diff --git a/azure-pipelines.yml b/azure-pipelines.yml
index 210b9767f3d..9c583a086e9 100644
--- a/azure-pipelines.yml
+++ b/azure-pipelines.yml
@@ -11,6 +11,12 @@ jobs:
     rust: $(nightly)
     name: rustfmt
 
+# Apply clippy lints to all crates
+- template: ci/azure-clippy.yml
+  parameters:
+    rust: $(nightly)
+    name: clippy
+
 # Test top level crate
 - template: ci/azure-test-stable.yml
   parameters:
diff --git a/ci/azure-clippy.yml b/ci/azure-clippy.yml
new file mode 100644
index 00000000000..11a1cf75138
--- /dev/null
+++ b/ci/azure-clippy.yml
@@ -0,0 +1,16 @@
+jobs:
+- job: ${{ parameters.name }}
+  displayName: Clippy
+  pool:
+    vmImage: ubuntu-16.04
+  steps:
+    - template: azure-install-rust.yml
+      parameters:
+        rust_version: ${{ parameters.rust }}
+    - script: |
+        rustup component add clippy
+        cargo clippy --version
+      displayName: Install clippy
+    - script: |
+        cargo clippy --all --all-features -- -D warnings -A clippy::mutex-atomic
+      displayName: cargo clippy --all
diff --git a/tokio-codec/src/bytes_codec.rs b/tokio-codec/src/bytes_codec.rs
index b4a0fa31a81..c5bf62b8007 100644
--- a/tokio-codec/src/bytes_codec.rs
+++ b/tokio-codec/src/bytes_codec.rs
@@ -4,7 +4,7 @@ use bytes::{BufMut, Bytes, BytesMut};
 use std::io;
 
 /// A simple `Codec` implementation that just ships bytes around.
-#[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash, Default)]
 pub struct BytesCodec(());
 
 impl BytesCodec {
@@ -19,7 +19,7 @@ impl Decoder for BytesCodec {
     type Error = io::Error;
 
     fn decode(&mut self, buf: &mut BytesMut) -> Result<Option<BytesMut>, io::Error> {
-        if buf.len() > 0 {
+        if !buf.is_empty() {
             let len = buf.len();
             Ok(Some(buf.split_to(len)))
         } else {
diff --git a/tokio-codec/src/framed_read.rs b/tokio-codec/src/framed_read.rs
index 163a59bac48..25fc26b418f 100644
--- a/tokio-codec/src/framed_read.rs
+++ b/tokio-codec/src/framed_read.rs
@@ -153,7 +153,7 @@ pub fn framed_read2_with_buffer<T>(inner: T, mut buf: BytesMut) -> FramedRead2<T
     FramedRead2 {
         inner,
         eof: false,
-        is_readable: buf.len() > 0,
+        is_readable: !buf.is_empty(),
         buffer: buf,
     }
 }
diff --git a/tokio-codec/src/lines_codec.rs b/tokio-codec/src/lines_codec.rs
index 4f7b08e7500..31c5990ebab 100644
--- a/tokio-codec/src/lines_codec.rs
+++ b/tokio-codec/src/lines_codec.rs
@@ -190,6 +190,12 @@ impl Encoder for LinesCodec {
     }
 }
 
+impl Default for LinesCodec {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 /// An error occured while encoding or decoding a line.
 #[derive(Debug)]
 pub enum LinesCodecError {
diff --git a/tokio-current-thread/src/lib.rs b/tokio-current-thread/src/lib.rs
index 21283e93fd2..009b1372475 100644
--- a/tokio-current-thread/src/lib.rs
+++ b/tokio-current-thread/src/lib.rs
@@ -348,7 +348,7 @@ impl<P: Park> CurrentThread<P> {
     }
 
     /// Bind `CurrentThread` instance with an execution context.
-    fn enter<'a>(&'a mut self) -> Entered<'a, P> {
+    fn enter(&mut self) -> Entered<'_, P> {
         Entered { executor: self }
     }
 
@@ -429,6 +429,12 @@ impl<P: Park> fmt::Debug for CurrentThread<P> {
     }
 }
 
+impl<P: Park + Default> Default for CurrentThread<P> {
+    fn default() -> Self {
+        CurrentThread::new_with_park(P::default())
+    }
+}
+
 // ===== impl Entered =====
 
 impl<'a, P: Park> Entered<'a, P> {
@@ -483,7 +489,7 @@ impl<'a, P: Park> Entered<'a, P> {
 
             self.tick();
 
-            if let Err(_) = self.executor.park.park() {
+            if self.executor.park.park().is_err() {
                 panic!("block_on park failed");
             }
         }
@@ -550,7 +556,7 @@ impl<'a, P: Park> Entered<'a, P> {
 
             match time {
                 Some((until, rem)) => {
-                    if let Err(_) = self.executor.park.park_timeout(rem) {
+                    if self.executor.park.park_timeout(rem).is_err() {
                         return Err(RunTimeoutError::new(false));
                     }
 
