Make constructs the future.

MakeAwaitableFuture wraps underlying future so that the callers can wait for future to become available.

MakeCompletedErrorFuture constructs completed ErrorFuture.

MakeCompletedFuture constructs future which returns specified value.

MustSet sets future value, and returns an error indicating if the value was set.

Wait is a helper function that waits until future becomes ready and returns its value.

AwaitableFuture is a future that can be waited on.

Future represents a value which will become ready in the future.