diff --git a/examples/file_download.rs b/examples/file_download.rs
index 7a31388..034352b 100644
--- a/examples/file_download.rs
+++ b/examples/file_download.rs
@@ -52,7 +52,7 @@ fn drop_packet() -> bool {
     OsRng.next_u32() >= (u32::MAX / 4 * 3)
 }
 
-fn process(peer: &Peer, recv_data: RecvOk<'_, &Transport, Payload, Payload, Payload>) {
+fn process(peer: &Peer, recv_data: RecvOk<'_, &Transport, Payload, Payload>) {
     use Payload::*;
     match recv_data.consume() {
         (Some((guard, RequestFile { filename })), None) => {
diff --git a/src/lib.rs b/src/lib.rs
index 6a331a3..ee1159c 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -13,5 +13,5 @@ pub use single_thread::*;
 #[cfg(feature = "std")]
 pub mod sync;
 
-#[cfg(feature = "tokio")]
-pub mod tokio;
+//#[cfg(feature = "tokio")]
+//pub mod tokio;
diff --git a/src/seq_queue.rs b/src/seq_queue.rs
index efbb6b5..03e5ae0 100644
--- a/src/seq_queue.rs
+++ b/src/seq_queue.rs
@@ -93,7 +93,7 @@ struct SendEntry<SendData> {
 }
 
 #[derive(Debug, Clone, PartialEq, Eq)]
-pub enum DirectRecvError {
+pub enum TryRecvError {
     DroppedTooEarly,
     DroppedDuplicate,
     DroppedDuplicateResendAck(SeqNo),
@@ -101,36 +101,36 @@ pub enum DirectRecvError {
     WaitingForReply,
 }
 #[cfg(feature = "std")]
-impl std::fmt::Display for DirectRecvError {
+impl std::fmt::Display for TryRecvError {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
-            DirectRecvError::DroppedTooEarly => write!(f, "packet arrived too early"),
-            DirectRecvError::DroppedDuplicate => write!(f, "packet was a duplicate"),
-            DirectRecvError::DroppedDuplicateResendAck(_) => write!(f, "packet was a duplicate, resending ack"),
-            DirectRecvError::WaitingForRecv => write!(f, "can't process until another packet is received"),
-            DirectRecvError::WaitingForReply => write!(f, "can't process until a reply is finished"),
+            TryRecvError::DroppedTooEarly => write!(f, "packet arrived too early"),
+            TryRecvError::DroppedDuplicate => write!(f, "packet was a duplicate"),
+            TryRecvError::DroppedDuplicateResendAck(_) => write!(f, "packet was a duplicate, resending ack"),
+            TryRecvError::WaitingForRecv => write!(f, "can't process until another packet is received"),
+            TryRecvError::WaitingForReply => write!(f, "can't process until a reply is finished"),
         }
     }
 }
 #[cfg(feature = "std")]
-impl std::error::Error for DirectRecvError {}
+impl std::error::Error for TryRecvError {}
 
 #[derive(Debug, Clone, PartialEq, Eq)]
-pub enum PumpError {
+pub enum TryError {
     WaitingForRecv,
     WaitingForReply,
 }
 #[cfg(feature = "std")]
-impl std::fmt::Display for PumpError {
+impl std::fmt::Display for TryError {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
-            PumpError::WaitingForRecv => write!(f, "can't process until another packet is received"),
-            PumpError::WaitingForReply => write!(f, "can't process until a reply is finished"),
+            TryError::WaitingForRecv => write!(f, "can't process until another packet is received"),
+            TryError::WaitingForReply => write!(f, "can't process until a reply is finished"),
         }
     }
 }
 #[cfg(feature = "std")]
-impl std::error::Error for PumpError {}
+impl std::error::Error for TryError {}
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
@@ -282,18 +282,18 @@ impl<SendData, RecvData, const CAP: usize> SeqEx<SendData, RecvData, CAP> {
         &mut self.send_window[seq_no as usize % self.send_window.len()]
     }
     #[inline]
-    fn is_full_inner(&self, is_for_send: bool, reply_no: Option<SeqNo>) -> Result<(), PumpError> {
+    fn is_full_inner(&self, reply_no: Option<SeqNo>) -> Result<(), TryError> {
         if self.concurrent_replies_total >= self.concurrent_replies.len() - 2 {
-            return Err(PumpError::WaitingForReply);
+            return Err(TryError::WaitingForReply);
         }
         let reply_idx = reply_no.map_or(self.send_window.len(), |r| r as usize % self.send_window.len());
-        for i in 0..1 + is_for_send as u32 + self.concurrent_replies_total as u32 {
+        for i in 0..1 + self.concurrent_replies_total as u32 {
             let idx = self.next_send_seq_no.wrapping_add(i) as usize % self.send_window.len();
             if self.send_window[idx].is_some() && reply_idx != idx {
-                return if i < 1 + is_for_send as u32 {
-                    Err(PumpError::WaitingForRecv)
+                return if i == 0 {
+                    Err(TryError::WaitingForRecv)
                 } else {
-                    Err(PumpError::WaitingForReply)
+                    Err(TryError::WaitingForReply)
                 }
             }
         }
@@ -348,7 +348,7 @@ impl<SendData, RecvData, const CAP: usize> SeqEx<SendData, RecvData, CAP> {
     /// `retry_interval`. `current_time` does not have to be monotonically increasing.
     ///
     /// Can mutate `next_service_timestamp`.
-    pub fn try_send_direct(&mut self, current_time: i64, seq_cst: bool, packet_data: SendData) -> Result<Packet<&SendData>, (PumpError, SendData)> {
+    pub fn try_send_direct(&mut self, current_time: i64, seq_cst: bool, packet_data: SendData) -> Result<Packet<&SendData>, (TryError, SendData)> {
         let mut tmp = Some(packet_data);
         self.try_send_direct_with(current_time, seq_cst, |_| tmp.take().unwrap())
             .map_err(|e| e.0)
@@ -360,8 +360,8 @@ impl<SendData, RecvData, const CAP: usize> SeqEx<SendData, RecvData, CAP> {
         current_time: i64,
         seq_cst: bool,
         packet_data: F,
-    ) -> Result<Packet<&SendData>, (PumpError, F)> {
-        if let Err(e) = self.is_full_inner(true, None) {
+    ) -> Result<Packet<&SendData>, (TryError, F)> {
+        if let Err(e) = self.is_full_inner(None) {
             return Err((e, packet_data));
         }
 