@@ -563,7 +569,7 @@ impl<'a, P: Park> Entered<'a, P> {
                     time = Some((until, until - now));
                 }
                 None => {
-                    if let Err(_) = self.executor.park.park() {
+                    if self.executor.park.park().is_err() {
                         return Err(RunTimeoutError::new(false));
                     }
                 }
@@ -790,6 +796,8 @@ impl CurrentRunner {
 
 unsafe fn hide_lt<'a>(p: *mut (dyn SpawnLocal + 'a)) -> *mut (dyn SpawnLocal + 'static) {
     use std::mem;
+    // false positive: https://github.com/rust-lang/rust-clippy/issues/2906
+    #[allow(clippy::transmute_ptr_to_ptr)]
     mem::transmute(p)
 }
 
diff --git a/tokio-current-thread/src/scheduler.rs b/tokio-current-thread/src/scheduler.rs
index 481e62985d3..29dc42e41a5 100644
--- a/tokio-current-thread/src/scheduler.rs
+++ b/tokio-current-thread/src/scheduler.rs
@@ -443,10 +443,8 @@ impl<U> Inner<U> {
         let tail = *self.tail_readiness.get();
         let next = (*tail).next_readiness.load(Acquire);
 
-        if tail == self.stub() {
-            if next.is_null() {
-                return false;
-            }
+        if tail == self.stub() && next.is_null() {
+            return false;
         }
 
         true
@@ -566,7 +564,7 @@ impl<U> List<U> {
 
         self.len += 1;
 
-        return ptr;
+        ptr
     }
 
     /// Pop an element from the front of the list
@@ -618,7 +616,7 @@ impl<U> List<U> {
 
         self.len -= 1;
 
-        return node;
+        node
     }
 }
 
@@ -773,7 +771,7 @@ impl<U> Drop for Node<U> {
 fn arc2ptr<T>(ptr: Arc<T>) -> *const T {
     let addr = &*ptr as *const T;
     mem::forget(ptr);
-    return addr;
+    addr
 }
 
 unsafe fn ptr2arc<T>(ptr: *const T) -> Arc<T> {
diff --git a/tokio-executor/src/global.rs b/tokio-executor/src/global.rs
index 49eeed80fae..6017d5f7348 100644
--- a/tokio-executor/src/global.rs
+++ b/tokio-executor/src/global.rs
@@ -180,6 +180,8 @@ where
 
 unsafe fn hide_lt<'a>(p: *mut (dyn Executor + 'a)) -> *mut (dyn Executor + 'static) {
     use std::mem;
+    // false positive: https://github.com/rust-lang/rust-clippy/issues/2906
+    #[allow(clippy::transmute_ptr_to_ptr)]
     mem::transmute(p)
 }
 
diff --git a/tokio-executor/src/park.rs b/tokio-executor/src/park.rs
index 35cd846b42e..e5d6acf4bca 100644
--- a/tokio-executor/src/park.rs
+++ b/tokio-executor/src/park.rs
@@ -218,6 +218,12 @@ impl Park for ParkThread {
     }
 }
 
+impl Default for ParkThread {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 // ===== impl UnparkThread =====
 
 impl Unpark for UnparkThread {
diff --git a/tokio-fs/src/file/open_options.rs b/tokio-fs/src/file/open_options.rs
index 124feb17e63..1a4f63c51c8 100644
--- a/tokio-fs/src/file/open_options.rs
+++ b/tokio-fs/src/file/open_options.rs
@@ -102,3 +102,9 @@ impl From<StdOpenOptions> for OpenOptions {
         OpenOptions(options)
     }
 }
+
+impl Default for OpenOptions {
+    fn default() -> Self {
+        Self::new()
+    }
+}
diff --git a/tokio-io/src/async_read.rs b/tokio-io/src/async_read.rs
index 1b7eaa6cea0..1a59692f44d 100644
--- a/tokio-io/src/async_read.rs
+++ b/tokio-io/src/async_read.rs
@@ -62,8 +62,8 @@ pub trait AsyncRead {
     /// [`io::Read`]: https://doc.rust-lang.org/std/io/trait.Read.html
     /// [`poll_read_buf`]: #method.poll_read_buf
     unsafe fn prepare_uninitialized_buffer(&self, buf: &mut [u8]) -> bool {
-        for i in 0..buf.len() {
-            buf[i] = 0;
+        for x in buf {
+            *x = 0;
         }
 
         true
diff --git a/tokio-macros/src/lib.rs b/tokio-macros/src/lib.rs
index 3a7b9ec42fd..2d24dd9a8ed 100644
--- a/tokio-macros/src/lib.rs
+++ b/tokio-macros/src/lib.rs
@@ -66,15 +66,12 @@ pub fn main(args: TokenStream, item: TokenStream) -> TokenStream {
     let mut runtime = RuntimeType::Multi;
 
