Question

这是对我之前的一个问题here的跟进。总而言之，我正在尝试为这个场景设计一个无锁设计，在我取消任务时我想调用第三方库的方法。在回答我的问题时，一位有用的SO参与者建议使用CancellationToken.Register，但我不知道在哪里以及如何在这里使用它。下面是我提出的代码。如果您发现此方法存在任何问题，或者有更好的替代方案可以解决此问题，请与我们联系。

class ProcessEmployees
    {
        private List<Employee> _Employees;
        CancellationTokenSource cs = new CancellationTokenSource();

        public  ProcessEmployees()
        {
            _Employees = new List<Employee>() 
            {
                new Employee() { ID = 1, FirstName = "John", LastName = "Doe" },
                new Employee() { ID = 2, FirstName = "Peter", LastName = "Saul" },
                new Employee() { ID = 3, FirstName = "Mike", LastName = "Sue" },
                new Employee() { ID = 4, FirstName = "Catherina", LastName = "Desoza" },
                new Employee() { ID = 5, FirstName = "Paul", LastName = "Smith" }
            };
        }

        public void StartProcessing()
        {
            try
            {
                Task[] tasks = this._Employees.AsParallel().WithCancellation(cs.Token).Select(x => this.ProcessThisEmployee(x, cs.Token)).ToArray();
                Task.WaitAll(tasks);
            }
            catch (AggregateException ae)
            {
                // error handling code
            }
            // other stuff
        }

        private async Task ProcessThisEmployee(Employee x, CancellationToken token)
        {
            ThirdPartyLibrary library = new ThirdPartyLibrary();
            if (token.IsCancellationRequested)
                token.ThrowIfCancellationRequested();
            await Task.Factory.StartNew(() => library.SomeAPI(x) );
            if (token.IsCancellationRequested)
            {
                library.Clean();
                token.ThrowIfCancellationRequested();
            }
        }
    }

Answer 1

您的流程代码可以简化为以下（这是您使用注册的方式）

private void ProcessThisEmployee(Employee x, CancellationToken token)
{
    ThirdPartyLibrary library = new ThirdPartyLibrary();
    token.ThrowIfCancellationRequested();
    using(token.Register(() => library.Clean())
    {
        library.SomeAPI(x);
    }
    token.ThrowIfCancellationRequested(); //Not sure why you cancel here in your original example.
}

如果在using语句的范围内取消令牌，它将调用library.Clean()如果之后调用它，则它不会调用该函数。我也摆脱了你的Task.Run，没有理由浪费额外的线索来做你正在做的事情。最后我摆脱了额外的if (token.IsCancellationRequested)检查，ThrowIfCancellationRequested()如果检查内部，你不需要事先检查。

此外，因为在我的简化中，您不再返回任务，您的StartProcessing代码变为

    public void StartProcessing()
    {
        try
        {
            this._Employees.AsParallel().WithCancellation(cs.Token).ForAll(x => this.ProcessThisEmployee(x, cs.Token));
        }
        catch (AggregateException ae)
        {
            // error handling code
        }
        // other stuff
    }

使用ForAll(代替Select(

对于这种情况，这是否是无锁设计的合理方法

1 个答案: