BTimedEventQueue

Derived from: (none)
Declared in:  be/media/TimedEventQueue.h
Library: libmedia.so
Allocation: Constructor only
Summary:  more...

The BTimedEventQueue class provides an easy way to queue a sequence of events within your node. You can use it to queue up start, stop, and seek requests, and to queue up incoming data buffers in preparation for handling them. Each queue element is tagged with the time at which the event should be processed, and functions are provided for locating the next event that should be handled.

Although you shouldn't need to subclass BTimedEventQueue, there's no reason you can't do it.

Cleaning Up After Nodes

Each event has a cleanup flag associated with it that indicates what sort of special action needs to be performed when the event is removed from the queue. If this value is B_NO_CLEANUP, nothing is done. If it's B_RECYCLE, and the event is a B_HANDLE_BUFFER event, BTimedEventQueue will automatically recycle the buffer associated with the event.

If the cleanup flag is B_DELETE or is B_USER_CLEANUP or greater, the cleanup hook function will be called. You can implement and establish a cleanup hook function to handle deleting event data yourself. The hook function is of type cleanup_hook:

typedef void (*cleanup_hook)(void *context, bigtime_t time, int32 what,          void *pointer, uint32 pointerCleanup, int64 data);

You specify the cleanup hook function by calling SetCleanupHook(), like this:

SetCleanupHook(MyCleanupFunction, contextPtr);

The contextPtr is a pointer that your cleanup hook function uses, and can contain whatever data you require.

Constructor and Destructor

BTimedEventQueue()

BTimedEventQueue()

Initializes a new, empty, timed event queue.

~BTimedEventQueue()

virtual ~BTimedEventQueue()

Flushes the queue and deallocates memory allocated by the object.

Member Functions

AddEvent()

status_t AddEvent(const media_timed_event &event)

Adds the specified event to the queue.

RETURN CODES

• B_OK. The event was added.

• B_BAD_VALUE. Unknown or invalid event type (you can't use B_NO_EVENT or B_ANY_EVENT).

• B_NO_INIT. The queue hasn't been initialized.

DoForEach()

status_t DoForEach(for_each_hook hook, void *context,       bigtime_t time,       time_direction direction,       bool inclusive = true,       int32 event = B_ANY_EVENT)

For each event in the queue matching the specified parameters, the hook function is called. The context pointer is passed through to the hook function, and may point to anything your hook function requires.

• Setting direction to B_ALWAYS indicates that all events of the type indicated by event should be processed. The time and includive arguments are ignored.

• Setting direction to B_BEFORE_TIME indicates that all matching events occurring before the specified time should be processed. If inclusive is true, events occurring at time are also processed.

• Setting direction to B_AT_TIME processes all matching events scheduled at the specified time. The inclusive argument is ignored.

• If direction is B_AFTER_TIME, all matching events scheduled to occur after the specified time are processed. If inclusive is true, events scheduled to occur at time are also processed.

This provides a means for you to scan through the queue and perform a particular act on every node (or all nodes of a certain type, or that occur at certain times). If you want to process all events, you can specify a time of B_INFINITE_TIMEOUT and a direction of B_BEFORE_TIME.

The hook function should return a queue_action value.

queue_action MyHook(media_timed_event *event, void *context) {    if (event->data == 0) {       /* countdown finished, do something */       return BTimedEventQueue::B_REMOVE_EVENT;    }    event->data--;    return BTimedEventQueue::B_NO_ACTION; }

In this example, the hook function processes the event (and indicates on return that it should be removed from the queue) if the data field of the event structure is zero; otherwise data is decremented and the event is left alone.

RETURN CODES

• B_OK. The events were processed.

• B_ERROR. An undefined error occurred.

EventCount()

int32 EventCount(void) const

Returns the number of events in the queue.

FindFirstMatch()

const media_timed_event *FindFirstMatch(bigtime_t eventTime,       time_direction direction,       bool inclusive = true,       int32 eventType = B_ANY_EVENT)

Searches the event queue for the first event matching the given specifications. The search begins at the time specified by eventTime, and progresses in the specified direction.

• Setting direction to B_ALWAYS indicates that all events of the type indicated by event should be scanned. The eventTime and includive arguments are ignored.

• Setting direction to B_BEFORE_TIME indicates that all matching events occurring before the specified eventTime should be scanned. If inclusive is true, events occurring at eventTime are also scanned.

• Setting direction to B_AT_TIME scans all matching events scheduled at the specified eventTime. The inclusive argument is ignored.

• If direction is B_AFTER_TIME, all matching events scheduled to occur after the specified eventTime are scanned. If inclusive is true, events scheduled to occur at eventTime are also scanned.

If you want to scan all events, you can specify a time of B_INFINITE_TIMEOUT and a direction of B_BEFORE_TIME.

If no matching event is found, NULL is returned.

FirstEvent() , FirstEventTime()

const media_timed_event *FirstEvent(void) const bigtime_t FirstEventTime(void) const

FirstEvent() returns the first event in the queue, without removing it from the queue.

FirstEventTime() returns the first event's time, in microseconds.

RETURN CODES

• B_OK. No error occurred.

• B_NO_INIT. The queue hasn't been initialized.

• B_INFINITE_TIMEOUT. The queue is empty (FirstEventTime() only).

FlushEvents()

status_t FlushEvents(bigtime_t time, time_direction direction,       bool inclusive = true,       int32 event = B_ANY_EVENT)

Flushes the specified events from the queue. You specify which events to flush by indicating a time from which events should be flushed, a direction in which to search for events to flush, and the type of events to flush:

• Setting direction to B_ALWAYS indicates that all events of the type indicated by event should be flushed. The time and includive arguments are ignored.

