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Supporting Partial-Instance Operations

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A provider is not required to support any partial-instance operations. However, a provider must either support all the semantics of a partial-instance operation, process a complete instance, or return WBEM_E_UNSUPPORTED_PARAMETER.

When creating a provider that supports partial-instance operations, you must observe the following rules:

  • Reuse the same context object that WMI sends to the provider. WMI uses the "__GET_EXT_CLIENT_REQUEST" named value to prevent deadlocks and removes this client before forwarding the context object to a provider.
  • For reentrant calls back into WMI that do not require a partial-instance operation, ensure to pass back the same context object without any modifications. WMI receives the context object without the "__GET_EXT_CLIENT_REQUEST" named value set and deletes all named values associated with partial-instance operations from the context object before passing it to other providers. Not changing the context object blocks other providers from receiving partial-instance retrieval operations intended for a different, unrelated object.
  • To perform a reentrant partial-instance operation while carrying out a request, set the missing "__GET_EXT_CLIENT_REQUEST" named value and property clear. Optionally, you can modify the properties in the "__GET_EXT_PROPERTIES" named value before sending the context object back into WMI with the reentrant call.
  • Do not access the context object after you return it to WMI during a reentrant call; other providers may modify the property lists or other values during reentrancy. You can examine or modify the context object only for the duration of the IWbemServices call that you implement.