giosrc: Add support for growing source files

Add a way for applications to specify that the underlying file is
growing which implies that the source won't EOS when reaching the end
of the file but instead start monitoring it and start reading it again
whenever a change is detected.

Also add a validate test to check the behavior

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/-/merge_requests/937>

docs/plugins/gst_plugins_cache.json

@@ -2459,6 +2459,18 @@
                         "type": "GFile",
                         "writable": true
                     },
+                    "is-growing": {
+                        "blurb": "Whether the file is growing, ignoring its end",
+                        "conditionally-available": false,
+                        "construct": false,
+                        "construct-only": false,
+                        "controllable": false,
+                        "default": "false",
+                        "mutable": "null",
+                        "readable": true,
+                        "type": "gboolean",
+                        "writable": true
+                    },
                     "location": {
                         "blurb": "URI location to read from",
                         "conditionally-available": false,
@@ -2472,7 +2484,19 @@
                         "writable": true
                     }
                 },
-                "rank": "secondary"
+                "rank": "secondary",
+                "signals": {
+                    "done-waiting-data": {
+                        "args": [],
+                        "return-type": "void",
+                        "when": "last"
+                    },
+                    "waiting-data": {
+                        "args": [],
+                        "return-type": "void",
+                        "when": "last"
+                    }
+                }
             },
             "giostreamsink": {
                 "author": "Sebastian Dröge <sebastian.droege@collabora.co.uk>",

gst/gio/gstgiobasesrc.c

@@ -328,6 +328,8 @@ gst_gio_base_src_create (GstBaseSrc * base_src, guint64 offset, guint size,
     GError *err = NULL;
     GstBuffer *newbuffer;
     GstMemory *mem;
+    gboolean waited_for_data = FALSE;
+    GstGioBaseSrcClass *klass = GST_GIO_BASE_SRC_GET_CLASS (src);
 
     newbuffer = gst_buffer_new ();
 
@@ -384,11 +386,24 @@ gst_gio_base_src_create (GstBaseSrc * base_src, guint64 offset, guint size,
     while (size - read > 0 && (res =
             g_input_stream_read (G_INPUT_STREAM (src->stream),
                 map.data + streamread, cachesize - streamread, src->cancel,
-                &err)) > 0) {
+                &err)) >= 0) {
+
       read += res;
       streamread += res;
       src->position += res;
+
+      if (res != 0)
+        continue;
+
+      if (!klass->wait_for_data || !klass->wait_for_data (src))
+        break;
+
+      waited_for_data = TRUE;
     }
+
+    if (waited_for_data && klass->waited_for_data)
+      klass->waited_for_data (src);
+
     gst_memory_unmap (mem, &map);
     gst_buffer_append_memory (src->cache, mem);
 

gst/gio/gstgiobasesrc.h

@@ -62,6 +62,12 @@ struct _GstGioBaseSrcClass
   GstBaseSrcClass parent_class;
 
   GInputStream * (*get_stream) (GstGioBaseSrc *bsrc);
+
+  /* Returns TRUE if the files grew and we should try
+    reading again, FALSE otherwise */
+  gboolean (*wait_for_data) (GstGioBaseSrc *bsrc);
+  void (*waited_for_data) (GstGioBaseSrc *bsrc);
+
   gboolean close_on_stop;
 };
 

gst/gio/gstgiosrc.c

@@ -83,9 +83,13 @@ enum
 {
   PROP_0,
   PROP_LOCATION,
-  PROP_FILE
+  PROP_FILE,
+  PROP_GROWING_FILE,
 };
 
+static gint waiting_data_signal = 0;
+static gint done_waiting_data_signal = 0;
+
 #define gst_gio_src_parent_class parent_class
 G_DEFINE_TYPE_WITH_CODE (GstGioSrc, gst_gio_src,
     GST_TYPE_GIO_BASE_SRC, gst_gio_uri_handler_do_init (g_define_type_id));
@@ -101,6 +105,113 @@ static GInputStream *gst_gio_src_get_stream (GstGioBaseSrc * bsrc);
 
 static gboolean gst_gio_src_query (GstBaseSrc * base_src, GstQuery * query);
 
