IMFAsyncCallback::GetParameters Method

Provides configuration information to the dispatching thread for a callback.

Syntax

HRESULT GetParameters(
  [out]  DWORD *pdwFlags,
  [out]  DWORD *pdwQueue
);

Parameter

• pdwFlags [out]
  Receives a flag indicating the behavior of the callback object's IMFAsyncCallback::Invoke method. The following values are defined. The default value is zero.

  Wert	Bedeutung
  Zero	The callback does not take a long time to complete, but has no specific restrictions on what system calls it makes. The callback generally takes less than 30 milliseconds to complete.
  MFASYNC_FAST_IO_PROCESSING_CALLBACK	The callback does very minimal processing. It takes less than 1 millisecond to complete. The callback must be invoked from one of the following work queues: MFASYNC_CALLBACK_QUEUE_IO MFASYNC_CALLBACK_QUEUE_TIMER
  MFASYNC_SIGNAL_CALLBACK	Implies MFASYNC_FAST_IO_PROCESSING_CALLBACK, with the additional restriction that the callback does no processing (less than 50 microseconds), and the only system call it makes is SetEvent. The callback must be invoked from one of the following work queues: MFASYNC_CALLBACK_QUEUE_IO MFASYNC_CALLBACK_QUEUE_TIMER

   

• pdwQueue [out]
  Receives the identifier of the work queue on which the callback is dispatched.

  This value can specify one of the standard Media Foundation work queues, or a work queue created by the application. For list of standard Media Foundation work queues, see Work Queue Identifiers. To create a new work queue, call MFAllocateWorkQueue. The default value is MFASYNC_CALLBACK_QUEUE_STANDARD.

  If the work queue is not compatible with the value returned in pdwFlags, the Media Foundation platform returns MF_E_INVALID_WORKQUEUE when it tries to dispatch the callback. (See MFPutWorkItem.)

Rückgabewert

The method returns an HRESULT. Possible values include, but are not limited to, those in the following table.

Hinweise

The GetParameters method returns information about the callback so that the dispatching thread can optimize the process that it uses to invoke the callback.

If the method returns a value other than zero in the pdwFlags parameter, your Invoke method must meet the requirements described here. Otherwise, the callback might delay the pipeline.

If you want default values for both parameters, return E_NOTIMPL. The default values are given in the parameter descriptions on this page.

This interface is available on the following platforms if the Windows Media Format 11 SDK redistributable components are installed:

• Windows XP mit Service Pack 2 (SP2) und höher.
• Windows XP Media Center Edition 2005 with KB900325 (Windows XP Media Center Edition 2005) and KB925766 (Oktober 2006 Updaterollup für Windows XP Media Center Edition) installed.

Anforderungen

Siehe auch

Asynchronous Callback Methods

Work Queues

IMFAsyncCallback