gui-cs.Terminal.Gui/Tests/UnitTestsParallelizable/Application/MainLoopCoordinatorTests.cs

#nullable enable
using System.Collections.Concurrent;
using System.Diagnostics;
// ReSharper disable AccessToDisposedClosure
#pragma warning disable xUnit1031

namespace ApplicationTests;

/// <summary>
///     Tests for <see cref="MainLoopCoordinator{TInputRecord}"/> to verify input loop lifecycle.
///     These tests ensure that the input thread starts, runs, and stops correctly when applications
///     are created, initialized, and disposed.
/// </summary>
public class MainLoopCoordinatorTests : IDisposable
{
    private readonly List<IApplication> _createdApps = new ();

    public void Dispose ()
    {
        // Cleanup any apps that weren't disposed in tests
        foreach (IApplication app in _createdApps)
        {
            try
            {
                app.Dispose ();
            }
            catch
            {
                // Ignore cleanup errors
            }
        }

        _createdApps.Clear ();
    }

    private IApplication CreateApp ()
    {
        IApplication app = Application.Create ();
        _createdApps.Add (app);

        return app;
    }

    /// <summary>
    ///     Verifies that Dispose() stops the input loop when using Application.Create().
    ///     This is the key test that proves the input thread respects cancellation.
    /// </summary>
    [Fact]
    public void Application_Dispose_Stops_Input_Loop ()
    {
        // Arrange
        IApplication app = CreateApp ();
        app.Init ("fake");

        // The input thread should now be running
        Assert.NotNull (app.Driver);
        Assert.True (app.Initialized);

        // Act - Dispose the application
        var sw = Stopwatch.StartNew ();
        app.Dispose ();
        sw.Stop ();

        // Assert - Dispose should complete quickly (within 1 second)
        // If the input thread doesn't stop, this will hang and the test will timeout
        Assert.True (sw.ElapsedMilliseconds < 1000, $"Dispose() took {sw.ElapsedMilliseconds}ms - input thread may not have stopped");

        // Verify the application is properly disposed
        Assert.Null (app.Driver);
        Assert.False (app.Initialized);

        _createdApps.Remove (app);
    }

    /// <summary>
    ///     Verifies that calling Dispose() multiple times doesn't cause issues.
    /// </summary>
    [Fact]
    public void Dispose_Called_Multiple_Times_Does_Not_Throw ()
    {
        // Arrange
        IApplication app = CreateApp ();
        app.Init ("fake");

        // Act - Call Dispose() multiple times
        Exception? exception = Record.Exception (() =>
                                                 {
                                                     app.Dispose ();
                                                     app.Dispose ();
                                                     app.Dispose ();
                                                 });

        // Assert - Should not throw
        Assert.Null (exception);

        _createdApps.Remove (app);
    }

    /// <summary>
    ///     Verifies that multiple applications can be created and disposed without thread leaks.
    ///     This simulates the ColorPicker test scenario where multiple ApplicationImpl instances
    ///     are created in parallel tests and must all be properly cleaned up.
    /// </summary>
    [Fact]
    public void Multiple_Applications_Dispose_Without_Thread_Leaks ()
    {
        const int COUNT = 5;
        IApplication [] apps = new IApplication [COUNT];

        // Arrange - Create multiple applications (simulating parallel test scenario)
        for (var i = 0; i < COUNT; i++)
        {
            apps [i] = Application.Create ();
            apps [i].Init ("fake");
        }

        // Act - Dispose all applications
        var sw = Stopwatch.StartNew ();

        for (var i = 0; i < COUNT; i++)
        {
            apps [i].Dispose ();
        }

        sw.Stop ();

        // Assert - All disposals should complete quickly
        // If input threads don't stop, this will hang or take a very long time
        Assert.True (sw.ElapsedMilliseconds < 5000, $"Disposing {COUNT} apps took {sw.ElapsedMilliseconds}ms - input threads may not have stopped");
    }

    /// <summary>
    ///     Verifies that the 20ms throttle limits the input loop poll rate to prevent CPU spinning.
    ///     This test proves throttling exists by verifying the poll rate is bounded (not millions of calls).
    ///     The test uses an upper bound approach to avoid timing sensitivity issues during parallel execution.
    /// </summary>
    [Fact (Skip = "Can't get this to run reliably.")]
    public void InputLoop_Throttle_Limits_Poll_Rate ()
    {
        // Arrange - Create a FakeInput and manually run it with throttling
        FakeInput input = new FakeInput ();
        ConcurrentQueue<ConsoleKeyInfo> queue = new ConcurrentQueue<ConsoleKeyInfo> ();
        input.Initialize (queue);

        CancellationTokenSource cts = new CancellationTokenSource ();

        // Act - Run the input loop for 500ms
        // Short duration reduces test time while still proving throttle exists
        Task inputTask = Task.Run (() => input.Run (cts.Token), cts.Token);

        Thread.Sleep (500);

        int peekCount = input.PeekCallCount;
        cts.Cancel ();

        // Wait for task to complete
        bool completed = inputTask.Wait (TimeSpan.FromSeconds (10));
        Assert.True (completed, "Input task did not complete within timeout");

        // Assert - The key insight: throttle prevents CPU spinning
        // With 20ms throttle: ~25 calls in 500ms (but can be much less under load)
        // WITHOUT throttle: Would be 10,000+ calls minimum (tight spin loop)
        //
        // We use an upper bound test: verify it's NOT spinning wildly
        // This is much more reliable than testing exact timing under parallel load
        //
        // Max 500 calls = average 1ms between polls (still proves 20ms throttle exists)
        // Without throttle = millions of calls (tight loop)
        Assert.True (peekCount < 500, $"Poll count {peekCount} suggests no throttling (expected <500 with 20ms throttle)");

        // Also verify the thread actually ran (not immediately cancelled)
        Assert.True (peekCount > 0, $"Poll count was {peekCount} - thread may not have started");

        input.Dispose ();
    }

    /// <summary>
    ///     Verifies that the 20ms throttle prevents CPU spinning even with many leaked applications.
    ///     Before the throttle fix, 10+ leaked apps would saturate the CPU with tight spin loops.
    /// </summary>
    [Fact]
    public void Throttle_Prevents_CPU_Saturation_With_Leaked_Apps ()
    {
        const int COUNT = 10;
        IApplication [] apps = new IApplication [COUNT];

        // Arrange - Create multiple applications WITHOUT disposing them (simulating the leak)
        for (var i = 0; i < COUNT; i++)
        {
            apps [i] = Application.Create ();
            apps [i].Init ("fake");
        }

        // Let them run for a moment
        Thread.Sleep (100);

        // Act - Now dispose them all and measure how long it takes
        var sw = Stopwatch.StartNew ();

        for (var i = 0; i < COUNT; i++)
        {
            apps [i].Dispose ();
        }

        sw.Stop ();

        // Assert - Even with 10 leaked apps, disposal should be fast
        // Before the throttle fix, this would take many seconds due to CPU saturation
        // With the throttle, each thread does Task.Delay(20ms) and exits within ~20-40ms
        Assert.True (sw.ElapsedMilliseconds < 2000, $"Disposing {COUNT} apps took {sw.ElapsedMilliseconds}ms - CPU may be saturated");
    }
}