GI.Gst.Objects.Bus

The Bus is an object responsible for delivering Message packets in a first-in first-out way from the streaming threads (see Task) 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 Source based notifications. This makes it possible to handle the delivery in the glib MainLoop.

The Source callback function busAsyncSignalFunc can be used to convert all bus messages into signal emissions.

A message is posted on the bus with the busPost method. With the busPeek and busPop methods one can look at or retrieve a previously posted message.

The bus can be polled with the busPoll 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 busPop the messages from the bus to handle them. Alternatively the application can register an asynchronous bus function using busAddWatch or gst_bus_add_watch(). This function will install a Source 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 busSetSyncHandler 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 Pipeline has one bus.

Note that a Pipeline will set its bus into flushing state when changing from READY to NULL state.

Exported types

newtype Bus

Memory-managed wrapper type.

Constructors

Bus (ManagedPtr Bus)

Instances

Eq Bus

Defined in GI.Gst.Objects.Bus

Methods

(==) :: Bus -> Bus -> Bool

(/=) :: Bus -> Bus -> Bool

GObject Bus

Defined in GI.Gst.Objects.Bus

ManagedPtrNewtype Bus

Defined in GI.Gst.Objects.Bus

Methods

toManagedPtr :: Bus -> ManagedPtr Bus

TypedObject Bus

Defined in GI.Gst.Objects.Bus

Methods

glibType :: IO GType

HasParentTypes Bus

Defined in GI.Gst.Objects.Bus

IsGValue (Maybe Bus)

Convert Bus to and from GValue. See toGValue and fromGValue.

Defined in GI.Gst.Objects.Bus

Methods

gvalueGType_ :: IO GType

gvalueSet_ :: Ptr GValue -> Maybe Bus -> IO ()

gvalueGet_ :: Ptr GValue -> IO (Maybe Bus)

type ParentTypes Bus

Defined in GI.Gst.Objects.Bus

type ParentTypes Bus = '[Object, Object]

class (GObject o, IsDescendantOf Bus o) => IsBus o

Type class for types which can be safely cast to Bus, for instance with toBus.

Instances

(GObject o, IsDescendantOf Bus o) => IsBus o

Defined in GI.Gst.Objects.Bus

toBus :: (MonadIO m, IsBus o) => o -> m Bus

Cast to Bus, for types for which this is known to be safe. For general casts, use castTo.

Methods

Click to display all available methods, including inherited ones

Methods

addControlBinding, addSignalWatch, addSignalWatchFull, addWatch, asyncSignalFunc, bindProperty, bindPropertyFull, createWatch, defaultError, disableSyncMessageEmission, enableSyncMessageEmission, forceFloating, freezeNotify, getv, hasActiveControlBindings, hasAncestor, hasAsAncestor, hasAsParent, havePending, isFloating, notify, notifyByPspec, peek, poll, pop, popFiltered, post, ref, refSink, removeControlBinding, removeSignalWatch, removeWatch, runDispose, stealData, stealQdata, suggestNextSync, syncSignalHandler, syncValues, thawNotify, timedPop, timedPopFiltered, unparent, unref, watchClosure.

Getters

getControlBinding, getControlRate, getData, getGValueArray, getName, getParent, getPathString, getPollfd, getProperty, getQdata, getValue.

Setters

setControlBindingDisabled, setControlBindingsDisabled, setControlRate, setData, setDataFull, setFlushing, setName, setParent, setProperty, setSyncHandler.

addSignalWatch

busAddSignalWatch

Arguments

:: (HasCallStack, MonadIO m, IsBus a)

=> a

bus: a Bus on which you want to receive the "message" signal

-> m ()

Adds a bus signal watch to the default main context with the default priority ( PRIORITY_DEFAULT ). It is also possible to use a non-default main context set up using mainContextPushThreadDefault (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 busRemoveSignalWatch as many times as this function is called.

addSignalWatchFull

busAddSignalWatchFull

Arguments

:: (HasCallStack, MonadIO m, IsBus a)

=> a

bus: a Bus on which you want to receive the "message" signal

-> Int32

priority: The priority of the watch.

-> m ()

Adds a bus signal watch to the default main context with the given priority (e.g. PRIORITY_DEFAULT). It is also possible to use a non-default main context set up using mainContextPushThreadDefault (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 MainLoop is running.

This function may be called multiple times. To clean up, the caller is responsible for calling busRemoveSignalWatch 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.

addWatch

busAddWatch

Arguments

:: (HasCallStack, MonadIO m, IsBus a)

=> a

bus: a Bus to create the watch for.

-> Int32

priority: The priority of the watch.

-> BusFunc

func: A function to call when a message is received.

-> m Word32

Returns: The event source id or 0 if bus already got an event source.

Adds a bus watch to the default main context with the given priority (e.g. PRIORITY_DEFAULT). It is also possible to use a non-default main context set up using mainContextPushThreadDefault (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 MainLoop 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 busRemoveWatch 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 sourceRemove.

