diff --git a/Cargo.toml b/Cargo.toml
index 23e0554..1fdc18b 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -17,6 +17,11 @@ async-trait = "0.1.42"
 futures = "0.3.8"
 anyhow = "1.0.34"
 crossbeam = "0.8.1"
+uuid = "0.8.2"
+tokio-util = "0.6.7"
+async-stream = "0.3.2"
+smallvec = "1.6.1"
+log = "0.4.14"
 
 [dev-dependencies]
 tokio = { version = "1", features = ["macros", "parking_lot", "rt-multi-thread", "io-util", "sync"] }
diff --git a/examples/demo_async.rs b/examples/demo_async.rs
index 6330cbb..dcbd72c 100644
--- a/examples/demo_async.rs
+++ b/examples/demo_async.rs
@@ -1,15 +1,24 @@
 use async_trait::async_trait;
-use messagebus::{receivers, AsyncHandler, Bus, Handler, Result as MbusResult};
+use messagebus::{receivers, AsyncHandler, Bus, Handler};
 
 struct TmpReceiver;
 struct TmpReceiver2;
 
 #[async_trait]
 impl AsyncHandler<f32> for TmpReceiver {
-    async fn handle(&self, msg: f32, bus: &Bus) -> MbusResult {
+    type Error = anyhow::Error;
+    type Response = ();
+
+    async fn handle(&self, msg: f32, bus: &Bus) -> Result<Self::Response, Self::Error> {
         bus.send(1u16).await?;
 
-        println!("---> f32 {}", msg);
+        println!("TmpReceiver ---> f32 {}", msg);
+
+        Ok(())
+    }
+
+    async fn sync(&self, _bus: &Bus) -> Result<(), Self::Error> {
+        println!("TmpReceiver f32: sync");
 
         Ok(())
     }
@@ -17,9 +26,18 @@ impl AsyncHandler<f32> for TmpReceiver {
 
 #[async_trait]
 impl AsyncHandler<u16> for TmpReceiver {
-    async fn handle(&self, msg: u16, bus: &Bus) -> MbusResult {
+    type Error = anyhow::Error;
+    type Response = ();
+
+    async fn handle(&self, msg: u16, bus: &Bus) -> Result<Self::Response, Self::Error> {
         bus.send(2u32).await?;
-        println!("---> u16 {}", msg);
+        println!("TmpReceiver ---> u16 {}", msg);
+
+        Ok(())
+    }
+
+    async fn sync(&self, _bus: &Bus) -> Result<(), Self::Error> {
+        println!("TmpReceiver u16: sync");
 
         Ok(())
     }
@@ -27,9 +45,17 @@ impl AsyncHandler<u16> for TmpReceiver {
 
 #[async_trait]
 impl AsyncHandler<u32> for TmpReceiver {
-    async fn handle(&self, msg: u32, bus: &Bus) -> MbusResult {
+    type Error = anyhow::Error;
+    type Response = ();
+
+    async fn handle(&self, msg: u32, bus: &Bus) -> Result<Self::Response, Self::Error> {
         bus.send(3i32).await?;
-        println!("---> u32 {}", msg);
+        println!("TmpReceiver ---> u32 {}", msg);
+
+        Ok(())
+    }
+    async fn sync(&self, _bus: &Bus) -> Result<(), Self::Error> {
+        println!("TmpReceiver u32: sync");
 
         Ok(())
     }
@@ -37,9 +63,18 @@ impl AsyncHandler<u32> for TmpReceiver {
 
 #[async_trait]
 impl AsyncHandler<i32> for TmpReceiver {
-    async fn handle(&self, msg: i32, bus: &Bus) -> MbusResult {
+    type Error = anyhow::Error;
+    type Response = ();
+
+    async fn handle(&self, msg: i32, bus: &Bus) -> Result<Self::Response, Self::Error> {
         bus.send(4i16).await?;
-        println!("---> i32 {}", msg);
+        println!("TmpReceiver ---> i32 {}", msg);
+
+        Ok(())
+    }
+
+    async fn sync(&self, _bus: &Bus) -> Result<(), Self::Error> {
+        println!("TmpReceiver i32: sync");
 
         Ok(())
     }
@@ -47,8 +82,16 @@ impl AsyncHandler<i32> for TmpReceiver {
 
 #[async_trait]
 impl AsyncHandler<i16> for TmpReceiver {
-    async fn handle(&self, msg: i16, _bus: &Bus) -> MbusResult {
-        println!("---> i16 {}", msg);
+    type Error = anyhow::Error;
+    type Response = ();
+
+    async fn handle(&self, msg: i16, _bus: &Bus) -> Result<Self::Response, Self::Error> {
+        println!("TmpReceiver ---> i16 {}", msg);
+
+        Ok(())
+    }
+    async fn sync(&self, _bus: &Bus) -> Result<(), Self::Error> {
+        println!("TmpReceiver i16: sync");
 
         Ok(())
     }
@@ -56,17 +99,35 @@ impl AsyncHandler<i16> for TmpReceiver {
 
 #[async_trait]
 impl AsyncHandler<i32> for TmpReceiver2 {
-    async fn handle(&self, msg: i32, bus: &Bus) -> MbusResult {
+    type Error = anyhow::Error;
+    type Response = ();
+
+    async fn handle(&self, msg: i32, bus: &Bus) -> Result<Self::Response, Self::Error> {
+        println!("!!!! TmpReceiver2: ---> 2 i32 {}", msg);
+
         bus.send(5i16).await?;
-        println!("---> 2 i32 {}", msg);
+
+        Ok(())
+    }
+    async fn sync(&self, _bus: &Bus) -> Result<(), Self::Error> {
+        println!("TmpReceiver2: i32: sync");
 
         Ok(())
     }
 }
 
 impl Handler<i16> for TmpReceiver2 {
-    fn handle(&self, msg: i16, _bus: &Bus) -> MbusResult {
-        println!("---> 2 i16 {}", msg);
+    type Error = anyhow::Error;
+    type Response = ();
+
+    fn handle(&self, msg: i16, _bus: &Bus) -> Result<Self::Response, Self::Error> {
+        println!("TmpReceiver2: ---> 2 i16 {}", msg);
+
+        Ok(())
+    }
+
+    fn sync(&self, _bus: &Bus) -> Result<(), Self::Error> {
+        println!("TmpReceiver2: i16: sync");
 
         Ok(())
     }
@@ -76,18 +137,26 @@ impl Handler<i16> for TmpReceiver2 {
 async fn main() {
     let (b, poller) = Bus::build()
         .register(TmpReceiver)
-        .subscribe::<f32, receivers::BufferUnorderedAsync<_>>(Default::default())
-        .subscribe::<u16, receivers::BufferUnorderedAsync<_>>(Default::default())
-        .subscribe::<u32, receivers::BufferUnorderedAsync<_>>(Default::default())
-        .subscribe::<i32, receivers::BufferUnorderedAsync<_>>(Default::default())
-        .subscribe::<i16, receivers::BufferUnorderedAsync<_>>(Default::default())
+        .subscribe::<f32, receivers::BufferUnorderedAsync<_>, _, _>(8, Default::default())
+        .subscribe::<u16, receivers::BufferUnorderedAsync<_>, _, _>(8, Default::default())
+        .subscribe::<u32, receivers::BufferUnorderedAsync<_>, _, _>(8, Default::default())
+        .subscribe::<i32, receivers::BufferUnorderedAsync<_>, _, _>(8, Default::default())
+        .subscribe::<i16, receivers::BufferUnorderedAsync<_>, _, _>(8, Default::default())
         .done()
         .register(TmpReceiver2)
-        .subscribe::<i32, receivers::BufferUnorderedAsync<_>>(Default::default())
-        .subscribe::<i16, receivers::BufferUnorderedSync<_>>(Default::default())
+            .subscribe::<i32, receivers::BufferUnorderedAsync<_>, _, _>(8, Default::default())
+            .subscribe::<i16, receivers::BufferUnorderedSync<_>, _, _>(8, Default::default())
         .done()
-        .build();
+    .build();
 
     b.send(0f32).await.unwrap();
-    poller.await
+
+    println!("flush");
+    b.flush().await;
+
+    println!("close");
+    b.close().await;
+
+    poller.await;
+    println!("[done]");
 }
diff --git a/examples/demo_backpressure.rs b/examples/demo_backpressure.rs
index 8fe85a3..7c21799 100644
--- a/examples/demo_backpressure.rs
+++ b/examples/demo_backpressure.rs
@@ -1,9 +1,14 @@
-use messagebus::{receivers, Bus, Handler, Result as MbusResult};
+use async_trait::async_trait;
+use messagebus::{receivers, Bus, AsyncHandler};
 
 struct TmpReceiver;
 
-impl Handler<f32> for TmpReceiver {
-    fn handle(&self, msg: f32, _bus: &Bus) -> MbusResult {
+#[async_trait]
+impl AsyncHandler<f32> for TmpReceiver {
+    type Error = anyhow::Error;
+    type Response = ();
+
+    async fn handle(&self, msg: f32, _bus: &Bus) -> Result<Self::Response, Self::Error> {
         println!("---> f32 {}", msg);
 
         std::thread::sleep(std::time::Duration::from_secs(1));
@@ -17,7 +22,7 @@ impl Handler<f32> for TmpReceiver {
 async fn main() {
     let (b, poller) = Bus::build()
         .register(TmpReceiver)
-        .subscribe::<f32, receivers::BufferUnorderedSync<_>>(receivers::BufferUnorderedConfig {
+        .subscribe::<f32, receivers::BufferUnorderedAsync<_>, _, _>(1, receivers::BufferUnorderedConfig {
             buffer_size: 1,
             max_parallel: 1,
         })
@@ -57,7 +62,12 @@ async fn main() {
     println!("sending 11");
     b.send(32f32).await.unwrap();
 