@@ -404,7 +404,7 @@ impl<SendData, RecvData, const CAP: usize> SeqEx<SendData, RecvData, CAP> {
     }
 
     /// If this returns `Ok` then `try_send` might succeed on next call.
-    pub fn receive_raw_and_direct<P: Into<RecvData>>(&mut self, packet: Packet<P>) -> Result<(RecvOkRaw<SendData, P>, bool), DirectRecvError> {
+    pub fn receive_raw_and_direct<P: Into<RecvData>>(&mut self, packet: Packet<P>) -> Result<(RecvOkRaw<SendData, P>, bool), TryRecvError> {
         let seq_cst = packet.is_seq_cst();
         let (seq_no, reply_no, recv_data) = match packet {
             Payload(seq_no, recv_data) | SeqCstPayload(seq_no, recv_data) => (seq_no, None, recv_data),
@@ -413,7 +413,7 @@ impl<SendData, RecvData, const CAP: usize> SeqEx<SendData, RecvData, CAP> {
                 return self
                     .take_send(reply_no)
                     .map(|send_data| (RecvOkRaw::Ack { send_data }, false))
-                    .ok_or(DirectRecvError::DroppedDuplicate)
+                    .ok_or(TryRecvError::DroppedDuplicate)
             }
         };
         // We only want to accept packets with sequence numbers in the range:
@@ -436,17 +436,17 @@ impl<SendData, RecvData, const CAP: usize> SeqEx<SendData, RecvData, CAP> {
             // resending the packet.
             for entry in self.send_window.iter().flatten() {
                 if entry.reply_no == Some(seq_no) {
-                    return Err(DirectRecvError::DroppedDuplicate);
+                    return Err(TryRecvError::DroppedDuplicate);
                 }
             }
             for i in 0..self.concurrent_replies_total {
                 if self.concurrent_replies[i] == seq_no {
-                    return Err(DirectRecvError::DroppedDuplicate);
+                    return Err(TryRecvError::DroppedDuplicate);
                 }
             }
-            return Err(DirectRecvError::DroppedDuplicateResendAck(seq_no));
+            return Err(TryRecvError::DroppedDuplicateResendAck(seq_no));
         } else if is_above_range {
-            return Err(DirectRecvError::DroppedTooEarly);
+            return Err(TryRecvError::DroppedTooEarly);
         }
 
         // Check whether or not we've already received this packet
@@ -462,19 +462,19 @@ impl<SendData, RecvData, const CAP: usize> SeqEx<SendData, RecvData, CAP> {
         // If the send window is full we cannot safely process received packets,
         // because there would be no way to reply.
         // We can only process this packet if processing it would make space in the send window.
-        let (wait_recv, wait_reply) = match self.is_full_inner(false, reply_no) {
+        let (wait_recv, wait_reply) = match self.is_full_inner(reply_no) {
             Ok(()) => (seq_cst && !is_next, seq_cst && self.is_locked),
-            Err(PumpError::WaitingForRecv) => (true, false),
-            Err(PumpError::WaitingForReply) => (false, true),
+            Err(TryError::WaitingForRecv) => (true, false),
+            Err(TryError::WaitingForReply) => (false, true),
         };
         if wait_recv || wait_reply {
             if !is_duplicate {
                 self.recv_window[i] = RecvEntry::Occupied { seq_no, reply_no, seq_cst, data: recv_data.into() }
             }
             return if wait_recv {
-                Err(DirectRecvError::WaitingForRecv)
+                Err(TryRecvError::WaitingForRecv)
             } else {
-                Err(DirectRecvError::WaitingForReply)
+                Err(TryRecvError::WaitingForReply)
             };
         }
 
@@ -494,19 +494,19 @@ impl<SendData, RecvData, const CAP: usize> SeqEx<SendData, RecvData, CAP> {
             self.is_locked = true;
         }
         if let Some(send_data) = reply_no.and_then(|r| self.take_send(r)) {
-            Ok((RecvOkRaw::Reply { reply_no: seq_no, recv_data, send_data, seq_cst }, do_pump, true))
+            Ok((RecvOkRaw::Reply { reply_no: seq_no, recv_data, send_data, seq_cst }, do_pump))
         } else {
-            Ok((RecvOkRaw::Payload { reply_no: seq_no, recv_data, seq_cst }, do_pump, false))
+            Ok((RecvOkRaw::Payload { reply_no: seq_no, recv_data, seq_cst }, do_pump))
         }
     }
     /// If this returns `Ok` then `try_send` might succeed on next call.
-    pub fn try_pump_raw(&mut self) -> Result<(RecvOkRaw<SendData, RecvData>, bool), PumpError> {
+    pub fn try_pump_raw(&mut self) -> Result<(RecvOkRaw<SendData, RecvData>, bool), TryError> {
         let next_seq_no = self.next_recv_seq_no;
         let i = next_seq_no as usize % self.recv_window.len();
         if let RecvEntry::Occupied { seq_no, reply_no, seq_cst, .. } = &self.recv_window[i] {
             debug_assert_eq!(*seq_no, next_seq_no);
             // We cannot safely reserve a reply no if the window is full.
-            self.is_full_inner(false, *reply_no)?;
+            self.is_full_inner(*reply_no)?;
 
