Portability | portable (depends on GHC) |
---|---|
Stability | alpha |
Maintainer | gtk2hs-devel@lists.sourceforge.net |
An asynchronous message bus subsystem.
- data Bus
- class ObjectClass o => BusClass o
- data BusSyncReply
- type BusSyncHandler = Bus -> Message -> IO BusSyncReply
- castToBus :: GObjectClass obj => obj -> Bus
- gTypeBus :: GType
- busGetFlags :: BusClass busT => busT -> IO [BusFlags]
- busSetFlags :: BusClass busT => busT -> [BusFlags] -> IO ()
- busUnsetFlags :: BusClass busT => busT -> [BusFlags] -> IO ()
- busNew :: IO Bus
- busPost :: BusClass busT => busT -> Message -> IO Bool
- busHavePending :: BusClass busT => busT -> IO Bool
- busPeek :: BusClass busT => busT -> IO (Maybe Message)
- busPop :: BusClass busT => busT -> IO (Maybe Message)
- busTimedPop :: BusClass busT => busT -> Maybe ClockTime -> IO (Maybe Message)
- busSetFlushing :: BusClass busT => busT -> Bool -> IO ()
- busSetSyncHandler :: BusClass busT => busT -> Maybe BusSyncHandler -> IO ()
- busUseSyncSignalHandler :: BusClass busT => busT -> IO ()
- busCreateWatch :: BusClass busT => busT -> IO Source
- busAddWatch :: BusClass busT => busT -> Priority -> BusFunc -> IO HandlerId
- busDisableSyncMessageEmission :: BusClass busT => busT -> IO ()
- busEnableSyncMessageEmission :: BusClass busT => busT -> IO ()
- busAddSignalWatch :: BusClass busT => busT -> Priority -> IO ()
- busRemoveSignalWatch :: BusClass busT => busT -> IO ()
- busPoll :: BusClass busT => busT -> [MessageType] -> ClockTimeDiff -> IO Message
- busMessage :: BusClass busT => Signal busT (Message -> IO ())
- busSyncMessage :: BusClass busT => Signal busT (Message -> IO ())
Detail
The Bus
is resposible for delivering Message
s in a
first-in, first-out order, from the streaming threads to the
application.
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
class ObjectClass o => BusClass o Source
The result of a BusSyncHandler
.
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 BusSyncReplySource
castToBus :: GObjectClass obj => obj -> BusSource
Bus Operations
Get the flags set on this bus.
Set flags on this bus.
Unset flags on this bus.
:: BusClass busT | |
=> busT |
|
-> Message |
|
-> IO Bool |
|
Post a message to the bus.
:: BusClass busT | |
=> busT |
|
-> IO Bool |
|
Check if there are pending messages on the bus.
:: BusClass busT | |
=> busT |
|
-> IO (Maybe Message) | the first |
Get the message at the front of the queue. Any message returned will remain on the queue.
:: BusClass busT | |
=> busT |
|
-> IO (Maybe Message) | the first |
Get the message at the front of the queue. It will be removed from the queue.
:: BusClass busT | |
=> busT |
|
-> Maybe 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.
Use a synchronous message handler that converts all messages to signals.
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.
:: BusClass busT | |
=> busT |
|
-> Priority |
|
-> BusFunc |
|
-> 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 System.Glib.MainLoop.sourceRemove
.
busDisableSyncMessageEmissionSource
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.
busEnableSyncMessageEmissionSource
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.
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.
Remove the signal watch that was added with busAddSignalWatch
.
:: BusClass busT | |
=> busT |
|
-> [MessageType] |
|
-> ClockTimeDiff |
|
-> 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
busSyncMessage :: BusClass busT => Signal busT (Message -> IO ())Source
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.