     for arg in args {
-        match arg {
-            syn::NestedMeta::Meta(syn::Meta::Word(ident)) => {
-                match ident.to_string().to_lowercase().as_str() {
-                    "multi_thread" => runtime = RuntimeType::Multi,
-                    "single_thread" => runtime = RuntimeType::Single,
-                    name => panic!("Unknown attribute {} is specified", name),
-                }
+        if let syn::NestedMeta::Meta(syn::Meta::Word(ident)) = arg {
+            match ident.to_string().to_lowercase().as_str() {
+                "multi_thread" => runtime = RuntimeType::Multi,
+                "single_thread" => runtime = RuntimeType::Single,
+                name => panic!("Unknown attribute {} is specified", name),
             }
-            _ => (),
         }
     }
 
diff --git a/tokio-reactor/src/lib.rs b/tokio-reactor/src/lib.rs
index 29db1faaab1..64f34e139d3 100644
--- a/tokio-reactor/src/lib.rs
+++ b/tokio-reactor/src/lib.rs
@@ -322,7 +322,7 @@ impl Reactor {
                 "loop process - {} events, {}.{:03}s",
                 events,
                 dur.as_secs(),
-                dur.subsec_nanos() / 1_000_000
+                dur.subsec_millis()
             );
         }
 
@@ -352,7 +352,7 @@ impl Reactor {
 
             io.readiness.fetch_or(ready.as_usize(), Relaxed);
 
-            if ready.is_writable() || platform::is_hup(&ready) {
+            if ready.is_writable() || platform::is_hup(ready) {
                 wr = io.writer.take_waker();
             }
 
@@ -570,8 +570,8 @@ impl Drop for Inner {
 }
 
 impl Direction {
-    fn mask(&self) -> mio::Ready {
-        match *self {
+    fn mask(self) -> mio::Ready {
+        match self {
             Direction::Read => {
                 // Everything except writable is signaled through read.
                 mio::Ready::all() - mio::Ready::writable()
@@ -590,8 +590,8 @@ mod platform {
         UnixReady::hup().into()
     }
 
-    pub fn is_hup(ready: &Ready) -> bool {
-        UnixReady::from(*ready).is_hup()
+    pub fn is_hup(ready: Ready) -> bool {
+        UnixReady::from(ready).is_hup()
     }
 }
 
@@ -603,7 +603,7 @@ mod platform {
         Ready::empty()
     }
 
-    pub fn is_hup(_: &Ready) -> bool {
+    pub fn is_hup(_: Ready) -> bool {
         false
     }
 }
diff --git a/tokio-reactor/src/poll_evented.rs b/tokio-reactor/src/poll_evented.rs
index 50f21434f43..2b62d352795 100644
--- a/tokio-reactor/src/poll_evented.rs
+++ b/tokio-reactor/src/poll_evented.rs
@@ -257,7 +257,7 @@ where
         // Cannot clear write readiness
         assert!(!ready.is_writable(), "cannot clear write readiness");
         assert!(
-            !crate::platform::is_hup(&ready),
+            !crate::platform::is_hup(ready),
             "cannot clear HUP readiness"
         );
 
diff --git a/tokio-reactor/src/registration.rs b/tokio-reactor/src/registration.rs
index 9592f6c80bf..940b19e6f92 100644
--- a/tokio-reactor/src/registration.rs
+++ b/tokio-reactor/src/registration.rs
@@ -114,7 +114,7 @@ impl Registration {
     where
         T: Evented,
     {
-        self.register2(io, || HandlePriv::try_current())
+        self.register2(io, HandlePriv::try_current)
     }
 
     /// Deregister the I/O resource from the reactor it is associated with.
@@ -416,6 +416,12 @@ impl Registration {
     }
 }
 
+impl Default for Registration {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 unsafe impl Send for Registration {}
 unsafe impl Sync for Registration {}
 
diff --git a/tokio-signal/src/registry.rs b/tokio-signal/src/registry.rs
index 5705fc1a631..215deceaabf 100644
--- a/tokio-signal/src/registry.rs
+++ b/tokio-signal/src/registry.rs
@@ -76,9 +76,9 @@ impl<S: Storage> Registry<S> {
     /// Mark `event_id` as having been delivered, without broadcasting it to
     /// any listeners.
     fn record_event(&self, event_id: EventId) {
-        self.storage
-            .event_info(event_id)
-            .map(|event_info| event_info.pending.store(true, Ordering::SeqCst));
+        if let Some(event_info) = self.storage.event_info(event_id) {
+            event_info.pending.store(true, Ordering::SeqCst)
+        }
     }
 
     /// Broadcast all previously recorded events to their respective listeners.
diff --git a/tokio-sync/src/mpsc/bounded.rs b/tokio-sync/src/mpsc/bounded.rs
index c549f5498f7..4e32a1ce4a0 100644
--- a/tokio-sync/src/mpsc/bounded.rs
+++ b/tokio-sync/src/mpsc/bounded.rs
@@ -132,6 +132,7 @@ impl<T> Receiver<T> {
     }
 
     /// TODO: Dox
+    #[allow(clippy::needless_lifetimes)] // false positive: https://github.com/rust-lang/rust-clippy/issues/3988
     pub async fn recv(&mut self) -> Option<T> {
         use async_util::future::poll_fn;
 
