text: /* GStreamer
   * Copyright (C) 2004 Wim Taymans <wim@fluendo.com>
   *
   * gstbus.c: GstBus subsystem
   *
   * This library is free software; you can redistribute it and/or
   * modify it under the terms of the GNU Library General Public
   * License as published by the Free Software Foundation; either
   * version 2 of the License, or (at your option) any later version.
   *
   * This library is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * Library General Public License for more details.
   *
   * You should have received a copy of the GNU Library General Public
   * License along with this library; if not, write to the
   * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
   * Boston, MA 02110-1301, USA.
   */
  
  /**
   * SECTION:gstbus
   * @title: GstBus
   * @short_description: Asynchronous message bus subsystem
   * @see_also: #GstMessage, #GstElement
   *
   * The #GstBus is an object responsible for delivering #GstMessage packets in
   * a first-in first-out way from the streaming threads (see #GstTask) to the
   * application.
   *
   * Since the application typically only wants to deal with delivery of these
   * messages from one thread, the GstBus will marshall the messages between
   * different threads. This is important since the actual streaming of media
   * is done in another thread than the application.
   *
   * The GstBus provides support for #GSource based notifications. This makes it
   * possible to handle the delivery in the glib mainloop.
   *
   * The #GSource callback function gst_bus_async_signal_func() can be used to
   * convert all bus messages into signal emissions.
   *
   * A message is posted on the bus with the gst_bus_post() method. With the
   * gst_bus_peek() and gst_bus_pop() methods one can look at or retrieve a
   * previously posted message.
   *
   * The bus can be polled with the gst_bus_poll() method. This methods blocks
   * up to the specified timeout value until one of the specified messages types
   * is posted on the bus. The application can then gst_bus_pop() the messages
   * from the bus to handle them.
   * Alternatively the application can register an asynchronous bus function
   * using gst_bus_add_watch_full() or gst_bus_add_watch(). This function will
   * install a #GSource in the default glib main loop and will deliver messages
   * a short while after they have been posted. Note that the main loop should
   * be running for the asynchronous callbacks.
   *
   * It is also possible to get messages from the bus without any thread
   * marshalling with the gst_bus_set_sync_handler() method. This makes it
   * possible to react to a message in the same thread that posted the
   * message on the bus. This should only be used if the application is able
   * to deal with messages from different threads.
   *
   * Every #GstPipeline has one bus.
   *
   * Note that a #GstPipeline will set its bus into flushing state when changing
   * from READY to NULL state.
   */
  
  #include "gst_private.h"
  #include <errno.h>
  #ifdef HAVE_UNISTD_H
  #  include <unistd.h>
  #endif
  #include <sys/types.h>
  
  #include "gstatomicqueue.h"
  #include "gstinfo.h"
  #include "gstpoll.h"
  
  #include "gstbus.h"
  #include "glib-compat-private.h"
  
  #ifdef G_OS_WIN32
  #  ifndef EWOULDBLOCK
  #  define EWOULDBLOCK EAGAIN    /* This is just to placate gcc */
  #  endif
  #endif /* G_OS_WIN32 */
  
  #define GST_CAT_DEFAULT GST_CAT_BUS
  /* bus signals */
  enum
  {
    SYNC_MESSAGE,
    ASYNC_MESSAGE,
    /* add more above */
    LAST_SIGNAL
  };
  
  #define DEFAULT_ENABLE_ASYNC (TRUE)
  
  enum
  {
    PROP_0,
    PROP_ENABLE_ASYNC
  };
  
  static void gst_bus_dispose (GObject * object);
  static void gst_bus_finalize (GObject * object);
  
  static guint gst_bus_signals[LAST_SIGNAL] = { 0 };
  
  struct _GstBusPrivate
  {
    GstAtomicQueue *queue;
    GMutex queue_lock;
  
    GstBusSyncHandler sync_handler;
    gpointer sync_handler_data;
    GDestroyNotify sync_handler_notify;
  
    guint num_signal_watchers;
  
    guint num_sync_message_emitters;
    GSource *signal_watch;
  
    gboolean enable_async;
    GstPoll *poll;
    GPollFD pollfd;
  };
  
  #define gst_bus_parent_class parent_class
  G_DEFINE_TYPE_WITH_PRIVATE (GstBus, gst_bus, GST_TYPE_OBJECT);
  
  static void
  gst_bus_set_property (GObject * object,
      guint prop_id, const GValue * value, GParamSpec * pspec)
  {
    GstBus *bus = GST_BUS_CAST (object);
  
    switch (prop_id) {
      case PROP_ENABLE_ASYNC:
        bus->priv->enable_async = g_value_get_boolean (value);
        break;
      default:
        G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
        break;
    }
  }
  
  static void
  gst_bus_constructed (GObject * object)
  {
    GstBus *bus = GST_BUS_CAST (object);
  
    if (bus->priv->enable_async) {
      bus->priv->poll = gst_poll_new_timer ();
      gst_poll_get_read_gpollfd (bus->priv->poll, &bus->priv->pollfd);
    }
  
    G_OBJECT_CLASS (gst_bus_parent_class)->constructed (object);
  }
  
  static void
  gst_bus_class_init (GstBusClass * klass)
  {
    GObjectClass *gobject_class = (GObjectClass *) klass;
  
    gobject_class->dispose = gst_bus_dispose;
    gobject_class->finalize = gst_bus_finalize;
    gobject_class->set_property = gst_bus_set_property;
    gobject_class->constructed = gst_bus_constructed;
  
    /**
     * GstBus::enable-async:
     *
     * Enable async message delivery support for bus watches,
     * gst_bus_pop() and similar API. Without this only the
     * synchronous message handlers are called.
     *
     * This property is used to create the child element buses
     * in #GstBin.
     */
    g_object_class_install_property (gobject_class, PROP_ENABLE_ASYNC,
        g_param_spec_boolean ("enable-async", "Enable Async",
            "Enable async message delivery for bus watches and gst_bus_pop()",
            DEFAULT_ENABLE_ASYNC,
            G_PARAM_CONSTRUCT_ONLY | G_PARAM_WRITABLE | G_PARAM_STATIC_STRINGS));
  