             if !*seq_cst || !self.is_locked {
                 let mut entry = RecvEntry::Empty;
@@ -530,10 +530,10 @@ impl<SendData, RecvData, const CAP: usize> SeqEx<SendData, RecvData, CAP> {
                     unreachable!();
                 }
             } else {
-                return Err(PumpError::WaitingForReply);
+                return Err(TryError::WaitingForReply);
             }
         }
-        Err(PumpError::WaitingForRecv)
+        Err(TryError::WaitingForRecv)
     }
     /// This function must be passed a reply number given by `receive_raw` or `pump_raw`, otherwise
     /// it will do nothing. This reply number can only be used to reply once.
diff --git a/src/single_thread.rs b/src/single_thread.rs
index bdea3bb..ca68ad9 100644
--- a/src/single_thread.rs
+++ b/src/single_thread.rs
@@ -1,4 +1,4 @@
-use crate::{DirectRecvError, Packet, PumpError, RecvOkRaw, SeqEx, SeqNo, TransportLayer, DEFAULT_WINDOW_CAP};
+use crate::{TryRecvError, Packet, TryError, RecvOkRaw, SeqEx, SeqNo, TransportLayer, DEFAULT_WINDOW_CAP};
 
 pub struct ReplyGuard<'a, TL: TransportLayer<SendData>, SendData, RecvData, const CAP: usize = DEFAULT_WINDOW_CAP> {
     seq: &'a mut SeqEx<SendData, RecvData, CAP>,
@@ -73,14 +73,14 @@ impl std::fmt::Display for RecvError {
 #[cfg(feature = "std")]
 impl std::error::Error for RecvError {}
 
-pub enum RecvOk<'a, TL: TransportLayer<SendData>, P, SendData, RecvData, const CAP: usize = DEFAULT_WINDOW_CAP> {
+pub enum RecvOk<'a, TL: TransportLayer<SendData>, SendData, RecvData, const CAP: usize = DEFAULT_WINDOW_CAP> {
     Payload {
         reply_guard: ReplyGuard<'a, TL, SendData, RecvData, CAP>,
-        recv_data: P,
+        recv_data: RecvData,
     },
     Reply {
         reply_guard: ReplyGuard<'a, TL, SendData, RecvData, CAP>,
-        recv_data: P,
+        recv_data: RecvData,
         send_data: SendData,
     },
     Ack {
@@ -90,8 +90,8 @@ pub enum RecvOk<'a, TL: TransportLayer<SendData>, P, SendData, RecvData, const C
 macro_rules! impl_recvok {
     ($recv:tt, $seq_ex:ty) => {
         #[cfg(feature = "std")]
-        impl<'a, TL: TransportLayer<SendData>, P: std::fmt::Debug, SendData: std::fmt::Debug, RecvData, const CAP: usize> std::fmt::Debug
-            for $recv<'a, TL, P, SendData, RecvData, CAP>
+        impl<'a, TL: TransportLayer<SendData>, SendData: std::fmt::Debug, RecvData: std::fmt::Debug, const CAP: usize> std::fmt::Debug
+            for $recv<'a, TL, SendData, RecvData, CAP>
         {
             fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
                 match self {
@@ -110,8 +110,8 @@ macro_rules! impl_recvok {
                 }
             }
         }
-        impl<'a, TL: TransportLayer<SendData>, P, SendData, RecvData, const CAP: usize> $recv<'a, TL, P, SendData, RecvData, CAP> {
-            fn from_raw(seq: $seq_ex, app: TL, value: RecvOkRaw<SendData, P>) -> Self {
+        impl<'a, TL: TransportLayer<SendData>, SendData, RecvData, const CAP: usize> $recv<'a, TL, SendData, RecvData, CAP> {
+            fn from_raw(seq: $seq_ex, app: TL, value: RecvOkRaw<SendData, RecvData>) -> Self {
                 match value {
                     RecvOkRaw::Payload { reply_no, seq_cst, recv_data } => Self::Payload {
                         reply_guard: ReplyGuard { seq, app: Some(app), reply_no, is_holding_lock: seq_cst },
@@ -125,14 +125,14 @@ macro_rules! impl_recvok {
                     RecvOkRaw::Ack { send_data } => Self::Ack { send_data },
                 }
             }
-            pub fn consume(self) -> (Option<(ReplyGuard<'a, TL, SendData, RecvData, CAP>, P)>, Option<SendData>) {
+            pub fn consume(self) -> (Option<(ReplyGuard<'a, TL, SendData, RecvData, CAP>, RecvData)>, Option<SendData>) {
                 match self {
                     Self::Payload { reply_guard, recv_data } => (Some((reply_guard, recv_data)), None),
                     Self::Reply { reply_guard, recv_data, send_data } => (Some((reply_guard, recv_data)), Some(send_data)),
                     Self::Ack { send_data } => (None, Some(send_data)),
                 }
             }
-            pub fn new(recv_data: Option<(ReplyGuard<'a, TL, SendData, RecvData, CAP>, P)>, send_data: Option<SendData>) -> Option<Self> {
+            pub fn new(recv_data: Option<(ReplyGuard<'a, TL, SendData, RecvData, CAP>, RecvData)>, send_data: Option<SendData>) -> Option<Self> {
                 match (recv_data, send_data) {
                     (Some((reply_guard, recv_data)), None) => Some(Self::Payload { reply_guard, recv_data }),
                     (Some((reply_guard, recv_data)), Some(send_data)) => Some(Self::Reply { reply_guard, recv_data, send_data }),
@@ -141,15 +141,6 @@ macro_rules! impl_recvok {
                 }
             }
         }
-        impl<'a, TL: TransportLayer<SendData>, P: Into<RecvData>, SendData, RecvData, const CAP: usize> $recv<'a, TL, P, SendData, RecvData, CAP> {
-            pub fn into(self) -> $recv<'a, TL, RecvData, SendData, RecvData, CAP> {
-                match self {
-                    Self::Payload { reply_guard, recv_data } => $recv::Payload { reply_guard, recv_data: recv_data.into() },
-                    Self::Reply { reply_guard, recv_data, send_data } => $recv::Reply { reply_guard, recv_data: recv_data.into(), send_data },
-                    Self::Ack { send_data } => $recv::Ack { send_data },
-                }
-            }
-        }
     };
 }
 impl_recvok!(RecvOk, &'a mut SeqEx<SendData, RecvData, CAP>);
@@ -157,7 +148,7 @@ pub(crate) use impl_recvok;
 