-    println!("finish");
+    println!("flush");
+    b.flush().await;
+
+    println!("close");
+    b.close().await;
 
     poller.await;
+    println!("[done]");
 }
diff --git a/examples/demo_slow.rs b/examples/demo_slow.rs
index ffcedaa..9031010 100644
--- a/examples/demo_slow.rs
+++ b/examples/demo_slow.rs
@@ -1,9 +1,12 @@
-use messagebus::{receivers, Bus, Handler, Result as MbusResult};
+use messagebus::{receivers, Bus, Handler};
 
 struct TmpReceiver;
 
 impl Handler<f32> for TmpReceiver {
-    fn handle(&self, msg: f32, _bus: &Bus) -> MbusResult {
+    type Error = anyhow::Error;
+    type Response = ();
+
+    fn handle(&self, msg: f32, _bus: &Bus) -> Result<Self::Response, Self::Error> {
         println!("---> f32 {}", msg);
 
         std::thread::sleep(std::time::Duration::from_secs(5));
@@ -15,14 +18,20 @@ impl Handler<f32> for TmpReceiver {
 }
 
 impl Handler<u16> for TmpReceiver {
-    fn handle(&self, msg: u16, _bus: &Bus) -> MbusResult {
+    type Error = anyhow::Error;
+    type Response = ();
+
+    fn handle(&self, msg: u16, _bus: &Bus) -> Result<Self::Response, Self::Error> {
         println!("---> u16 {}", msg);
         Ok(())
     }
 }
 
 impl Handler<u32> for TmpReceiver {
-    fn handle(&self, msg: u32, _bus: &Bus) -> MbusResult {
+    type Error = anyhow::Error;
+    type Response = ();
+
+    fn handle(&self, msg: u32, _bus: &Bus) -> Result<Self::Response, Self::Error> {
         println!("---> u32 {}", msg);
         Ok(())
     }
@@ -32,9 +41,9 @@ impl Handler<u32> for TmpReceiver {
 async fn main() {
     let (b, poller) = Bus::build()
         .register(TmpReceiver)
-        .subscribe::<f32, receivers::BufferUnorderedSync<_>>(Default::default())
-        .subscribe::<u16, receivers::BufferUnorderedSync<_>>(Default::default())
-        .subscribe::<u32, receivers::BufferUnorderedSync<_>>(Default::default())
+        .subscribe::<f32, receivers::BufferUnorderedSync<_>, _, _>(8, Default::default())
+        .subscribe::<u16, receivers::BufferUnorderedSync<_>, _, _>(8, Default::default())
+        .subscribe::<u32, receivers::BufferUnorderedSync<_>, _, _>(8, Default::default())
         .done()
         .build();
 
@@ -42,5 +51,12 @@ async fn main() {
     b.send(11u16).await.unwrap();
     b.send(32u32).await.unwrap();
 
-    poller.await
+    println!("flush");
+    b.flush().await;
+
+    println!("close");
+    b.close().await;
+
+    poller.await;
+    println!("[done]");
 }
diff --git a/src/builder.rs b/src/builder.rs
index c9237bf..f7c4b9e 100644
--- a/src/builder.rs
+++ b/src/builder.rs
@@ -20,7 +20,13 @@ pub trait ReceiverSubscriber<T: 'static> {
     );
 }
 
-pub trait ReceiverSubscriberBuilder<M, T: 'static> {
+pub trait ReceiverSubscriberBuilder<T, M, R, E> 
+    where
+        T: 'static,
+        M: Message,
+        R: Message,
+        E: crate::Error
+{
     type Entry: ReceiverSubscriber<T>;
     type Config: Default;
 
@@ -44,6 +50,7 @@ pub struct RegisterEntry<K, T> {
                 )
                     -> Box<dyn FnOnce(Bus) -> Pin<Box<dyn Future<Output = ()> + Send>>>,
             >,
+            Box<dyn FnOnce(Bus) -> Pin<Box<dyn Future<Output = ()> + Send>>>
         )>,
     >,
     _m: PhantomData<(K, T)>,
@@ -54,10 +61,10 @@ impl<K, T: 'static> RegisterEntry<K, T> {
         let mut builder = self.builder;
 
         for (tid, v) in self.receivers {
-            for (r, poller) in v {
+            for (r, poller, poller2) in v {
                 let poller = poller(self.item.clone());
 
-                builder.add_recevier((tid, r), poller);
+                builder.add_recevier((tid, r), poller, poller2);
             }
         }
 
@@ -65,39 +72,45 @@ impl<K, T: 'static> RegisterEntry<K, T> {
     }
 }
 
-impl<T: Send + 'static> RegisterEntry<UnsyncEntry, T> {
-    pub fn subscribe<M, R>(mut self, cfg: R::Config) -> Self
+impl<T> RegisterEntry<UnsyncEntry, T> {
+    pub fn subscribe<M, S, R, E>(mut self, queue: u64, cfg: S::Config) -> Self
     where
         T: Send + 'static,
-        M: Message + 'static,
-        R: ReceiverSubscriberBuilder<M, T> + 'static,
+        M: Message,
+        R: Message,
+        E: crate::Error,
+        S: ReceiverSubscriberBuilder<T, M, R, E> + 'static,
     {
-        let (inner, poller) = R::build(cfg).subscribe();
+        let (inner, poller) = S::build(cfg).subscribe();
 
-        let receiver = Receiver::new(inner);
+        let receiver = Receiver::new(queue, inner);
+        let poller2 = receiver.start_polling_events::<R, E>();
         self.receivers
             .entry(TypeId::of::<M>())
             .or_insert_with(Vec::new)
-            .push((receiver, poller));
+            .push((receiver, poller, poller2));
 
         self
     }
 }
 
-impl<T: Send + Sync + 'static> RegisterEntry<SyncEntry, T> {
-    pub fn subscribe<M, R>(mut self, cfg: R::Config) -> Self
+impl<T> RegisterEntry<SyncEntry, T> {
+    pub fn subscribe<M, S, R, E>(mut self, queue: u64, cfg: S::Config) -> Self
     where
-        T: Send + 'static,
-        M: Message + 'static,
-        R: ReceiverSubscriberBuilder<M, T> + 'static,
+        T: Send + Sync + 'static,
+        M: Message,
+        R: Message,
+        E: crate::Error,
+        S: ReceiverSubscriberBuilder<T, M, R, E> + 'static,
     {
-        let (inner, poller) = R::build(cfg).subscribe();
+        let (inner, poller) = S::build(cfg).subscribe();
 
-        let receiver = Receiver::new(inner);
+        let receiver = Receiver::new(queue, inner);
+        let poller2 = receiver.start_polling_events::<R, E>();
         self.receivers
             .entry(TypeId::of::<M>())
             .or_insert_with(Vec::new)
-            .push((receiver, poller));
+            .push((receiver, poller, poller2));
 
         self
     }
@@ -138,9 +151,11 @@ impl BusBuilder {
         &mut self,
         val: (TypeId, Receiver),
         poller: Box<dyn FnOnce(Bus) -> Pin<Box<dyn Future<Output = ()> + Send>>>,
+        poller2: Box<dyn FnOnce(Bus) -> Pin<Box<dyn Future<Output = ()> + Send>>>,
     ) {
         self.receivers.push(val);
         self.pollings.push(poller);
+        self.pollings.push(poller2);
     }
 
     pub fn build(self) -> (Bus, impl Future<Output = ()>) {
@@ -148,7 +163,7 @@ impl BusBuilder {
             inner: Arc::new(BusInner::new(self.receivers)),
         };
 
-        let mut futs = Vec::with_capacity(self.pollings.len());
+        let mut futs = Vec::with_capacity(self.pollings.len() * 2);
         for poller in self.pollings {
             futs.push(tokio::task::spawn(poller(bus.clone())));
         }
diff --git a/src/handler.rs b/src/handler.rs
index 7facd70..26b15ec 100644
--- a/src/handler.rs
+++ b/src/handler.rs
@@ -2,91 +2,128 @@ use crate::{Bus, Message};
 use async_trait::async_trait;
 
 pub trait Handler<M: Message>: Send + Sync {
-    fn handle(&self, msg: M, bus: &Bus) -> anyhow::Result<()>;
-    fn sync(&self, _bus: &Bus) -> anyhow::Result<()> {
+    type Error: crate::Error;
+    type Response: Message;
+
+    fn handle(&self, msg: M, bus: &Bus) -> Result<Self::Response, Self::Error>;
+    fn sync(&self, _bus: &Bus) -> Result<(), Self::Error> {
         Ok(())
     }
 }
 
 #[async_trait]
 pub trait AsyncHandler<M: Message>: Send + Sync {
-    async fn handle(&self, msg: M, bus: &Bus) -> anyhow::Result<()>;
-    async fn sync(&self, _bus: &Bus) -> anyhow::Result<()> {
+    type Error: crate::Error;
+    type Response: Message;
+
+    async fn handle(&self, msg: M, bus: &Bus) -> Result<Self::Response, Self::Error>;
+    async fn sync(&self, _bus: &Bus) -> Result<(), Self::Error> {
         Ok(())
     }
 }
 
 pub trait SynchronizedHandler<M: Message>: Send {
-    fn handle(&mut self, msg: M, bus: &Bus) -> anyhow::Result<()>;
-    fn sync(&mut self, _bus: &Bus) -> anyhow::Result<()> {
+    type Error: crate::Error;
+    type Response: Message;
+
+    fn handle(&mut self, msg: M, bus: &Bus) -> Result<Self::Response, Self::Error>;
+    fn sync(&mut self, _bus: &Bus) -> Result<(), Self::Error> {
         Ok(())
     }
 }
 
 #[async_trait]
 pub trait AsyncSynchronizedHandler<M: Message>: Send {
-    async fn handle(&mut self, msg: M, bus: &Bus) -> anyhow::Result<()>;
-    async fn sync(&mut self, _bus: &Bus) -> anyhow::Result<()> {
+    type Error: crate::Error;
+    type Response: Message;
+
+    async fn handle(&mut self, msg: M, bus: &Bus) -> Result<Self::Response, Self::Error>;
+    async fn sync(&mut self, _bus: &Bus) -> Result<(), Self::Error> {
         Ok(())
     }
 }
 
 pub trait BatchHandler<M: Message>: Send + Sync {
-    fn handle(&self, msg: Vec<M>, bus: &Bus) -> anyhow::Result<()>;
-    fn sync(&self, _bus: &Bus) -> anyhow::Result<()> {
+    type Error: crate::Error;
+    type Response: Message;
+
+    fn handle(&self, msg: Vec<M>, bus: &Bus) -> Result<Vec<Self::Response>, Self::Error>;
+    fn sync(&self, _bus: &Bus) -> Result<(), Self::Error> {
         Ok(())
     }
 }
 
 #[async_trait]
 pub trait AsyncBatchHandler<M: Message>: Send + Sync {
-    async fn handle(&self, msg: Vec<M>, bus: &Bus) -> anyhow::Result<()>;
-    async fn sync(&self, _bus: &Bus) -> anyhow::Result<()> {
+    type Error: crate::Error;
+    type Response: Message;
+
+    async fn handle(&self, msg: Vec<M>, bus: &Bus) -> Result<Vec<Self::Response>, Self::Error>;
+    async fn sync(&self, _bus: &Bus) -> Result<(), Self::Error> {
         Ok(())
     }
 }
 
 pub trait BatchSynchronizedHandler<M: Message>: Send {
-    fn handle(&mut self, msg: Vec<M>, bus: &Bus) -> anyhow::Result<()>;
-    fn sync(&mut self, _bus: &Bus) -> anyhow::Result<()> {
+    type Error: crate::Error;
+    type Response: Message;
+
+    fn handle(&mut self, msg: Vec<M>, bus: &Bus) -> Result<Vec<Self::Response>, Self::Error>;
+    fn sync(&mut self, _bus: &Bus) -> Result<(), Self::Error> {
         Ok(())
     }
 }
 