+static void
+gst_gio_src_file_changed_cb (GstGioSrc * src)
+{
+  GST_DEBUG_OBJECT (src, "Underlying file changed.");
+  GST_OBJECT_LOCK (src);
+  src->changed = TRUE;
+  if (src->monitoring_mainloop)
+    g_main_loop_quit (src->monitoring_mainloop);
+  GST_OBJECT_UNLOCK (src);
+}
+
+static void
+gst_gio_src_waited_for_data (GstGioBaseSrc * bsrc)
+{
+  GstGioSrc *src = GST_GIO_SRC (bsrc);
+
+  src->waiting_for_data = FALSE;
+  g_signal_emit (bsrc, done_waiting_data_signal, 0, NULL);
+}
+
+static gboolean
+gst_gio_src_wait_for_data (GstGioBaseSrc * bsrc)
+{
+  GMainContext *ctx;
+  GstGioSrc *src = GST_GIO_SRC (bsrc);
+
+  g_return_val_if_fail (!src->monitor, FALSE);
+
+  GST_OBJECT_LOCK (src);
+  if (!src->is_growing) {
+    GST_OBJECT_UNLOCK (src);
+
+    return FALSE;
+  }
+
+  src->monitor = g_file_monitor (src->file, G_FILE_MONITOR_NONE,
+      bsrc->cancel, NULL);
+
+  if (!src->monitor) {
+    GST_OBJECT_UNLOCK (src);
+
+    GST_WARNING_OBJECT (bsrc, "Could not create a monitor");
+    return FALSE;
+  }
+
+  g_signal_connect_swapped (src->monitor, "changed",
+      G_CALLBACK (gst_gio_src_file_changed_cb), src);
+  GST_OBJECT_UNLOCK (src);
+
+  if (!src->waiting_for_data) {
+    g_signal_emit (src, waiting_data_signal, 0, NULL);
+    src->waiting_for_data = TRUE;
+  }
+
+  ctx = g_main_context_new ();
+  g_main_context_push_thread_default (ctx);
+  GST_OBJECT_LOCK (src);
+  src->changed = FALSE;
+  src->monitoring_mainloop = g_main_loop_new (ctx, FALSE);
+  GST_OBJECT_UNLOCK (src);
+
+  g_main_loop_run (src->monitoring_mainloop);
+
+  g_signal_handlers_disconnect_by_func (src->monitor,
+      gst_gio_src_file_changed_cb, src);
+
+  GST_OBJECT_LOCK (src);
+  gst_clear_object (&src->monitor);
+  g_main_loop_unref (src->monitoring_mainloop);
+  src->monitoring_mainloop = NULL;
+  GST_OBJECT_UNLOCK (src);
+
+  g_main_context_pop_thread_default (ctx);
+  g_main_context_unref (ctx);
+
+  return src->changed;
+}
+
+static gboolean
+gst_gio_src_unlock (GstBaseSrc * base_src)
+{
+  GstGioSrc *src = GST_GIO_SRC (base_src);
+
+  GST_LOG_OBJECT (src, "triggering cancellation");
+
+  GST_OBJECT_LOCK (src);
+  while (src->monitoring_mainloop) {
+    /* Ensure that we have already started the mainloop */
+    if (!g_main_loop_is_running (src->monitoring_mainloop)) {
+      GST_OBJECT_UNLOCK (src);
+
+      /* Letting a chance for the waiting for data function to cleanup the
+       * mainloop. */
+      g_thread_yield ();
+
+      GST_OBJECT_LOCK (src);
+      continue;
+    }
+    g_main_loop_quit (src->monitoring_mainloop);
+    break;
+  }
+  GST_OBJECT_UNLOCK (src);
+
+  return GST_CALL_PARENT_WITH_DEFAULT (GST_BASE_SRC_CLASS, unlock, (base_src),
+      TRUE);
+}
+
 static void
 gst_gio_src_class_init (GstGioSrcClass * klass)
 {
@@ -122,22 +233,64 @@ gst_gio_src_class_init (GstGioSrcClass * klass)
   /**
    * GstGioSrc:file:
    *
-   * %GFile to read from.
+   * #GFile to read from.
    */
   g_object_class_install_property (gobject_class, PROP_FILE,
       g_param_spec_object ("file", "File", "GFile to read from",
           G_TYPE_FILE, G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
 