@@ -204,6 +205,7 @@ impl<T> Sender<T> {
     /// ```
     /// unimplemented!();
     /// ```
+    #[allow(clippy::needless_lifetimes)] // false positive: https://github.com/rust-lang/rust-clippy/issues/3988
     pub async fn send(&mut self, value: T) -> Result<(), SendError> {
         use async_util::future::poll_fn;
 
diff --git a/tokio-sync/src/mpsc/unbounded.rs b/tokio-sync/src/mpsc/unbounded.rs
index dd1664a467c..9de0ae12fa0 100644
--- a/tokio-sync/src/mpsc/unbounded.rs
+++ b/tokio-sync/src/mpsc/unbounded.rs
@@ -93,6 +93,7 @@ impl<T> UnboundedReceiver<T> {
     }
 
     /// TODO: Dox
+    #[allow(clippy::needless_lifetimes)] // false positive: https://github.com/rust-lang/rust-clippy/issues/3988
     pub async fn recv(&mut self) -> Option<T> {
         use async_util::future::poll_fn;
 
diff --git a/tokio-sync/src/oneshot.rs b/tokio-sync/src/oneshot.rs
index 179e45e8e1a..a51f8028948 100644
--- a/tokio-sync/src/oneshot.rs
+++ b/tokio-sync/src/oneshot.rs
@@ -220,6 +220,7 @@ impl<T> Sender<T> {
     /// ```
     /// unimplemented!();
     /// ```
+    #[allow(clippy::needless_lifetimes)] // false positive: https://github.com/rust-lang/rust-clippy/issues/3988
     pub async fn closed(&mut self) {
         use async_util::future::poll_fn;
 
@@ -384,10 +385,10 @@ impl<T> Inner<T> {
                         None => Ready(Err(RecvError(()))),
                     }
                 } else {
-                    return Pending;
+                    Pending
                 }
             } else {
-                return Pending;
+                Pending
             }
         }
     }
@@ -498,7 +499,7 @@ impl State {
         State(0)
     }
 
-    fn is_complete(&self) -> bool {
+    fn is_complete(self) -> bool {
         self.0 & VALUE_SENT == VALUE_SENT
     }
 
@@ -510,7 +511,7 @@ impl State {
         State(val)
     }
 
-    fn is_rx_task_set(&self) -> bool {
+    fn is_rx_task_set(self) -> bool {
         self.0 & RX_TASK_SET == RX_TASK_SET
     }
 
@@ -524,7 +525,7 @@ impl State {
         State(val & !RX_TASK_SET)
     }
 
-    fn is_closed(&self) -> bool {
+    fn is_closed(self) -> bool {
         self.0 & CLOSED == CLOSED
     }
 
@@ -545,7 +546,7 @@ impl State {
         State(val & !TX_TASK_SET)
     }
 
-    fn is_tx_task_set(&self) -> bool {
+    fn is_tx_task_set(self) -> bool {
         self.0 & TX_TASK_SET == TX_TASK_SET
     }
 
diff --git a/tokio-sync/src/semaphore.rs b/tokio-sync/src/semaphore.rs
index 4803085cdfc..4dcfddb9945 100644
--- a/tokio-sync/src/semaphore.rs
+++ b/tokio-sync/src/semaphore.rs
@@ -597,9 +597,9 @@ impl Permit {
         }
 
         match semaphore.poll_permit(Some((cx, self)))? {
-            Ready(v) => {
+            Ready(()) => {
                 self.state = PermitState::Acquired;
-                Ready(Ok(v))
+                Ready(Ok(()))
             }
             Pending => {
                 self.state = PermitState::Waiting;
@@ -671,6 +671,12 @@ impl Permit {
     }
 }
 
+impl Default for Permit {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 // ===== impl AcquireError ====
 
 impl AcquireError {
@@ -874,8 +880,9 @@ impl WaiterNode {
         NodeState::store(&self.state, Idle, Relaxed);
     }
 
-    fn into_non_null(arc: Arc<WaiterNode>) -> NonNull<WaiterNode> {
-        let ptr = Arc::into_raw(arc);
+    #[allow(clippy::wrong_self_convention)] // https://github.com/rust-lang/rust-clippy/issues/4293
+    fn into_non_null(self: Arc<WaiterNode>) -> NonNull<WaiterNode> {
+        let ptr = Arc::into_raw(self);
         unsafe { NonNull::new_unchecked(ptr as *mut _) }
     }
 }
@@ -921,7 +928,7 @@ impl SemState {
     }
 
     /// Returns the amount of remaining capacity
-    fn available_permits(&self) -> usize {
+    fn available_permits(self) -> usize {
         if !self.has_available_permits() {
             return 0;
         }
@@ -930,11 +937,11 @@ impl SemState {
     }
 
     /// Returns true if the state has permits that can be claimed by a waiter.
-    fn has_available_permits(&self) -> bool {
+    fn has_available_permits(self) -> bool {
         self.0 & NUM_FLAG == NUM_FLAG
     }
 