The bus watch will take its own reference to the bus, so it is safe to unref bus using objectUnref after setting the bus watch.

asyncSignalFunc

busAsyncSignalFunc

Arguments

:: (HasCallStack, MonadIO m, IsBus a)

=> a

bus: a Bus

-> Message

message: the Message received

-> Ptr ()

data: user data

-> m Bool

Returns: True

A helper BusFunc that can be used to convert all asynchronous messages into signals.

createWatch

busCreateWatch

Arguments

:: (HasCallStack, MonadIO m, IsBus a)

=> a

bus: a Bus to create the watch for

-> m (Maybe Source)

Returns: a Source that can be added to a MainLoop.

Create watch for this bus. The Source will be dispatched whenever a message is on the bus. After the GSource is dispatched, the message is popped off the bus and unreffed.

As with other watches, there can only be one watch on the bus, including any signal watch added with gst_bus_add_signal_watch.

disableSyncMessageEmission

busDisableSyncMessageEmission

Arguments

:: (HasCallStack, MonadIO m, IsBus a)

=> a

bus: a Bus on which you previously called busEnableSyncMessageEmission

-> m ()

Instructs GStreamer to stop emitting the "sync-message" signal for this bus. See busEnableSyncMessageEmission for more information.

In the event that multiple pieces of code have called busEnableSyncMessageEmission, the sync-message emissions will only be stopped after all calls to busEnableSyncMessageEmission were "cancelled" by calling this function. In this way the semantics are exactly the same as objectRef that which calls enable should also call disable.

enableSyncMessageEmission

busEnableSyncMessageEmission

Arguments

:: (HasCallStack, MonadIO m, IsBus a)

=> a

bus: a Bus on which you want to receive the "sync-message" signal

-> m ()

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 busDisableSyncMessageEmission as many times as this function is called.

While this function looks similar to busAddSignalWatch, it is not exactly the same -- this function enables *synchronous* emission of signals when messages arrive; busAddSignalWatch adds an idle callback to pop messages off the bus *asynchronously*. 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 MainLoop.

getPollfd

busGetPollfd

Arguments

:: (HasCallStack, MonadIO m, IsBus a)

=> a

bus: A Bus

-> m PollFD

Gets the file descriptor from the bus which can be used to get notified about messages being available with functions like poll, and allows integration into other event loops based on file descriptors. Whenever a message is available, the POLLIN / IOConditionIn event is set.

Warning: NEVER read or write anything to the returned fd but only use it for getting notifications via poll or similar and then use the normal GstBus API, e.g. busPop.

Since: 1.14

havePending

busHavePending

Arguments

:: (HasCallStack, MonadIO m, IsBus a)

=> a

bus: a Bus to check

-> m Bool

Returns: True if there are messages on the bus to be handled, False otherwise.

Checks if there are pending messages on the bus that should be handled.

new

busNew

Arguments

:: (HasCallStack, MonadIO m)

=> m Bus

Returns: a new Bus instance

Creates a new Bus instance.

peek

busPeek

Arguments

:: (HasCallStack, MonadIO m, IsBus a)

=> a

bus: a Bus

-> m (Maybe Message)

Returns: the Message that is on the bus, or Nothing if the bus is empty.

Peeks the message on the top of the bus' queue. The message will remain on the bus' message queue.

poll

busPoll

Arguments

:: (HasCallStack, MonadIO m, IsBus a)

=> a

bus: a Bus

-> [MessageType]

events: a mask of MessageType, representing the set of message types to poll for (note special handling of extended message types below)

-> Word64

timeout: the poll timeout, as a GstClockTime, or CLOCK_TIME_NONE to poll indefinitely.

-> m (Maybe Message)

Returns: the message that was received, or Nothing if the poll timed out.

Polls 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 busAddSignalWatch, calling busPoll 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 MainLoop 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 busPoll 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 busPopFiltered instead of this function; for other short timeouts use busTimedPopFiltered; everything else is better handled by setting up an asynchronous bus watch and doing things from there.

pop

busPop

Arguments

:: (HasCallStack, MonadIO m, IsBus a)

=> a

bus: a Bus to pop

-> m (Maybe Message)

Returns: the Message that is on the bus, or Nothing if the bus is empty.

Gets a message from the bus.

popFiltered

busPopFiltered

Arguments

:: (HasCallStack, MonadIO m, IsBus a)

=> a

bus: a Bus to pop

-> [MessageType]

types: message types to take into account

-> m (Maybe Message)

Returns: the next Message matching type that is on the bus, or Nothing if the bus is empty or there is no message matching type.

Gets 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.

post

busPost

Arguments

:: (HasCallStack, MonadIO m, IsBus a)

=> a

bus: a Bus to post on

-> Message

message: the Message to post

-> m Bool

Returns: True if the message could be posted, False if the bus is flushing.

Posts a message on the given bus. Ownership of the message is taken by the bus.

removeSignalWatch

busRemoveSignalWatch

Arguments

:: (HasCallStack, MonadIO m, IsBus a)

=> a

bus: a Bus you previously added a signal watch to

-> m ()

Removes a signal watch previously added with busAddSignalWatch.

removeWatch

busRemoveWatch

Arguments

:: (HasCallStack, MonadIO m, IsBus a)

=> a

bus: a Bus to remove the watch from.