    /**
     * GstBus::sync-message:
     * @bus: the object which received the signal
     * @message: the message that has been posted synchronously
     *
     * A message has been posted on the bus. This signal is emitted from the
     * thread that posted the message so one has to be careful with locking.
     *
     * This signal will not be emitted by default, you have to call
     * gst_bus_enable_sync_message_emission() before.
     */
    gst_bus_signals[SYNC_MESSAGE] =
        g_signal_new ("sync-message", G_TYPE_FROM_CLASS (klass),
        G_SIGNAL_RUN_LAST | G_SIGNAL_DETAILED,
        G_STRUCT_OFFSET (GstBusClass, sync_message), NULL, NULL,
        g_cclosure_marshal_generic, G_TYPE_NONE, 1, GST_TYPE_MESSAGE);
  
    /**
     * GstBus::message:
     * @bus: the object which received the signal
     * @message: the message that has been posted asynchronously
     *
     * A message has been posted on the bus. This signal is emitted from a
     * GSource added to the mainloop. this signal will only be emitted when
     * there is a mainloop running.
     */
    gst_bus_signals[ASYNC_MESSAGE] =
        g_signal_new ("message", G_TYPE_FROM_CLASS (klass),
        G_SIGNAL_RUN_LAST | G_SIGNAL_DETAILED,
        G_STRUCT_OFFSET (GstBusClass, message), NULL, NULL,
        g_cclosure_marshal_generic, G_TYPE_NONE, 1, GST_TYPE_MESSAGE);
  }
  
  static void
  gst_bus_init (GstBus * bus)
  {
    bus->priv = gst_bus_get_instance_private (bus);
    bus->priv->enable_async = DEFAULT_ENABLE_ASYNC;
    g_mutex_init (&bus->priv->queue_lock);
    bus->priv->queue = gst_atomic_queue_new (32);
  
    GST_DEBUG_OBJECT (bus, "created");
  }
  
  static void
  gst_bus_dispose (GObject * object)
  {
    GstBus *bus = GST_BUS (object);
  
    if (bus->priv->queue) {
      GstMessage *message;
  
      g_mutex_lock (&bus->priv->queue_lock);
      do {
        message = gst_atomic_queue_pop (bus->priv->queue);
        if (message)
          gst_message_unref (message);
      } while (message != NULL);
      gst_atomic_queue_unref (bus->priv->queue);
      bus->priv->queue = NULL;
      g_mutex_unlock (&bus->priv->queue_lock);
      g_mutex_clear (&bus->priv->queue_lock);
  
      if (bus->priv->poll)
        gst_poll_free (bus->priv->poll);
      bus->priv->poll = NULL;
    }
  
    G_OBJECT_CLASS (parent_class)->dispose (object);
  }
  
  static void
  gst_bus_finalize (GObject * object)
  {
    GstBus *bus = GST_BUS (object);
  
    if (bus->priv->sync_handler_notify)
      bus->priv->sync_handler_notify (bus->priv->sync_handler_data);
  
    G_OBJECT_CLASS (parent_class)->finalize (object);
  }
  
  /**
   * gst_bus_new:
   *
   * Creates a new #GstBus instance.
   *
   * Returns: (transfer full): a new #GstBus instance
   */
  GstBus *
  gst_bus_new (void)
  {
    GstBus *result;
  
    result = g_object_new (gst_bus_get_type (), NULL);
    GST_DEBUG_OBJECT (result, "created new bus");
  
    /* clear floating flag */
    gst_object_ref_sink (result);
  
    return result;
  }
  
  /**
   * gst_bus_post:
   * @bus: a #GstBus to post on
   * @message: (transfer full): the #GstMessage to post
   *
   * Post a message on the given bus. Ownership of the message
   * is taken by the bus.
   *
   * Returns: %TRUE if the message could be posted, %FALSE if the bus is flushing.
   *
   * MT safe.
   */
  gboolean
  gst_bus_post (GstBus * bus, GstMessage * message)
  {
    GstBusSyncReply reply = GST_BUS_PASS;
    GstBusSyncHandler handler;
    gboolean emit_sync_message;
    gpointer handler_data;
  
    g_return_val_if_fail (GST_IS_BUS (bus), FALSE);
    g_return_val_if_fail (GST_IS_MESSAGE (message), FALSE);
  
    GST_DEBUG_OBJECT (bus, "[msg %p] posting on bus %" GST_PTR_FORMAT, message,
        message);
  
    /* check we didn't accidentally add a public flag that maps to same value */
    g_assert (!GST_MINI_OBJECT_FLAG_IS_SET (message,
            GST_MESSAGE_FLAG_ASYNC_DELIVERY));
  
    GST_OBJECT_LOCK (bus);
    /* check if the bus is flushing */
    if (GST_OBJECT_FLAG_IS_SET (bus, GST_BUS_FLUSHING))
      goto is_flushing;
  
    handler = bus->priv->sync_handler;
    handler_data = bus->priv->sync_handler_data;
    emit_sync_message = bus->priv->num_sync_message_emitters > 0;
    GST_OBJECT_UNLOCK (bus);
  
    /* first call the sync handler if it is installed */
    if (handler)
      reply = handler (bus, message, handler_data);
  
    /* emit sync-message if requested to do so via
       gst_bus_enable_sync_message_emission. terrible but effective */
    if (emit_sync_message && reply != GST_BUS_DROP
        && handler != gst_bus_sync_signal_handler)
      gst_bus_sync_signal_handler (bus, message, NULL);
  
    /* If this is a bus without async message delivery
     * always drop the message */
    if (!bus->priv->poll)
      reply = GST_BUS_DROP;
  
    /* now see what we should do with the message */
    switch (reply) {
      case GST_BUS_DROP:
        /* drop the message */
        GST_DEBUG_OBJECT (bus, "[msg %p] dropped", message);
        break;
      case GST_BUS_PASS:
        /* pass the message to the async queue, refcount passed in the queue */
        GST_DEBUG_OBJECT (bus, "[msg %p] pushing on async queue", message);
        gst_atomic_queue_push (bus->priv->queue, message);
        gst_poll_write_control (bus->priv->poll);
        GST_DEBUG_OBJECT (bus, "[msg %p] pushed on async queue", message);
  
        break;
      case GST_BUS_ASYNC:
      {
        /* async delivery, we need a mutex and a cond to block
         * on */
        GCond *cond = GST_MESSAGE_GET_COND (message);
        GMutex *lock = GST_MESSAGE_GET_LOCK (message);
  
        g_cond_init (cond);
        g_mutex_init (lock);
  