-    fn has_waiter(&self, stub: &WaiterNode) -> bool {
+    fn has_waiter(self, stub: &WaiterNode) -> bool {
         !self.has_available_permits() && !self.is_stub(stub)
     }
 
@@ -978,12 +985,12 @@ impl SemState {
         self.0 += permits << NUM_SHIFT;
     }
 
-    fn is_waiter(&self) -> bool {
+    fn is_waiter(self) -> bool {
         self.0 & NUM_FLAG == 0
     }
 
     /// Returns the waiter, if one is set.
-    fn waiter(&self) -> Option<NonNull<WaiterNode>> {
+    fn waiter(self) -> Option<NonNull<WaiterNode>> {
         if self.is_waiter() {
             let waiter = NonNull::new(self.as_ptr()).expect("null pointer stored");
 
@@ -994,7 +1001,7 @@ impl SemState {
     }
 
     /// Assumes `self` represents a pointer
-    fn as_ptr(&self) -> *mut WaiterNode {
+    fn as_ptr(self) -> *mut WaiterNode {
         (self.0 & !CLOSED_FLAG) as *mut WaiterNode
     }
 
@@ -1009,7 +1016,7 @@ impl SemState {
         self.0 = waiter;
     }
 
-    fn is_stub(&self, stub: &WaiterNode) -> bool {
+    fn is_stub(self, stub: &WaiterNode) -> bool {
         self.as_ptr() as usize == stub as *const _ as usize
     }
 
@@ -1021,7 +1028,7 @@ impl SemState {
     }
 
     /// Swap the values
-    fn swap(&self, cell: &AtomicUsize, ordering: Ordering) -> SemState {
+    fn swap(self, cell: &AtomicUsize, ordering: Ordering) -> SemState {
         let prev = SemState(cell.swap(self.to_usize(), ordering));
         debug_assert_eq!(prev.is_closed(), self.is_closed());
         prev
@@ -1029,7 +1036,7 @@ impl SemState {
 
     /// Compare and exchange the current value into the provided cell
     fn compare_exchange(
-        &self,
+        self,
         cell: &AtomicUsize,
         prev: SemState,
         success: Ordering,
@@ -1054,12 +1061,12 @@ impl SemState {
         SemState(value)
     }
 
-    fn is_closed(&self) -> bool {
+    fn is_closed(self) -> bool {
         self.0 & CLOSED_FLAG == CLOSED_FLAG
     }
 
     /// Converts the state into a `usize` representation.
-    fn to_usize(&self) -> usize {
+    fn to_usize(self) -> usize {
         self.0
     }
 }
@@ -1108,7 +1115,7 @@ impl NodeState {
     }
 
     fn compare_exchange(
-        &self,
+        self,
         cell: &AtomicUsize,
         prev: NodeState,
         success: Ordering,
@@ -1120,16 +1127,16 @@ impl NodeState {
     }
 
     /// Returns `true` if `self` represents a queued state.
-    fn is_queued(&self) -> bool {
+    fn is_queued(self) -> bool {
         use self::NodeState::*;
 
-        match *self {
+        match self {
             Queued | QueuedWaiting => true,
             _ => false,
         }
     }
 
-    fn to_usize(&self) -> usize {
-        *self as usize
+    fn to_usize(self) -> usize {
+        self as usize
     }
 }
diff --git a/tokio-sync/src/watch.rs b/tokio-sync/src/watch.rs
index 2e90154d5db..6efe437db3b 100644
--- a/tokio-sync/src/watch.rs
+++ b/tokio-sync/src/watch.rs
@@ -270,6 +270,7 @@ impl<T: Clone> Receiver<T> {
     /// Attempts to clone the latest value sent via the channel.
     ///
     /// This is equivalent to calling `Clone` on the value returned by `poll_ref`.
+    #[allow(clippy::map_clone)] // false positive: https://github.com/rust-lang/rust-clippy/issues/3274
     pub fn poll_next(&mut self, cx: &mut Context<'_>) -> Poll<Option<T>> {
         let item = ready!(self.poll_ref(cx));
         Ready(item.map(|v_ref| v_ref.clone()))
@@ -280,6 +281,7 @@ impl<T: Clone> Receiver<T> {
 impl<T: Clone> futures_core::Stream for Receiver<T> {
     type Item = T;
 
