<!--
  Note: if the issue is about documentation or the website, please file it at:
  https://github.com/reactjs/reactjs.org/issues/new
-->

**Do you want to request a *feature* or report a *bug*?**

Bug

**What is the current behavior?**

Referring to [this twitter conversation](https://twitter.com/milankinen/status/1161718618633248768?s=20), it seems that `use-subscription` can cause "UI tearing" in some random cases due to a (possible) race condition w.r.t. the combination of `subscribe` and `getCurrentValue` in internal usage.

Here is a minimalistic application demonstrating the behaviour: https://github.com/milankinen/use-subscription-tearing-demo

**What is the expected behavior?**

I'd expect counters in the example application to *always* render same number.

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**

Tested React version: 16.9.0 (haven't tested with older ones)
OS: OSX 10.14.6
Hardware: MacBook Pro (Retina, 15-inch, Mid 2015) 2.8 GHz Intel Core i7 & 16GB RAM
Browser: Chrome Version 76.0.3809.100 (Official Build) (64-bit)



@bvaughn 
expect(Scheduler).toHaveYielded(['initial']);
    act(() => observable.next('updated'));
    expect(Scheduler).toHaveYielded(['updated']);
    Scheduler.unstable_flushAll();
    
    observable = createReplaySubject(undefined);
    act(() => renderer.update(<Subscription source={observable} />));
    expect(Scheduler).toHaveYielded(['default']);
  });
  it('should unsubscribe from old sources and subscribe to new sources when memoized props change', () => {
    function Child({value = 'default'}) {
      Scheduler.unstable_yieldValue(value);
      return null;
    }
    let subscriptions = [];
    function Subscription({source}) {
      const value = useSubscription(
        React.useMemo(
          () => ({
            getCurrentValue: () => source.getValue(),
            subscribe: callback => {
              subscriptions.push(source);
              const subscription = source.subscribe(callback);
              return () => subscription.unsubscribe();
            },
          }),
          [source],
        ),
      );
      return <Child value={value} />;