-> m Bool

Returns: True on success or False if bus has no event source.

Removes an installed bus watch from bus.

Since: 1.6

setFlushing

busSetFlushing

Arguments

:: (HasCallStack, MonadIO m, IsBus a)

=> a

bus: a Bus

-> Bool

flushing: whether or not to flush the bus

-> m ()

If flushing, flushes out and unrefs any messages queued in the bus. Releases references to the message origin objects. Will flush future messages until busSetFlushing sets flushing to False.

setSyncHandler

busSetSyncHandler

Arguments

:: (HasCallStack, MonadIO m, IsBus a)

=> a

bus: a Bus to install the handler on

-> Maybe BusSyncHandler

func: The handler function to install

-> m ()

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.

Before 1.16.3 it was not possible to replace an existing handler and clearing an existing handler with Nothing was not thread-safe.

syncSignalHandler

busSyncSignalHandler

Arguments

:: (HasCallStack, MonadIO m, IsBus a)

=> a

bus: a Bus

-> Message

message: the Message received

-> Ptr ()

data: user data

-> m BusSyncReply

Returns: BusSyncReplyPass

A helper BusSyncHandler that can be used to convert all synchronous messages into signals.

timedPop

busTimedPop

Arguments

:: (HasCallStack, MonadIO m, IsBus a)

=> a

bus: a Bus to pop

-> Word64

timeout: a timeout

-> m (Maybe Message)

Returns: the Message that is on the bus after the specified timeout or Nothing if the bus is empty after the timeout expired.

Gets a message from the bus, waiting up to the specified timeout.

If timeout is 0, this function behaves like busPop. If timeout is CLOCK_TIME_NONE, this function will block forever until a message was posted on the bus.

timedPopFiltered

busTimedPopFiltered

Arguments

:: (HasCallStack, MonadIO m, IsBus a)

=> a

bus: a Bus to pop from

-> Word64

timeout: a timeout in nanoseconds, or CLOCK_TIME_NONE to wait forever

-> [MessageType]

types: message types to take into account, MessageTypeAny for any type

-> m (Maybe Message)

Returns: a Message matching the filter in types, or Nothing if no matching message was found on the bus until the timeout expired.

Gets 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 busPopFiltered. If timeout is CLOCK_TIME_NONE, this function will block forever until a matching message was posted on the bus.

Properties

enableAsync

Enables async message delivery support for bus watches, busPop and similar API. Without this only the synchronous message handlers are called.

This property is used to create the child element buses in Bin.

constructBusEnableAsync :: (IsBus o, MonadIO m) => Bool -> m (GValueConstruct o)

Construct a GValueConstruct with valid value for the “enable-async” property. This is rarely needed directly, but it is used by new.

Signals

message

type BusMessageCallback

Arguments

 = Message

message: the message that has been posted asynchronously

-> IO ()

A message has been posted on the bus. This signal is emitted from a Source added to the mainloop. this signal will only be emitted when there is a MainLoop running.

afterBusMessage :: (IsBus a, MonadIO m) => a -> Maybe Text -> ((?self :: a) => BusMessageCallback) -> m SignalHandlerId

Connect a signal handler for the message signal, to be run after the default handler. When overloading is enabled, this is equivalent to

after bus #message callback

This signal admits a optional parameter detail. If it's not Nothing, we will connect to “message::detail” instead.

By default the object invoking the signal is not passed to the callback. If you need to access it, you can use the implit ?self parameter. Note that this requires activating the ImplicitParams GHC extension.

onBusMessage :: (IsBus a, MonadIO m) => a -> Maybe Text -> ((?self :: a) => BusMessageCallback) -> m SignalHandlerId

Connect a signal handler for the message signal, to be run before the default handler. When overloading is enabled, this is equivalent to

on bus #message callback

This signal admits a optional parameter detail. If it's not Nothing, we will connect to “message::detail” instead.

syncMessage

type BusSyncMessageCallback

Arguments

 = Message

message: the message that has been posted synchronously

-> IO ()

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 busEnableSyncMessageEmission before.

afterBusSyncMessage :: (IsBus a, MonadIO m) => a -> Maybe Text -> ((?self :: a) => BusSyncMessageCallback) -> m SignalHandlerId

Connect a signal handler for the syncMessage signal, to be run after the default handler. When overloading is enabled, this is equivalent to

after bus #syncMessage callback

This signal admits a optional parameter detail. If it's not Nothing, we will connect to “sync-message::detail” instead.

By default the object invoking the signal is not passed to the callback. If you need to access it, you can use the implit ?self parameter. Note that this requires activating the ImplicitParams GHC extension.

onBusSyncMessage :: (IsBus a, MonadIO m) => a -> Maybe Text -> ((?self :: a) => BusSyncMessageCallback) -> m SignalHandlerId

Connect a signal handler for the syncMessage signal, to be run before the default handler. When overloading is enabled, this is equivalent to

on bus #syncMessage callback

This signal admits a optional parameter detail. If it's not Nothing, we will connect to “sync-message::detail” instead.