        GST_MINI_OBJECT_FLAG_SET (message, GST_MESSAGE_FLAG_ASYNC_DELIVERY);
  
        GST_DEBUG_OBJECT (bus, "[msg %p] waiting for async delivery", message);
  
        /* now we lock the message mutex, send the message to the async
         * queue. When the message is handled by the app and destroyed,
         * the cond will be signalled and we can continue */
        g_mutex_lock (lock);
  
        gst_atomic_queue_push (bus->priv->queue, message);
        gst_poll_write_control (bus->priv->poll);
  
        /* now block till the message is freed */
        g_cond_wait (cond, lock);
  
        /* we acquired a new ref from gst_message_dispose() so we can clean up */
        g_mutex_unlock (lock);
  
        GST_DEBUG_OBJECT (bus, "[msg %p] delivered asynchronously", message);
  
        GST_MINI_OBJECT_FLAG_UNSET (message, GST_MESSAGE_FLAG_ASYNC_DELIVERY);
  
        g_mutex_clear (lock);
        g_cond_clear (cond);
  
        gst_message_unref (message);
        break;
      }
      default:
        g_warning ("invalid return from bus sync handler");
        break;
    }
    return TRUE;
  
    /* ERRORS */
  is_flushing:
    {
      GST_DEBUG_OBJECT (bus, "bus is flushing");
      GST_OBJECT_UNLOCK (bus);
      gst_message_unref (message);
  
      return FALSE;
    }
  }
  
  /**
   * gst_bus_have_pending:
   * @bus: a #GstBus to check
   *
   * Check if there are pending messages on the bus that
   * should be handled.
   *
   * Returns: %TRUE if there are messages on the bus to be handled, %FALSE
   * otherwise.
   *
   * MT safe.
   */
  gboolean
  gst_bus_have_pending (GstBus * bus)
  {
    gboolean result;
  
    g_return_val_if_fail (GST_IS_BUS (bus), FALSE);
  
    /* see if there is a message on the bus */
    result = gst_atomic_queue_length (bus->priv->queue) != 0;
  
    return result;
  }
  
  /**
   * gst_bus_set_flushing:
   * @bus: a #GstBus
   * @flushing: whether or not to flush the bus
   *
   * If @flushing, flush out and unref any messages queued in the bus. Releases
   * references to the message origin objects. Will flush future messages until
   * gst_bus_set_flushing() sets @flushing to %FALSE.
   *
   * MT safe.
   */
  void
  gst_bus_set_flushing (GstBus * bus, gboolean flushing)
  {
    GstMessage *message;
    GList *message_list = NULL;
  
    g_return_if_fail (GST_IS_BUS (bus));
  
    GST_OBJECT_LOCK (bus);
  
    if (flushing) {
      GST_OBJECT_FLAG_SET (bus, GST_BUS_FLUSHING);
  
      GST_DEBUG_OBJECT (bus, "set bus flushing");
  
      while ((message = gst_bus_pop (bus)))
        message_list = g_list_prepend (message_list, message);
    } else {
      GST_DEBUG_OBJECT (bus, "unset bus flushing");
      GST_OBJECT_FLAG_UNSET (bus, GST_BUS_FLUSHING);
    }
  
    GST_OBJECT_UNLOCK (bus);
  
    g_list_free_full (message_list, (GDestroyNotify) gst_message_unref);
  }
  
  /**
   * gst_bus_timed_pop_filtered:
   * @bus: a #GstBus to pop from
   * @timeout: a timeout in nanoseconds, or GST_CLOCK_TIME_NONE to wait forever
   * @types: message types to take into account, GST_MESSAGE_ANY for any type
   *
   * Get a message from the bus whose type matches the message type mask @types,
   * waiting up to the specified timeout (and discarding any messages that do not
   * match the mask provided).
   *
   * If @timeout is 0, this function behaves like gst_bus_pop_filtered(). If
   * @timeout is #GST_CLOCK_TIME_NONE, this function will block forever until a
   * matching message was posted on the bus.
   *
   * Returns: (transfer full) (nullable): a #GstMessage matching the
   *     filter in @types, or %NULL if no matching message was found on
   *     the bus until the timeout expired. The message is taken from
   *     the bus and needs to be unreffed with gst_message_unref() after
   *     usage.
   *
   * MT safe.
   */
  GstMessage *
  gst_bus_timed_pop_filtered (GstBus * bus, GstClockTime timeout,
      GstMessageType types)
  {
    GstMessage *message;
    GTimeVal now, then;
    gboolean first_round = TRUE;
    GstClockTime elapsed = 0;
  
    g_return_val_if_fail (GST_IS_BUS (bus), NULL);
    g_return_val_if_fail (types != 0, NULL);
    g_return_val_if_fail (timeout == 0 || bus->priv->poll != NULL, NULL);
  
    g_mutex_lock (&bus->priv->queue_lock);
  
    while (TRUE) {
      gint ret;
  
      GST_LOG_OBJECT (bus, "have %d messages",
          gst_atomic_queue_length (bus->priv->queue));
  
      while ((message = gst_atomic_queue_pop (bus->priv->queue))) {
        if (bus->priv->poll) {
          while (!gst_poll_read_control (bus->priv->poll)) {
            if (errno == EWOULDBLOCK) {
              /* Retry, this can happen if pushing to the queue has finished,
               * popping here succeeded but writing control did not finish
               * before we got to this line. */
              /* Give other threads the chance to do something */
              g_thread_yield ();
              continue;
            } else {
              /* This is a real error and means that either the bus is in an
               * inconsistent state, or the GstPoll is invalid. GstPoll already
               * prints a critical warning about this, no need to do that again
               * ourselves */
              break;
            }
          }
        }
  