 impl<SendData, RecvData, const CAP: usize> SeqEx<SendData, RecvData, CAP> {
     /// Can mutate `next_service_timestamp`.
-    pub fn try_send(&mut self, mut app: impl TransportLayer<SendData>, seq_cst: bool, packet_data: SendData) -> Result<(), SendData> {
+    pub fn try_send(&mut self, mut app: impl TransportLayer<SendData>, seq_cst: bool, packet_data: SendData) -> Result<(), (TryError, SendData)> {
         match self.try_send_direct(app.time(), seq_cst, packet_data) {
             Ok(p) => {
                 app.send(p);
@@ -172,7 +163,7 @@ impl<SendData, RecvData, const CAP: usize> SeqEx<SendData, RecvData, CAP> {
         mut app: impl TransportLayer<SendData>,
         seq_cst: bool,
         packet_data: F,
-    ) -> Result<(), F> {
+    ) -> Result<(), (TryError, F)> {
         match self.try_send_direct_with(app.time(), seq_cst, packet_data) {
             Ok(p) => {
                 app.send(p);
@@ -186,17 +177,17 @@ impl<SendData, RecvData, const CAP: usize> SeqEx<SendData, RecvData, CAP> {
         &mut self,
         mut app: impl TransportLayer<SendData>,
         packet: Packet<P>,
-    ) -> Result<RecvOkRaw<SendData, P>, RecvError> {
+    ) -> Result<(RecvOkRaw<SendData, P>, bool), RecvError> {
         match self.receive_raw_and_direct(packet) {
             Ok(a) => Ok(a),
-            Err(DirectRecvError::DroppedDuplicateResendAck(reply_no)) => {
+            Err(TryRecvError::DroppedDuplicateResendAck(reply_no)) => {
                 app.send(Packet::Ack(reply_no));
                 Err(RecvError::DroppedDuplicate)
             }
-            Err(DirectRecvError::DroppedTooEarly) => Err(RecvError::DroppedTooEarly),
-            Err(DirectRecvError::DroppedDuplicate) => Err(RecvError::DroppedDuplicate),
-            Err(DirectRecvError::WaitingForRecv) => Err(RecvError::WaitingForRecv),
-            Err(DirectRecvError::WaitingForReply) => Err(RecvError::WaitingForReply),
+            Err(TryRecvError::DroppedTooEarly) => Err(RecvError::DroppedTooEarly),
+            Err(TryRecvError::DroppedDuplicate) => Err(RecvError::DroppedDuplicate),
+            Err(TryRecvError::WaitingForRecv) => Err(RecvError::WaitingForRecv),
+            Err(TryRecvError::WaitingForReply) => Err(RecvError::WaitingForReply),
         }
     }
     /// Can mutate `next_service_timestamp`.
@@ -229,14 +220,14 @@ impl<SendData, RecvData, const CAP: usize> SeqEx<SendData, RecvData, CAP> {
         }
         self.resend_interval.min(self.next_service_timestamp - current_time)
     }
-    pub fn receive<TL: TransportLayer<SendData>, P: Into<RecvData>>(
+    pub fn receive<TL: TransportLayer<SendData>>(
         &mut self,
         app: TL,
-        packet: Packet<P>,
-    ) -> Result<RecvOk<'_, TL, P, SendData, RecvData, CAP>, RecvError> {
-        self.receive_raw(app.clone(), packet).map(|r| RecvOk::from_raw(self, app, r))
+        packet: Packet<RecvData>,
+    ) -> Result<(RecvOk<'_, TL, SendData, RecvData, CAP>, bool), RecvError> {
+        self.receive_raw(app.clone(), packet).map(|(r, do_pump)| (RecvOk::from_raw(self, app, r), do_pump))
     }
-    pub fn try_pump<TL: TransportLayer<SendData>>(&mut self, app: TL) -> Result<RecvOk<'_, TL, RecvData, SendData, RecvData, CAP>, PumpError> {
-        self.try_pump_raw().map(|r| RecvOk::from_raw(self, app, r))
+    pub fn try_pump<TL: TransportLayer<SendData>>(&mut self, app: TL) -> Result<(RecvOk<'_, TL, SendData, RecvData, CAP>, bool), TryError> {
+        self.try_pump_raw().map(|(r, do_pump)| (RecvOk::from_raw(self, app, r), do_pump))
     }
 }
diff --git a/src/sync.rs b/src/sync.rs
index c7b5e20..c22d889 100644
--- a/src/sync.rs
+++ b/src/sync.rs
@@ -1,19 +1,26 @@
 use std::{
     sync::{
         mpsc::{channel, Receiver, Sender},
-        Condvar, Mutex,
+        Condvar, Mutex, MutexGuard,
     },
     time::Instant,
 };
 
