Enumerable overload of Zip does not synchronize enumerator disposal

[glopesdev]

Iterators are synchronized structures that do not expect to be called reentrantly.

The current implementation of Zip that takes in an IEnumerable source calls the Dispose method of the iterator directly when the subscription is disposed. However, this raises the possibility that active MoveNext calls are still being executed asynchronously on another thread.

The example below illustrates this scenario.

static IEnumerable<int> MyEnum()
{
    try
    {
        Console.WriteLine("start");
        Thread.Sleep(2000);
        Console.WriteLine("yield");
        yield return 0;
    }
    finally
    {
        Console.WriteLine("dispose");
    }
}

static void Main(string[] args)
{
    var timer = Observable.Timer(TimeSpan.Zero, TimeSpan.FromSeconds(1));
    var handle = timer.Zip(MyEnum(), (x, y) => y).Subscribe();
    Thread.Sleep(500);
    handle.Dispose();
    Console.ReadLine();
}

[akarnokd]

Sounds like a forgotten bug. I'll look into it for 4.x.