ArcGIS Engine Developer Guide

.NET APPLICATION PROGRAMMING INTERFACE
In the case of SDE data sources, the cursor holds on to an SDE stream, and if
the application has multiple clients, each may get and hold on to an SDE stream,
eventually exhausting the maximum allowable streams. The effect of the number
of SDE streams exceeding the maximum is that other clients will fail to open
their own cursors to query the database.
Because of the above reasons, it’s important to ensure that your reference to any
cursor your application opens is released in a timely manner. In .NET, your reference
on the cursor (or any other COM object) will not be released until garbage
collection kicks in. In a Web application or Web service that services multiple
concurrent sessions and requests, relying on garbage collection to release references
on objects will result in cursors and their resources not being released in a
timely manner.
To ensure a COM object is released when it goes out of scope, the WebControls
assembly contains a helper object called WebObject. Use the ManageLifetime
method to add your COM object to the set of objects that will be explicitly
released when the WebObject is disposed. You must scope the use of WebObject
within a using block. When you scope the use of WebObject within a using block,
any object (including your cursor) that you have added to the WebObject using the
ManageLifetime method will be explicitly released at the end of the using block.
The following example demonstrates this coding pattern:
[VB.NET]
Private SubSystem.object doSomething_Click(ByVal sender As System.Object,
ByVal e As System.EventArgs) Handles doSomething.Click
Dim webobj As WebObject = New WebObject
Dim ctx As IServerContext = Nothing
Try
Dim serverConn As ServerConnection = New ServerConnection("doug", True)
Dim som As IServerObjectManager = serverConn.ServerObjectManager
ctx = som.CreateServerContext("Yellowstone", "MapServer")
Dim mapsrv As IMapServer = ctx.ServerObject
Dim mapo As IMapServerObjects = mapsrv
Dim map As IMap = mapo.Map(mapsrv.DefaultMapName)
Dim flayer As IFeatureLayer = map.Layer(0)
Dim fClass As IFeatureClass = flayer.FeatureClass
Dim fcursor As IFeatureCursor = fClass.Search(Nothing, True)
webobj.ManageLifetime(fcursor)
Dim f As IFeature = fcursor.NextFeature()
Do Until f Is Nothing
' Do something with the feature.
f = fcursor.NextFeature()
Loop
Finally
ctx.ReleaseContext()
webobj.Dispose()
Chapter 4 • Developer environments • 177