+    #[allow(clippy::map_clone)] // false positive: https://github.com/rust-lang/rust-clippy/issues/3274
     fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<T>> {
         let item = ready!(self.poll_ref(cx));
         Ready(item.map(|v_ref| v_ref.clone()))
@@ -376,7 +378,7 @@ impl<T> futures_sink::Sink<T> for Sender<T> {
     }
 
     fn start_send(self: Pin<&mut Self>, item: T) -> Result<(), Self::Error> {
-        let _ = self.as_ref().get_ref().broadcast(item)?;
+        self.as_ref().get_ref().broadcast(item)?;
         Ok(())
     }
 
diff --git a/tokio-tcp/src/listener.rs b/tokio-tcp/src/listener.rs
index 4eb39a65461..66392a699a7 100644
--- a/tokio-tcp/src/listener.rs
+++ b/tokio-tcp/src/listener.rs
@@ -124,6 +124,7 @@ impl TcpListener {
     /// ```
     /// unimplemented!();
     /// ```
+    #[allow(clippy::needless_lifetimes)] // false positive: https://github.com/rust-lang/rust-clippy/issues/3988
     pub async fn accept(&mut self) -> io::Result<(TcpStream, SocketAddr)> {
         use async_util::future::poll_fn;
         poll_fn(|cx| self.poll_accept(cx)).await
diff --git a/tokio-tcp/src/split.rs b/tokio-tcp/src/split.rs
index cafbd492671..a6b98f3427c 100644
--- a/tokio-tcp/src/split.rs
+++ b/tokio-tcp/src/split.rs
@@ -53,9 +53,9 @@ pub struct TcpStreamReadHalfMut<'a>(&'a TcpStream);
 #[derive(Debug)]
 pub struct TcpStreamWriteHalfMut<'a>(&'a TcpStream);
 
-pub(crate) fn split_mut<'a>(
-    stream: &'a mut TcpStream,
-) -> (TcpStreamReadHalfMut<'a>, TcpStreamWriteHalfMut<'a>) {
+pub(crate) fn split_mut(
+    stream: &mut TcpStream,
+) -> (TcpStreamReadHalfMut<'_>, TcpStreamWriteHalfMut<'_>) {
     (
         TcpStreamReadHalfMut(&*stream),
         TcpStreamWriteHalfMut(&*stream),
diff --git a/tokio-tcp/src/stream.rs b/tokio-tcp/src/stream.rs
index 978e42fbe84..397906f299c 100644
--- a/tokio-tcp/src/stream.rs
+++ b/tokio-tcp/src/stream.rs
@@ -732,7 +732,7 @@ impl TcpStream {
     ///
     /// See the module level documenation of [`split`](super::split) for more
     /// details.
-    pub fn split_mut<'a>(&'a mut self) -> (TcpStreamReadHalfMut<'a>, TcpStreamWriteHalfMut<'a>) {
+    pub fn split_mut(&mut self) -> (TcpStreamReadHalfMut<'_>, TcpStreamWriteHalfMut<'_>) {
         split_mut(self)
     }
 
diff --git a/tokio-test/src/clock.rs b/tokio-test/src/clock.rs
index 37e6acc3c76..9c1ebb82edd 100644
--- a/tokio-test/src/clock.rs
+++ b/tokio-test/src/clock.rs
@@ -138,6 +138,12 @@ impl MockClock {
     }
 }
 
+impl Default for MockClock {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 impl Handle {
     pub(self) fn new(timer: Timer<MockPark>, time: MockTime) -> Self {
         Handle { timer, time }
diff --git a/tokio-test/src/io.rs b/tokio-test/src/io.rs
index 4e4ec1b3fb9..468190913c6 100644
--- a/tokio-test/src/io.rs
+++ b/tokio-test/src/io.rs
@@ -187,11 +187,8 @@ impl Inner {
             return Err(io::ErrorKind::BrokenPipe.into());
         }
 
-        match self.action() {
-            Some(&mut Action::Wait(..)) => {
-                return Err(io::ErrorKind::WouldBlock.into());
-            }
-            _ => {}
+        if let Some(&mut Action::Wait(..)) = self.action() {
+            return Err(io::ErrorKind::WouldBlock.into());
         }
 
         for i in 0..self.actions.len() {
diff --git a/tokio-test/src/task.rs b/tokio-test/src/task.rs
index f8944a74e46..8462ae2d453 100644
--- a/tokio-test/src/task.rs
+++ b/tokio-test/src/task.rs
@@ -98,6 +98,12 @@ impl MockTask {
     }
 }
 
+impl Default for MockTask {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 impl ThreadWaker {
     fn new() -> Self {
         ThreadWaker {
diff --git a/tokio-threadpool/src/builder.rs b/tokio-threadpool/src/builder.rs
index ae53a30b3e6..0b8bf3b2900 100644
--- a/tokio-threadpool/src/builder.rs
+++ b/tokio-threadpool/src/builder.rs
@@ -420,3 +420,9 @@ impl fmt::Debug for Builder {
             .finish()
     }
 }
+
+impl Default for Builder {
+    fn default() -> Self {
+        Self::new()
+    }
+}
diff --git a/tokio-threadpool/src/config.rs b/tokio-threadpool/src/config.rs
index 42fa13ddae4..31a951cec1d 100644
--- a/tokio-threadpool/src/config.rs
+++ b/tokio-threadpool/src/config.rs
@@ -14,9 +14,12 @@ pub(crate) struct Config {
     pub around_worker: Option<Callback>,
     pub after_start: Option<Arc<dyn Fn() + Send + Sync>>,
     pub before_stop: Option<Arc<dyn Fn() + Send + Sync>>,
-    pub panic_handler: Option<Arc<dyn Fn(Box<dyn Any + Send>) + Send + Sync>>,
+    pub panic_handler: Option<PanicHandler>,
 }
 