        GST_DEBUG_OBJECT (bus, "got message %p, %s from %s, type mask is %u",
            message, GST_MESSAGE_TYPE_NAME (message),
            GST_MESSAGE_SRC_NAME (message), (guint) types);
        if ((GST_MESSAGE_TYPE (message) & types) != 0) {
          /* Extra check to ensure extended types don't get matched unless
           * asked for */
          if ((!GST_MESSAGE_TYPE_IS_EXTENDED (message))
              || (types & GST_MESSAGE_EXTENDED)) {
            /* exit the loop, we have a message */
            goto beach;
          }
        }
  
        GST_DEBUG_OBJECT (bus, "discarding message, does not match mask");
        gst_message_unref (message);
        message = NULL;
      }
  
      /* no need to wait, exit loop */
      if (timeout == 0)
        break;
  
      else if (timeout != GST_CLOCK_TIME_NONE) {
        if (first_round) {
          g_get_current_time (&then);
          first_round = FALSE;
        } else {
          g_get_current_time (&now);
  
          elapsed = GST_TIMEVAL_TO_TIME (now) - GST_TIMEVAL_TO_TIME (then);
  
          if (elapsed > timeout)
            break;
        }
      }
  
      /* only here in timeout case */
      g_assert (bus->priv->poll);
      g_mutex_unlock (&bus->priv->queue_lock);
      ret = gst_poll_wait (bus->priv->poll, timeout - elapsed);
      g_mutex_lock (&bus->priv->queue_lock);
  
      if (ret == 0) {
        GST_INFO_OBJECT (bus, "timed out, breaking loop");
        break;
      } else {
        GST_INFO_OBJECT (bus, "we got woken up, recheck for message");
      }
    }
  
  beach:
  
    g_mutex_unlock (&bus->priv->queue_lock);
  
    return message;
  }
  
  
  /**
   * gst_bus_timed_pop:
   * @bus: a #GstBus to pop
   * @timeout: a timeout
   *
   * Get a message from the bus, waiting up to the specified timeout.
   *
   * If @timeout is 0, this function behaves like gst_bus_pop(). If @timeout is
   * #GST_CLOCK_TIME_NONE, this function will block forever until a message was
   * posted on the bus.
   *
   * Returns: (transfer full) (nullable): the #GstMessage that is on the
   *     bus after the specified timeout or %NULL if the bus is empty
   *     after the timeout expired.  The message is taken from the bus
   *     and needs to be unreffed with gst_message_unref() after usage.
   *
   * MT safe.
   */
  GstMessage *
  gst_bus_timed_pop (GstBus * bus, GstClockTime timeout)
  {
    g_return_val_if_fail (GST_IS_BUS (bus), NULL);
  
    return gst_bus_timed_pop_filtered (bus, timeout, GST_MESSAGE_ANY);
  }
  
  /**
   * gst_bus_pop_filtered:
   * @bus: a #GstBus to pop
   * @types: message types to take into account
   *
   * Get a message matching @type from the bus.  Will discard all messages on
   * the bus that do not match @type and that have been posted before the first
   * message that does match @type.  If there is no message matching @type on
   * the bus, all messages will be discarded. It is not possible to use message
   * enums beyond #GST_MESSAGE_EXTENDED in the @events mask.
   *
   * Returns: (transfer full) (nullable): the next #GstMessage matching
   *     @type that is on the bus, or %NULL if the bus is empty or there
   *     is no message matching @type. The message is taken from the bus
   *     and needs to be unreffed with gst_message_unref() after usage.
   *
   * MT safe.
   */
  GstMessage *
  gst_bus_pop_filtered (GstBus * bus, GstMessageType types)
  {
    g_return_val_if_fail (GST_IS_BUS (bus), NULL);
    g_return_val_if_fail (types != 0, NULL);
  
    return gst_bus_timed_pop_filtered (bus, 0, types);
  }
  
  /**
   * gst_bus_pop:
   * @bus: a #GstBus to pop
   *
   * Get a message from the bus.
   *
   * Returns: (transfer full) (nullable): the #GstMessage that is on the
   *     bus, or %NULL if the bus is empty. The message is taken from
   *     the bus and needs to be unreffed with gst_message_unref() after
   *     usage.
   *
   * MT safe.
   */
  GstMessage *
  gst_bus_pop (GstBus * bus)
  {
    g_return_val_if_fail (GST_IS_BUS (bus), NULL);
  
    return gst_bus_timed_pop_filtered (bus, 0, GST_MESSAGE_ANY);
  }
  
  /**
   * gst_bus_peek:
   * @bus: a #GstBus
   *
   * Peek the message on the top of the bus' queue. The message will remain
   * on the bus' message queue. A reference is returned, and needs to be unreffed
   * by the caller.
   *
   * Returns: (transfer full) (nullable): the #GstMessage that is on the
   *     bus, or %NULL if the bus is empty.
   *
   * MT safe.
   */
  GstMessage *
  gst_bus_peek (GstBus * bus)
  {
    GstMessage *message;
  
    g_return_val_if_fail (GST_IS_BUS (bus), NULL);
  
    g_mutex_lock (&bus->priv->queue_lock);
    message = gst_atomic_queue_peek (bus->priv->queue);
    if (message)
      gst_message_ref (message);
    g_mutex_unlock (&bus->priv->queue_lock);
  
    GST_DEBUG_OBJECT (bus, "peek on bus, got message %p", message);
  
    return message;
  }
  
  /**
   * gst_bus_set_sync_handler:
   * @bus: a #GstBus to install the handler on
   * @func: (allow-none): The handler function to install
   * @user_data: User data that will be sent to the handler function.
   * @notify: called when @user_data becomes unused
   *
   * Sets the synchronous handler on the bus. The function will be called
   * every time a new message is posted on the bus. Note that the function
   * will be called in the same thread context as the posting object. This
   * function is usually only called by the creator of the bus. Applications
   * should handle messages asynchronously using the gst_bus watch and poll
   * functions.
   *
   * You cannot replace an existing sync_handler. You can pass %NULL to this
   * function, which will clear the existing handler.
   */
  void
  gst_bus_set_sync_handler (GstBus * bus, GstBusSyncHandler func,
      gpointer user_data, GDestroyNotify notify)
  {
    GDestroyNotify old_notify;
  
    g_return_if_fail (GST_IS_BUS (bus));
  
