High CPU usage with 1.0.781-prerelease

[AbeniMatteo]

Description
High CPU usage while doing nothing. This problem is only present from 1.0.781-prerelease.
1.0.721-prerelease and 1.0.705.50 are ok.

Version
SDK: 1.0.781-prerelease
Runtime: 89.0.774.8 (Official build) dev (64-bit)
Framework: .NET 5.0.102 + WPF
OS: Win10 10.0.19042 Build 19042

Repro Steps
Run the following code:

Program.cs

namespace Repro
{
    using System;
    using System.Windows;
    using Microsoft.Web.WebView2.Wpf;

    static class Program
    {
        [STAThread]
        static void Main()
        {
            // Init Application.Current
            new Application();
            var w = new Window();
            w.Content = new WebView2();
            w.ShowDialog();
        }
    }
}

Repro.csproj

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>WinExe</OutputType>
    <TargetFramework>net5.0-windows</TargetFramework>
    <UseWPF>true</UseWPF>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.Web.WebView2" Version="1.0.781-prerelease" />
  </ItemGroup>
</Project>

AB#31577027

[albahari]

I've reproduced this problem with both the WPF and WinForms controls.

It's caused by a continuous stream of WM_PAINT messages being generated, keeping the UI thread close to 100% busy. This also saturates the message loop and sometimes prevents other controls from receiving a WM_PAINT. You can verify this as follows:

public class WebView2Ex : WebView2
{
    protected override IntPtr WndProc (IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
    {
        Debug.WriteLine (msg);
        return base.WndProc (hwnd, msg, wParam, lParam, ref handled);
    }
}

This needs to be fixed ASAP, because the control is close to unusable right now.

[tildebox]

~15% CPU usage. I had to downgrade to 1.0.705.50.

[champnic]

Thanks for finding this - I've filed a bug on our backlog and we're taking a look right away.

[johna-ms]

Hello all! We are working on getting another release turned around as soon as possible with the fix for this. In the mean time, you can try this workaround:

• Extend the WebView control with your own control
• Override the WndProc method
• Check for the WM_PAINT window message (0x000F), call BeginPaint, EndPaint, and return IntPtr.Zero
  • Begin/EndPaint are Win32 APIs and you'll need to DllImport them. Here's the code we used:

  •  `[StructLayout(LayoutKind.Sequential)]
        public struct Rect
        {
            public int left;
            public int top;
            public int right;
            public int bottom;
        }
    
        [StructLayout(LayoutKind.Sequential)]
        public struct PaintStruct
        {
            public IntPtr hdc;
            public bool fErase;
            public Rect rcPaint;
            public bool fRestore;
            public bool fIncUpdate;
            [MarshalAs(UnmanagedType.ByValArray, SizeConst=32)] public byte[] rgbReserved;
        }
    
        [DllImport("user32.dll", SetLastError = true)]
        public static extern IntPtr BeginPaint(IntPtr hwnd, out PaintStruct lpPaint);
    
        [DllImport("user32.dll", SetLastError = true)]
        public static extern bool EndPaint(IntPtr hwnd, ref PaintStruct lpPaint);`
    

[ukandrewc]

This sort of works, but still got the issues with z-order. Any WebView2 that paints, comes to the front.

[johna-ms]

@ukandrewc does your code in WndProc look like this?

    `protected override void WndProc(ref Message m)
    {
        switch (unchecked((NativeMethods.WM)m.Msg))
        {
            case NativeMethods.WM.PAINT:
            {
                NativeMethods.PaintStruct lpPaint;
                NativeMethods.BeginPaint(m.HWnd, out lpPaint);
                NativeMethods.EndPaint(m.HWnd, ref lpPaint);
                m.Result = IntPtr.Zero;
                return;
            }
        }
        base.WndProc(ref m);
    }`

Re: your last message, you don't need to fill out PaintStruct at all

[ukandrewc]

@johna-ms Yes, it does (I work in VB, but it's the same)

I've attached a screen-capture (had to zip as GitHub not accepting wmv)

There are two WebView2s controlled by z-order (Web1, Web2)

When the 2nd tab is clicked it calls web2.BringToFront(), but when eBay (Web1) refreshes, it becomes visible again. Not sure if it's transparency or Z order.

Video_2021-02-04_130715.zip

For anyone else in VB:

Imports System.Runtime.InteropServices
Public Class WVBrowser : Inherits WebView2

	<StructLayout(LayoutKind.Sequential)>
	Private Structure Rect
		Public left As Integer
		Public top As Integer
		Public right As Integer
		Public bottom As Integer
	End Structure

	<StructLayout(LayoutKind.Sequential)>
	Private Structure PaintStruct
		Public hdc As IntPtr
		Public fErase As Boolean
		Public rcPaint As Rect
		Public fRestore As Boolean
		Public fIncUpdate As Boolean
		<MarshalAs(UnmanagedType.ByValArray, SizeConst:=32)>
		Public rgbReserved As Byte()
	End Structure

	<DllImport("user32.dll", SetLastError:=True)>
	Private Shared Function BeginPaint(ByVal hwnd As IntPtr, <Out> ByRef lpPaint As PaintStruct) As IntPtr
	End Function

	<DllImport("user32.dll", SetLastError:=True)>
	Private Shared Function EndPaint(ByVal hwnd As IntPtr, ByRef lpPaint As PaintStruct) As Boolean
	End Function

	Protected Overrides Sub WndProc(ByRef m As Message)
		If m.Msg = &HF Then
			Dim PS As New PaintStruct
			BeginPaint(m.HWnd, PS)
			EndPaint(m.HWnd, PS)
			m.Result = IntPtr.Zero
		Else
			MyBase.WndProc(m)
		End If
	End Sub

End Class

Thanks, I deleted the question once I'd read your code properly (been a while since I've done any winapi) ;-)

[johna-ms]

So this fixes the CPU issue for you but not the related issue about items refreshing on the form?

Seems like you're finding a different issue? So this doesn't repro on the older prerelease package? I'm going to work on a repro for this to investigate.

[ukandrewc]

Yes, sorry, just realised this issue is only for High CPU usage, not #875.

It does allow other controls on the form to refresh normally, but I'm still still seeing transparency issues with Z order (Shown in the video above)

I also had to add Web2.Refresh() after Web2.BringToFront()

[ukandrewc]

It seems that whichever WebView2 paints last, gets to be visible, but this doesn't affect main scrollbars.

When Web2 is at the front of Z order, and Web1 is refreshed, it becomes visible. Scrolling Web2, shows it's content again (until Web1 content changes).

[johna-ms]

Ok that's definitely weird. We're tracking it on our end as a separate issue. Thanks!

[ukandrewc]

In the video Web2 is at the front (HTML Table)
When Web1 banner (eBay) refreshes, it is visible.
Scrolling Web2 (scrollbar is Web2's) shows it again (until eBay content changes)

Video_2021-02-04_194717.mp4

[johna-ms]

Tracking this on github here

#897

[ukandrewc]

Thanks

[champnic]

The high CPU usage should now be fixed in 1.0.790-prerelease SDK package. Thanks!