From 3839e9836d2e4740efd9610a1aa50dd792e78a59 Mon Sep 17 00:00:00 2001
From: Nirbheek Chauhan <nirbheek@centricular.com>
Date: Wed, 9 Jul 2014 21:38:32 +0530
Subject: appsink: Use a GMutex to control when we pull samples

We can only pull a new sample and write it out if the previous one has been
written, otherwise we get a segfault in SoupMessage.
---
 src/lib.h  |  1 +
 src/main.c | 62 ++++++++++++++++++++++++++++----------------------------------
 2 files changed, 29 insertions(+), 34 deletions(-)

diff --git a/src/lib.h b/src/lib.h
index 733212c..14ec096 100644
--- a/src/lib.h
+++ b/src/lib.h
@@ -34,6 +34,7 @@ struct _TranscodeClientCtx {
   SoupMessage *msg;
   GstElement *appsink;
   GstPad *ghostsinkpad;
+  GMutex can_write_chunk;
   gulong first_sample_handler_id;
   /* The transcode server context */
   TranscodeServerCtx *server_ctx;
diff --git a/src/main.c b/src/main.c
index 1a710ed..7834c53 100644
--- a/src/main.c
+++ b/src/main.c
@@ -105,14 +105,29 @@ err:
 }
 
 static void
-write_next_client_chunk_cb (SoupMessage        *msg,
-                            TranscodeClientCtx *ctx)
+can_write_next_client_chunk_cb (SoupMessage        *msg,
+                                TranscodeClientCtx *ctx)
+{
+  g_mutex_unlock (&ctx->can_write_chunk);
+}
+
+static GstFlowReturn
+write_client_chunk_cb (GstElement         *appsink,
+                       TranscodeClientCtx *ctx)
 {
   GstMapInfo info;
   GstSample *sample;
   GstBuffer *buffer;
   GstMemory *memory;
   gboolean eos;
+  
+  if (!g_mutex_trylock (&ctx->can_write_chunk))
+    /* We cannot safely append to the message body till
+     * the previous chunk is written out, otherwise we get
+     * a segfault. This is likely because SoupMessageBody 
+     * uses a GSList for the chunks, which isn't MT-safe. */
+    return GST_FLOW_OK;
+
 
   g_print ("*");
   g_signal_emit_by_name (ctx->appsink, "pull-sample", &sample);
@@ -120,39 +135,26 @@ write_next_client_chunk_cb (SoupMessage        *msg,
     g_print ("Null sample, ending stream\n");
     g_object_get (ctx->appsink, "eos", &eos, NULL);
     if (eos)
-      soup_message_set_status (msg, SOUP_STATUS_OK);
+      soup_message_set_status (ctx->msg, SOUP_STATUS_OK);
     else
-      soup_message_set_status (msg, SOUP_STATUS_INTERNAL_SERVER_ERROR);
-    soup_message_body_complete (msg->response_body);
-    return;
+      soup_message_set_status (ctx->msg, SOUP_STATUS_INTERNAL_SERVER_ERROR);
+    soup_message_body_complete (ctx->msg->response_body);
+    return GST_FLOW_OK;
   }
 
   buffer = gst_sample_get_buffer (sample);
   memory = gst_buffer_get_all_memory (buffer); /* copy */
   gst_memory_map (memory, &info, GST_MAP_READ);
 
-  soup_message_body_append (msg->response_body, SOUP_MEMORY_COPY,
+  soup_message_body_append (ctx->msg->response_body, SOUP_MEMORY_COPY,
                             info.data, info.size); /* copy */
 
   gst_memory_unmap (memory, &info);
   gst_memory_unref (memory);
   gst_sample_unref (sample);
 
-  soup_server_unpause_message (server, msg);
+  soup_server_unpause_message (server, ctx->msg);
   g_print (".");
-  return;
-}
-
-static GstFlowReturn
-write_first_client_chunk_cb (GstElement         *appsink,
-                             TranscodeClientCtx *ctx)
-{
-  g_assert (ctx->first_sample_handler_id);
-
-  //g_signal_handler_disconnect (appsink, ctx->first_sample_handler_id);
-  //ctx->first_sample_handler_id = 0;
-
-  write_next_client_chunk_cb (ctx->msg, ctx);
 
   return GST_FLOW_OK;
 }
@@ -253,6 +255,7 @@ GET:
     client_ctx = g_new0 (TranscodeClientCtx, 1);
     client_ctx->msg = msg;
     client_ctx->server_ctx = server_ctx;
+    g_mutex_init (&client_ctx->can_write_chunk);
  
     bin = gst_bin_new (NULL);
 
@@ -296,9 +299,9 @@ GET:
 
     client_ctx->first_sample_handler_id =
       g_signal_connect (appsink, "new-sample",
-                        G_CALLBACK (write_first_client_chunk_cb), client_ctx);
-    /*g_signal_connect (client_ctx->msg, "wrote-chunk",
-                      G_CALLBACK (write_next_client_chunk_cb), client_ctx);*/
+                        G_CALLBACK (write_client_chunk_cb), client_ctx);
+    g_signal_connect (client_ctx->msg, "wrote-chunk",
+                      G_CALLBACK (can_write_next_client_chunk_cb), client_ctx);
     g_signal_connect (client_ctx->msg, "finished",
                       G_CALLBACK (client_finished_cb), client_ctx);
 
@@ -479,16 +482,7 @@ request_read_cb (SoupServer        *server,
 
 PUT:
   {
-    gboolean ret;
-    TranscodeServerCtx *ctx;
-
-    ctx = get_server_ctx_from_msg (msg, ctx_table);
-    g_return_if_fail (ctx);
-
-    /* Incoming stream has ended */
-    g_signal_emit_by_name (ctx->appsrc, "end-of-stream", &ret);
-    if (!ret)
-      g_printerr ("Unable to emit end-of-stream\n");
+    /* Everything is handled in the "finished" signal. Nothing to do. */
   }
 
 GET:
-- 
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