Fix feature sync isolations.

Author: johnteee

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "fp_rust"
-version = "0.3.4"
+version = "0.3.5"
 license = "MIT"
 authors = ["JunYi JohnTeee Lee <johnteee@gmail.com>"]
 edition = "2018"

src/sync.rs

@@ -24,7 +24,10 @@ use std::pin::Pin;
 use std::task::{Context, Poll, Waker};
 
 use super::common::{Observable, RawFunc, SubscriptionFunc};
+
+#[cfg(feature = "handler")]
 use super::handler::{Handler, HandlerThread};
+#[cfg(feature = "publisher")]
 use super::publisher::Publisher;
 
 /**