+// Define type alias to avoid clippy::type_complexity.
+type PanicHandler = Arc<dyn Fn(Box<dyn Any + Send>) + Send + Sync>;
+
 /// Max number of workers that can be part of a pool. This is the most that can
 /// fit in the scheduler state. Note, that this is the max number of **active**
 /// threads. There can be more standby threads.
diff --git a/tokio-threadpool/src/park/default_park.rs b/tokio-threadpool/src/park/default_park.rs
index 3a4380b50d6..dd071389402 100644
--- a/tokio-threadpool/src/park/default_park.rs
+++ b/tokio-threadpool/src/park/default_park.rs
@@ -72,6 +72,12 @@ impl Park for DefaultPark {
     }
 }
 
+impl Default for DefaultPark {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 // ===== impl DefaultUnpark =====
 
 impl Unpark for DefaultUnpark {
diff --git a/tokio-threadpool/src/pool/backup.rs b/tokio-threadpool/src/pool/backup.rs
index cb7f7ff5c22..bba3a4f5c93 100644
--- a/tokio-threadpool/src/pool/backup.rs
+++ b/tokio-threadpool/src/pool/backup.rs
@@ -235,12 +235,12 @@ impl Backup {
 
 impl State {
     /// Returns a new, default, thread `State`
-    pub fn new() -> State {
+    pub(crate) fn new() -> State {
         State(0)
     }
 
     /// Returns true if the thread entry is pushed in the sleeper stack
-    pub fn is_pushed(&self) -> bool {
+    pub(crate) fn is_pushed(self) -> bool {
         self.0 & PUSHED == PUSHED
     }
 
@@ -248,19 +248,19 @@ impl State {
         self.0 &= !PUSHED;
     }
 
-    pub fn is_running(&self) -> bool {
+    pub(crate) fn is_running(self) -> bool {
         self.0 & RUNNING == RUNNING
     }
 
-    pub fn set_running(&mut self) {
+    pub(crate) fn set_running(&mut self) {
         self.0 |= RUNNING;
     }
 
-    pub fn unset_running(&mut self) {
+    pub(crate) fn unset_running(&mut self) {
         self.0 &= !RUNNING;
     }
 
-    pub fn is_terminated(&self) -> bool {
+    pub(crate) fn is_terminated(self) -> bool {
         self.0 & TERMINATED == TERMINATED
     }
 
diff --git a/tokio-threadpool/src/pool/backup_stack.rs b/tokio-threadpool/src/pool/backup_stack.rs
index 0c3af37555d..52d7c3de7c8 100644
--- a/tokio-threadpool/src/pool/backup_stack.rs
+++ b/tokio-threadpool/src/pool/backup_stack.rs
@@ -93,10 +93,7 @@ impl BackupStack {
     /// * `Err(_)` is returned if the pool has been shutdown.
     pub fn pop(&self, entries: &[Backup], terminate: bool) -> Result<Option<BackupId>, ()> {
         // Figure out the empty value
-        let terminal = match terminate {
-            true => TERMINATED,
-            false => EMPTY,
-        };
+        let terminal = if terminate { TERMINATED } else { EMPTY };
 
         let mut state: State = self.state.load(Acquire).into();
 
@@ -164,7 +161,7 @@ impl State {
         State(EMPTY.0)
     }
 
-    fn head(&self) -> BackupId {
+    fn head(self) -> BackupId {
         BackupId(self.0 & STACK_MASK)
     }
 
diff --git a/tokio-threadpool/src/pool/state.rs b/tokio-threadpool/src/pool/state.rs
index 8806c956633..d9da1cbbf7d 100644
--- a/tokio-threadpool/src/pool/state.rs
+++ b/tokio-threadpool/src/pool/state.rs
@@ -33,19 +33,19 @@ pub(crate) const MAX_FUTURES: usize = usize::MAX >> NUM_FUTURES_OFFSET;
 
 impl State {
     #[inline]
-    pub fn new() -> State {
+    pub(crate) fn new() -> State {
         State(0)
     }
 
     /// Returns the number of futures still pending completion.
-    pub fn num_futures(&self) -> usize {
+    pub(crate) fn num_futures(self) -> usize {
         self.0 >> NUM_FUTURES_OFFSET
     }
 
     /// Increment the number of futures pending completion.
     ///
     /// Returns false on failure.
-    pub fn inc_num_futures(&mut self) {
+    pub(crate) fn inc_num_futures(&mut self) {
         debug_assert!(self.num_futures() < MAX_FUTURES);
         debug_assert!(self.lifecycle() < Lifecycle::ShutdownNow);
 
