subscribe
Registers a weak subscriber that will be called when the value of this Provider changes. If multiple threads update the value concurrently, subscriber invocations may be skipped and values may be out of order. If resolving the value of this Provider throws an exception, subscriber invocations will be skipped silently. The subscriber will be automatically removed when the owner is garbage collected.
Registering a subscriber disables lazy evaluation of the provider.
The given value is not guaranteed to still be the current value at the time of invocation.