 #[async_trait]
 pub trait AsyncBatchSynchronizedHandler<M: Message>: Send {
-    async fn handle(&mut self, msg: Vec<M>, bus: &Bus) -> anyhow::Result<()>;
-    async fn sync(&mut self, _bus: &Bus) -> anyhow::Result<()> {
+    type Error: crate::Error;
+    type Response: Message;
+
+    async fn handle(&mut self, msg: Vec<M>, bus: &Bus) -> Result<Vec<Self::Response>, Self::Error>;
+    async fn sync(&mut self, _bus: &Bus) -> Result<(), Self::Error> {
         Ok(())
     }
 }
 
 pub trait LocalHandler<M: Message> {
-    fn handle(&mut self, msg: Vec<M>, bus: &Bus) -> anyhow::Result<()>;
-    fn sync(&mut self, _bus: &Bus) -> anyhow::Result<()> {
+    type Error: crate::Error;
+    type Response: Message;
+
+    fn handle(&mut self, msg: Vec<M>, bus: &Bus) -> Result<Self::Response, Self::Error>;
+    fn sync(&mut self, _bus: &Bus) -> Result<(), Self::Error> {
         Ok(())
     }
 }
 
 #[async_trait]
 pub trait LocalAsyncHandler<M: Message> {
-    async fn handle(&mut self, msg: Vec<M>, bus: &Bus) -> anyhow::Result<()>;
-    async fn sync(&mut self, _bus: &Bus) -> anyhow::Result<()> {
+    type Error: crate::Error;
+    type Response: Message;
+
+    async fn handle(&mut self, msg: Vec<M>, bus: &Bus) -> Result<Self::Response, Self::Error>;
+    async fn sync(&mut self, _bus: &Bus) -> Result<(), Self::Error> {
         Ok(())
     }
 }
 
+
 pub trait LocalBatchHandler<M: Message> {
-    fn handle(&mut self, msg: Vec<M>, bus: &Bus) -> anyhow::Result<()>;
-    fn sync(&mut self, _bus: &Bus) -> anyhow::Result<()> {
+    type Error: crate::Error;
+    type Response: Message;
+
+    fn handle(&mut self, msg: Vec<M>, bus: &Bus) -> Result<Vec<Self::Response>, Self::Error>;
+    fn sync(&mut self, _bus: &Bus) -> Result<(), Self::Error> {
         Ok(())
     }
 }
 
 #[async_trait]
 pub trait LocalAsyncBatchHandler<M: Message> {
-    async fn handle(&mut self, msg: Vec<M>, bus: &Bus) -> anyhow::Result<()>;
-    async fn sync(&mut self, _bus: &Bus) -> anyhow::Result<()> {
+    type Error: crate::Error;
+    type Response: Message;
+
+    async fn handle(&mut self, msg: Vec<M>, bus: &Bus) -> Result<Vec<Self::Response>, Self::Error>;
+    async fn sync(&mut self, _bus: &Bus) -> Result<(), Self::Error> {
         Ok(())
     }
 }
diff --git a/src/lib.rs b/src/lib.rs
index ac7dfe7..b295bad 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -5,32 +5,44 @@ pub mod msgs;
 mod receiver;
 pub mod receivers;
 mod trait_object;
-mod utils;
+
+#[macro_use]
+extern crate log;
 
 use builder::BusBuilder;
 pub use envelop::Message;
 pub use handler::*;
 pub use receiver::SendError;
 use receiver::{Receiver, ReceiverStats};
-use utils::binary_search_range_by_key;
+use smallvec::SmallVec;
 
 use core::any::{Any, TypeId};
-use std::sync::{
-    atomic::{AtomicBool, Ordering},
-    Arc,
-};
+use std::{collections::HashMap, sync::{Arc, atomic::{AtomicBool, AtomicU64, Ordering}}};
+
+use crate::receivers::Permit;
 
 pub type Untyped = Arc<dyn Any + Send + Sync>;
-pub type Result = anyhow::Result<()>;
+
+// pub trait ErrorTrait: std::error::Error + Send + Sync + 'static {}
+pub trait Error: Into<anyhow::Error> + Send + Sync + 'static {}
+impl <T: Into<anyhow::Error> + Send + Sync + 'static> Error for T {}
+
+static ID_COUNTER: AtomicU64 = AtomicU64::new(1);
 
 pub struct BusInner {
-    receivers: Vec<(TypeId, Receiver)>,
+    receivers: HashMap<TypeId, SmallVec<[Receiver; 4]>>,
     closed: AtomicBool,
 }
 
 impl BusInner {
-    pub(crate) fn new(mut receivers: Vec<(TypeId, Receiver)>) -> Self {
-        receivers.sort_unstable_by_key(|(k, _)| *k);
+    pub(crate) fn new(input: Vec<(TypeId, Receiver)>) -> Self {
+        let mut receivers = HashMap::new();
+
+        for (key, value) in input {
+            receivers.entry(key)
+                .or_insert_with(SmallVec::new)
+                .push(value);
+        }
 
         Self {
             receivers,
@@ -38,42 +50,101 @@ impl BusInner {
         }
     }
 
-    pub fn close(&self) {
+    pub async fn close(&self) {
         self.closed.store(true, Ordering::SeqCst);
 
-        for (_, r) in &self.receivers {
-            r.close();
+        for (_, rs) in &self.receivers {
+            for r in rs {
+                r.close().await;
+            }
         }
     }
 
-    pub async fn sync(&self) {
-        for (_, r) in &self.receivers {
-            r.sync().await;
+    pub async fn flush(&self) {
+        let fuse_count = 32i32;
+        let mut breaked = false;
+        let mut iters = 0usize;
+        for _ in 0..fuse_count {
+            iters += 1;
+            let mut flushed = false;
+            for (_, rs) in &self.receivers {
+                
+                for r in rs {
+                    if r.need_flush() {
+                        flushed = true; 
+                        r.flush().await;
+                    }
+                }
+            }
+
+            if !flushed {
+                breaked = true;
+                break;
+            }
+        }
+
+        if !breaked {
+            warn!("!!! WARNING: unable to reach equilibrium in {} iterations !!!", fuse_count);
+        } else {
+            info!("flushed in {} iterations !!!", iters);
+        }
+    } 
+
+    pub async fn flash_and_sync(&self) {
+        self.flush().await;
+
+        for (_, rs) in &self.receivers {
+            for r in rs {
+                r.sync().await;
+            }
         }
     }
 
-    pub fn stats(&self) -> impl Iterator<Item = ReceiverStats> + '_ {
-        self.receivers.iter().map(|(_, r)| r.stats())
-    }
+    // pub fn stats(&self) -> impl Iterator<Item = ReceiverStats> + '_ {
+    //     self.receivers.iter()
+    //         .map(|(_, i)|i.iter())
+    //         .flatten()
+    //         .map(|r| r.stats())
+    // }
 
     pub fn try_send<M: Message>(&self, msg: M) -> core::result::Result<(), SendError<M>> {
         if self.closed.load(Ordering::SeqCst) {
-            println!("Bus closed. Skipping send!");
+            warn!("Bus closed. Skipping send!");
             return Ok(());
         }
 
+        let mid = ID_COUNTER.fetch_add(1, Ordering::Relaxed);
         let tid = TypeId::of::<M>();
-        let range = binary_search_range_by_key(&self.receivers, &tid, |(k, _)| *k);
 
-        for i in (range.start + 1)..range.end {
-            self.receivers[i].1.try_broadcast(msg.clone())?;
+        if let Some(rs) = self.receivers.get(&tid) {
+            let mut permits = SmallVec::<[Permit; 32]>::new();
+
+            for r in rs {
+                if let Some(prmt) = r.try_reserve() {
+                    permits.push(prmt);
+                } else {
+                    return Err(SendError::Full(msg));
+                };
+            }
+
+            let mut iter = permits.into_iter().zip(rs.iter());
+            let mut counter = 1;
+            let total = rs.len();
+
+            while counter < total {
+                let (p, r) = iter.next().unwrap();
+                let _ = r.send(mid, p, msg.clone());
+
+                counter += 1;
+            }
+
+            if let Some((p, r)) = iter.next() {
+                let _ = r.send(mid, p, msg);
+                return Ok(());
+            }
         }
 
-        if let Some((_, r)) = self.receivers.get(range.start) {
-            r.try_broadcast(msg.clone())?;
-        } else {
-            println!("Unhandled message {:?}", core::any::type_name::<M>());
-        }
+        warn!("Unhandled message {:?}: no receivers", core::any::type_name::<M>());
 
         Ok(())
     }
@@ -88,19 +159,48 @@ impl BusInner {
             return Err(SendError::Closed(msg));
         }
 
+        let mid = ID_COUNTER.fetch_add(1, Ordering::Relaxed);
         let tid = TypeId::of::<M>();
-        let range = binary_search_range_by_key(&self.receivers, &tid, |(k, _)| *k);
 
-        for i in (range.start + 1)..range.end {
-            self.receivers[i].1.broadcast(msg.clone()).await?;
+        if let Some(rs) = self.receivers.get(&tid) {
+            if let Some((last, head)) = rs.split_last() {
+                for r in head {
+                    let _ = r.send(mid, r.reserve().await, msg.clone());
+                }
+
+                let _ = last.send(mid, last.reserve().await, msg.clone());
+
+                return Ok(());
+            }
         }
 
-        if let Some((_, r)) = self.receivers.get(range.start) {
-            r.broadcast(msg.clone()).await?;
-        } else {
-            println!("Unhandled message {:?}", core::any::type_name::<M>());
+        warn!("Unhandled message {:?}: no receivers", core::any::type_name::<M>());
+
+        Ok(())
+    }
+
+    pub async fn force_send<M: Message>(&self, msg: M) -> core::result::Result<(), SendError<M>> {
+        if self.closed.load(Ordering::SeqCst) {
+            return Err(SendError::Closed(msg));
         }
 
