IMediaObject::Lock method (mediaobj.h)

[The feature associated with this page, DirectShow, is a legacy feature. It has been superseded by MediaPlayer, IMFMediaEngine, and Audio/Video Capture in Media Foundation. Those features have been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use MediaPlayer, IMFMediaEngine and Audio/Video Capture in Media Foundation instead of DirectShow, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]

The Lock method acquires or releases a lock on the DMO. Call this method to keep the DMO serialized when performing multiple operations.

Syntax

HRESULT Lock(
  LONG bLock
);

Parameters

bLock

Value that specifies whether to acquire or release the lock. If the value is non-zero, a lock is acquired. If the value is zero, the lock is released.

Return value

Returns an HRESULT value. Possible values include those in the following table.

Return code	Description
E_FAIL	Failure
S_OK	Success

Remarks

This method prevents other threads from calling methods on the DMO. If another thread calls a method on the DMO, the thread blocks until the lock is released.

If you are using the Active Template Library (ATL) to implement a DMO, the name of the Lock method conflicts with the CComObjectRootEx::Lock method. To work around this problem, define the preprocessor symbol FIX_LOCK_NAME before including the header file Dmo.h:

#define FIX_LOCK_NAME
#include <dmo.h>

This directive causes the preprocessor to rename the IMediaObject method to DMOLock. In your DMO, implement the method as DMOLock. In your implementation, call the ATL Lock or Unlock method, depending on the value of bLock. Applications can still invoke the method using the name Lock because the vtable order does not change.

Requirements

Requirement	Value
Target Platform	Windows
Header	mediaobj.h (include Dmo.h)
Library	Dmoguids.lib