    GST_OBJECT_LOCK (bus);
    /* Assert if the user attempts to replace an existing sync_handler,
     * other than to clear it */
    if (func != NULL && bus->priv->sync_handler != NULL)
      goto no_replace;
  
    if ((old_notify = bus->priv->sync_handler_notify)) {
      gpointer old_data = bus->priv->sync_handler_data;
  
      bus->priv->sync_handler_data = NULL;
      bus->priv->sync_handler_notify = NULL;
      GST_OBJECT_UNLOCK (bus);
  
      old_notify (old_data);
  
      GST_OBJECT_LOCK (bus);
    }
    bus->priv->sync_handler = func;
    bus->priv->sync_handler_data = user_data;
    bus->priv->sync_handler_notify = notify;
    GST_OBJECT_UNLOCK (bus);
  
    return;
  
  no_replace:
    {
      GST_OBJECT_UNLOCK (bus);
      g_warning ("cannot replace existing sync handler");
      return;
    }
  }
  
  /**
   * gst_bus_get_pollfd:
   * @bus: A #GstBus
   * @fd: (out): A GPollFD to fill
   *
   * Gets the file descriptor from the bus which can be used to get notified about
   * messages being available with functions like g_poll(), and allows integration
   * into other event loops based on file descriptors.
   * Whenever a message is available, the POLLIN / %G_IO_IN event is set.
   *
   * Warning: NEVER read or write anything to the returned fd but only use it
   * for getting notifications via g_poll() or similar and then use the normal
   * GstBus API, e.g. gst_bus_pop().
   *
   * Since: 1.14
   */
  void
  gst_bus_get_pollfd (GstBus * bus, GPollFD * fd)
  {
    g_return_if_fail (GST_IS_BUS (bus));
    g_return_if_fail (bus->priv->poll != NULL);
  
    *fd = bus->priv->pollfd;
  }
  
  /* GSource for the bus
   */
  typedef struct
  {
    GSource source;
    GstBus *bus;
  } GstBusSource;
  
  static gboolean
  gst_bus_source_prepare (GSource * source, gint * timeout)
  {
    *timeout = -1;
    return FALSE;
  }
  
  static gboolean
  gst_bus_source_check (GSource * source)
  {
    GstBusSource *bsrc = (GstBusSource *) source;
  
    return bsrc->bus->priv->pollfd.revents & (G_IO_IN | G_IO_HUP | G_IO_ERR);
  }
  
  static gboolean
  gst_bus_source_dispatch (GSource * source, GSourceFunc callback,
      gpointer user_data)
  {
    GstBusFunc handler = (GstBusFunc) callback;
    GstBusSource *bsource = (GstBusSource *) source;
    GstMessage *message;
    gboolean keep;
    GstBus *bus;
  
    g_return_val_if_fail (bsource != NULL, FALSE);
  
    bus = bsource->bus;
  
    g_return_val_if_fail (GST_IS_BUS (bus), FALSE);
  
    message = gst_bus_pop (bus);
  
    /* The message queue might be empty if some other thread or callback set
     * the bus to flushing between check/prepare and dispatch */
    if (G_UNLIKELY (message == NULL))
      return TRUE;
  
    if (!handler)
      goto no_handler;
  
    GST_DEBUG_OBJECT (bus, "source %p calling dispatch with %" GST_PTR_FORMAT,
        source, message);
  
    keep = handler (bus, message, user_data);
    gst_message_unref (message);
  
    GST_DEBUG_OBJECT (bus, "source %p handler returns %d", source, keep);
  
    return keep;
  
  no_handler:
    {
      g_warning ("GstBus watch dispatched without callback\n"
          "You must call g_source_set_callback().");
      gst_message_unref (message);
      return FALSE;
    }
  }
  
  static void
  gst_bus_source_finalize (GSource * source)
  {
    GstBusSource *bsource = (GstBusSource *) source;
    GstBus *bus;
  
    bus = bsource->bus;
  
    GST_DEBUG_OBJECT (bus, "finalize source %p", source);
  
    GST_OBJECT_LOCK (bus);
    if (bus->priv->signal_watch == source)
      bus->priv->signal_watch = NULL;
    GST_OBJECT_UNLOCK (bus);
  
    gst_object_unref (bsource->bus);
    bsource->bus = NULL;
  }
  
  static GSourceFuncs gst_bus_source_funcs = {
    gst_bus_source_prepare,
    gst_bus_source_check,
    gst_bus_source_dispatch,
    gst_bus_source_finalize
  };
  
  /**
   * gst_bus_create_watch:
   * @bus: a #GstBus to create the watch for
   *
   * Create watch for this bus. The GSource will be dispatched whenever
   * a message is on the bus. After the GSource is dispatched, the
   * message is popped off the bus and unreffed.
   *
   * Returns: (transfer full) (nullable): a #GSource that can be added to a mainloop.
   */
  GSource *
  gst_bus_create_watch (GstBus * bus)
  {
    GstBusSource *source;
  
    g_return_val_if_fail (GST_IS_BUS (bus), NULL);
    g_return_val_if_fail (bus->priv->poll != NULL, NULL);
  
    source = (GstBusSource *) g_source_new (&gst_bus_source_funcs,
        sizeof (GstBusSource));
  
    g_source_set_name ((GSource *) source, "GStreamer message bus watch");
  
    source->bus = gst_object_ref (bus);
    g_source_add_poll ((GSource *) source, &bus->priv->pollfd);
  
    return (GSource *) source;
  }
  
  /* must be called with the bus OBJECT LOCK */
  static guint
  gst_bus_add_watch_full_unlocked (GstBus * bus, gint priority,
      GstBusFunc func, gpointer user_data, GDestroyNotify notify)
  {
    GMainContext *ctx;
    guint id;
    GSource *source;
  
    if (bus->priv->signal_watch) {
      GST_ERROR_OBJECT (bus,
          "Tried to add new watch while one was already there");
      return 0;
    }
  
    source = gst_bus_create_watch (bus);
    if (!source) {
      g_critical ("Creating bus watch failed");
      return 0;
    }
  
    if (priority != G_PRIORITY_DEFAULT)
      g_source_set_priority (source, priority);
  
    g_source_set_callback (source, (GSourceFunc) func, user_data, notify);
  
    ctx = g_main_context_get_thread_default ();
    id = g_source_attach (source, ctx);
    g_source_unref (source);
  
    if (id) {
      bus->priv->signal_watch = source;
    }
  
    GST_DEBUG_OBJECT (bus, "New source %p with id %u", source, id);
    return id;
  }
  