+        let mid = ID_COUNTER.fetch_add(1, Ordering::Relaxed);
+        let tid = TypeId::of::<M>();
+
+        if let Some(rs) = self.receivers.get(&tid) {
+            if let Some((last, head)) = rs.split_last() {
+                for r in head {
+                    let _ = r.force_send(mid, msg.clone());
+                }
+
+                let _ = last.force_send(mid, msg.clone());
+
+                return Ok(());
+            }
+        }
+
+        warn!("Unhandled message {:?}: no receivers", core::any::type_name::<M>());
+
         Ok(())
     }
 }
diff --git a/src/receiver.rs b/src/receiver.rs
index b5d7907..d2ae4e0 100644
--- a/src/receiver.rs
+++ b/src/receiver.rs
@@ -1,15 +1,10 @@
-use crate::{trait_object::TraitObject, Bus, Message};
-use core::{
-    any::TypeId,
-    fmt,
-    future::Future,
-    marker::PhantomData,
-    mem,
-    pin::Pin,
-    task::{Context, Poll},
-};
+use crate::{Bus, Message, msgs, receivers::{Event, Permit, PermitDrop}, trait_object::TraitObject};
+use core::{any::TypeId, fmt, marker::PhantomData, mem, pin::Pin, task::{Context, Poll}};
 use futures::future::poll_fn;
-use std::{borrow::Cow, sync::Arc};
+use tokio::sync::Notify;
+use std::{borrow::Cow, sync::{Arc, atomic::{AtomicBool, AtomicU64, Ordering}}};
+use futures::Future;
+
 
 pub struct AnyReceiver<'a> {
     dyn_typed_receiver_trait_object: TraitObject,
@@ -17,19 +12,52 @@ pub struct AnyReceiver<'a> {
     _m: PhantomData<&'a usize>,
 }
 
+unsafe impl Send for AnyReceiver<'_> {}
+
 impl<'a> AnyReceiver<'a> {
-    pub fn new<M: Message, R: TypedReceiver<M> + 'static>(rcvr: &'a R) -> Self {
-        let trcvr = rcvr as &(dyn TypedReceiver<M>);
+    pub fn new<M: Message, R: SendTypedReceiver<M> + 'static>(rcvr: &'a R) -> Self {
+        let trcvr = rcvr as &(dyn SendTypedReceiver<M>);
 
         Self {
             dyn_typed_receiver_trait_object: unsafe { mem::transmute(trcvr) },
-            type_id: TypeId::of::<dyn TypedReceiver<M>>(),
+            type_id: TypeId::of::<dyn SendTypedReceiver<M>>(),
             _m: Default::default(),
         }
     }
 
-    pub fn dyn_typed_receiver<M: Message>(&'a self) -> &'a dyn TypedReceiver<M> {
-        assert_eq!(self.type_id, TypeId::of::<dyn TypedReceiver<M>>());
+    pub fn dyn_typed_receiver<M: Message>(&'a self) -> &'a dyn SendTypedReceiver<M> {
+        assert_eq!(self.type_id, TypeId::of::<dyn SendTypedReceiver<M>>());
+
+        unsafe { mem::transmute(self.dyn_typed_receiver_trait_object) }
+    }
+}
+
+pub struct AnyPoller<'a> {
+    dyn_typed_receiver_trait_object: TraitObject,
+    type_id: TypeId,
+    _m: PhantomData<&'a usize>,
+}
+
+unsafe impl Send for AnyPoller<'_> {}
+
+impl<'a> AnyPoller<'a> {
+    pub fn new<M, E, R>(rcvr: &'a R) -> Self 
+        where 
+            M: Message,
+            E: crate::Error,
+            R: ReciveTypedReceiver<M, E> + 'static
+    {
+        let trcvr = rcvr as &(dyn ReciveTypedReceiver<M, E>);
+
+        Self {
+            dyn_typed_receiver_trait_object: unsafe { mem::transmute(trcvr) },
+            type_id: TypeId::of::<dyn ReciveTypedReceiver<M, E>>(),
+            _m: Default::default(),
+        }
+    }
+
+    pub fn dyn_typed_receiver<M: Message, E: crate::Error>(&'a self) -> &'a dyn ReciveTypedReceiver<M, E> {
+        assert_eq!(self.type_id, TypeId::of::<dyn ReciveTypedReceiver<M, E>>());
 
         unsafe { mem::transmute(self.dyn_typed_receiver_trait_object) }
     }
@@ -87,26 +115,51 @@ impl fmt::Display for ReceiverStats {
     }
 }
 
-pub trait TypedReceiver<M: Message>: Sync {
-    fn poll_ready(&self, ctx: &mut Context<'_>) -> Poll<()>;
-    fn try_send(&self, msg: M) -> Result<(), SendError<M>>;
+pub trait SendTypedReceiver<M: Message>: Sync {
+    fn send(&self, mid: u64, msg: M) -> Result<(), SendError<M>>;
+}
+
+pub trait ReciveTypedReceiver<M, E>: Sync 
+    where M: Message,
+          E: crate::Error
+{
+    fn poll_events(&self, ctx: &mut Context<'_>) -> Poll<Event<M, E>>;
 }
 
 pub trait ReceiverTrait: Send + Sync {
     fn typed(&self) -> AnyReceiver<'_>;
+    fn poller(&self) -> AnyPoller<'_>;
     fn type_id(&self) -> TypeId;
-    fn close(&self);
-    fn stats(&self) -> ReceiverStats;
-    fn sync(&self);
-    fn poll_synchronized(&self, ctx: &mut Context<'_>) -> Poll<()>;
+    fn stats(&self) -> Result<(), SendError<()>>;
+    fn close(&self) -> Result<(), SendError<()>>;
+    fn sync(&self) -> Result<(), SendError<()>>;
+    fn flush(&self) -> Result<(), SendError<()>>;
 }
 
 pub trait ReceiverPollerBuilder {
     fn build(bus: Bus) -> Box<dyn Future<Output = ()>>;
 }
 
+struct ReceiverContext {
+    limit: u64,
+    processing: AtomicU64,
+    need_flush: AtomicBool,
+    flushed: Notify,
+    synchronized: Notify,
+    closed: Notify,
+    response: Notify,
+    statistics: Notify,
+}
+
+impl PermitDrop for ReceiverContext {
+    fn permit_drop(&self) {
+        self.processing.fetch_sub(1, Ordering::SeqCst);
+    }
+}
+
 pub struct Receiver {
     inner: Arc<dyn ReceiverTrait>,
+    context: Arc<ReceiverContext>,
 }
 
 impl fmt::Debug for Receiver {
@@ -124,49 +177,21 @@ impl core::cmp::PartialEq for Receiver {
 
 impl core::cmp::Eq for Receiver {}
 
-pub struct ReceiverPoller<'a, M: Message> {
-    inner: &'a dyn ReceiverTrait,
-    msg: Option<M>,
-}
-
-impl<'a, M: Message> Unpin for ReceiverPoller<'a, M> {}
-impl<'a, M: Message> Future for ReceiverPoller<'a, M> {
-    type Output = Result<(), SendError<M>>;
-
-    fn poll(self: Pin<&mut Self>, ctx: &mut Context<'_>) -> Poll<Self::Output> {
-        let this = self.get_mut();
-
-        let mut msg = if let Some(msg) = this.msg.take() {
-            msg
-        } else {
-            return Poll::Ready(Ok(()));
-        };
-
-        let any_receiver = this.inner.typed();
-        let receiver = any_receiver.dyn_typed_receiver::<M>();
-
-        loop {
-            match receiver.poll_ready(ctx) {
-                Poll::Ready(_) => (),
-                Poll::Pending => {
-                    this.msg = Some(msg);
-                    return Poll::Pending;
-                }
-            }
-
-            msg = match receiver.try_send(msg) {
-                Ok(_) => break Poll::Ready(Ok(())),
-                Err(SendError::Full(m)) => m,
-                Err(err) => break Poll::Ready(Err(err)),
-            }
-        }
-    }
-}
-
 impl Receiver {
     #[inline]
-    pub(crate) fn new(inner: Arc<dyn ReceiverTrait>) -> Self {
-        Self { inner }
+    pub(crate) fn new(limit: u64, inner: Arc<dyn ReceiverTrait>) -> Self {
+        let context = Arc::new(ReceiverContext {
+            limit,
+            processing: AtomicU64::new(0),
+            need_flush: AtomicBool::new(false),
+            flushed: Notify::new(),
+            synchronized: Notify::new(),
+            closed: Notify::new(),
+            response: Notify::new(),
+            statistics: Notify::new(),
+        });
+
+        Self { inner, context }
     }
 
     #[inline]
@@ -175,38 +200,157 @@ impl Receiver {
     }
 
     #[inline]
-    pub fn broadcast<M: Message>(
-        &self,
-        msg: M,
-    ) -> impl Future<Output = Result<(), SendError<M>>> + '_ {
-        ReceiverPoller {
-            inner: self.inner.as_ref(),
-            msg: Some(msg),
+    pub fn need_flush(&self) -> bool {
+        self.context.need_flush.load(Ordering::SeqCst)
+    }
+
+    #[inline]
+    pub async fn reserve(&self) -> Permit {
+        loop {
+            let count = self.context.processing.load(Ordering::Relaxed);
+            if count < self.context.limit {
+                let res = self.context.processing.compare_exchange(count, count + 1, Ordering::SeqCst, Ordering::SeqCst);
+                if res.is_ok() {
+                    break Permit {
+                        fuse: false,
+                        inner: self.context.clone(),
+                    };
+                }
+
+                // continue
+            } else {
+                self.context.response.notified()
+                    .await
+            }
         }
     }
 
     #[inline]
-    pub fn try_broadcast<M: Message>(&self, msg: M) -> Result<(), SendError<M>> {
+    pub fn try_reserve(&self) -> Option<Permit> {
+        loop {
+            let count = self.context.processing.load(Ordering::Relaxed);
+            
+            if count < self.context.limit {
+                let res = self.context.processing.compare_exchange(count, count + 1, Ordering::SeqCst, Ordering::SeqCst);
+                if res.is_ok() {
+                    break Some(Permit {
+                        fuse: false,
+                        inner: self.context.clone(),
+                    });
+                }
+
+                // continue
+            } else {
+                break None;
+            }
+        }
+    }
+
+    #[inline]
+    pub fn send<M: Message>(&self, mid: u64, mut permit: Permit, msg: M) -> Result<(), SendError<M>> {
         let any_receiver = self.inner.typed();
         let receiver = any_receiver.dyn_typed_receiver::<M>();
+        let res = receiver.send(mid, msg);
+        permit.fuse = true;
 
-        receiver.try_send(msg)
+        if !res.is_err() {
+            self.context.need_flush.store(true, Ordering::SeqCst);
+        }
+
+        res
     }
 