 use crate::{
-    Packet, PumpError, RecvError, RecvOkRaw, SeqEx, SeqNo, TransportLayer, DEFAULT_INITIAL_SEQ_NO, DEFAULT_RESEND_INTERVAL_MS, DEFAULT_WINDOW_CAP,
+    Packet, TryError, RecvError, RecvOkRaw, SeqEx, SeqNo, TransportLayer, DEFAULT_INITIAL_SEQ_NO, DEFAULT_RESEND_INTERVAL_MS, DEFAULT_WINDOW_CAP,
 };
 
 pub struct SeqExSync<SendData, RecvData, const CAP: usize = DEFAULT_WINDOW_CAP> {
-    seq_ex: Mutex<(SeqEx<SendData, RecvData, CAP>, usize, bool)>,
-    send_block: Condvar,
-    reply_block: Condvar,
+    inner: Mutex<SeqExInner<SendData, RecvData, CAP>>,
+    wait_on_recv: Condvar,
+    wait_on_reply_sender: Condvar,
+    wait_on_reply_receiver: Condvar,
+}
+struct SeqExInner<SendData, RecvData, const CAP: usize> {
+    seq: SeqEx<SendData, RecvData, CAP>,
+    recv_waiters: usize,
+    reply_sender_waiters: bool,
+    reply_receiver_waiters: bool,
 }
 
 pub struct ReplyGuard<'a, TL: TransportLayer<SendData>, SendData, RecvData, const CAP: usize = DEFAULT_WINDOW_CAP> {
@@ -25,15 +32,11 @@ pub struct ReplyGuard<'a, TL: TransportLayer<SendData>, SendData, RecvData, cons
 impl<'a, TL: TransportLayer<SendData>, SendData, RecvData, const CAP: usize> ReplyGuard<'a, TL, SendData, RecvData, CAP> {
     fn reply_with(mut self, seq_cst: bool, packet_data: impl FnOnce(SeqNo, SeqNo) -> SendData) {
         let app = self.app.take().unwrap();
-        let mut seq = self.seq.seq_ex.lock().unwrap();
-        let seq_no = seq.0.seq_no();
-        seq.0
+        let mut inner = self.seq.inner.lock().unwrap();
+        let seq_no = inner.seq.seq_no();
+        inner.seq
             .reply_raw(app, self.reply_no, self.is_holding_lock, seq_cst, packet_data(seq_no, self.reply_no));
-        if seq.2 {
-            seq.2 = false;
-            drop(seq);
-            self.seq.reply_block.notify_all();
-        }
+        self.seq.notify_reply(inner);
     }
     /// If you need to reply more than once, say to fragment a large file, then include in your
     /// first reply some identifier, and then `send` all fragments with the same included identifier.
@@ -54,13 +57,9 @@ impl<'a, TL: TransportLayer<SendData>, SendData, RecvData, const CAP: usize> Rep
 impl<'a, TL: TransportLayer<SendData>, SendData, RecvData, const CAP: usize> Drop for ReplyGuard<'a, TL, SendData, RecvData, CAP> {
     fn drop(&mut self) {
         if let Some(app) = self.app.take() {
-            let mut seq = self.seq.seq_ex.lock().unwrap();
-            seq.0.ack_raw(app, self.reply_no, self.is_holding_lock);
-            if seq.2 {
-                seq.2 = false;
-                drop(seq);
-                self.seq.reply_block.notify_all();
-            }
+            let mut inner = self.seq.inner.lock().unwrap();
+            inner.seq.ack_raw(app, self.reply_no, self.is_holding_lock);
+            self.seq.notify_reply(inner);
         }
     }
 }
@@ -73,14 +72,14 @@ impl<'a, TL: TransportLayer<SendData>, SendData, RecvData, const CAP: usize> std
     }
 }
 
-pub enum RecvOk<'a, TL: TransportLayer<SendData>, P, SendData, RecvData, const CAP: usize = DEFAULT_WINDOW_CAP> {
+pub enum RecvOk<'a, TL: TransportLayer<SendData>, SendData, RecvData, const CAP: usize = DEFAULT_WINDOW_CAP> {
     Payload {
         reply_guard: ReplyGuard<'a, TL, SendData, RecvData, CAP>,
-        recv_data: P,
+        recv_data: RecvData,
     },
     Reply {
         reply_guard: ReplyGuard<'a, TL, SendData, RecvData, CAP>,
-        recv_data: P,
+        recv_data: RecvData,
         send_data: SendData,
     },
     Ack {
@@ -89,138 +88,167 @@ pub enum RecvOk<'a, TL: TransportLayer<SendData>, P, SendData, RecvData, const C
 }
 crate::impl_recvok!(RecvOk, &'a SeqExSync<SendData, RecvData, CAP>);
 