  /**
   * gst_bus_add_watch_full: (rename-to gst_bus_add_watch)
   * @bus: a #GstBus to create the watch for.
   * @priority: The priority of the watch.
   * @func: A function to call when a message is received.
   * @user_data: user data passed to @func.
   * @notify: the function to call when the source is removed.
   *
   * Adds a bus watch to the default main context with the given @priority (e.g.
   * %G_PRIORITY_DEFAULT). It is also possible to use a non-default  main
   * context set up using g_main_context_push_thread_default() (before
   * one had to create a bus watch source and attach it to the desired main
   * context 'manually').
   *
   * This function is used to receive asynchronous messages in the main loop.
   * There can only be a single bus watch per bus, you must remove it before you
   * can set a new one.
   *
   * The bus watch will only work if a GLib main loop is being run.
   *
   * When @func is called, the message belongs to the caller; if you want to
   * keep a copy of it, call gst_message_ref() before leaving @func.
   *
   * The watch can be removed using gst_bus_remove_watch() or by returning %FALSE
   * from @func. If the watch was added to the default main context it is also
   * possible to remove the watch using g_source_remove().
   *
   * The bus watch will take its own reference to the @bus, so it is safe to unref
   * @bus using gst_object_unref() after setting the bus watch.
   *
   * MT safe.
   *
   * Returns: The event source id or 0 if @bus already got an event source.
   */
  guint
  gst_bus_add_watch_full (GstBus * bus, gint priority,
      GstBusFunc func, gpointer user_data, GDestroyNotify notify)
  {
    guint id;
  
    g_return_val_if_fail (GST_IS_BUS (bus), 0);
  
    GST_OBJECT_LOCK (bus);
    id = gst_bus_add_watch_full_unlocked (bus, priority, func, user_data, notify);
    GST_OBJECT_UNLOCK (bus);
  
    return id;
  }
  
  /**
   * gst_bus_add_watch: (skip)
   * @bus: a #GstBus to create the watch for
   * @func: A function to call when a message is received.
   * @user_data: user data passed to @func.
   *
   * Adds a bus watch to the default main context with the default priority
   * (%G_PRIORITY_DEFAULT). It is also possible to use a non-default main
   * context set up using g_main_context_push_thread_default() (before
   * one had to create a bus watch source and attach it to the desired main
   * context 'manually').
   *
   * This function is used to receive asynchronous messages in the main loop.
   * There can only be a single bus watch per bus, you must remove it before you
   * can set a new one.
   *
   * The bus watch will only work if a GLib main loop is being run.
   *
   * The watch can be removed using gst_bus_remove_watch() or by returning %FALSE
   * from @func. If the watch was added to the default main context it is also
   * possible to remove the watch using g_source_remove().
   *
   * The bus watch will take its own reference to the @bus, so it is safe to unref
   * @bus using gst_object_unref() after setting the bus watch.
   *
   * MT safe.
   *
   * Returns: The event source id or 0 if @bus already got an event source.
   */
  guint
  gst_bus_add_watch (GstBus * bus, GstBusFunc func, gpointer user_data)
  {
    return gst_bus_add_watch_full (bus, G_PRIORITY_DEFAULT, func,
        user_data, NULL);
  }
  
  /**
   * gst_bus_remove_watch:
   * @bus: a #GstBus to remove the watch from.
   *
   * Removes an installed bus watch from @bus.
   *
   * Returns: %TRUE on success or %FALSE if @bus has no event source.
   *
   * Since: 1.6
   *
   */
  gboolean
  gst_bus_remove_watch (GstBus * bus)
  {
    GSource *source;
  
    g_return_val_if_fail (GST_IS_BUS (bus), FALSE);
  
    GST_OBJECT_LOCK (bus);
  
    if (bus->priv->signal_watch == NULL) {
      GST_ERROR_OBJECT (bus, "no bus watch was present");
      goto error;
    }
  
    if (bus->priv->num_signal_watchers > 0) {
      GST_ERROR_OBJECT (bus,
          "trying to remove signal watch with gst_bus_remove_watch()");
      goto error;
    }
  
    source =
        bus->priv->signal_watch ? g_source_ref (bus->priv->signal_watch) : NULL;
  
    GST_OBJECT_UNLOCK (bus);
  
    if (source) {
      g_source_destroy (source);
      g_source_unref (source);
    }
  
    return TRUE;
  
  error:
    GST_OBJECT_UNLOCK (bus);
  
    return FALSE;
  }
  
  typedef struct
  {
    GMainLoop *loop;
    guint timeout_id;
    gboolean source_running;
    GstMessageType events;
    GstMessage *message;
  } GstBusPollData;
  
  static void
  poll_func (GstBus * bus, GstMessage * message, GstBusPollData * poll_data)
  {
    GstMessageType type;
  
    if (!g_main_loop_is_running (poll_data->loop)) {
      GST_DEBUG ("mainloop %p not running", poll_data->loop);
      return;
    }
  
    type = GST_MESSAGE_TYPE (message);
  
    if (type & poll_data->events) {
      g_assert (poll_data->message == NULL);
      /* keep ref to message */
      poll_data->message = gst_message_ref (message);
      GST_DEBUG ("mainloop %p quit", poll_data->loop);
      g_main_loop_quit (poll_data->loop);
    } else {
      GST_DEBUG ("type %08x does not match %08x", type, poll_data->events);
    }
  }
  
  static gboolean
  poll_timeout (GstBusPollData * poll_data)
  {
    GST_DEBUG ("mainloop %p quit", poll_data->loop);
    g_main_loop_quit (poll_data->loop);
  
    /* we don't remove the GSource as this would free our poll_data,
     * which we still need */
    return TRUE;
  }
  
  static void
  poll_destroy (GstBusPollData * poll_data, gpointer unused)
  {
    poll_data->source_running = FALSE;
    if (!poll_data->timeout_id) {
      g_main_loop_unref (poll_data->loop);
      g_slice_free (GstBusPollData, poll_data);
    }
  }
  
  static void
  poll_destroy_timeout (GstBusPollData * poll_data)
  {
    poll_data->timeout_id = 0;
    if (!poll_data->source_running) {
      g_main_loop_unref (poll_data->loop);
      g_slice_free (GstBusPollData, poll_data);
    }
  }
  