+  /**
+   * GstGioSrc:is-growing:
+   *
+   * Whether the file is currently growing. When activated EOS is never pushed
+   * and the user needs to handle it himself. This modes allows to keep reading
+   * the file while it is being written on file.
+   *
+   * You can reset the property to %FALSE at any time and the file will start
+   * not being considered growing and EOS will be pushed when required.
+   *
+   * Since: 1.20
+   */
+  g_object_class_install_property (gobject_class, PROP_GROWING_FILE,
+      g_param_spec_boolean ("is-growing", "File is growing",
+          "Whether the file is growing, ignoring its end",
+          FALSE, G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
+
   gst_element_class_set_static_metadata (gstelement_class, "GIO source",
       "Source/File",
       "Read from any GIO-supported location",
       "Ren\xc3\xa9 Stadler <mail@renestadler.de>, "
       "Sebastian Dröge <sebastian.droege@collabora.co.uk>");
 
   gstbasesrc_class->query = GST_DEBUG_FUNCPTR (gst_gio_src_query);
+  gstbasesrc_class->unlock = GST_DEBUG_FUNCPTR (gst_gio_src_unlock);
 
   gstgiobasesrc_class->get_stream = GST_DEBUG_FUNCPTR (gst_gio_src_get_stream);
   gstgiobasesrc_class->close_on_stop = TRUE;
+  gstgiobasesrc_class->wait_for_data = gst_gio_src_wait_for_data;
+  gstgiobasesrc_class->waited_for_data = gst_gio_src_waited_for_data;
+
+  /**
+   * GstGioSrc::waiting-data:
+   *
+   * Signal notifying that we are stalled waiting for data
+   *
+   * Since: 1.20
+   */
+  waiting_data_signal = g_signal_new ("waiting-data",
+      G_TYPE_FROM_CLASS (klass), G_SIGNAL_RUN_LAST, 0, NULL, NULL,
+      NULL, G_TYPE_NONE, 0);
+
+  /**
+   * GstGioSrc::done-waiting-data:
+   *
+   * Signal notifying that we are done waiting for data
+   *
+   * Since: 1.20
+   */
+  done_waiting_data_signal = g_signal_new ("done-waiting-data",
+      G_TYPE_FROM_CLASS (klass), G_SIGNAL_RUN_LAST, 0, NULL, NULL,
+      NULL, G_TYPE_NONE, 0);
 }
 
