Called by a Data Adapter to signal to Lightstreamer Kernel that the current Snapshot of the Item has suddenly become empty. More precisely: 

- for subscriptions in MERGE mode, the current state of the Item will be cleared, as though an update with all fields valued as null were issued; 

- for subscriptions in COMMAND mode, the current state of the Item will be cleared, as though a DELETE event for each key were issued; 

- for subscriptions in DISTINCT mode, a suitable notification that the Snapshot for the Item should be cleared will be sent to all the clients currently subscribed to the Item (clients based on some old client library versions may not be notified); at the same time, the current recent update history kept by the Server for the Item will be cleared and this will affect the Snapshot for new subscriptions; 

- for subscriptions in RAW mode, there will be no effect. 

Note that this is a real-time event, not a Snapshot event; hence, in order to issue this call, it is not needed that the Data Adapter has returned true to IsSnapshotAvailable for the specified Item; moreover, if invoked while the Snapshot is being supplied, the Kernel will infer that the Snapshot has been completed. 

The Adapter should ensure that, after an unsubscribe call for the Item has returned, a possible pending ClearSnapshot call related with the previous subscription request is no longer issued. This assures that, upon a new subscription for the Item, no trailing events due to the previous subscription can be received by the Kernel. Note that the method is nonblocking; moreover, it only takes locks to first order mutexes; so, it can safely be called while holding a custom lock.  

void ClearSnapshot(string itemName);

void ClearSnapshot(string itemName);

Function ClearSnapshot(itemName As string) As void