  /**
   * gst_bus_poll:
   * @bus: a #GstBus
   * @events: a mask of #GstMessageType, representing the set of message types to
   * poll for (note special handling of extended message types below)
   * @timeout: the poll timeout, as a #GstClockTime, or #GST_CLOCK_TIME_NONE to poll
   * indefinitely.
   *
   * Poll the bus for messages. Will block while waiting for messages to come.
   * You can specify a maximum time to poll with the @timeout parameter. If
   * @timeout is negative, this function will block indefinitely.
   *
   * All messages not in @events will be popped off the bus and will be ignored.
   * It is not possible to use message enums beyond #GST_MESSAGE_EXTENDED in the
   * @events mask
   *
   * Because poll is implemented using the "message" signal enabled by
   * gst_bus_add_signal_watch(), calling gst_bus_poll() will cause the "message"
   * signal to be emitted for every message that poll sees. Thus a "message"
   * signal handler will see the same messages that this function sees -- neither
   * will steal messages from the other.
   *
   * This function will run a main loop from the default main context when
   * polling.
   *
   * You should never use this function, since it is pure evil. This is
   * especially true for GUI applications based on Gtk+ or Qt, but also for any
   * other non-trivial application that uses the GLib main loop. As this function
   * runs a GLib main loop, any callback attached to the default GLib main
   * context may be invoked. This could be timeouts, GUI events, I/O events etc.;
   * even if gst_bus_poll() is called with a 0 timeout. Any of these callbacks
   * may do things you do not expect, e.g. destroy the main application window or
   * some other resource; change other application state; display a dialog and
   * run another main loop until the user clicks it away. In short, using this
   * function may add a lot of complexity to your code through unexpected
   * re-entrancy and unexpected changes to your application's state.
   *
   * For 0 timeouts use gst_bus_pop_filtered() instead of this function; for
   * other short timeouts use gst_bus_timed_pop_filtered(); everything else is
   * better handled by setting up an asynchronous bus watch and doing things
   * from there.
   *
   * Returns: (transfer full) (nullable): the message that was received,
   *     or %NULL if the poll timed out. The message is taken from the
   *     bus and needs to be unreffed with gst_message_unref() after
   *     usage.
   */
  GstMessage *
  gst_bus_poll (GstBus * bus, GstMessageType events, GstClockTime timeout)
  {
    GstBusPollData *poll_data;
    GstMessage *ret;
    gulong id;
  
    g_return_val_if_fail (GST_IS_BUS (bus), NULL);
  
    poll_data = g_slice_new (GstBusPollData);
    poll_data->source_running = TRUE;
    poll_data->loop = g_main_loop_new (NULL, FALSE);
    poll_data->events = events;
    poll_data->message = NULL;
  
    if (timeout != GST_CLOCK_TIME_NONE)
      poll_data->timeout_id = g_timeout_add_full (G_PRIORITY_DEFAULT_IDLE,
          timeout / GST_MSECOND, (GSourceFunc) poll_timeout, poll_data,
          (GDestroyNotify) poll_destroy_timeout);
    else
      poll_data->timeout_id = 0;
  
    id = g_signal_connect_data (bus, "message", G_CALLBACK (poll_func), poll_data,
        (GClosureNotify) poll_destroy, 0);
  
    /* these can be nested, so it's ok */
    gst_bus_add_signal_watch (bus);
  
    GST_DEBUG ("running mainloop %p", poll_data->loop);
    g_main_loop_run (poll_data->loop);
    GST_DEBUG ("mainloop stopped %p", poll_data->loop);
  
    gst_bus_remove_signal_watch (bus);
  
    /* holds a ref */
    ret = poll_data->message;
  
    if (poll_data->timeout_id)
      g_source_remove (poll_data->timeout_id);
  
    /* poll_data will be freed now */
    g_signal_handler_disconnect (bus, id);
  
    GST_DEBUG_OBJECT (bus, "finished poll with message %p", ret);
  
    return ret;
  }
  
  /**
   * gst_bus_async_signal_func:
   * @bus: a #GstBus
   * @message: the #GstMessage received
   * @data: user data
   *
   * A helper #GstBusFunc that can be used to convert all asynchronous messages
   * into signals.
   *
   * Returns: %TRUE
   */
  gboolean
  gst_bus_async_signal_func (GstBus * bus, GstMessage * message, gpointer data)
  {
    GQuark detail = 0;
  
    g_return_val_if_fail (GST_IS_BUS (bus), TRUE);
    g_return_val_if_fail (message != NULL, TRUE);
  
    detail = gst_message_type_to_quark (GST_MESSAGE_TYPE (message));
  
    g_signal_emit (bus, gst_bus_signals[ASYNC_MESSAGE], detail, message);
  
    /* we never remove this source based on signal emission return values */
    return TRUE;
  }
  
  /**
   * gst_bus_sync_signal_handler:
   * @bus: a #GstBus
   * @message: the #GstMessage received
   * @data: user data
   *
   * A helper GstBusSyncHandler that can be used to convert all synchronous
   * messages into signals.
   *
   * Returns: GST_BUS_PASS
   */
  GstBusSyncReply
  gst_bus_sync_signal_handler (GstBus * bus, GstMessage * message, gpointer data)
  {
    GQuark detail = 0;
  
    g_return_val_if_fail (GST_IS_BUS (bus), GST_BUS_DROP);
    g_return_val_if_fail (message != NULL, GST_BUS_DROP);
  
    detail = gst_message_type_to_quark (GST_MESSAGE_TYPE (message));
  
    g_signal_emit (bus, gst_bus_signals[SYNC_MESSAGE], detail, message);
  
    return GST_BUS_PASS;
  }
  
  /**
   * gst_bus_enable_sync_message_emission:
   * @bus: a #GstBus on which you want to receive the "sync-message" signal
   *
   * Instructs GStreamer to emit the "sync-message" signal after running the bus's
   * sync handler. This function is here so that code can ensure that they can
   * synchronously receive messages without having to affect what the bin's sync
   * handler is.
   *
   * This function may be called multiple times. To clean up, the caller is
   * responsible for calling gst_bus_disable_sync_message_emission() as many times
   * as this function is called.
   *
   * While this function looks similar to gst_bus_add_signal_watch(), it is not
   * exactly the same -- this function enables <emphasis>synchronous</emphasis> emission of
   * signals when messages arrive; gst_bus_add_signal_watch() adds an idle callback
   * to pop messages off the bus <emphasis>asynchronously</emphasis>. The sync-message signal
   * comes from the thread of whatever object posted the message; the "message"
   * signal is marshalled to the main thread via the main loop.
   *
   * MT safe.
   */
  void
  gst_bus_enable_sync_message_emission (GstBus * bus)
  {
    g_return_if_fail (GST_IS_BUS (bus));
  