-pub struct RecvIter<'a, TL: TransportLayer<SendData>, P, SendData, RecvData, const CAP: usize = DEFAULT_WINDOW_CAP> {
+pub struct RecvIter<'a, TL: TransportLayer<SendData>, SendData, RecvData, const CAP: usize = DEFAULT_WINDOW_CAP> {
     seq: Option<&'a SeqExSync<SendData, RecvData, CAP>>,
     app: TL,
-    first: Option<RecvOk<'a, TL, P, SendData, RecvData, CAP>>,
+    first: Option<RecvOk<'a, TL, SendData, RecvData, CAP>>,
     blocking: bool,
 }
 
 impl<SendData, RecvData, const CAP: usize> SeqExSync<SendData, RecvData, CAP> {
     pub fn new(retry_interval: i64, initial_seq_no: SeqNo) -> Self {
         Self {
-            seq_ex: Mutex::new((SeqEx::new(retry_interval, initial_seq_no), 0, false)),
-            send_block: Condvar::default(),
-            reply_block: Condvar::default(),
+            inner: Mutex::new(SeqExInner { seq: SeqEx::new(retry_interval, initial_seq_no), recv_waiters: 0, reply_sender_waiters: false, reply_receiver_waiters: false }),
+            wait_on_recv: Condvar::default(),
+            wait_on_reply_receiver: Condvar::default(),
+            wait_on_reply_sender: Condvar::default(),
+        }
+    }
+    fn notify_reply(&self, mut inner: MutexGuard<'_, SeqExInner<SendData, RecvData, CAP>>) {
+        if inner.reply_receiver_waiters {
+            inner.reply_receiver_waiters = false;
+            drop(inner);
+            self.wait_on_reply_receiver.notify_all();
+        } else if inner.reply_sender_waiters {
+            inner.reply_sender_waiters = false;
+            drop(inner);
+            self.wait_on_reply_sender.notify_all();
+        }
+    }
+    fn notify_recv(&self, mut inner: MutexGuard<'_, SeqExInner<SendData, RecvData, CAP>>) {
+        if inner.recv_waiters > 0 {
+            inner.recv_waiters -= 1;
+            drop(inner);
+            self.wait_on_recv.notify_one();
         }
     }
 
-    pub fn receive<TL: TransportLayer<SendData>, P: Into<RecvData>>(
+    pub fn try_receive<TL: TransportLayer<SendData>>(
         &self,
         app: TL,
-        packet: Packet<P>,
-    ) -> Result<RecvOk<'_, TL, P, SendData, RecvData, CAP>, RecvError> {
-        let mut seq = self.seq_ex.lock().unwrap();
-        match seq.0.receive_raw(app.clone(), packet) {
-            Ok(r) => {
-                if seq.1 > 0 {
-                    seq.1 -= 1;
-                    drop(seq);
-                    self.send_block.notify_one();
-                }
-                Ok(RecvOk::from_raw(self, app, r))
+        packet: Packet<RecvData>,
+    ) -> Result<(RecvOk<'_, TL, SendData, RecvData, CAP>, bool), RecvError> {
+        let mut inner = self.inner.lock().unwrap();
+        match inner.seq.receive_raw(app.clone(), packet) {
+            Ok((r, do_pump)) => {
+                self.notify_recv(inner);
+                Ok((RecvOk::from_raw(self, app, r), do_pump))
             }
             Err(e) => Err(e),
         }
     }
-    pub fn try_pump<TL: TransportLayer<SendData>>(&self, app: TL) -> Result<RecvOk<'_, TL, RecvData, SendData, RecvData, CAP>, PumpError> {
-        let mut seq = self.seq_ex.lock().unwrap();
-        // Enforce that only one thread may pump at a time.
-        if seq.2 {
-            return Err(PumpError::WaitingForReply);
+    pub fn receive<TL: TransportLayer<SendData>>(
+        &self,
+        app: TL,
+        packet: Packet<RecvData>,
+    ) -> Option<(RecvOk<'_, TL, SendData, RecvData, CAP>, bool)> {
+        let result = self.try_receive(app.clone(), packet);
+        if let Err(RecvError::WaitingForReply) = result {
+            self.pump(app)
+        } else {
+            result.ok()
         }
-        match seq.0.try_pump_raw() {
-            Ok(r) => {
-                if seq.1 > 0 {
-                    seq.1 -= 1;
-                    drop(seq);
-                    self.send_block.notify_one();
-                }
-                Ok(RecvOk::from_raw(self, app, r))
+    }
+    pub fn try_pump<TL: TransportLayer<SendData>>(&self, app: TL) -> Result<(RecvOk<'_, TL, SendData, RecvData, CAP>, bool), TryError> {
+        let mut inner = self.inner.lock().unwrap();
+        match inner.seq.try_pump_raw() {
+            Ok((r, do_pump)) => {
+                self.notify_recv(inner);
+                Ok((RecvOk::from_raw(self, app, r), do_pump))
             }
             Err(e) => Err(e),
         }
     }
-    pub fn pump<TL: TransportLayer<SendData>>(&self, app: TL) -> Option<RecvOk<'_, TL, RecvData, SendData, RecvData, CAP>> {
-        let mut seq = self.seq_ex.lock().unwrap();
-        // Enforce that only one thread may pump at a time.
-        if seq.2 {
+    pub fn pump<TL: TransportLayer<SendData>>(&self, app: TL) -> Option<(RecvOk<'_, TL, SendData, RecvData, CAP>, bool)> {
+        let mut inner = self.inner.lock().unwrap();
+        // Enforce that only one thread may wait to pump at a time.
+        if inner.reply_receiver_waiters {
             return None;
         }
         loop {
-            match seq.0.try_pump_raw() {
-                Ok(r) => {
-                    if seq.1 > 0 {
-                        seq.1 -= 1;
-                        drop(seq);
-                        self.send_block.notify_one();
-                    }
-                    return Some(RecvOk::from_raw(self, app, r));
+            match inner.seq.try_pump_raw() {
+                Ok((r, do_pump)) => {
+                    self.notify_recv(inner);
+                    return Some((RecvOk::from_raw(self, app, r), do_pump));
                 }
-                Err(PumpError::WaitingForRecv) => return None,
-                Err(PumpError::WaitingForReply) => {
-                    seq.2 = true;
-                    seq = self.reply_block.wait(seq).unwrap();
+                Err(TryError::WaitingForRecv) => return None,
+                Err(TryError::WaitingForReply) => {
+                    inner.reply_receiver_waiters = true;
+                    inner = self.wait_on_reply_receiver.wait(inner).unwrap();
                 }
             }
         }
     }
 