• Setting direction to B_BEFORE_TIME indicates that all matching events occurring before the specified time should be flushed. If inclusive is true, events occurring at time are also flushed.

• Setting direction to B_AT_TIME flushes all matching events scheduled at the specified time. The inclusive argument is ignored.

• If direction is B_AFTER_TIME, all matching events scheduled to occur after the specified time are flushed. If inclusive is true, events scheduled to occur at time are also flushed.

If you want to flush all events, you can specify a time of B_INFINITE_TIMEOUT and a direction of B_BEFORE_TIME.

RETURN CODES

• B_OK. The events were flushed.

• B_ERROR. An undefined error occurred.

HasEvents()

bool HasEvents(void)

Returns true if there are events in the queue, otherwise returns false.

LastEvent() , LastEventTime()

const media_timed_event *LastEvent(void) const bigtime_t LastEventTime(void) const

LastEvent() returns the last event in the queue, without removing it from the queue.

LastEventTime() returns the last event's time, in microseconds.

RETURN CODES

• B_OK. No error occurred.

• B_NO_INIT. The queue hasn't been initialized.

• B_INFINITE_TIMEOUT. The queue is empty (LastEventTime() only).

RemoveEvent() , RemoveFirstEvent()

status_t RemoveEvent(const media_timed_event *event) status_t RemoveFirstEvent(const media_timed_event *outEvent = NULL)

RemoveEvent() removes the specified event from the queue.

RemoveFirstEvent() removes the first event from the queue. If outEvent isn't NULL, the specified buffer is filled with a copy of the event that's been removed.

RETURN CODES

• B_OK. The event was removed.

• B_NO_INIT. The queue hasn't been initialized.

SetCleanupHook()

void SetCleanupHook(cleanup_hook hook, void *context)

Sets up the cleanup hook function specified by hook to be called for events as they're removed from the queue. The hook will be called only for events with cleanup_flag values of B_DELETE or B_USER_CLEANUP or greater.

Constants

cleanup_flag

Declared in:  be/media/TimedEventQueue.h

Constant	Description
B_NO_CLEANUP	Don't clean up when the event is removed from the queue.
B_RECYCLE_BUFFER	BTimedEventQueue should recycle the buffer when the buffer event is removed from the queue.
B_EXPIRE_TIMER	Call TimerExpired() on the event's data field.
B_USER_CLEANUP	Base value for user-defined cleanup types.

These values define how BTimedEventQueue should handle removing events from the queue. If the flag is B_USER_CLEANUP or greater, the cleanup hook function is called when the event is removed.

event_type

Declared in:  be/media/TimedEventQueue.h

Constant	Description
B_NO_EVENT	Don't push buffers of this type. It's a return value only.
B_ANY_EVENT	Don't push buffers of this type; it's used in searches only.
B_START	A start event.
B_STOP	A stop event.
B_SEEK	A seek event.
B_WARP	A warp event.
B_TIMER	A timer event.
B_HANDLE_BUFFER	Represents a buffer queued to be handled. The event's pointer is a pointer to a BBuffer object.
B_DATA_STATUS	Represents a data status event.
B_HARDWARE	A hardware event.
B_PARAMETER	The buffer contains changes to parameter values; pass it to BControllable::ApplyParameterData().
B_USER_EVENT	Base value for user-defined events.

These values describe type types of events that a BTimedEventQueue can handle.

queue_action

Declared in:  be/media/TimedEventQueue.h

Constant	Description
B_DONE	End the DoForEach() pass.
B_NO_ACTION	Do nothing for this event.
B_REMOVE_EVENT	Remove the event.
B_RESORT_QUEUE	Sort the queue again to ensure that events are still in the right order.

These queue action values are returned by the hook function used by DoForEach(); these values indicate what DoForEach() should do to the event after the hook has processed it.

time_direction

Declared in:  be/media/TimedEventQueue.h

Constant	Description
B_ALWAYS	Matches events occurring at any time.
B_BEFORE_TIME	Matches events occurring before a specified time.
B_AT_TIME	Matches events occurring at a specified time.
B_AFTER_TIME	Matches events occurring after a specified time.

These values are used to indicate a search direction through the time continuum.

Defined Types

cleanup_hook

Declared in:  be/media/TimedEventQueue.h

typedef queue_action (*cleanup_hook)(media_timed_event *event, void *context);

The cleanup_hook type is used to define a hook function called while removing an event from the queue; it's set by calling SetCleanupHook().

for_each_hook

Declared in:  be/media/TimedEventQueue.h

typedef queue_action (*for_each_hook)(media_timed_event *event, void *context);

The for_each_hook type is used to define a hook function called by DoForEach().

media_timed_event

Declared in:  be/media/TimedEventQueue.h

struct media_timed_event {    media_timed_event();    media_timed_event(bigtime_t inTime, int32 inType);    media_timed_event(bigtime_t inTime, int32 inType, void *inPointer,             uint32 inCleanup);    media_timed_event(bigtime_t inTime, int32 inType,             void *inPointer, uint32 inCleanup,             int32 inData, int64 inBigdata,             char *inUserData, size_t dataSize = 0);    media_timed_event(const media_timed_event &clone);    void operator=(const media_timed_event &clone);    ~media_timed_event();    bigtime_t event_time;    int32 type;    void *pointer;    uint32 cleanup;    int32 data;    int64 bigdata;    char user_data[64];    uint32 _reserved_media_timed_event_[8]; };

Describes a media event:

• event_time indicates the time at which the event is scheduled to occur.

• type indicates the type of event, as an event_type.

• pointer is a pointer to event-specific data owned by the event.

• cleanup is the cleanup_flag value for the event.

• data is an event-specific 32-bit value.

• bigdata is an event-specific 64-bit value.

• user_data is user-defined data.