Microsoft Windows CE 3.0  

COutputQueue Class

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Output pins use the COutputQueueto send samples to another filter by using the local memory-based transport (that is, to input pins that support the IMemInputPininterface). COutputQueueuses IMemInputPin::ReceiveCanBlockto determine if the connected input pin has a blocking implementation of IMemInputPin::Receive. If so, all samples are queued in COutputQueueand a thread is created to pass samples from the queue to the connected input pin. If the input pin's IMemInputPin::Receivemethod does not block, samples are passed directly to IMemInputPin::Receive. COutputQueuecan also batch samples to reduce the number of calls to the downstream pin.

COutputQueueis useful when the filter has other work to do while samples that it has already completed are being processed downstream. This occurs, for example, in a filter that can read more data off disk while data is being processed, or when it has more than one output pin and does not want to starve an output pin because IMemInputPin::Receivehas no optional batching of samples.

To use this class, create one COutputQueueobject for every output pin for which it will be used. This can either be created when the pin is created and deleted when the pin is disconnected, or it can be created when the pin goes active and deleted when the pin goes inactive.

The samples sent to this object by calling its COutputQueue::Receiveor COutputQueue::ReceiveMultiplemember function should have references added by means of IUnknown::AddRef(as they usually are if they were obtained directly from an allocator). This object then calls IUnknown::Releaseon all samples it receives, whether they were processed successfully or not. Note that Releaseis not called for special (control) samples.

Some control information, such as end of stream, needs to be queued with the data and processed once all the data has been delivered. This information is queued in the form of special control packets. COutputQueueimplements a sticky HRESULTso it will not send any more data after it gets a return code that is not S_OK from the downstream ReceiveMultiplecall. (A sticky state setting is one that persists even after execution of operations that would usually reset the setting.) This sticky state is reset by the EndFlushand EOScalls. However, if the sticky HRESULTis not S_OK, EOSitself is not sent downstream; the HRESULTis just reset. Because of this, if this object is not deleted when the pin goes inactive, BeginFlushand EndFlushshould be called at that time to free the state.

In many ways this object acts as a proxy for the connected input pin, supporting a similar set of methods for stream control.

Protected Data Members

m_bBatchExact TRUE if commands are batched; FALSE if commands are sent singly.
m_bFlushed Flag to signify if samples have been flushed.
m_bFlushing Flag for flushing state.
m_bSendAnyway Flag to override batch processing.
m_bTerminate Termination flag.
m_evFlushComplete Event signaling that flushing has finished.
m_hSem Handle used for signaling.
m_hr HRESULTstructure for return values; used to implement a sticky return value (one that persists even after operations that would usually change the value).
m_hThread Worker thread handle.
m_lBatchSize Work in batches of this batch size. Ignored if m_bBatchExactis not TRUE.
m_List Pointer to a CSampleListobject. The class CSampleListis a generic list ( CGenericList) of objects of IMediaSampletype. It is defined as follows:
typedef CGenericList<IMediaSample>
m_lWaiting Variable set to nonzero value when waiting for a free element.
m_nBatched Number of samples currently batched awaiting processing.
m_pInputPin Pointer to the connected input pin.
m_pPin Pointer to the output pin.
m_ppSamples Pointer to an array of batched samples.

Member Functions

BeginFlush Causes all unsent samples to be discarded and sets flushing state.
COutputQueue Constructs a COutputQueueobject.
EndFlush Finalizes flush of batched or queued samples and resets flushing state.
EOS Queues an end-of-stream call to the connected input pin after all batched and queued samples have been passed to the input pin.
FreeSamples Removes and releases batched and queued samples.
InitialThreadProc Executed by the thread on thread creation.
IsIdle Determines if the output queue is idle.
IsQueued Determines if samples are being queued or being sent directly.
IsSpecialSample Determines if the sample is a control sample.
NotifyThread Notifies the thread that there is something to do.
NewSegment Queues an IPin::NewSegmentcall to the connected input pin after all queued samples have been passed to the input pin.
QueueSample Queues the prepared sample.
Receive Passes in a single sample to send to the input pin.
ReceiveMultiple Passes a set of samples to send to the input pin.
Reset Resets the deferred return code m_hrto allow the output queue to be ready for more data.
SendAnyway Frees any batches samples to be sent to the input pin.
ThreadProc Implements the thread that sends samples downstream.