     #[inline]
-    pub fn close(&self) {
-        self.inner.close();
+    pub fn force_send<M: Message>(&self, mid: u64, msg: M) -> Result<(), SendError<M>> {
+        let any_receiver = self.inner.typed();
+        let receiver = any_receiver.dyn_typed_receiver::<M>();
+        let res = receiver.send(mid, msg);
+
+        if !res.is_err() {
+            self.context.need_flush.store(true, Ordering::SeqCst);
+        }
+
+        res
+    }
+
+    pub fn start_polling_events<M, E>(&self) -> Box<dyn FnOnce(Bus) -> Pin<Box<dyn Future<Output = ()> + Send>>> 
+        where 
+            M: Message,
+            E: crate::Error
+    {
+        let ctx_clone = self.context.clone();
+        let inner_clone = self.inner.clone();
+
+        Box::new(move |bus| Box::pin(async move {
+            let any_receiver = inner_clone.poller();
+            let receiver = any_receiver.dyn_typed_receiver::<M, E>();
+
+            loop {
+                let event = poll_fn(move |ctx| receiver.poll_events(ctx))
+                    .await;
+
+                match event {
+                    Event::Exited => {
+                        ctx_clone.closed.notify_waiters();
+                        break;
+                    },
+
+                    Event::Flushed => ctx_clone.flushed.notify_waiters(),
+                    Event::Synchronized => ctx_clone.synchronized.notify_waiters(),
+                    Event::Response(_mid, resp) => {
+                        ctx_clone.processing.fetch_sub(1, Ordering::SeqCst);
+                        ctx_clone.response.notify_one();
+
+                        match resp {
+                            Ok(_msg) => (),
+                            Err(err) => { bus.try_send(msgs::Error(Arc::new(err.into()))).ok(); }
+                        }
+                    },
+                    _ => unimplemented!()
+                }
+            }
+        }))
+    }
+
+    // #[inline]
+    // pub fn stats(&self) -> ReceiverStats {
+    //     if self.inner.stats().is_ok() {
+    //         self.context.stats.notified()
+    //             .await
+    //     } else {
+    //         warn!("close failed!");
+    //     }
+    // }
+
+    #[inline]
+    pub async fn close(&self) {
+        if self.inner.close().is_ok() {
+            self.context.closed.notified()
+                .await
+        } else {
+            warn!("close failed!");
+        }
     }
 
     #[inline]
-    pub fn stats(&self) -> ReceiverStats {
-        self.inner.stats()
+    pub async fn sync(&self) {
+        if self.inner.sync().is_ok() {
+            self.context.synchronized.notified()
+                .await
+        } else {
+            warn!("sync failed!");
+        }
     }
 
     #[inline]
-    pub fn sync(&self) -> impl Future<Output = ()> + '_ {
-        self.inner.sync();
-
-        poll_fn(move |ctx| self.inner.poll_synchronized(ctx))
+    pub async fn flush(&self) {
+        if self.inner.flush().is_ok() {
+            self.context.flushed.notified()
+                .await;
+                
+            self.context.need_flush.store(false, Ordering::SeqCst);
+        } else {
+            warn!("flush failed!");
+        }
     }
 }
diff --git a/src/receivers/buffer_unordered/async.rs b/src/receivers/buffer_unordered/async.rs
index 155296d..96b2dbe 100644
--- a/src/receivers/buffer_unordered/async.rs
+++ b/src/receivers/buffer_unordered/async.rs
@@ -9,30 +9,37 @@ use std::{
     task::{Context, Poll},
 };
 
-use crate::{receiver::ReceiverStats, receivers::mpsc};
-use futures::{Future, StreamExt};
+use crate::{receiver::{AnyPoller, ReceiverStats, ReciveTypedReceiver}, receivers::{Action, Event}};
+use anyhow::Result;
+use futures::{Future, StreamExt, stream::FuturesUnordered};
 
 use super::{BufferUnorderedConfig, BufferUnorderedStats};
 use crate::{
     builder::{ReceiverSubscriber, ReceiverSubscriberBuilder},
-    msgs,
-    receiver::{AnyReceiver, ReceiverTrait, SendError, TypedReceiver},
+    receiver::{AnyReceiver, ReceiverTrait, SendError, SendTypedReceiver},
     AsyncHandler, Bus, Message, Untyped,
 };
+use parking_lot::Mutex;
+use tokio::sync::mpsc;
 
-pub struct BufferUnorderedAsyncSubscriber<T, M>
+
+pub struct BufferUnorderedAsyncSubscriber<T, M, R, E>
 where
-    T: AsyncHandler<M> + 'static,
+    T: AsyncHandler<M, Response = R, Error = E> + 'static,
     M: Message,
+    R: Message,
+    E: crate::Error
 {
     cfg: BufferUnorderedConfig,
     _m: PhantomData<(T, M)>,
 }
 
-impl<T, M> ReceiverSubscriber<T> for BufferUnorderedAsyncSubscriber<T, M>
+impl<T, M, R, E> ReceiverSubscriber<T> for BufferUnorderedAsyncSubscriber<T, M, R, E>
 where
-    T: AsyncHandler<M> + 'static,
+    T: AsyncHandler<M, Response = R, Error = E> + 'static,
     M: Message,
+    R: Message,
+    E: crate::Error
 {
     fn subscribe(
         self,
@@ -50,15 +57,17 @@ where
             parallel_total: AtomicU64::new(cfg.max_parallel as _),
         });
 
-        let (tx, rx) = mpsc::channel(cfg.buffer_size);
-        let arc = Arc::new(BufferUnorderedAsync::<M> {
+        let (stx, srx) = mpsc::unbounded_channel();
+        let (tx, rx) = mpsc::unbounded_channel();
+        let arc = Arc::new(BufferUnorderedAsync::<M, R, E> {
             tx,
             stats: stats.clone(),
+            srx: Mutex::new(srx),
         });
 
         let poller = Box::new(move |ut| {
             Box::new(move |bus| {
-                Box::pin(buffer_unordered_poller::<T, M>(rx, bus, ut, stats, cfg))
+                Box::pin(buffer_unordered_poller::<T, M, R, E>(rx, bus, ut, stats, cfg, stx))
                     as Pin<Box<dyn Future<Output = ()> + Send>>
             }) as Box<dyn FnOnce(Bus) -> Pin<Box<dyn Future<Output = ()> + Send>>>
         });
@@ -67,68 +76,129 @@ where
     }
 }
 
-async fn buffer_unordered_poller<T, M>(
-    rx: mpsc::Receiver<M>,
+fn buffer_unordered_poller<T, M, R, E>(
+    mut rx: mpsc::UnboundedReceiver<Action<M>>,
     bus: Bus,
     ut: Untyped,
     stats: Arc<BufferUnorderedStats>,
     cfg: BufferUnorderedConfig,
-) where
-    T: AsyncHandler<M> + 'static,
+    stx: mpsc::UnboundedSender<Event<R, E>>,
+) -> impl Future<Output = ()>
+where
+    T: AsyncHandler<M, Response = R, Error = E> + 'static,
     M: Message,
+    R: Message,
+    E: crate::Error
 {
     let ut = ut.downcast::<T>().unwrap();
+    let mut queue = FuturesUnordered::new();
+    let mut sync_future: Option<Pin<Box<dyn Future<Output = Result<(), E>> + Send>>> = None;
+    let mut need_sync = false;
+    let mut rx_closed = false;
+    let mut need_flush = false;
 
-    let mut x = rx
-        .map(|msg| {
-            stats.buffer.fetch_sub(1, Ordering::Relaxed);
-            stats.parallel.fetch_add(1, Ordering::Relaxed);
-            let bus = bus.clone();
-            let ut = ut.clone();
+    futures::future::poll_fn(move |cx| loop {
+        if !rx_closed && !need_flush && !need_sync {
+            while queue.len() < cfg.max_parallel {
+                match rx.poll_recv(cx) {
+                    Poll::Ready(Some(a)) => {
+                        match a {
+                            Action::Request(mid, msg) => {
+                                stats.buffer.fetch_sub(1, Ordering::Relaxed);
+                                stats.parallel.fetch_add(1, Ordering::Relaxed);
 
-            tokio::task::spawn(async move { ut.handle(msg, &bus).await })
-        })
-        .buffer_unordered(cfg.max_parallel);
-
-    while let Some(err) = x.next().await {
-        stats.parallel.fetch_sub(1, Ordering::Relaxed);
-
-        match err {
-            Ok(Err(err)) => {
-                let _ = bus.send(msgs::Error(Arc::new(err))).await;
+                                let bus = bus.clone();
+                                let ut = ut.clone();
+                                queue.push(tokio::task::spawn(async move { (mid, ut.handle(msg, &bus).await) }));
+                            },
+                            Action::Flush => need_flush = true,
+                            Action::Sync => need_sync = true,
+                            Action::Close => rx.close(),
+                            _ => unimplemented!()
+                        }
+                    },
+                    Poll::Ready(None) => {
+                        need_sync = true;
+                        rx_closed = true;
+                    },
+                    Poll::Pending => break,
+                }
             }
-            _ => (),
         }
-    }
 
-    let ut = ut.clone();
-    let bus_clone = bus.clone();
-    let res = tokio::task::spawn(async move { ut.sync(&bus_clone).await }).await;
+        let queue_len = queue.len();
+        
+        loop {
+            if queue_len != 0 {
+                loop {
+                    match queue.poll_next_unpin(cx) {
+                        Poll::Pending => return Poll::Pending,
+                        Poll::Ready(Some(Ok((mid, res)))) => {
+                            stx.send(Event::Response(mid, res)).ok();
+                        },
+                        Poll::Ready(None) => break,
+                        _ => {}
+                    }
+                }
+            }
 
-    match res {
-        Ok(Err(err)) => {
-            let _ = bus.send(msgs::Error(Arc::new(err))).await;
+            if need_flush {
+                need_flush = false;
+                stx.send(Event::Flushed).ok();
+            }
+
+            if need_sync {
+                if let Some(mut fut) = sync_future.take() {
+                    match fut.as_mut().poll(cx) {
+                        Poll::Pending => {
+                            sync_future = Some(fut);
+                            return Poll::Pending;
+                        },
+                        Poll::Ready(res) => {
+                            need_sync = false;
+
+                            if let Err(err) = res {
+                                stx.send(Event::SyncResponse(err)).ok();
+                            }
+                        }
+                    }
+                } else {
+                    let ut = ut.clone();
+                    let bus_clone = bus.clone();
+                    sync_future.replace(Box::pin(async move { 
+                        ut.sync(&bus_clone).await 
+                    }));
+                }
+            } else {
+                break;
+            }
         }
-        _ => (),
-    }
 
-    println!(
-        "[EXIT] BufferUnorderedAsync<{}>",
-        std::any::type_name::<M>()
-    );
+        if queue_len == queue.len() {
+            return if rx_closed { Poll::Ready(()) } else { Poll::Pending };
+        }
+    })
 }
 
