.NET Framework March 1, 2019 Cumulative Update for Windows 10 version 1809 and Windows Server 2019
Today, March 1, we released the February 2019 Cumulative Update for Windows 10 version 1809 and Windows Server 2019.
Quality and Reliability
This release contains the following quality and reliability improvements.
- Addresses an issue in System.Threading.Timer where a single global queue that was protected by a single process-wide lock causing a issues with scalability where Timers are used frequently on multi-CPU machine. The fix can be opted into with an AppContext switch below. See instructions for enabling the switch. 
- Switch name: Switch.System.Threading.UseNetCoreTimer
- Switch value to enable: true Don’t rely on applying the setting programmatically – the switch value is read only once per AppDomain at the time when the System.Threading.Timer type is loaded.
- Addresses an issue that caused compatibility breaks seen in some System.Data.SqlClient usage scenarios. 
- Addresses an issue in .NET 3.5 Windows Forms applications that may not be able to render the application UI and, instead, render a white screen that contains a red “X” symbol. Additionally, it addresses a double prompt for file save dialogue and folder browser dialogue.” 
- Improved the memory allocation and cleanup scheduling behavior of the weak-event pattern. The fix can be opted into with an AppContext switch below. See instructions for enabling the switch. 
- Switch name: Switch.MS.Internal.EnableWeakEventMemoryImprovements
- Switch name: Switch.MS.Internal.EnableCleanupSchedulingImprovements
- Switch value to enable: true
Getting the Update
The Preview of Quality Rollup is available via Windows Update, Windows Server Update Services, and Microsoft Update Catalog.
Microsoft Update Catalog
You can get the update via the Microsoft Update Catalog. For Windows 10 update 1809, the .NET Framework updates are part of the Windows 10 .NET Framework Cumulative Update.
|Product Version||Cumulative Update KB|
|Windows 10 1809 (October 2018 Update)||Catalog 4486553|
|.NET Framework 3.5, 4.7.2||4486553|
Previous Monthly Rollups
The last few .NET Framework Cumulative updates are listed below for your convenience:
- February 2019 Security and Quality Rollup
- January 22, 2018 Cumulative Update for Windows 10 version 1809 and Windows Server 2019
- January 2019 Security and Quality Rollup
What exactly does the WPF Improved the memory allocation refer to? What versions of the .net framework does this fix? Why is this not just on by default?