 static void
@@ -193,6 +346,32 @@ gst_gio_src_set_property (GObject * object, guint prop_id,
       GST_OBJECT_UNLOCK (GST_OBJECT (src));
       break;
     }
+    case PROP_GROWING_FILE:
+    {
+      gboolean was_growing;
+
+      GST_OBJECT_LOCK (src);
+      was_growing = src->is_growing;
+      src->is_growing = g_value_get_boolean (value);
+      gst_base_src_set_dynamic_size (GST_BASE_SRC (src), src->is_growing);
+      gst_base_src_set_automatic_eos (GST_BASE_SRC (src), !src->is_growing);
+
+      while (was_growing && !src->is_growing && src->monitoring_mainloop) {
+        /* Ensure that we have already started the mainloop */
+        if (!g_main_loop_is_running (src->monitoring_mainloop)) {
+          GST_OBJECT_UNLOCK (src);
+          /* Letting a chance for the waiting for data function to cleanup the
+           * mainloop. */
+          GST_OBJECT_LOCK (src);
+          continue;
+        }
+        g_main_loop_quit (src->monitoring_mainloop);
+        break;
+      }
+      GST_OBJECT_UNLOCK (src);
+
+      break;
+    }
     case PROP_FILE:
       if (GST_STATE (src) == GST_STATE_PLAYING ||
           GST_STATE (src) == GST_STATE_PAUSED) {
@@ -241,6 +420,11 @@ gst_gio_src_get_property (GObject * object, guint prop_id,
       g_value_set_object (value, src->file);
       GST_OBJECT_UNLOCK (GST_OBJECT (src));
       break;
+    case PROP_GROWING_FILE:
+    {
+      g_value_set_boolean (value, src->is_growing);
+      break;
+    }
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
       break;
@@ -281,8 +465,10 @@ gst_gio_src_query (GstBaseSrc * base_src, GstQuery * query)
 
       gst_query_set_scheduling (query, flags, 1, -1, 0);
       gst_query_add_scheduling_mode (query, GST_PAD_MODE_PUSH);
-      if (flags & GST_SCHEDULING_FLAG_SEEKABLE)
+      GST_OBJECT_LOCK (src);
+      if (flags & GST_SCHEDULING_FLAG_SEEKABLE && !src->is_growing)
         gst_query_add_scheduling_mode (query, GST_PAD_MODE_PULL);
+      GST_OBJECT_UNLOCK (src);
 
       res = TRUE;
       break;

gst/gio/gstgiosrc.h

@@ -43,6 +43,12 @@ struct _GstGioSrc
 
   /*< private >*/
   GFile *file;
+
+  gboolean is_growing;
+  GFileMonitor *monitor;
+  GMainLoop *monitoring_mainloop;
+  gboolean changed;
+  gboolean waiting_for_data;
 };
 
 G_END_DECLS

tests/validate/giosrc/read-growing-file.validatetest

@@ -0,0 +1,42 @@
+# Pipeline with 2 branches, the first one write random data into a file in $(growing_file_location).
+# That branch is synchronized on the test clock that we drive in the scenario.
+# The second branch reads it with giosrc and does some tests like waiting for the
+# `done-waiting-signal` signals on the source etc...
+#
+# The whole dataflow is checked and we ensure that the exact same buffer content
+# is read from the giosrc.
+set-globals, growing_file_location="$(logsdir)/$(test_name)-growing.rand"
+meta,
+    seek=false,
+    handles-states=false,
+    args = {
+        "fakesrc num-buffers=30 datarate=30 filltype=pattern-span sizetype=fixed filltype=random format=time ! filesink sync=true location=$(growing_file_location) name=filesink buffer-mode=unbuffered \
+         giosrc name=giosrc is-growing=true location=file://$(growing_file_location) ! fakesink name=growing-file-sink async=false" \
+    },
+    configs = {
+       "$(validateflow), pad=filesink:sink, record-buffers=true, ignored-fields=\"stream-start={stream-id,group-id,stream}\", buffers-checksum=as-id",
+       "$(validateflow), pad=growing-file-sink:sink, record-buffers=true, ignored-fields=\"stream-start={stream-id,group-id,stream}\", buffers-checksum=as-id",
+    }
+
+
+crank-clock, repeat=5
+wait, signal-name=waiting-data, target-element-name=giosrc
+
+checkpoint
+
+crank-clock, repeat=5
+wait, signal-name=waiting-data, target-element-name=giosrc
+
+wait, signal-name=done-waiting-data, target-element-name=giosrc, non-blocking=true
+crank-clock, repeat=21
+
+checkpoint
+
+wait, signal-name=waiting-data, target-element-name=giosrc
+
+checkpoint
+
+# Make sure EOS is outputted now.
+set-properties, giosrc::is_growing=false
+
+stop, on-message=eos