1. 使用单例模式确保只有一个任务正在运行。

public class BackgroundTaskService {
    private readonly SemaphoreSlim _semaphore = new SemaphoreSlim(1);

    private bool _isRunning;

    public async Task StartAsync() {
        if (!_isRunning) {
            await _semaphore.WaitAsync();

            try {
                if (!_isRunning) {
                    _isRunning = true;

                    // Start background task here
                }
            } finally {
                _semaphore.Release();
            }
        }
    }

    public void Stop() {
        if (_isRunning) {
            _isRunning = false;

            // Stop background task here
        }
    }
}

2. 使用 CancellationTokenSource 取消正在运行的任务，然后启动新任务。

public static class BackgroundTask {
    private static CancellationTokenSource _cancellationTokenSource;

    public static void Start() {
        if (_cancellationTokenSource != null && !_cancellationTokenSource.IsCancellationRequested) {
            _cancellationTokenSource.Cancel();

            // Wait for previous task to exit
            try {
                Task.Delay(1000).Wait();
            } catch (AggregateException) {
            }
        }

        _cancellationTokenSource = new CancellationTokenSource();

        Task.Run(() => {
            while (true) {
                if (_cancellationTokenSource.IsCancellationRequested) {
                    break;
                }

                // Do work here

                Thread.Sleep(1000);
            }
        }, _cancellationTokenSource.Token);
    }

    public static void Stop() {
        if (_cancellationTokenSource != null && !_cancellationTokenSource.IsCancellationRequested) {
            _cancellationTokenSource.Cancel();

            // Wait for task to exit
            try {
                Task.Delay(1000).Wait();
            } catch (AggregateException) {
            }
        }
    }
}