What are the default Schedulers for each observable operator?

c#, system.reactive

Solution

Wow, that was not trivial to find...

Deep within the bowels of the `System.Reactive.Concurrency` namespace, there is an internal static class called `SchedulerDefaults`, which is declared as:

internal static class SchedulerDefaults
{
    internal static IScheduler AsyncConversions 
    { get { return DefaultScheduler.Instance; }}

    internal static IScheduler ConstantTimeOperations 
    { get { return ImmediateScheduler.Instance; }}

    internal static IScheduler Iteration 
    { get { return CurrentThreadScheduler.Instance; }}

    internal static IScheduler TailRecursion 
    { get { return ImmediateScheduler.Instance; }}

    internal static IScheduler TimeBasedOperations 
    { get { return DefaultScheduler.Instance; }}
}

`AsyncConversions` is used by:

Start, ToAsync, FromAsyncPattern

`ConstantTimeOperations` is used by:

Empty, GetSchedulerForCurrentContext, Return, StartWith, Throw

`Iteration` is used by:

Generate, Range, Repeat, TakeLast, ToObservable, and the ReplaySubject<T>

`TailRecursion` is used by:

Run

`TimeBasedOperations` is used by:

Buffer, Delay, DelaySubscription, Generate, Interval, Sample, Skip, SkipLast
SkipUntil, Take, TakeLast, TakeLastBuffer, TakeUntil, Throttle, TimeInterval,
Timeout, Timer, Timestamp, Window

Problem

This page on MSDN states that If you do not use the overload which takes a scheduler as an argument, Rx will pick a default scheduler by using the principle of least concurrency. This means that the scheduler which introduces the least amount of concurrency that satisfies the needs of the operator is chosen. For example, for operators returning an observable with a finite and small number of messages, Rx calls Immediate. For operators returning a potentially large or infinite number of messages, CurrentThread is called. For operators which use timers, ThreadPool is used. I would like to actually have a reference sheet for which observable operators use which default Scheduler, but I can't find one anywhere. What are the default Schedulers for each observable operator?

Original source