netsim: add "allow-reordering" property

Reordering of packets is not very common in networks, and the delay
functions will always introduce reordering if delay > packet-spacing,
so by setting allow-reordering to FALSE you guarantee that the packets
are in order, while at the same time introducing delay/jitter to them.

gst/netsim/gstnetsim.c

@@ -65,6 +65,7 @@ enum
   PROP_DROP_PACKETS,
   PROP_MAX_KBPS,
   PROP_MAX_BUCKET_SIZE,
+  PROP_ALLOW_REORDERING,
 };
 
 /* these numbers are nothing but wild guesses and dont reflect any reality */
@@ -77,6 +78,7 @@ enum
 #define DEFAULT_DROP_PACKETS 0
 #define DEFAULT_MAX_KBPS -1
 #define DEFAULT_MAX_BUCKET_SIZE -1
+#define DEFAULT_ALLOW_REORDERING TRUE
 
 static GstStaticPadTemplate gst_net_sim_sink_template =
 GST_STATIC_PAD_TEMPLATE ("sink",
@@ -92,6 +94,21 @@ GST_STATIC_PAD_TEMPLATE ("src",
 
 G_DEFINE_TYPE (GstNetSim, gst_net_sim, GST_TYPE_ELEMENT);
 
+static gboolean
+gst_net_sim_source_dispatch (GSource * source,
+    GSourceFunc callback, gpointer user_data)
+{
+  callback (user_data);
+  return FALSE;
+}
+
+GSourceFuncs gst_net_sim_source_funcs = {
+  NULL,                         /* prepare */
+  NULL,                         /* check */
+  gst_net_sim_source_dispatch,
+  NULL                          /* finalize */
+};
+
 static void
 gst_net_sim_loop (GstNetSim * netsim)
 {
@@ -309,7 +326,6 @@ get_random_value_gamma (GRand * rand_seed, gint32 low, gint32 high,
   return round (x + low);
 }
 
-
 static GstFlowReturn
 gst_net_sim_delay_buffer (GstNetSim * netsim, GstBuffer * buf)
 {
@@ -321,6 +337,7 @@ gst_net_sim_delay_buffer (GstNetSim * netsim, GstBuffer * buf)
     gint delay;
     PushBufferCtx *ctx;
     GSource *source;
+    gint64 ready_time;
 
     switch (netsim->delay_distribution) {
       case DISTRIBUTION_UNIFORM:
@@ -344,9 +361,17 @@ gst_net_sim_delay_buffer (GstNetSim * netsim, GstBuffer * buf)
       delay = 0;
 
     ctx = push_buffer_ctx_new (netsim->srcpad, buf);
-    source = g_timeout_source_new (delay);
 
-    GST_DEBUG_OBJECT (netsim, "Delaying packet by %d", delay);
+    source = g_source_new (&gst_net_sim_source_funcs, sizeof (GSource));
+    ready_time = g_get_monotonic_time () + delay * 1000;
+    if (!netsim->allow_reordering && ready_time < netsim->last_ready_time)
+      ready_time = netsim->last_ready_time + 1;
+
+    GST_DEBUG_OBJECT (netsim, "Delaying packet by %ldms",
+        (ready_time - netsim->last_ready_time) / 1000);
+    netsim->last_ready_time = ready_time;
+
+    g_source_set_ready_time (source, ready_time);
     g_source_set_callback (source, (GSourceFunc) push_buffer_ctx_push,
         ctx, (GDestroyNotify) push_buffer_ctx_free);
     g_source_attach (source, g_main_loop_get_context (netsim->main_loop));
@@ -518,6 +543,9 @@ gst_net_sim_set_property (GObject * object,
       if (netsim->max_bucket_size != -1)
         netsim->bucket_size = netsim->max_bucket_size * 1000;
       break;
+    case PROP_ALLOW_REORDERING:
+      netsim->allow_reordering = g_value_get_boolean (value);
+      break;
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
       break;
@@ -558,6 +586,9 @@ gst_net_sim_get_property (GObject * object,
     case PROP_MAX_BUCKET_SIZE:
       g_value_set_int (value, netsim->max_bucket_size);
       break;
+    case PROP_ALLOW_REORDERING:
+      g_value_set_boolean (value, netsim->allow_reordering);
+      break;
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
       break;
@@ -714,6 +745,22 @@ gst_net_sim_class_init (GstNetSimClass * klass)
           "(-1 = unlimited)", -1, G_MAXINT, DEFAULT_MAX_BUCKET_SIZE,
           G_PARAM_READWRITE | G_PARAM_CONSTRUCT | G_PARAM_STATIC_STRINGS));
 
+  /**
+   * GstNetSim:allow-reordering:
+   *
+   * When delaying packets, are they allowed to be reordered or not. By
+   * default this is enabled, but in the real world packet reordering is
+   * fairly uncommon, yet the delay functions will always introduce reordering
+   * if delay > packet-spacing, This property allows switching that off.
+   *
+   * Since: 1.14
+   */
+  g_object_class_install_property (gobject_class, PROP_ALLOW_REORDERING,
+      g_param_spec_boolean ("allow-reordering", "Allow Reordering",
+          "When delaying packets, are they allowed to be reordered or not",
+          DEFAULT_ALLOW_REORDERING,
+          G_PARAM_READWRITE | G_PARAM_CONSTRUCT | G_PARAM_STATIC_STRINGS));
+
   GST_DEBUG_CATEGORY_INIT (netsim_debug, "netsim", 0, "Network simulator");
 }
 

gst/netsim/gstnetsim.h

@@ -75,6 +75,7 @@ struct _GstNetSim
   gsize bucket_size;
   GstClockTime prev_time;
   NormalDistributionState delay_state;
+  gint64 last_ready_time;
 
   /* properties */
   gint min_delay;
@@ -86,6 +87,7 @@ struct _GstNetSim
   guint drop_packets;
   gint max_kbps;
   gint max_bucket_size;
+  gboolean allow_reordering;
 };
 
 struct _GstNetSimClass