节流Rx.Observable而不跳过值

Question

如果其他人跟随太快，则Throttle方法会从可观察序列中跳过值。 但我需要一种方法来延迟它们。 也就是说，我需要在项目之间设置最小延迟，而不是跳过任何项目 。

实际例子：有一个Web服务可以接受不超过一秒的请求; 有一个用户可以单独或批量添加请求。 没有Rx，我将创建一个列表和一个计时器。 当用户添加请求时，我会将它们添加到列表中。 在计时器事件中，我将检查列表是否为空。 如果不是，我将发送请求并删除相应的项目。 随着锁和所有的东西。 现在，使用Rx，我可以创建Subject ，在用户添加请求时添加项目。 但我需要一种方法来确保Web服务不会因应用延迟而泛滥。

我是Rx的新手，所以也许我错过了一些明显的东西。

Answer 1

使用EventLoopScheduler有一种相当简单的方法可以做你想做的EventLoopScheduler 。

我从一个observable开始，每隔0到3秒就会随机产生一次值。

var rnd = new Random();

var xs =
    Observable
        .Generate(
            0,
            x => x < 20,
            x => x + 1,
            x => x,
            x => TimeSpan.FromSeconds(rnd.NextDouble() * 3.0));

现在，要立即生成此输出值，除非最后一个值在一秒钟之内，我这样做：

var ys =
    Observable.Create<int>(o =>
    {
        var els = new EventLoopScheduler();
        return xs
            .ObserveOn(els)
            .Do(x => els.Schedule(() => Thread.Sleep(1000)))
            .Subscribe(o);
    });

这有效地观察了EventLoopScheduler上的EventLoopScheduler ，然后在每个OnNext之后将其置于休眠状态1秒，这样它只能在唤醒之后开始下一个OnNext 。

我测试它使用此代码：

ys
    .Timestamp()
    .Select(x => x.Timestamp.Second + (double)x.Timestamp.Millisecond/1000.0)
    .Subscribe(x => Console.WriteLine(x));

我希望这有帮助。

Answer 2

我想建议使用Observable.Zip的方法：

// Incoming requests
var requests = new[] {1, 2, 3, 4, 5}.ToObservable();

// defines the frequency of the incoming requests
// This is the way to emulate flood of incoming requests.
// Which, by the way, uses the same approach that will be used in the solution
var requestsTimer = Observable.Interval(TimeSpan.FromSeconds(0.1)); 
var incomingRequests = Observable.Zip(requests, requestsTimer, (number, time) => {return number;});
incomingRequests.Subscribe((number) =>
{
    Console.WriteLine($"Request received: {number}");
});

// This the minimum interval at which we want to process the incoming requests
var processingTimeInterval = Observable.Interval(TimeSpan.FromSeconds(1));

// Zipping incoming requests with the interval
var requestsToProcess = Observable.Zip(incomingRequests, processingTimeInterval, (data, time) => {return data;});

requestsToProcess.Subscribe((number) =>
{
    Console.WriteLine($"Request processed: {number}");
});

Answer 3

一个简单的扩展方法怎么样：

public static IObservable<T> StepInterval<T>(this IObservable<T> source, TimeSpan minDelay)
{
    return source.Select(x => 
        Observable.Empty<T>()
            .Delay(minDelay)
            .StartWith(x)
    ).Concat();
}

用法：

var bufferedSource = source.StepInterval(TimeSpan.FromSeconds(1));

Answer 4

我正在玩这个并发现.Zip（如前所述）是最简单的方法：

var stream = "ThisFastObservable".ToObservable();
var slowStream = 
    stream.Zip(
        Observable.Interval(TimeSpan.FromSeconds(1)), //Time delay 
        (x, y) => x); // We just care about the original stream value (x), not the interval ticks (y)

slowStream.TimeInterval().Subscribe(x => Console.WriteLine($"{x.Value} arrived after {x.Interval}"));

输出：

T arrived after 00:00:01.0393840
h arrived after 00:00:00.9787150
i arrived after 00:00:01.0080400
s arrived after 00:00:00.9963000
F arrived after 00:00:01.0002530
a arrived after 00:00:01.0003770
s arrived after 00:00:00.9963710
t arrived after 00:00:01.0026450
O arrived after 00:00:00.9995360
b arrived after 00:00:01.0014620
s arrived after 00:00:00.9993100
e arrived after 00:00:00.9972710
r arrived after 00:00:01.0001240
v arrived after 00:00:01.0016600
a arrived after 00:00:00.9981140
b arrived after 00:00:01.0033980
l arrived after 00:00:00.9992570
e arrived after 00:00:01.0003520

Answer 5

如何使用可观察的计时器从阻塞队列中获取？ 下面的代码未经测试，但应该让您了解我的意思......

//assuming somewhere there is 
BlockingCollection<MyWebServiceRequestData> workQueue = ...

Observable
  .Timer(new TimeSpan(0,0,1), new EventLoopScheduler())
  .Do(i => myWebService.Send(workQueue.Take()));

// Then just add items to the queue using workQueue.Add(...)

Answer 6

考虑使用缓冲区。

http://msdn.microsoft.com/en-us/library/hh212130(v=vs.103).aspx

正如名称所示，它在可观察的事件流中缓冲元素而不“丢弃”它们中的任何一个。

-G

Answer 7

.Buffer(TimeSpan.FromSeconds(0.2)).Where(i => i.Any())
.Subscribe(buffer => 
{
     foreach(var item in buffer) Console.WriteLine(item)
});