Media.Streaming.GStreamer.Core.Bus

Since the application typically only wants to deal with delivery of these messages from one thread, the Bus will marshal the messages between different threads. This is important since the actual streaming of media is done in a thread separate from the application.

The Bus provides support for Source based notifications. This makes it possible to handle the delivery in the GLib Source.

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 pop the messages from the bus to handle them. Alternatively the application can register an asynchronous bus function using busAddWatch. 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 StateReady to StateNull.

Types

data Bus

Instances

BusClass Bus

GObjectClass Bus

ObjectClass Bus

class ObjectClass o => BusClass o

Instances

BusClass Bus

The result of a BusSyncHandler.

data BusSyncReply

Instances

Enum BusSyncReply

Eq BusSyncReply

Show BusSyncReply

A handler that will be invoked synchronously when a new message is injected into the bus. This function is mostly used internally. Only one sync handler may be attached to a given bus.

type BusSyncHandler = Bus -> Message -> IO BusSyncReply

castToBus :: GObjectClass obj => obj -> Bus

toBus :: BusClass o => o -> Bus

Bus Operations

busGetFlags

:: BusClass busT
=> busT	`bus` - a `Bus`
-> IO [BusFlags]	the flags set on `bus`
Get the flags set on this bus.

busSetFlags

:: BusClass busT
=> busT	`bus` - a `Bus`
-> [BusFlags]	the flags to set on `bus`
-> IO ()
Set flags on this bus.

busUnsetFlags

:: BusClass busT
=> busT	`bus` - a `Bus`
-> [BusFlags]	the flags to unset on `bus`
-> IO ()
Unset flags on this bus.

busNew

:: IO Bus	the newly created `Bus` object
Create a new bus.

busPost

:: BusClass busT
=> busT	`bus` - a `Bus`
-> Message	`message` - the message to post
-> IO Bool	True if the message was posted, or False if the bus is flushing
Post a message to the bus.

busHavePending

:: BusClass busT
=> busT	`bus` - a `Bus`
-> IO Bool	True if there are messages on the bus to be handled, otherwise False
Check if there are pending messages on the bus.

busPeek

:: BusClass busT
=> busT	`bus` - a `Bus`
-> IO (Maybe Message)	the first `Message` on the bus, or Nothing if the bus is empty
Get the message at the front of the queue. Any message returned will remain on the queue.

busPop

:: BusClass busT
=> busT	`bus` - a `Bus`
-> IO (Maybe Message)	the first `Message` on the bus, or Nothing if the bus is empty
Get the message at the front of the queue. It will be removed from the queue.

busTimedPop

:: BusClass busT
=> busT	`bus` - a `Bus`
-> Maybe ClockTime	`timeoutM` - the time to wait for, or Nothing to wait forever
-> IO (Maybe Message)	the first message recieved, or Nothing if the timeout has expired
Get a message from the bus, waiting up to the specified timeout. If the time given is Nothing, the function will wait forever. If the time given is `0`, the function will behave like `busPop`. Since 0.10.12.

busSetFlushing

:: BusClass busT
=> busT	`bus` - a `Bus`
-> Bool	`flushing` - the new flushing state
-> IO ()
If `flushing` is True, the bus will flush out any queued messages, as well as any future messages, until the function is called with `flushing` set to False.

busSetSyncHandler

:: BusClass busT
=> busT	`bus` - a `Bus`
-> Maybe BusSyncHandler	`busSyncHandlerM` - the new `BusSyncHandler`
-> IO ()
Set the synchronous message handler on the bus. The function will be called every time a new message is posted to the bus. Note that the function will be called from the thread context of the poster. Calling this function will replace any previously set sync handler. If Nothing is passed to this function, it will unset the handler.

busUseSyncSignalHandler

:: BusClass busT
=> busT	`bus` - a `Bus`
-> IO ()
Use a synchronous message handler that converts all messages to signals.

busCreateWatch

:: BusClass busT
=> busT	`bus` - a `Bus`
-> IO Source	the new event `Source`
Create a watch for the bus. The `Source` will dispatch a signal whenever a message is on the bus. After the signal is dispatched, the message is popped off the bus.

busAddWatch

:: BusClass busT
=> busT	`bus` - a `Bus`
-> Priority	`priority` - the priority of the watch
-> BusFunc	`func` - the action to perform when a message is recieved
-> IO HandlerId	the event source ID
Adds a bus watch to the default main context with the given priority. This function is used to receive asynchronous messages in the main loop. The watch can be removed by calling `sourceRemove`.

busDisableSyncMessageEmission

:: BusClass busT
=> busT	`bus` - a `Bus`
-> IO ()
Instructs GStreamer to stop emitting the `busSyncMessage` 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.

busEnableSyncMessageEmission

:: BusClass busT
=> busT	`bus` - a `Bus`
-> IO ()
Instructs GStreamer to emit the `busSyncMessage` signal after running the bus's sync handler. This function is here so that programmers 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 `busSyncMessage` signal comes from the thread of whatever object posted the message; the `busMessage` signal is marshalled to the main thread via the main loop.

busAddSignalWatch

:: BusClass busT
=> busT	`bus` - a `Bus`
-> Priority	`priority` - the priority of the watch
-> IO ()
Adds a bus signal watch to the default main context with the given priority. After calling this method, the bus will emit the `busMessage` 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.

busRemoveSignalWatch

:: BusClass busT
=> busT	`bus` - a `Bus`
-> IO ()
Remove the signal watch that was added with `busAddSignalWatch`.

busPoll

:: BusClass busT
=> busT	`bus` - a `Bus`
-> [MessageType]	`events` - the set of messages to poll for
-> ClockTimeDiff	`timeout` - the time to wait, or -1 to wait indefinitely
-> IO Message
Poll the bus for a message. Will block while waiting for messages to come. You can specify the maximum amount of time to wait with the `timeout` parameter. If `timeout` is negative, the function will wait indefinitely. Messages not in `events` will be popped off the bus and ignored. Because `busPoll` is implemented using the `busMessage` signal enabled by `busAddSignalWatch`, calling `busPoll` will cause the `busMessage` signal to be emitted for every message that the function sees. Thus, a `busMessage` signal handler will see every message that `busPoll` sees -- neither will steal messages from the other. This function will run a main loop in the default main context while polling.

Bus Signals

busMessage :: BusClass busT => Signal busT (Message -> IO ())

A message has been posted on the bus. This signal is emitted from a Source added to the MainLoop, and only when it is running.

busSyncMessage :: BusClass busT => Signal busT (Message -> 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 must first call busUseSyncSignalHandler if you want this signal to be emitted when a message is posted on the bus.

Produced by Haddock version 0.8