->h.data_slices_per_group);
 	ret = fec_decode(pfd->fec, fg->data, fg->idx, sb);
 	if (ret < 0)
@@ -339,7 +366,7 @@ static int dispatch_slice(char *buf, size_t len, struct fec_header *h,
 		struct filter_node *fn)
 {
 	struct fecdec_group *fg;
-	int ret;
+	int ret, k, n;
 	struct private_fecdec_data *pfd = fn->private_data;
 
 	if (h->slice_bytes > len) /* can not use the thing, try to read more */
@@ -350,17 +377,34 @@ static int dispatch_slice(char *buf, size_t len, struct fec_header *h,
 	if (!add_slice(buf, fg))
 		return 1;
 	if (group_complete(fg)) {
-		if (!pfd->fec) {
-			int k = h->data_slices_per_group, n = h->slices_per_group;
-			PARA_NOTICE_LOG("init fec (%d, %d)\n", k, n);
-			ret = fec_new(k, n, &pfd->fec);
-			if (ret < 0)
-				return ret;
+		if (pfd->completion_status == GCS_NO_COMPLETE_GROUP) {
+			pfd->completion_status = GCS_FIRST_GROUP_COMPLETE;
+			pfd->first_complete_group = fg;
+			return 1;
 		}
+		assert(pfd->fec);
 		ret = decode_group(fg, fn);
 		if (ret < 0)
 			return ret;
+		return 1;
 	}
+	if (pfd->completion_status == GCS_NO_COMPLETE_GROUP)
+		return 1;
+	if (pfd->completion_status == GCS_FIRST_GROUP_DECODED)
+		return 1;
+	if (fg == pfd->first_complete_group)
+		return 1;
+	assert(!pfd->fec);
+	k = h->data_slices_per_group;
+	n = h->slices_per_group;
+	PARA_NOTICE_LOG("init fec (%d, %d)\n", k, n);
+	ret = fec_new(k, n, &pfd->fec);
+	if (ret < 0)
+		return ret;
+	ret = decode_group(pfd->first_complete_group, fn);
+	if (ret < 0)
+		return ret;
+	pfd->completion_status = GCS_FIRST_GROUP_DECODED;
 	return 1;
 }
 
@@ -400,9 +444,12 @@ static void fecdec_close(struct filter_node *fn)
 
 static void fecdec_open(struct filter_node *fn)
 {
+	struct private_fecdec_data *pfd;
 	fn->bufsize = FECDEC_DEFAULT_OUTBUF_SIZE;
 	fn->buf = para_malloc(fn->bufsize);
-	fn->private_data = para_calloc(sizeof(struct private_fecdec_data));
+	pfd = para_calloc(sizeof(*pfd));
+	pfd->completion_status = GCS_NO_COMPLETE_GROUP;
+	fn->private_data = pfd;
 	fn->loaded = 0;
 }