    GST_OBJECT_LOCK (bus);
    bus->priv->num_sync_message_emitters++;
    GST_OBJECT_UNLOCK (bus);
  }
  
  /**
   * gst_bus_disable_sync_message_emission:
   * @bus: a #GstBus on which you previously called
   * gst_bus_enable_sync_message_emission()
   *
   * Instructs GStreamer to stop emitting the "sync-message" signal for this bus.
   * See gst_bus_enable_sync_message_emission() for more information.
   *
   * In the event that multiple pieces of code have called
   * gst_bus_enable_sync_message_emission(), the sync-message emissions will only
   * be stopped after all calls to gst_bus_enable_sync_message_emission() were
   * "cancelled" by calling this function. In this way the semantics are exactly
   * the same as gst_object_ref() that which calls enable should also call
   * disable.
   *
   * MT safe.
   */
  void
  gst_bus_disable_sync_message_emission (GstBus * bus)
  {
    g_return_if_fail (GST_IS_BUS (bus));
    g_return_if_fail (bus->priv->num_sync_message_emitters > 0);
  
    GST_OBJECT_LOCK (bus);
    bus->priv->num_sync_message_emitters--;
    GST_OBJECT_UNLOCK (bus);
  }
  
  /**
   * gst_bus_add_signal_watch_full:
   * @bus: a #GstBus on which you want to receive the "message" signal
   * @priority: The priority of the watch.
   *
   * Adds a bus signal watch to the default main context with the given @priority
   * (e.g. %G_PRIORITY_DEFAULT). It is also possible to use a non-default main
   * context set up using g_main_context_push_thread_default()
   * (before one had to create a bus watch source and attach it to the desired
   * main context 'manually').
   *
   * After calling this statement, the bus will emit the "message" signal for each
   * message posted on the bus when the main loop is running.
   *
   * This function may be called multiple times. To clean up, the caller is
   * responsible for calling gst_bus_remove_signal_watch() as many times as this
   * function is called.
   *
   * There can only be a single bus watch per bus, you must remove any signal
   * watch before you can set another type of watch.
   *
   * MT safe.
   */
  void
  gst_bus_add_signal_watch_full (GstBus * bus, gint priority)
  {
    g_return_if_fail (GST_IS_BUS (bus));
  
    /* I know the callees don't take this lock, so go ahead and abuse it */
    GST_OBJECT_LOCK (bus);
  
    if (bus->priv->num_signal_watchers > 0)
      goto done;
  
    /* this should not fail because the counter above takes care of it */
    g_assert (!bus->priv->signal_watch);
  
    gst_bus_add_watch_full_unlocked (bus, priority, gst_bus_async_signal_func,
        NULL, NULL);
  
    if (G_UNLIKELY (!bus->priv->signal_watch))
      goto add_failed;
  
  done:
  
    bus->priv->num_signal_watchers++;
  
    GST_OBJECT_UNLOCK (bus);
    return;
  
    /* ERRORS */
  add_failed:
    {
      g_critical ("Could not add signal watch to bus %s", GST_OBJECT_NAME (bus));
      GST_OBJECT_UNLOCK (bus);
      return;
    }
  }
  
  /**
   * gst_bus_add_signal_watch:
   * @bus: a #GstBus on which you want to receive the "message" signal
   *
   * Adds a bus signal watch to the default main context with the default priority
   * (%G_PRIORITY_DEFAULT). It is also possible to use a non-default
   * main context set up using g_main_context_push_thread_default() (before
   * one had to create a bus watch source and attach it to the desired main
   * context 'manually').
   *
   * After calling this statement, the bus will emit the "message" signal for each
   * message posted on the bus.
   *
   * This function may be called multiple times. To clean up, the caller is
   * responsible for calling gst_bus_remove_signal_watch() as many times as this
   * function is called.
   *
   * MT safe.
   */
  void
  gst_bus_add_signal_watch (GstBus * bus)
  {
    gst_bus_add_signal_watch_full (bus, G_PRIORITY_DEFAULT);
  }
  
  /**
   * gst_bus_remove_signal_watch:
   * @bus: a #GstBus you previously added a signal watch to
   *
   * Removes a signal watch previously added with gst_bus_add_signal_watch().
   *
   * MT safe.
   */
  void
  gst_bus_remove_signal_watch (GstBus * bus)
  {
    GSource *source = NULL;
  
    g_return_if_fail (GST_IS_BUS (bus));
  
    /* I know the callees don't take this lock, so go ahead and abuse it */
    GST_OBJECT_LOCK (bus);
  
    if (bus->priv->num_signal_watchers == 0)
      goto error;
  
    bus->priv->num_signal_watchers--;
  
    if (bus->priv->num_signal_watchers > 0)
      goto done;
  
    GST_DEBUG_OBJECT (bus, "removing signal watch %u",
        g_source_get_id (bus->priv->signal_watch));
  
    source =
        bus->priv->signal_watch ? g_source_ref (bus->priv->signal_watch) : NULL;
  
  done:
    GST_OBJECT_UNLOCK (bus);
  
    if (source) {
      g_source_destroy (source);
      g_source_unref (source);
    }
  
    return;
  
    /* ERRORS */
  error:
    {
      g_critical ("Bus %s has no signal watches attached", GST_OBJECT_NAME (bus));
      GST_OBJECT_UNLOCK (bus);
      return;
    }
  }
  