HelloWebView contains race condition

[marler8997]

I based my usage of WebView2 on the HelloWebView.cpp sample, however, a recent windows update (sometime on or before Decmber 11, 2023) broke our application because the startup scripts are no longer executed. We fixed the issue by moving the calls to AddScriptToExecuteOnDocumentCreated to occur before calling Navigate. I recommend updating the samples to do the same (such as https://github.com/MicrosoftEdge/WebView2Samples/blob/85e53c9dc4245ed74fc737554640644d4b0f3bb5/GettingStartedGuides/Win32_GettingStarted/HelloWebView.cpp).

I've investigated a bit more and determined this race condition seems to always occur if you are navigating to a local file URL, i.e.

webview->AddScriptToExecuteOnDocumentCreated(L"console.log('A')", nullptr);
webview->Navigate(L"file:///C:/temp/testpage.html");
webview->AddScriptToExecuteOnDocumentCreated(L"console.log('B')", nullptr);

In that example the first console log will show up, but not the second. If you modify the example to go to an HTTP URL, both will show up.

[pieths-ms]

Hi @marler8997 , what version of the WebView2 runtime are you using for your application?

[marler8997]

Our application is currently using 1.0.1661.34. However, the behavior occurs with or without our project. If you copy/paste the code in the description into the HelloWorld win32 application you'll see the same behavior. Here's the relevant line in the vcxproj file that shows which version HelloWorld is using:

<Import Project="packages\Microsoft.Web.WebView2.1.0.902.49\build\native\Microsoft.Web.WebView2.targets" Condition="Exists('packages\Microsoft.Web.WebView2.1.0.902.49\build\native\Microsoft.Web.WebView2.targets')" />

Here's the modified version of HelloWebView.cpp. The modifications are to use a file:// based URL, and the inserts a couple console.log statements so you can see that the one added before calling Navigate works but the one added after does not.

// compile with: /D_UNICODE /DUNICODE /DWIN32 /D_WINDOWS /c

#include <windows.h>
#include <stdlib.h>
#include <string>
#include <tchar.h>
#include <wrl.h>
#include <wil/com.h>
// <IncludeHeader>
// include WebView2 header
#include "WebView2.h"
// </IncludeHeader>

using namespace Microsoft::WRL;

// Global variables

// The main window class name.
static TCHAR szWindowClass[] = _T("DesktopApp");

// The string that appears in the application's title bar.
static TCHAR szTitle[] = _T("WebView sample");

HINSTANCE hInst;

// Forward declarations of functions included in this code module:
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

// Pointer to WebViewController
static wil::com_ptr<ICoreWebView2Controller> webviewController;

// Pointer to WebView window
static wil::com_ptr<ICoreWebView2> webview;

int CALLBACK WinMain(
    _In_ HINSTANCE hInstance,
    _In_ HINSTANCE hPrevInstance,
    _In_ LPSTR     lpCmdLine,
    _In_ int       nCmdShow
)
{
    WNDCLASSEX wcex;

    wcex.cbSize = sizeof(WNDCLASSEX);
    wcex.style = CS_HREDRAW | CS_VREDRAW;
    wcex.lpfnWndProc = WndProc;
    wcex.cbClsExtra = 0;
    wcex.cbWndExtra = 0;
    wcex.hInstance = hInstance;
    wcex.hIcon = LoadIcon(hInstance, IDI_APPLICATION);
    wcex.hCursor = LoadCursor(NULL, IDC_ARROW);
    wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
    wcex.lpszMenuName = NULL;
    wcex.lpszClassName = szWindowClass;
    wcex.hIconSm = LoadIcon(wcex.hInstance, IDI_APPLICATION);

    if (!RegisterClassEx(&wcex))
    {
        MessageBox(NULL,
            _T("Call to RegisterClassEx failed!"),
            _T("Windows Desktop Guided Tour"),
            NULL);

        return 1;
    }

    // Store instance handle in our global variable
    hInst = hInstance;