-pub struct BufferUnorderedAsync<M: Message> {
-    tx: mpsc::Sender<M>,
-    stats: Arc<BufferUnorderedStats>,
-}
-
-impl<T, M> ReceiverSubscriberBuilder<M, T> for BufferUnorderedAsync<M>
-where
-    T: AsyncHandler<M> + 'static,
-    M: Message,
+pub struct BufferUnorderedAsync<M, R = (), E = anyhow::Error> 
+    where 
+        M: Message,
+        R: Message,
+        E: crate::Error
 {
-    type Entry = BufferUnorderedAsyncSubscriber<T, M>;
+    tx: mpsc::UnboundedSender<Action<M>>,
+    stats: Arc<BufferUnorderedStats>,
+    srx: Mutex<mpsc::UnboundedReceiver<Event<R, E>>>,
+}
+
+impl<T, M, R, E> ReceiverSubscriberBuilder<T, M, R, E> for BufferUnorderedAsync<M, R, E>
+    where
+        T: AsyncHandler<M, Response = R, Error = E> + 'static,
+        R: Message,
+        M: Message,
+        E: crate::Error
+{
+    type Entry = BufferUnorderedAsyncSubscriber<T, M, R, E>;
     type Config = BufferUnorderedConfig;
 
     fn build(cfg: Self::Config) -> Self::Entry {
@@ -139,65 +209,102 @@ where
     }
 }
 
-impl<M: Message> TypedReceiver<M> for BufferUnorderedAsync<M> {
-    fn poll_ready(&self, ctx: &mut Context<'_>) -> Poll<()> {
-        match self.tx.poll_ready(ctx) {
-            Poll::Ready(_) => Poll::Ready(()),
-            Poll::Pending => Poll::Pending,
-        }
-    }
-
-    fn try_send(&self, m: M) -> Result<(), SendError<M>> {
-        match self.tx.try_send(m) {
+impl<M, R, E> SendTypedReceiver<M> for BufferUnorderedAsync<M, R, E> 
+    where
+        M: Message,
+        R: Message,
+        E: crate::Error
+{
+    fn send(&self, mid: u64, m: M) -> Result<(), SendError<M>> {
+        match self.tx.send(Action::Request(mid, m)) {
             Ok(_) => {
                 self.stats.buffer.fetch_add(1, Ordering::Relaxed);
 
                 Ok(())
             }
-            Err(err) => Err(err),
+            Err(mpsc::error::SendError(Action::Request(_, msg))) => Err(SendError::Closed(msg)),
+            _ => unimplemented!()
         }
     }
 }
 
-impl<M: Message> ReceiverTrait for BufferUnorderedAsync<M> {
+impl<M, R, E> ReciveTypedReceiver<R, E> for BufferUnorderedAsync<M, R, E> 
+    where
+        M: Message,
+        R: Message,
+        E: crate::Error
+{
+    fn poll_events(&self, ctx: &mut Context<'_>) -> Poll<Event<R, E>> {
+        let poll = self.srx.lock().poll_recv(ctx);
+        match poll {
+            Poll::Pending => Poll::Pending,
+            Poll::Ready(Some(event)) => Poll::Ready(event),
+            Poll::Ready(None) => Poll::Ready(Event::Exited),
+        }
+    }
+}
+
+impl<M, R, E> ReceiverTrait for BufferUnorderedAsync<M, R, E> 
+    where
+        M: Message,
+        R: Message,
+        E: crate::Error
+{
     fn typed(&self) -> AnyReceiver<'_> {
         AnyReceiver::new(self)
     }
 
+    fn poller(&self) -> AnyPoller<'_> {
+        AnyPoller::new(self)
+    }
+
     fn type_id(&self) -> TypeId {
-        TypeId::of::<BufferUnorderedAsync<M>>()
+        TypeId::of::<BufferUnorderedAsync<M, R, E>>()
     }
 
-    fn close(&self) {
-        self.tx.close();
+    fn stats(&self) -> Result<(), SendError<()>> {
+        match self.tx.send(Action::Stats) {
+            Ok(_) => Ok(()),
+            Err(_) => Err(SendError::Closed(()))
+        }
+        // ReceiverStats {
+        //     name: std::any::type_name::<M>().into(),
+        //     fields: vec![
+        //         ("buffer".into(), self.stats.buffer.load(Ordering::SeqCst)),
+        //         (
+        //             "buffer_total".into(),
+        //             self.stats.buffer_total.load(Ordering::SeqCst),
+        //         ),
+        //         (
+        //             "parallel".into(),
+        //             self.stats.parallel.load(Ordering::SeqCst),
+        //         ),
+        //         (
+        //             "parallel_total".into(),
+        //             self.stats.parallel_total.load(Ordering::SeqCst),
+        //         ),
+        //     ],
+        // }
     }
 
-    fn stats(&self) -> ReceiverStats {
-        ReceiverStats {
-            name: std::any::type_name::<M>().into(),
-            fields: vec![
-                ("buffer".into(), self.stats.buffer.load(Ordering::SeqCst)),
-                (
-                    "buffer_total".into(),
-                    self.stats.buffer_total.load(Ordering::SeqCst),
-                ),
-                (
-                    "parallel".into(),
-                    self.stats.parallel.load(Ordering::SeqCst),
-                ),
-                (
-                    "parallel_total".into(),
-                    self.stats.parallel_total.load(Ordering::SeqCst),
-                ),
-            ],
+    fn close(&self) -> Result<(), SendError<()>> {
+        match self.tx.send(Action::Close) {
+            Ok(_) => Ok(()),
+            Err(_) => Err(SendError::Closed(()))
         }
     }
 
-    fn sync(&self) {
-        self.tx.flush();
+    fn sync(&self) -> Result<(), SendError<()>> {
+        match self.tx.send(Action::Sync) {
+            Ok(_) => Ok(()),
+            Err(_) => Err(SendError::Closed(()))
+        }
     }
 
-    fn poll_synchronized(&self, _ctx: &mut Context<'_>) -> Poll<()> {
-        Poll::Ready(())
+    fn flush(&self) -> Result<(), SendError<()>> {
+        match self.tx.send(Action::Flush) {
+            Ok(_) => Ok(()),
+            Err(_) => Err(SendError::Closed(()))
+        }
     }
 }
diff --git a/src/receivers/buffer_unordered/sync.rs b/src/receivers/buffer_unordered/sync.rs
index d8955a9..631c2f1 100644
--- a/src/receivers/buffer_unordered/sync.rs
+++ b/src/receivers/buffer_unordered/sync.rs
@@ -1,5 +1,3 @@
-use crate::{receiver::ReceiverStats, receivers::mpsc};
-use futures::{Future, StreamExt};
 use std::{
     any::TypeId,
     marker::PhantomData,
@@ -11,27 +9,37 @@ use std::{
     task::{Context, Poll},
 };
 
+use crate::{receiver::{AnyPoller, ReceiverStats, ReciveTypedReceiver}, receivers::{Action, Event}};
+use anyhow::Result;
+use futures::{Future, StreamExt, stream::FuturesUnordered};
+
 use super::{BufferUnorderedConfig, BufferUnorderedStats};
 use crate::{
     builder::{ReceiverSubscriber, ReceiverSubscriberBuilder},
-    msgs,
-    receiver::{AnyReceiver, ReceiverTrait, SendError, TypedReceiver},
-    Bus, Handler, Message, Untyped,
+    receiver::{AnyReceiver, ReceiverTrait, SendError, SendTypedReceiver},
+    Handler, Bus, Message, Untyped,
 };
+use parking_lot::Mutex;
+use tokio::sync::mpsc;
 
-pub struct BufferUnorderedSyncSubscriber<T, M>
+
+pub struct BufferUnorderedSyncSubscriber<T, M, R, E>
 where
-    T: Handler<M> + 'static,
+    T: Handler<M, Response = R, Error = E> + 'static,
     M: Message,
+    R: Message,
+    E: crate::Error
 {
     cfg: BufferUnorderedConfig,
-    _m: PhantomData<(M, T)>,
+    _m: PhantomData<(T, M)>,
 }
 
-impl<T, M> ReceiverSubscriber<T> for BufferUnorderedSyncSubscriber<T, M>
+impl<T, M, R, E> ReceiverSubscriber<T> for BufferUnorderedSyncSubscriber<T, M, R, E>
 where
-    T: Handler<M> + 'static,
+    T: Handler<M, Response = R, Error = E> + 'static,
     M: Message,
+    R: Message,
+    E: crate::Error
 {
     fn subscribe(
         self,
@@ -42,7 +50,6 @@ where
         >,
     ) {
         let cfg = self.cfg;
-        let (tx, rx) = mpsc::channel(cfg.buffer_size);
         let stats = Arc::new(BufferUnorderedStats {
             buffer: AtomicU64::new(0),
             buffer_total: AtomicU64::new(cfg.buffer_size as _),
@@ -50,14 +57,17 @@ where
             parallel_total: AtomicU64::new(cfg.max_parallel as _),
         });
 
-        let arc = Arc::new(BufferUnorderedSync::<M> {
+        let (stx, srx) = mpsc::unbounded_channel();
+        let (tx, rx) = mpsc::unbounded_channel();
+        let arc = Arc::new(BufferUnorderedSync::<M, R, E> {
             tx,
             stats: stats.clone(),
+            srx: Mutex::new(srx),
         });
 
         let poller = Box::new(move |ut| {
             Box::new(move |bus| {
-                Box::pin(buffer_unordered_poller::<T, M>(rx, bus, ut, stats, cfg))
+                Box::pin(buffer_unordered_poller::<T, M, R, E>(rx, bus, ut, stats, cfg, stx))
                     as Pin<Box<dyn Future<Output = ()> + Send>>
             }) as Box<dyn FnOnce(Bus) -> Pin<Box<dyn Future<Output = ()> + Send>>>
         });
@@ -66,69 +76,129 @@ where
     }
 }
 
-async fn buffer_unordered_poller<T, M>(
-    rx: mpsc::Receiver<M>,
+fn buffer_unordered_poller<T, M, R, E>(
+    mut rx: mpsc::UnboundedReceiver<Action<M>>,
     bus: Bus,
     ut: Untyped,
     stats: Arc<BufferUnorderedStats>,
     cfg: BufferUnorderedConfig,
-) where
-    T: Handler<M> + 'static,
+    stx: mpsc::UnboundedSender<Event<R, E>>,
+) -> impl Future<Output = ()>
+where
+    T: Handler<M, Response = R, Error = E> + 'static,
     M: Message,
+    R: Message,
+    E: crate::Error
 {
     let ut = ut.downcast::<T>().unwrap();
+    let mut queue = FuturesUnordered::new();
+    let mut sync_future: Option<Pin<Box<dyn Future<Output = Result<(), E>> + Send>>> = None;
+    let mut need_sync = false;
+    let mut rx_closed = false;
+    let mut need_flush = false;
 
-    let mut x = rx
-        .map(|msg| {
-            stats.buffer.fetch_sub(1, Ordering::Relaxed);
-            stats.parallel.fetch_add(1, Ordering::Relaxed);
+    futures::future::poll_fn(move |cx| loop {
+        if !rx_closed && !need_flush && !need_sync {
+            while queue.len() < cfg.max_parallel {
+                match rx.poll_recv(cx) {
+                    Poll::Ready(Some(a)) => {
+                        match a {
+                            Action::Request(mid, msg) => {
+                                stats.buffer.fetch_sub(1, Ordering::Relaxed);
+                                stats.parallel.fetch_add(1, Ordering::Relaxed);
 