-    fn receive_all_inner<TL: TransportLayer<SendData>, P: Into<RecvData>>(
+    pub fn receive_all<TL: TransportLayer<SendData>>(
         &self,
         app: TL,
-        blocking: bool,
-        packet: Packet<P>,
-    ) -> RecvIter<'_, TL, P, SendData, RecvData, CAP> {
-        match self.receive(app.clone(), packet) {
-            Ok(r) => RecvIter { seq: Some(self), app, first: Some(r), blocking },
-            Err(RecvError::WaitingForReply) if blocking => RecvIter { seq: Some(self), app, first: None, blocking },
-            Err(_) => RecvIter { seq: None, app, first: None, blocking },
+        packet: Packet<RecvData>,
+    ) -> RecvIter<'_, TL, SendData, RecvData, CAP> {
+        let ret = self.receive(app.clone(), packet);
+        if let Some((first, do_pump)) = ret {
+            RecvIter { seq: do_pump.then_some(self), app, first: Some(first), blocking: true }
+        } else {
+            RecvIter { seq: None, app, first: None, blocking: true }
         }
     }
-    pub fn receive_all<TL: TransportLayer<SendData>, P: Into<RecvData>>(
+    pub fn try_receive_all<TL: TransportLayer<SendData>>(
         &self,
         app: TL,
-        packet: Packet<P>,
-    ) -> RecvIter<'_, TL, P, SendData, RecvData, CAP> {
-        self.receive_all_inner(app, true, packet)
-    }
-    pub fn try_receive_all<TL: TransportLayer<SendData>, P: Into<RecvData>>(
-        &self,
-        app: TL,
-        packet: Packet<P>,
-    ) -> RecvIter<'_, TL, P, SendData, RecvData, CAP> {
-        self.receive_all_inner(app, false, packet)
+        packet: Packet<RecvData>,
+    ) -> RecvIter<'_, TL, SendData, RecvData, CAP> {
+        let ret = self.try_receive(app.clone(), packet);
+        if let Ok((first, do_pump)) = ret {
+            RecvIter { seq: do_pump.then_some(self), app, first: Some(first), blocking: false }
+        } else {
+            RecvIter { seq: None, app, first: None, blocking: false }
+        }
     }
 
-    pub fn try_send_with<TL: TransportLayer<SendData>, F: FnOnce(SeqNo) -> SendData>(&self, app: TL, seq_cst: bool, packet_data: F) -> Result<(), F> {
-        let mut seq = self.seq_ex.lock().unwrap();
-        seq.0.try_send_with(app, seq_cst, packet_data)
+    pub fn try_send_with<TL: TransportLayer<SendData>, F: FnOnce(SeqNo) -> SendData>(&self, app: TL, seq_cst: bool, packet_data: F) -> Result<(), (TryError, F)> {
+        let mut inner = self.inner.lock().unwrap();
+        inner.seq.try_send_with(app, seq_cst, packet_data)
     }
-    pub fn try_send<TL: TransportLayer<SendData>>(&self, app: TL, seq_cst: bool, packet_data: SendData) -> Result<(), SendData> {
-        let mut seq = self.seq_ex.lock().unwrap();
-        seq.0.try_send(app, seq_cst, packet_data)
+    pub fn try_send<TL: TransportLayer<SendData>>(&self, app: TL, seq_cst: bool, packet_data: SendData) -> Result<(), (TryError, SendData)> {
+        let mut inner = self.inner.lock().unwrap();
+        inner.seq.try_send(app, seq_cst, packet_data)
     }
 
     pub fn send_with<TL: TransportLayer<SendData>>(&self, app: TL, seq_cst: bool, mut packet_data: impl FnOnce(SeqNo) -> SendData) {
-        let mut seq = self.seq_ex.lock().unwrap();
-        while let Err(p) = seq.0.try_send_with(app.clone(), seq_cst, packet_data) {
+        let mut inner = self.inner.lock().unwrap();
+        while let Err((e, p)) = inner.seq.try_send_with(app.clone(), seq_cst, packet_data) {
             packet_data = p;
-            seq.1 += 1;
-            seq = self.send_block.wait(seq).unwrap();
+            match e {
+                TryError::WaitingForRecv => {
+                    inner.recv_waiters += 1;
+                    inner = self.wait_on_recv.wait(inner).unwrap();
+                }
+                TryError::WaitingForReply => {
+                    inner.reply_sender_waiters = true;
+                    inner = self.wait_on_reply_sender.wait(inner).unwrap();
+                }
+            }
         }
     }
     pub fn send<TL: TransportLayer<SendData>>(&self, app: TL, seq_cst: bool, mut packet_data: SendData) {
-        let mut seq = self.seq_ex.lock().unwrap();
-        while let Err(p) = seq.0.try_send(app.clone(), seq_cst, packet_data) {
+        let mut inner = self.inner.lock().unwrap();
+        while let Err((e, p)) = inner.seq.try_send(app.clone(), seq_cst, packet_data) {
             packet_data = p;
-            seq.1 += 1;
-            seq = self.send_block.wait(seq).unwrap();
+            match e {
+                TryError::WaitingForRecv => {
+                    inner.recv_waiters += 1;
+                    inner = self.wait_on_recv.wait(inner).unwrap();
+                }
+                TryError::WaitingForReply => {
+                    inner.reply_sender_waiters = true;
+                    inner = self.wait_on_reply_sender.wait(inner).unwrap();
+                }
+            }
         }
     }
 
