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Notification Data Object

The notification data is handled as an object that exposes the IPrintAsyncNotifyDataObject interface. Clients of the spooler notification pipe can define their own data schema and can send any data type back and forth. However, the spooler queries the notification data object for a BYTE* pointer, the length of the data, and the notification type. The notification type is a GUID, as described in Notification Types.

#define INTERFACE IPrintAsyncNotifyDataObject
DECLARE_INTERFACE_(IPrintAsyncNotifyDataObject, IUnknown)
        REFIID riid,
        void** ppvObj
        ) PURE;
        ) PURE;

    STDMETHOD_(ULONG, Release)(
        ) PURE;
         OUT BYTE**,
         OUT ULONG*,
         OUT PrintAsyncNotificationType**
         ) PURE;
        ) PURE;

The notification sender must pack the data in an IPrintAsyncNotifyDataObject object. The sender must implement the IUnknown interface.

The listening client calls the IPrintAsyncNotifyDataObject::AcquireData method to obtain a raw pointer to the notification data, the size of the notification data, and the notification type.

When the listening client is finished with the data, it must call the IPrintAsyncNotifyDataObject::ReleaseData method. The clients of the spooler notification pipe must implement the IPrintAsyncNotifyDataObject interface in such a way that if the IPrintAsyncNotifyDataObject::Release method is called before the IPrintAsyncNotifyDataObject::ReleaseData method is called, the object is not released. It is recommended that a call to the IPrintAsyncNotifyDataObject::AcquireData method should increment the object's reference count, and that a call to the ReleaseData method should decrement object's reference count.

The spooler defines a special notification type GUID named NOTIFICATION_RELEASE. When either the spooler or the listening application dies, the rundown code announces the "still alive" end of the channel by calling the IPrintAsyncNotifyChannel::CloseChannel method.

A call to the IPrintAsyncNotifyDataObject::AcquireData method against this notification returns with the BYTE** parameter set to NULL, the ULONG* parameter set to 0, and the GUID* parameter set to NOTIFICATION_RELEASE.



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