The CCmdQueue class is a base class that provides a queue of CDeferredCommand objects and member functions to add, remove, check status, and invoke the queued commands. A CCmdQueue object is a part of an object that implements IQueueCommand methods. The filter graph manager implements IQueueCommand methods so that applications can queue commands to the filter graph. Filters that implement the IQueueCommand interface directly use this class. If you want to use CDeferredCommand objects, your queue must be derived from this class.
There are two modes of synchronization: coarse and accurate. In coarse mode, the application waits until a specified time arrives and then executes the command. In accurate mode, the application waits until processing begins on the sample that appears at the time, and then executes the command. The filter determines which one it will implement. The filter graph manager always implements coarse mode for commands that are queued at the filter graph manager.
If you want coarse synchronization, you probably want to wait until there is a command due, and then execute it. You can do this by calling CCmdQueue::GetDueCommand. If you have several things to wait for, get the event handle from CCmdQueue::GetDueHandle and then call CCmdQueue::GetDueCommand when this is signaled. stream time will advance only between calls to the CCmdQueue::Run and CCmdQueue::EndRun member functions. There is no guarantee that if the handle is set, there will be a command ready. Each time the event is signaled, call the GetDueCommand member function (probably with a time-out of zero); this can return E_ABORT if no command is ready.
If you want accurate synchronization, call the CCmdQueue::GetCommandDueFor member function and pass the samples you are about to process as a parameter. This returns the following:
If you want accurate synchronization for samples that might be processed during paused mode, you must use stream-time commands.
In all cases, commands remain queued until called or canceled. The setting and resetting of the event handle is managed entirely by this queue object.
m_bRunning Flag for running state; set TRUE when running. m_dwAdvise Advise identifier from the reference clock (zero if no outstanding advise). m_evDue Sets the time when any commands are due. m_listPresentation Stores commands queued in presentation time. m_listStream Stores commands queued in stream time. m_Lock Protects access to lists. m_pClock Current reference clock. m_StreamTimeOffset Contains the stream time offset when m_bRunning is true. m_tCurrentAdvise Advise time is for this presentation time.
CCmdQueue Constructs a CCmdQueue object. CheckTime Determines if a given time is due. GetDueHandle Retrieves the event handle that will be signaled.
EndRun Switches to stopped or paused mode. GetCommandDueFor Retrieves a deferred command that is scheduled at a specified time. GetDueCommand Retrieves a pointer to the next command that is due. Insert Adds the CDeferredCommand object to the queue. New Initializes a command to be run and returns a new CDeferredCommand object. Remove Removes the CDeferredCommand object from the queue. Run Switches to running mode. SetSyncSource Sets the clock used for timing. SetTimeAdvise Sets up a timer event with the reference clock.
Constructs a CCmdQueue object.
Syntax
CCmdQueue(void);
Return Value
No return value.
Determines if a specified time is due.
Syntax
BOOL CheckTime( CRefTime time, BOOL bStream );
Parameters
- time
- Time to check.
- bStream
- TRUE if the time parameter is a stream-time value; FALSE if time is a presentation-time value.
Return Value
Returns TRUE if the specified time has not yet passed.
Switches to the stopped or paused mode.
Syntax
virtual HRESULT EndRun(void);
Return Value
Returns an HRESULT value that depends on the implementation. The HRESULT indicates the error and can be one of the following standard constants, or other values not listed.
E_FAIL Failure. E_POINTER Null pointer argument. E_INVALIDARG Invalid argument. S_OK or NOERROR Success.
Remarks
Time mapping between stream time and presentation time is not known after this member function has been called. Call the CCmdQueue::Run member function to carry out this mapping.
Retrieves a deferred command that is scheduled at a specified time.
Syntax
virtual HRESULT GetCommandDueFor( REFERENCE_TIME tStream, CDeferredCommand **ppCmd );
Parameters
- tStream
- Time for which the command is scheduled.
- ppCmd
- Address of a pointer to the deferred command to be carried out at the time specified in the tStream parameter.
Return Value
Returns VFW_E_NOT_FOUND if no commands are due; otherwise, returns S_OK.
Remarks
This member function takes a stream time and returns the deferred command scheduled at that time. The actual stream-time offset is calculated when the command queue is run. Commands remain queued until run or canceled. This member function will not block.
Retrieves a pointer to the next command that is due.
Syntax
virtual HRESULT GetDueCommand( CDeferredCommand **ppCmd, long msTimeout );
Parameters
- ppCmd
- Address of a pointer to the deferred command.