-            let bus = bus.clone();
-            let ut = ut.clone();
-
-            tokio::task::spawn_blocking(move || ut.handle(msg, &bus))
-        })
-        .buffer_unordered(cfg.max_parallel);
-
-    while let Some(err) = x.next().await {
-        stats.parallel.fetch_sub(1, Ordering::Relaxed);
-
-        match err {
-            Ok(Err(err)) => {
-                let _ = bus.send(msgs::Error(Arc::new(err))).await;
+                                let bus = bus.clone();
+                                let ut = ut.clone();
+                                queue.push( tokio::task::spawn_blocking(move || (mid, ut.handle(msg, &bus))));
+                            },
+                            Action::Flush => need_flush = true,
+                            Action::Sync => need_sync = true,
+                            Action::Close => rx.close(),
+                            _ => unimplemented!()
+                        }
+                    },
+                    Poll::Ready(None) => {
+                        need_sync = true;
+                        rx_closed = true;
+                    },
+                    Poll::Pending => break,
+                }
             }
-            _ => (),
         }
-    }
 
-    let ut = ut.clone();
-    let bus_clone = bus.clone();
-    let res = tokio::task::spawn_blocking(move || ut.sync(&bus_clone)).await;
+        let queue_len = queue.len();
+        
+        loop {
+            if queue_len != 0 {
+                loop {
+                    match queue.poll_next_unpin(cx) {
+                        Poll::Pending => return Poll::Pending,
+                        Poll::Ready(Some(Ok((mid, res)))) => {
+                            stx.send(Event::Response(mid, res)).ok();
+                        },
+                        Poll::Ready(None) => break,
+                        _ => {}
+                    }
+                }
+            }
 
-    match res {
-        Ok(Err(err)) => {
-            let _ = bus.send(msgs::Error(Arc::new(err))).await;
+            if need_flush {
+                need_flush = false;
+                stx.send(Event::Flushed).ok();
+            }
+
+            if need_sync {
+                if let Some(mut fut) = sync_future.take() {
+                    match fut.as_mut().poll(cx) {
+                        Poll::Pending => {
+                            sync_future = Some(fut);
+                            return Poll::Pending;
+                        },
+                        Poll::Ready(res) => {
+                            need_sync = false;
+
+                            if let Err(err) = res {
+                                stx.send(Event::SyncResponse(err)).ok();
+                            }
+                        }
+                    }
+                } else {
+                    let ut = ut.clone();
+                    let bus_clone = bus.clone();
+                    sync_future.replace(Box::pin(async move {
+                        tokio::task::spawn_blocking(move || ut.sync(&bus_clone)).await.unwrap()
+                    }));
+                }
+            } else {
+                break;
+            }
         }
-        _ => (),
-    }
 
-    println!(
-        "[EXIT] BufferUnorderedSync<{}>",
-        std::any::type_name::<M>()
-    );
+        if queue_len == queue.len() {
+            return if rx_closed { Poll::Ready(()) } else { Poll::Pending };
+        }
+    })
 }
 
-pub struct BufferUnorderedSync<M: Message> {
-    tx: mpsc::Sender<M>,
-    stats: Arc<BufferUnorderedStats>,
-}
-
-impl<T, M> ReceiverSubscriberBuilder<M, T> for BufferUnorderedSync<M>
-where
-    T: Handler<M> + 'static,
-    M: Message,
+pub struct BufferUnorderedSync<M, R = (), E = anyhow::Error> 
+    where 
+        M: Message,
+        R: Message,
+        E: crate::Error
 {
-    type Entry = BufferUnorderedSyncSubscriber<T, M>;
+    tx: mpsc::UnboundedSender<Action<M>>,
+    stats: Arc<BufferUnorderedStats>,
+    srx: Mutex<mpsc::UnboundedReceiver<Event<R, E>>>,
+}
+
+impl<T, M, R, E> ReceiverSubscriberBuilder<T, M, R, E> for BufferUnorderedSync<M, R, E>
+    where
+        T: Handler<M, Response = R, Error = E> + 'static,
+        R: Message,
+        M: Message,
+        E: crate::Error
+{
+    type Entry = BufferUnorderedSyncSubscriber<T, M, R, E>;
     type Config = BufferUnorderedConfig;
 
     fn build(cfg: Self::Config) -> Self::Entry {
@@ -139,65 +209,102 @@ where
     }
 }
 
-impl<M: Message> TypedReceiver<M> for BufferUnorderedSync<M> {
-    fn poll_ready(&self, ctx: &mut Context<'_>) -> Poll<()> {
-        match self.tx.poll_ready(ctx) {
-            Poll::Ready(_) => Poll::Ready(()),
-            Poll::Pending => Poll::Pending,
-        }
-    }
-
-    fn try_send(&self, m: M) -> Result<(), SendError<M>> {
-        match self.tx.try_send(m) {
+impl<M, R, E> SendTypedReceiver<M> for BufferUnorderedSync<M, R, E> 
+    where
+        M: Message,
+        R: Message,
+        E: crate::Error
+{
+    fn send(&self, mid: u64, m: M) -> Result<(), SendError<M>> {
+        match self.tx.send(Action::Request(mid, m)) {
             Ok(_) => {
                 self.stats.buffer.fetch_add(1, Ordering::Relaxed);
 
                 Ok(())
             }
-            Err(err) => Err(err),
+            Err(mpsc::error::SendError(Action::Request(_, msg))) => Err(SendError::Closed(msg)),
+            _ => unimplemented!()
         }
     }
 }
 
-impl<M: Message> ReceiverTrait for BufferUnorderedSync<M> {
+impl<M, R, E> ReciveTypedReceiver<R, E> for BufferUnorderedSync<M, R, E> 
+    where
+        M: Message,
+        R: Message,
+        E: crate::Error
+{
+    fn poll_events(&self, ctx: &mut Context<'_>) -> Poll<Event<R, E>> {
+        let poll = self.srx.lock().poll_recv(ctx);
+        match poll {
+            Poll::Pending => Poll::Pending,
+            Poll::Ready(Some(event)) => Poll::Ready(event),
+            Poll::Ready(None) => Poll::Ready(Event::Exited),
+        }
+    }
+}
+
+impl<M, R, E> ReceiverTrait for BufferUnorderedSync<M, R, E> 
+    where
+        M: Message,
+        R: Message,
+        E: crate::Error
+{
     fn typed(&self) -> AnyReceiver<'_> {
         AnyReceiver::new(self)
     }
 
-    fn type_id(&self) -> TypeId {
-        TypeId::of::<BufferUnorderedSync<M>>()
+    fn poller(&self) -> AnyPoller<'_> {
+        AnyPoller::new(self)
     }
 
-    fn stats(&self) -> ReceiverStats {
-        ReceiverStats {
-            name: std::any::type_name::<M>().into(),
-            fields: vec![
-                ("buffer".into(), self.stats.buffer.load(Ordering::SeqCst)),
-                (
-                    "buffer_total".into(),
-                    self.stats.buffer_total.load(Ordering::SeqCst),
-                ),
-                (
-                    "parallel".into(),
-                    self.stats.parallel.load(Ordering::SeqCst),
-                ),
-                (
-                    "parallel_total".into(),
-                    self.stats.parallel_total.load(Ordering::SeqCst),
-                ),
-            ],
+    fn type_id(&self) -> TypeId {
+        TypeId::of::<BufferUnorderedSync<M, R, E>>()
+    }
+
+    fn stats(&self) -> Result<(), SendError<()>> {
+        match self.tx.send(Action::Stats) {
+            Ok(_) => Ok(()),
+            Err(_) => Err(SendError::Closed(()))
+        }
+        // ReceiverStats {
+        //     name: std::any::type_name::<M>().into(),
+        //     fields: vec![
+        //         ("buffer".into(), self.stats.buffer.load(Ordering::SeqCst)),
+        //         (
+        //             "buffer_total".into(),
+        //             self.stats.buffer_total.load(Ordering::SeqCst),
+        //         ),
+        //         (
+        //             "parallel".into(),
+        //             self.stats.parallel.load(Ordering::SeqCst),
+        //         ),
+        //         (
+        //             "parallel_total".into(),
+        //             self.stats.parallel_total.load(Ordering::SeqCst),
+        //         ),
+        //     ],
+        // }
+    }
+
+    fn close(&self) -> Result<(), SendError<()>> {
+        match self.tx.send(Action::Close) {
+            Ok(_) => Ok(()),
+            Err(_) => Err(SendError::Closed(()))
         }
     }
 
-    fn close(&self) {
-        self.tx.close();
+    fn sync(&self) -> Result<(), SendError<()>> {
+        match self.tx.send(Action::Sync) {
+            Ok(_) => Ok(()),
+            Err(_) => Err(SendError::Closed(()))
+        }
     }
 
-    fn sync(&self) {
-        self.tx.flush();
-    }
-
-    fn poll_synchronized(&self, _ctx: &mut Context<'_>) -> Poll<()> {
-        Poll::Ready(())
+    fn flush(&self) -> Result<(), SendError<()>> {
+        match self.tx.send(Action::Flush) {
+            Ok(_) => Ok(()),
+            Err(_) => Err(SendError::Closed(()))
+        }
     }
 }
diff --git a/src/receivers/mod.rs b/src/receivers/mod.rs
index a8c8c25..e0cde1f 100644
--- a/src/receivers/mod.rs
+++ b/src/receivers/mod.rs
@@ -1,11 +1,68 @@
 mod buffer_unordered;
-mod buffer_unordered_batched;
-mod mpsc_futures;
-mod synchronize_batched;
-mod synchronized;
+// mod buffer_unordered_batched;
+// mod mpsc_futures;
+// mod synchronize_batched;
+// mod synchronized;
 
