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Although you shouldn't need to subclass BTimedEventQueue, there's no reason you can't do it.
Cleaning Up After NodesEach 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()
Initializes a new, empty, timed event queue.
~BTimedEventQueue()
Flushes the queue and deallocates memory allocated by the object.
Member Functions
AddEvent()
Adds the specified event to the queue. RETURN CODES B_OK. The event was added.
DoForEach()
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.
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.
EventCount()
Returns the number of events in the queue.
FindFirstMatch()
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.
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()
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.
FlushEvents()
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:
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.
HasEvents()
Returns true if there are events in the queue, otherwise returns false.
LastEvent() , LastEventTime()
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.
RemoveEvent() , RemoveFirstEvent()
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.
SetCleanupHook()
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_flagDeclared in: <be/media/TimedEventQueue.h>
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_typeDeclared in: <be/media/TimedEventQueue.h>
These values describe type types of events that a BTimedEventQueue can handle.
queue_actionDeclared in: <be/media/TimedEventQueue.h>
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_directionDeclared in: <be/media/TimedEventQueue.h>
These values are used to indicate a search direction through the time continuum.
Defined Types
cleanup_hookDeclared 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_hookDeclared 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_eventDeclared 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:
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