- msTimeout
- Amount of time to wait before carrying out the time-out.
Return Value
Returns E_ABORT if a time-out occurs. Returns S_OK if successful; otherwise, returns an error. Returns an object that has been incremented using IUnknown::AddRef.
Remarks
This member function blocks until a pending command is due. The member function blocks for the amount of time, in milliseconds, specified in the msTimeout parameter. Stream-time commands become due only between the CCmdQueue::Run and CCmdQueue::EndRun member functions. The command remains queued until run or canceled.
Retrieves the event handle to be signaled.
Syntax
HANDLE GetDueHandle(void);
Return Value
Returns the event handle.
Remarks
Return the event handle whenever there are deferred commands that are due for execution (when CCmdQueue::GetDueCommand will not block).
Adds the CDeferredCommand object to the queue.
Syntax
virtual HRESULT Insert( CDeferredCommand *pCmd );
Parameters
- pCmd
- Pointer to the CDeferredCommand object to add to the queue.
Return Value
Returns S_OK in the default implementation.
Initializes a command to be run and returns a new CDeferredCommand object.
Syntax
virtual HRESULT New( CDeferredCommand **ppCmd, LPUNKNOWN pUnk, REFTIME time, GUID *iid, long dispidMethod, short wFlags, long cArgs, VARIANT *pDispParams, VARIANT *pvarResult, short *puArgErr, BOOL bStream );
Parameters
- ppCmd
- Address of a pointer to a CDeferredCommand object by which an application can cancel the command, set a new presentation time for it, or retrieve estimate information.
- pUnk
- Pointer to the object that will run the command.
- time
- Time at which to run the queued command or commands.
- iid
- Pointer to the globally unique identifier (GUID) of the interface to call.
- dispidMethod
- Method on the interface to be called.
- wFlags
- Flags describing the context of the call. This parameter supports the same flags as the OLE IDispatch::Invoke method.
- cArgs
- Number of arguments passed.
- pDispParams
- Pointer to the list of variant types associated with the dispatch parameters.
- pvarResult
- Pointer to the list where results, if any, are to be returned.
- puArgErr
- Pointer to the index within the pDispParams parameter list where the last error occurred.
- bStream
- Value indicating whether the time parameter is a stream-time value (TRUE) or a presentation-time value (FALSE).
Return Value
Returns S_OK if successful. Returns E_OUTOFMEMORY if ppCmd returns from creating the new CDeferredCommand object with a value of NULL. Otherwise, returns an HRESULT that indicates an error from attempting to create a new CDeferredCommand object. If there is an error, no object has been queued.
Remarks
The new CDeferredCommand object will be initialized with the parameters and will be added to the queue during construction. This method is similar to the OLE IDispatch::Invoke method.
Values for the wFlags parameter include the following:
DISPATCH_METHOD The member is being run as a method. If a property has the same name, both this and the DISPATCH_PROPERTYGET flag can be set. DISPATCH_PROPERTYGET The member is being retrieved as a property or data member. DISPATCH_PROPERTYPUT The member is being changed as a property or data member. DISPATCH_PROPERTYPUTREF The member is being changed via a reference assignment, rather than a value assignment. This value is valid only when the property accepts a reference to an object.
Removes the CDeferredCommand object from the queue.
Syntax
virtual HRESULT Remove( CDeferredCommand *pCmd );
Parameters
- pCmd
- Pointer to the CDeferredCommand object to remove from the queue.
Return Value
Returns VFW_E_NOT_FOUND if the object is not found in the queue. Otherwise, returns S_OK.
Switches to running mode so that commands that are deferred by the stream time can be run.
Syntax
virtual HRESULT Run( REFERENCE_TIME tStreamTimeOffset );
Parameters
- tStreamTimeOffset
- Offset time.
Return Value
Returns S_OK in the default implementation.
Remarks
During running mode, stream-time-to-presentation-time mapping is known.
Sets the clock used for timing.
Syntax
virtual HRESULT SetSyncSource( IReferenceClock *pIrc );
Parameters
- pIrc
- Pointer to the IReferenceClock interface.
Return Value
Returns S_OK in the default implementation.
Sets up a timer event with the reference clock.
Syntax
void SetTimeAdvise(void);
Return Value
No return value.
Remarks
This member function calls the IReferenceClock::AdviseTime method to set up a notification for the earliest time required in the queue. Presentation-time commands that are deferred are always checked. If the filter graph is in running mode, deferred commands using stream time are also checked.
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