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IPinFlowControl::Block

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Microsoft DirectShow 9.0

IPinFlowControl::Block

The Block method blocks or unblocks the flow of data from the pin.

Syntax

  HRESULT Block(
  DWORD dwBlockFlags,
  HANDLE hEvent
);

Parameters

dwBlockFlags

[in] Flag that indicates whether to block or unblock the pin. Must be one of the following values:

  • Zero: Unblock data flow from the pin.
  • AM_PIN_FLOW_CONTROL_BLOCK: Block data flow from the pin.

hEvent

[in] Handle to an event object, or NULL. If this parameter is non-NULL, the method is asynchronous and returns immediately. The event is signaled when the operation completes. If this parameter is NULL, the method is synchronous and does not complete until the pin is blocked. If dwBlockFlags is zero, this parameter must be NULL.

Return Value

Returns an HRESULT value. Possible values include the following.

Value Description
S_FALSE Pin is already unblocked.
S_OK Success.
VFW_E_PIN_ALREADY_BLOCKED Pin is already blocked on another thread.
VFW_E_PIN_ALREADY_BLOCKED_ON_THIS_THREAD Pin is already blocked on the calling thread.

Remarks

This method can be synchronous or asynchronous:

  • To call it asynchronously, use the CreateEvent function to create an event object. Pass the event handle in the hEvent parameter. The method returns immediately and signals the event when the operation has completed. Call a wait function such as WaitForSingleObject to wait for the event.
  • To call this method synchronously, set the hEvent parameter to NULL. The method blocks until it completes. The method might not complete until the pin is ready to deliver a sample. If the filter is paused, the method might block indefinitely. Therefore, you should not call this method synchronously from your main application thread.

Requirements

Header: Declared in Strmif.h; include Dshow.h.

Library: Use Strmiids.lib.

See Also