KB0044 - High memory usage in a long running, complex App

KB0044 - High memory usage in a long running, complex App

Problem

Memory usage can grow continuously in a complex app that is either long running and\or very busy. 

Root Cause

Apps maintain user state as the users interact with the app. This state includes variables that are set and event handlers that are defined within the app. Even if the user closes the tab, the state is maintained in order to support browsers that automatically reconnect after pausing the page, such as mobile web browsers. After 25 minutes (the default session timeout), the session and tab state will be released if the user has not accessed the page again. If an app is busy, with many users connecting and disconnecting from the app, it can continue to consume memory at an increasing rate. 

While it is possible to reduce the session timeout value, it may not be ideal. 

Workaround

As of PowerShell Universal 4.0.x. page state does not offer a specific timeout value and is tied to the session timeout value. Using the following sample, you can time out pages that haven't been accessed for 1 minute. The sample will also list the currently saved page states for the current session. Refreshing the page will produce a new page state. After 1 minute, the page state will begin to disappear from the tab. This is a sign that the event handlers and variables are being released and memory is being freed. 
  2. $EndpointSchedule = New-UDEndpointSchedule -Every 1 -Minute
  3. $Endpoint = New-UDEndpoint -Schedule $EndpointSchedule -Endpoint {
  4.     $EndpointService.SessionManager.Sessions.Values | ForEach-Object {
  5.         $_.Pages.Values | ForEach-Object {
  6.             $OneMinuteAgo = [DateTime]::UtcNow.AddMinutes(-1)
  7.             if ($_.LastTouched -lt $OneMinuteAgo) {
  8.                 $_.LastTouched = [DateTime]::MinValue
  9.             }
  10.         }
  11.     }
  12.     $TimeSpan = New-TimeSpan -Minutes 25
  13.     $EndpointService.SessionManager.ClearTimedOutSessions($TimeSpan);
  14. }
  15. New-UDApp -Title 'PowerShell Universal' -Content {
  16.     New-UDDynamic -Content {
  17.         New-UDDynamic -Content {
  18.             New-UDButton -OnClick {
  19.             }
  20.         }
  21.     }

  23.     New-UDDynamic -Content {
  24.         $Pages = @()
  25.         $EndpointService.SessionManager.Sessions.Values | ForEach-Object {
  26.             $_.Pages.Values | ForEach-Object {
  27.                 $Pages += $_
  28.             }
  29.         }
  30.         New-UDTable -Data $Pages -Columns @(
  31.             New-UDTableColumn -Property 'Id'
  32.             New-UDTableColumn -Property 'LastTouched'
  33.         )
  34.     } -AutoRefresh -AutoRefreshInterval 3
  35. }

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