Asynchronous console program hangs on completion of task using CefSharp

问题

In my quest to create the perfect string result = browser.Browse(url) method, I have created a simple class library to demonstrate CefSharp. The code for that is:

public class CefSharpHeadlessBrowser
{
    public CefSharpHeadlessBrowser()
    {
        Cef.Initialize(new CefSettings { CachePath = "cache" }, false, true);
    }

    public string Browse(string url)
    {
        Task<string> result;

        var browserSettings = new BrowserSettings { WindowlessFrameRate = 1 };

        using (var browser = new ChromiumWebBrowser(url, browserSettings))
        {
            browser.WaitForBrowserToInitialize();

            browser.LoadPageAsync();

            // Wait awhile for Javascript to finish executing.
            Thread.Sleep(2000);

            result = browser.GetSourceAsync();
            Thread.Sleep(100);
        }
        return result.Result;
    }
}

public static class CefExtensions
{
    public static void WaitForBrowserToInitialize(this ChromiumWebBrowser browser)
    {
        while (!browser.IsBrowserInitialized)
        {
            Task.Delay(100);
        }
    }

    public static Task LoadPageAsync(this IWebBrowser browser)
    {
        var tcs = new TaskCompletionSource<bool>();

        EventHandler<LoadingStateChangedEventArgs> handler = null;
        handler = (sender, args) =>
        {
            if (!args.IsLoading)
            {
                browser.LoadingStateChanged -= handler;
                tcs.TrySetResult(true);
            }
        };

        browser.LoadingStateChanged += handler;
        return tcs.Task;
    }
}

This is the test harness, in a separate console project that references the CefSharpHeadlessBrowser project:

class Program
{
    static void Main(string[] args)
    {
        const string searchUrl = "https://www.google.com";

        var browser = new CefSharpHeadlessBrowser();

        var result = browser.Browse(searchUrl);
        Console.Write(result);
    }
}

This actually works; it gets the HTML page source properly and displays it in the console window, just as it should. But here's the problem: the console program hangs after displaying the page source. It should exit immediately. Which must mean that I'm doing something wrong with the asynchronous operations and causing a deadlock.

What could be the issue?

回答1:

CefSharp has a Shutdown command; I was able to solve the problem by adding the following method to the CefSharpHeadlessBrowser class:

    public void Shutdown()
    {
        Cef.Shutdown();
    }

And then changing the Test Harness to:

class Program
{
    static void Main(string[] args)
    {
        const string searchUrl = "https://www.google.com";

        var browser = new CefSharpHeadlessBrowser();

        var result = browser.Browse(searchUrl);
        Console.WriteLine(result);
        browser.Shutdown();  // Added 
    }
}

This undoubtedly frees up any remaining threads that are running.

I'll probably make the class IDisposable and wrap the calling code in a using statement.

来源：https://stackoverflow.com/questions/36923015/asynchronous-console-program-hangs-on-completion-of-task-using-cefsharp

标签

cefsharp

cefsharp.offscreen