     pub fn service<TL: TransportLayer<SendData>>(&self, app: TL) -> i64 {
-        self.seq_ex.lock().unwrap().0.service(app)
+        self.inner.lock().unwrap().seq.service(app)
     }
 }
 impl<SendData, RecvData, const CAP: usize> Default for SeqExSync<SendData, RecvData, CAP> {
@@ -229,23 +257,26 @@ impl<SendData, RecvData, const CAP: usize> Default for SeqExSync<SendData, RecvD
     }
 }
 
-impl<'a, TL: TransportLayer<SendData>, P, SendData, RecvData, const CAP: usize> RecvIter<'a, TL, P, SendData, RecvData, CAP> {
-    pub fn take_first(&mut self) -> Option<RecvOk<'a, TL, P, SendData, RecvData, CAP>> {
-        self.first.take()
-    }
-}
-impl<'a, TL: TransportLayer<SendData>, P: Into<RecvData>, SendData, RecvData, const CAP: usize> Iterator
-    for RecvIter<'a, TL, P, SendData, RecvData, CAP>
+impl<'a, TL: TransportLayer<SendData>, SendData, RecvData, const CAP: usize> Iterator
+    for RecvIter<'a, TL, SendData, RecvData, CAP>
 {
-    type Item = RecvOk<'a, TL, RecvData, SendData, RecvData, CAP>;
+    type Item = RecvOk<'a, TL, SendData, RecvData, CAP>;
     fn next(&mut self) -> Option<Self::Item> {
-        if let Some(g) = self.first.take() {
-            Some(g.into())
+        if let Some(item) = self.first.take() {
+            Some(item)
         } else if let Some(origin) = self.seq {
-            if self.blocking {
+            let ret = if self.blocking {
                 origin.pump(self.app.clone())
             } else {
                 origin.try_pump(self.app.clone()).ok()
+            };
+            if let Some((item, do_pump)) = ret {
+                if !do_pump {
+                    self.seq = None;
+                }
+                Some(item)
+            } else {
+                None
             }
         } else {
             None
diff --git a/src/tokio.rs b/src/tokio.rs
index ee68bab..6be57c4 100644
--- a/src/tokio.rs
+++ b/src/tokio.rs
@@ -4,7 +4,7 @@ use tokio::{
     time,
 };
 
-use crate::{Packet, PumpError, RecvOkRaw, SeqEx, SeqNo, TransportLayer, DEFAULT_INITIAL_SEQ_NO, DEFAULT_RESEND_INTERVAL_MS, DEFAULT_WINDOW_CAP};
+use crate::{Packet, TryError, RecvOkRaw, SeqEx, SeqNo, TransportLayer, DEFAULT_INITIAL_SEQ_NO, DEFAULT_RESEND_INTERVAL_MS, DEFAULT_WINDOW_CAP};
 
 type SendData<Payload> = (oneshot::Sender<Option<(SeqNo, bool, Payload)>>, Payload);
 
@@ -211,7 +211,7 @@ impl<Payload, const CAP: usize> SeqExTokio<Payload, CAP> {
         &self,
         app: TL,
         blocking: bool,
-    ) -> Result<(ReplyGuard<'_, TL, Payload, CAP>, Payload), PumpError> {
+    ) -> Result<(ReplyGuard<'_, TL, Payload, CAP>, Payload), TryError> {
         let mut seq = self.seq_ex.lock().unwrap();
         // Enforce that only one thread may pump at a time.
         loop {
@@ -225,23 +225,23 @@ impl<Payload, const CAP: usize> SeqExTokio<Payload, CAP> {
                         return Ok(ret);
                     }
                 }
-                Err(PumpError::WaitingForRecv) => return Err(PumpError::WaitingForRecv),
-                Err(PumpError::WaitingForReply) => {
+                Err(TryError::WaitingForRecv) => return Err(TryError::WaitingForRecv),
+                Err(TryError::WaitingForReply) => {
                     seq.2 |= blocking;
-                    return Err(PumpError::WaitingForReply);
+                    return Err(TryError::WaitingForReply);
                 }
             }
         }
     }
-    pub fn try_pump<TL: TokioLayer<Payload = Payload>>(&self, app: TL) -> Result<(ReplyGuard<'_, TL, Payload, CAP>, Payload), PumpError> {
+    pub fn try_pump<TL: TokioLayer<Payload = Payload>>(&self, app: TL) -> Result<(ReplyGuard<'_, TL, Payload, CAP>, Payload), TryError> {
         self.try_pump_inner(app, false)
     }
     pub async fn pump<TL: TokioLayer<Payload = Payload>>(&self, app: TL) -> Option<(ReplyGuard<'_, TL, Payload, CAP>, Payload)> {
         loop {
             match self.try_pump_inner(app.clone(), true) {
                 Ok(ret) => return Some(ret),
-                Err(PumpError::WaitingForRecv) => return None,
-                Err(PumpError::WaitingForReply) => {
+                Err(TryError::WaitingForRecv) => return None,
+                Err(TryError::WaitingForReply) => {
                     self.reply_block.notified().await;
                 }
             }