-mod mpsc {
-    pub use super::mpsc_futures::*;
+
+// mod mpsc;
+// mod mpsc {
+//     pub use super::mpsc_futures::*;
+// }
+
+use std::sync::Arc;
+
+#[derive(Debug, Clone)]
+pub struct Stats {
+    pub has_queue: bool,
+    pub queue_capacity: u64,
+    pub queue_size: u64,
+
+    pub has_parallel: bool,
+    pub parallel_capacity: u64,
+    pub parallel_size: u64,
+
+    pub has_batch: bool,
+    pub batch_capacity: u64,
+    pub batch_size: u64,
+}
+
+#[non_exhaustive]
+#[derive(Debug)]
+pub enum Action<M> {
+    Request(u64, M),
+    Flush,
+    Sync,
+    Close,
+    Stats,
+}
+
+#[non_exhaustive]
+#[derive(Debug, Clone)]
+pub enum Event<M, E> {
+    Response(u64, Result<M, E>),
+    SyncResponse(E),
+    Stats(Stats),
+    Synchronized,
+    Flushed,
+    Exited,
+}
+
+pub struct Permit {
+    pub(crate) fuse: bool,
+    pub(crate) inner: Arc<dyn PermitDrop>
+}
+
+pub trait PermitDrop {
+    fn permit_drop(&self);
+}
+
+impl Drop for Permit {
+    fn drop(&mut self) {
+        if !self.fuse {
+            self.inner.permit_drop();
+        }
+    }
 }
 
 pub use buffer_unordered::{
@@ -13,17 +70,17 @@ pub use buffer_unordered::{
     BufferUnorderedSync, BufferUnorderedSyncSubscriber,
 };
 
-pub use buffer_unordered_batched::{
-    BufferUnorderedBatchedAsync, BufferUnorderedBatchedAsyncSubscriber, BufferUnorderedBatchedConfig,
-    BufferUnorderedBatchedSync, BufferUnorderedBatchedSyncSubscriber,
-};
+// pub use buffer_unordered_batched::{
+//     BufferUnorderedBatchedAsync, BufferUnorderedBatchedAsyncSubscriber, BufferUnorderedBatchedConfig,
+//     BufferUnorderedBatchedSync, BufferUnorderedBatchedSyncSubscriber,
+// };
 
-pub use synchronized::{
-    SynchronizedAsync, SynchronizedAsyncSubscriber, SynchronizedConfig, SynchronizedSync,
-    SynchronizedSyncSubscriber,
-};
+// pub use synchronized::{
+//     SynchronizedAsync, SynchronizedAsyncSubscriber, SynchronizedConfig, SynchronizedSync,
+//     SynchronizedSyncSubscriber,
+// };
 
-pub use synchronize_batched::{
-    SynchronizeBatchedAsync, SynchronizeBatchedAsyncSubscriber, SynchronizeBatchedConfig,
-    SynchronizeBatchedSync, SynchronizeBatchedSyncSubscriber,
-};
+// pub use synchronize_batched::{
+//     SynchronizeBatchedAsync, SynchronizeBatchedAsyncSubscriber, SynchronizeBatchedConfig,
+//     SynchronizeBatchedSync, SynchronizeBatchedSyncSubscriber,
+// };
diff --git a/src/receivers/mpsc.rs b/src/receivers/mpsc.rs
deleted file mode 100644
index 6a62d8c..0000000
--- a/src/receivers/mpsc.rs
+++ /dev/null
@@ -1,142 +0,0 @@
-use futures::{Stream, StreamExt};
-use core::pin::Pin;
-use crossbeam::queue::ArrayQueue;
-use crossbeam::atomic::AtomicCell;
-use core::task::{Waker, Context, Poll};
-use std::sync::{Arc, atomic::*};
-
-use crate::receiver::SendError;
-
-
-
-struct ChannelInner<T> {
-    queue: ArrayQueue<T>,
-    send_waker: AtomicCell<Option<Box<Waker>>>,
-    recv_waker: AtomicCell<Option<Box<Waker>>>,
-    closed: AtomicBool,
-}
-
-pub fn channel<T>(buffer: usize) -> (Sender<T>, Receiver<T>) {
-    let inner = Arc::new(ChannelInner {
-        queue: ArrayQueue::new(buffer),
-        send_waker: AtomicCell::new(None),
-        recv_waker: AtomicCell::new(None),
-        closed: AtomicBool::new(false),
-    });
-    
-    (
-        Sender {
-            inner: inner.clone(),
-        },
-        Receiver {
-            inner,
-        }
-    )
-}
-
-
-#[derive(Clone)]
-pub struct Sender<T> {
-    inner: Arc<ChannelInner<T>>
-}
-
-impl <T> Sender<T> {
-    pub fn poll_ready(&self, cx: &mut Context<'_>) -> Poll<()> {
-        if self.inner.closed.load(Ordering::SeqCst) {
-            return Poll::Ready(());
-        }
-
-        if self.inner.queue.is_full() {
-            self.inner.send_waker.store(Some(Box::new(cx.waker().clone())));
-        }
-        
-        let mut counter = 4;
-        loop {
-            if self.inner.queue.is_full() {
-                if counter > 0 {
-                    counter -= 1;
-                    continue;
-                } else {
-                    break Poll::Pending;
-                }
-            } else {
-                break Poll::Ready(());
-            }
-        }
-    }
-    
-    pub fn try_send(&self, mut item: T) -> Result<(), SendError<T>> {
-        if self.inner.closed.load(Ordering::SeqCst) {
-            return Err(SendError::Closed(item));
-        }
-
-        let mut counter = 0;
-        loop {
-            match self.inner.queue.push(item) {
-                Ok(_) => {
-                    if let Some(waker) = self.inner.recv_waker.take() {
-                        waker.wake();
-                    }
-                    
-                    break Ok(());
-                }
-                
-                Err(inner) => {
-                    if counter >= 4 {
-                        break Err(SendError::Full(inner));
-                    } else {
-                        item = inner;
-                        counter += 1;
-                    }
-                }
-            }
-        }
-    }
-
-    pub fn close(&self) {
-        self.inner.closed.store(true, Ordering::SeqCst);
-        if let Some(waker) = self.inner.recv_waker.take() {
-            waker.wake();
-        }
-    }    
-}
-
-pub struct Receiver<T> {
-    inner: Arc<ChannelInner<T>>
-}
-
-impl <T> Stream for Receiver<T> {
-    type Item = T;
-    
-    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
-        let this = self.get_mut();
-        let mut counter = 0;
-        
-        loop {
-            match this.inner.queue.pop() {
-                Some(inner) => {
-                    if let Some(waker) = this.inner.send_waker.take() {
-                        waker.wake();
-                    }
-                    
-                    break Poll::Ready(Some(inner));
-                },
-                None => {
-                    if this.inner.closed.load(Ordering::SeqCst) {
-                        break Poll::Ready(None);
-                    } else {
-                        if counter == 0 {
-                            this.inner.recv_waker.store(Some(Box::new(cx.waker().clone())));
-                        }
-                        
-                        if counter >= 8 {
-                            break Poll::Pending;
-                        } else {
-                            counter += 1;
-                        }
-                    }
-                }
-            }
-        }
-    }
-}
diff --git a/src/receivers/mpsc_futures.rs b/src/receivers/mpsc_futures.rs
deleted file mode 100644
index 18bbba9..0000000
--- a/src/receivers/mpsc_futures.rs
+++ /dev/null
@@ -1,107 +0,0 @@
-use crate::receiver::SendError;
-use core::pin::Pin;
-use core::task::{Context, Poll};
-use crossbeam::queue::SegQueue;
-use futures::{channel::mpsc, Stream};
-use std::{
-    sync::{
-        atomic::{AtomicUsize, Ordering},
-        Arc,
-    },
-    task::Waker,
-};
-
-pub struct State {
-    buffer: usize,
-    counter: AtomicUsize,
-    send_wakers: SegQueue<Waker>,
-}
-
-pub fn channel<T>(buffer: usize) -> (Sender<T>, Receiver<T>) {
-    let state = Arc::new(State {
-        buffer,
-        counter: AtomicUsize::new(0),
-        send_wakers: SegQueue::new(),
-    });
-    let (tx, rx) = mpsc::unbounded();
-
-    (
-        Sender {
-            inner: tx,
-            state: state.clone(),
-        },
-        Receiver { inner: rx, state },
-    )
-}
-
-pub struct Sender<T> {
-    inner: mpsc::UnboundedSender<T>,
-    state: Arc<State>,
-}
-
-impl<T> Sender<T> {
-    pub fn poll_ready(&self, cx: &mut Context<'_>) -> Poll<()> {
-        if self.state.counter.load(Ordering::SeqCst) >= self.state.buffer {
-            self.state.send_wakers.push(cx.waker().clone());
-            return Poll::Pending;
-        }
-
-        Poll::Ready(())
-    }
-
-    pub fn try_send(&self, item: T) -> Result<(), SendError<T>> {
-        if self.state.counter.load(Ordering::Relaxed) >= self.state.buffer {
-            return Err(SendError::Full(item));
-        }
-
-        self.state.counter.fetch_add(1, Ordering::SeqCst);
-        match self.inner.unbounded_send(item) {
-            Ok(_) => Ok(()),
-            Err(err) if err.is_full() => Err(SendError::Full(err.into_inner())),
-            Err(err) => Err(SendError::Closed(err.into_inner())),
-        }
-    }
-
-    #[inline]
-    pub fn flush(&self) {}
-
-    #[inline]
-    pub fn close(&self) {
-        self.inner.close_channel();
-    }
-}
-
-pub struct Receiver<T> {
-    inner: mpsc::UnboundedReceiver<T>,
-    state: Arc<State>,
-}
-
-impl<T> Stream for Receiver<T> {
-    type Item = T;
-
-    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
-        let this = self.get_mut();
-        match Pin::new(&mut this.inner).poll_next(cx) {
-            Poll::Ready(inner) => {
-                let val = this.state.buffer - this.state.counter.fetch_sub(1, Ordering::SeqCst) + 1;
-
-                for _ in 0..val {
-                    if let Some(waker) = this.state.send_wakers.pop() {
-                        waker.wake();
-                    } else {
-                        break;
-                    }
-                }
-
-                Poll::Ready(inner)
-            }
-            Poll::Pending => {
-                while let Some(waker) = this.state.send_wakers.pop() {
-                    waker.wake();
-                }
-
-                Poll::Pending
-            },
-        }
-    }
-}
diff --git a/src/utils.rs b/src/utils.rs
deleted file mode 100644
index 1e3ab7d..0000000
--- a/src/utils.rs
+++ /dev/null
@@ -1,33 +0,0 @@
-use core::cmp::{Ord, Ordering};
-use core::ops::Range;
-
-pub fn binary_search_range_by_key<'a, T, B, F>(data: &'a [T], item: &B, mut f: F) -> Range<usize>
-where
-    F: FnMut(&'a T) -> B,
-    B: Ord,
-{
-    if let Ok(index) = data.binary_search_by_key(item, &mut f) {
-        let mut begin = index;
-        let mut end = index + 1;
-
-        for i in (0..index).rev() {
-            if f(unsafe { data.get_unchecked(i) }).cmp(item) != Ordering::Equal {
-                break;
-            }
-
-            begin = i;
-        }
-
-        for i in end..data.len() {
-            end = i;
-
-            if f(unsafe { data.get_unchecked(i) }).cmp(item) != Ordering::Equal {
-                break;
-            }
-        }
-
-        begin..end
-    } else {
-        data.len()..data.len()
-    }
-}