IMemAllocator::Decommit method (strmif.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 It has been superseded by MediaPlayer, IMFMediaEngine, and Audio/Video Capture in Media Foundation.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 Decommit method releases the buffer memory.

Syntax

HRESULT Decommit();

Return value

Returns S_OK if successful, or an HRESULT value indicating the cause of the error.

Remarks

Any threads waiting in the IMemAllocator::GetBuffer method return with an error. Further calls to GetBuffer fail, until the IMemAllocator::Commit method is called.

The purpose of the Decommit method is to prevent filters from getting any more samples from the allocator. Filters that already hold a reference count on a sample are not affected. After a filter releases a sample and the reference count goes to zero, however, the sample is no longer available.

The allocator may free the memory belonging to any sample with a reference count of zero. Thus, the Decommit method "releases" the memory in the sense that filters stop having access to it. Whether the memory actually returns to the heap depends on the implementation of the allocator. Some allocators wait until their own destructor method. However, an allocator must not leave any allocated memory behind when it deletes itself. Therefore, an allocator's destructor must wait until all of its samples are released.

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Target Platform	Windows
Header	strmif.h (include Dshow.h)
Library	Strmiids.lib

See also

Error and Success Codes

IMemAllocator Interface