SWbemSink object

The SWbemSink object is implemented by client applications to receive the results of asynchronous operations and event notifications. To make an asynchronous call, you must create an instance of an SWbemSink object and pass it as the ObjWbemSink parameter. The events in your implementation of SWbemSink are triggered when status or results are returned, or when the call is complete. The VBScript CreateObject call creates this object.

Members

The SWbemSink object has these types of members:

Methods

The SWbemSink object has these methods.

MethodDescription
Cancel

Cancels all asynchronous operations that are associated with this sink.

 

Remarks

An asynchronous callback allows a non-authenticated user to provide data to the sink. This poses security risks to your scripts and applications. To eliminate the risks, use either semisynchronous communication or synchronous communication. For more information, see Calling a Method.

Events

You can implement subroutines to be called when events are triggered. For example, if you want to process each object that is returned by an asynchronous query call such as SWbemServices.ExecQueryAsync, create a subroutine using the sink that is specified in the asynchronous call, as shown in the following example.


Sub SinkName_OnObjectReady(objObject, objAsyncContext)

Use the following table as a reference to identify events and trigger descriptions.

EventDescription
OnCompleted Triggered when an asynchronous operation is complete.
OnObjectPut Triggered when an asynchronous Put operation is complete.
OnObjectReady Triggered when an object provided by an asynchronous call is available.
OnProgress Triggered to provide the status of a asynchronous operation.

 

Asynchronously Retrieving Event Log Statistics

WMI supports both asynchronous and semi-synchronous scripts. When retrieving events from the event logs, asynchronous scripts often retrieve this data much faster.

In an asynchronous script, a query is issued and control is immediately returned to the script. The query continues to process on a separate thread while the script begins to immediately act on the information that is returned. Asynchronous scripts are event driven: each time an event record is retrieved, the OnObjectReady event is fired. When the query has completed, the OnCompleted event will fire, and the script can continue based on the fact that all the available records have been returned.

In a semi-synchronous script, by contrast, a query is issued and the script then queues a large amount of retrieved information before acting upon it. For many objects, semi-synchronous processing is adequate; for example, when querying a disk drive for its properties, there might be only a split second between the time the query is issued and the time the information is returned and acted upon. This is due in large part to the fact that the amount of information returned is relatively small.

When querying an event log, however, the interval between the time the query is issued and the time that a semi-synchronous script can finish returning and acting on the information can take hours. On top of that, the script might run out of memory and fail on its own before completing.

For event logs with a large number of records, the difference in processing time can be considerable. On a Windows 2000-based test computer with 2,000 records in the event log, a semi-synchronous query that retrieved all the events and displayed them in a command window took 10 minutes 45 seconds. An asynchronous query that performed the same operation took one minute 54 seconds.

Examples

The following VBScript asynchronously queries the event logs for all records.


Const POPUP_DURATION = 10
Const OK_BUTTON = 0
Set objWSHShell = Wscript.CreateObject("Wscript.Shell")
strComputer = "."
Set objWMIService = GetObject("winmgmts:" _
 & "{impersonationLevel=impersonate}!\\" & strComputer & "\root\cimv2")
Set objSink = WScript.CreateObject("WbemScripting.SWbemSink","SINK_")
objWMIService.InstancesOfAsync objSink, "Win32_NTLogEvent"
errReturn = objWshShell.Popup("Retrieving events", POPUP_DURATION, _
"Event Retrieval", OK_BUTTON)
Sub SINK_OnCompleted(iHResult, objErrorObject, objAsyncContext)
 WScript.Echo "Asynchronous operation is done."
End Sub
Sub SINK_OnObjectReady(objEvent, objAsyncContext)
 Wscript.Echo "Category: " & objEvent.Category
 Wscript.Echo "Computer Name: " & objEvent.ComputerName
 Wscript.Echo "Event Code: " & objEvent.EventCode
 Wscript.Echo "Message: " & objEvent.Message
 Wscript.Echo "Record Number: " & objEvent.RecordNumber
 Wscript.Echo "Source Name: " & objEvent.SourceName
 Wscript.Echo "Time Written: " & objEvent.TimeWritten
 Wscript.Echo "Event Type: " & objEvent.Type
 Wscript.Echo "User: " & objEvent.User
End Sub

Requirements

Minimum supported client

Windows Vista

Minimum supported server

Windows Server 2003

Header

Wbemdisp.h

IDL

Wbemdisp.idl

DLL

Wbemdisp.dll

See also

Scripting API Objects

 

 

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