    // The parameters to CreateWindow explained:
    // szWindowClass: the name of the application
    // szTitle: the text that appears in the title bar
    // WS_OVERLAPPEDWINDOW: the type of window to create
    // CW_USEDEFAULT, CW_USEDEFAULT: initial position (x, y)
    // 500, 100: initial size (width, length)
    // NULL: the parent of this window
    // NULL: this application does not have a menu bar
    // hInstance: the first parameter from WinMain
    // NULL: not used in this application
    HWND hWnd = CreateWindow(
        szWindowClass,
        szTitle,
        WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT,
        1200, 900,
        NULL,
        NULL,
        hInstance,
        NULL
    );

    if (!hWnd)
    {
        MessageBox(NULL,
            _T("Call to CreateWindow failed!"),
            _T("Windows Desktop Guided Tour"),
            NULL);

        return 1;
    }

    // The parameters to ShowWindow explained:
    // hWnd: the value returned from CreateWindow
    // nCmdShow: the fourth parameter from WinMain
    ShowWindow(hWnd,
        nCmdShow);
    UpdateWindow(hWnd);

    // <-- WebView2 sample code starts here -->
    // Step 3 - Create a single WebView within the parent window
    // Locate the browser and set up the environment for WebView
    CreateCoreWebView2EnvironmentWithOptions(nullptr, nullptr, nullptr,
        Callback<ICoreWebView2CreateCoreWebView2EnvironmentCompletedHandler>(
            [hWnd](HRESULT result, ICoreWebView2Environment* env) -> HRESULT {

                // Create a CoreWebView2Controller and get the associated CoreWebView2 whose parent is the main window hWnd
                env->CreateCoreWebView2Controller(hWnd, Callback<ICoreWebView2CreateCoreWebView2ControllerCompletedHandler>(
                    [hWnd](HRESULT result, ICoreWebView2Controller* controller) -> HRESULT {
                        if (controller != nullptr) {
                            webviewController = controller;
                            webviewController->get_CoreWebView2(&webview);
                        }

                        // Add a few settings for the webview
                        // The demo step is redundant since the values are the default settings
                        wil::com_ptr<ICoreWebView2Settings> settings;
                        webview->get_Settings(&settings);
                        settings->put_IsScriptEnabled(TRUE);
                        settings->put_AreDefaultScriptDialogsEnabled(TRUE);
                        settings->put_IsWebMessageEnabled(TRUE);

                        // Resize WebView to fit the bounds of the parent window
                        RECT bounds;
                        GetClientRect(hWnd, &bounds);
                        webviewController->put_Bounds(bounds);
                        webview->AddScriptToExecuteOnDocumentCreated(L"console.log('A')", nullptr);

                        // Schedule an async task to navigate to Bing
                        //webview->Navigate(L"https://www.bing.com/");
                        webview->Navigate(L"file:///C:/temp/testpage.html");

                        // Race condition!
                        webview->AddScriptToExecuteOnDocumentCreated(L"console.log('B')", nullptr);
                        return S_OK;
                    }).Get());
                return S_OK;
            }).Get());

    // <-- WebView2 sample code ends here -->

    // Main message loop:
    MSG msg;
    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    return (int)msg.wParam;
}

//  FUNCTION: WndProc(HWND, UINT, WPARAM, LPARAM)
//
//  PURPOSE:  Processes messages for the main window.
//
//  WM_DESTROY  - post a quit message and return
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    TCHAR greeting[] = _T("Hello, Windows desktop!");

    switch (message)
    {
    case WM_SIZE:
        if (webviewController != nullptr) {
            RECT bounds;
            GetClientRect(hWnd, &bounds);
            webviewController->put_Bounds(bounds);
        };
        break;
    case WM_DESTROY:
        PostQuitMessage(0);
        break;
    default:
        return DefWindowProc(hWnd, message, wParam, lParam);
        break;
    }

    return 0;
}