@@ -53,7 +53,7 @@ impl State {
     }
 
     /// Decrement the number of futures pending completion.
-    pub fn dec_num_futures(&mut self) {
+    pub(crate) fn dec_num_futures(&mut self) {
         let num_futures = self.num_futures();
 
         if num_futures == 0 {
@@ -69,19 +69,19 @@ impl State {
     }
 
     /// Set the number of futures pending completion to zero
-    pub fn clear_num_futures(&mut self) {
-        self.0 = self.0 & LIFECYCLE_MASK;
+    pub(crate) fn clear_num_futures(&mut self) {
+        self.0 &= LIFECYCLE_MASK;
     }
 
-    pub fn lifecycle(&self) -> Lifecycle {
+    pub(crate) fn lifecycle(self) -> Lifecycle {
         (self.0 & LIFECYCLE_MASK).into()
     }
 
-    pub fn set_lifecycle(&mut self, val: Lifecycle) {
+    pub(crate) fn set_lifecycle(&mut self, val: Lifecycle) {
         self.0 = (self.0 & NUM_FUTURES_MASK) | (val as usize);
     }
 
-    pub fn is_terminated(&self) -> bool {
+    pub(crate) fn is_terminated(self) -> bool {
         self.lifecycle() == Lifecycle::ShutdownNow && self.num_futures() == 0
     }
 }
diff --git a/tokio-threadpool/src/task/blocking.rs b/tokio-threadpool/src/task/blocking.rs
index feb8e187dfa..2640149f0e8 100644
--- a/tokio-threadpool/src/task/blocking.rs
+++ b/tokio-threadpool/src/task/blocking.rs
@@ -393,7 +393,7 @@ impl State {
         State((capacity << NUM_SHIFT) | NUM_FLAG)
     }
 
-    fn remaining_capacity(&self) -> usize {
+    fn remaining_capacity(self) -> usize {
         if !self.has_remaining_capacity() {
             return 0;
         }
@@ -401,15 +401,15 @@ impl State {
         self.0 >> 1
     }
 
-    fn has_remaining_capacity(&self) -> bool {
+    fn has_remaining_capacity(self) -> bool {
         self.0 & NUM_FLAG == NUM_FLAG
     }
 
-    fn has_task(&self, stub: &Task) -> bool {
+    fn has_task(self, stub: &Task) -> bool {
         !(self.has_remaining_capacity() || self.is_stub(stub))
     }
 
-    fn is_stub(&self, stub: &Task) -> bool {
+    fn is_stub(self, stub: &Task) -> bool {
         self.0 == stub as *const _ as usize
     }
 
@@ -452,11 +452,11 @@ impl State {
         }
     }
 
-    fn is_ptr(&self) -> bool {
+    fn is_ptr(self) -> bool {
         self.0 & NUM_FLAG == 0
     }
 
-    fn ptr(&self) -> Option<*const Task> {
+    fn ptr(self) -> Option<*const Task> {
         if self.is_ptr() {
             Some(self.0 as *const Task)
         } else {
diff --git a/tokio-threadpool/src/task/blocking_state.rs b/tokio-threadpool/src/task/blocking_state.rs
index 36f49d038f9..db419fccbca 100644
--- a/tokio-threadpool/src/task/blocking_state.rs
+++ b/tokio-threadpool/src/task/blocking_state.rs
@@ -18,26 +18,26 @@ const ALLOCATED: usize = 0b10;
 
 impl BlockingState {
     /// Create a new, default, `BlockingState`.
-    pub fn new() -> BlockingState {
+    pub(crate) fn new() -> BlockingState {
         BlockingState(0)
     }
 
     /// Returns `true` if the state represents the associated task being queued
     /// in the pending blocking capacity channel
-    pub fn is_queued(&self) -> bool {
+    pub(crate) fn is_queued(&self) -> bool {
         self.0 & QUEUED == QUEUED
     }
 
     /// Toggle the queued flag
     ///
     /// Returns the state before the flag has been toggled.
-    pub fn toggle_queued(state: &AtomicUsize, ordering: Ordering) -> BlockingState {
+    pub(crate) fn toggle_queued(state: &AtomicUsize, ordering: Ordering) -> BlockingState {
         state.fetch_xor(QUEUED, ordering).into()
     }
 
     /// Returns `true` if the state represents the associated task having been
     /// allocated capacity to block.
-    pub fn is_allocated(&self) -> bool {
+    pub(crate) fn is_allocated(&self) -> bool {
         self.0 & ALLOCATED == ALLOCATED
     }
 
@@ -46,7 +46,7 @@ impl BlockingState {
     ///
     /// If this returns `true`, then the task has the ability to block for the
     /// duration of the `poll`.
-    pub fn consume_allocation(state: &AtomicUsize, ordering: Ordering) -> CanBlock {
+    pub(crate) fn consume_allocation(state: &AtomicUsize, ordering: Ordering) -> CanBlock {
         let state: Self = state.fetch_and(!ALLOCATED, ordering).into();
 
         if state.is_allocated() {
@@ -58,7 +58,7 @@ impl BlockingState {
         }
     }
 
-    pub fn notify_blocking(state: &AtomicUsize, ordering: Ordering) {
+    pub(crate) fn notify_blocking(state: &AtomicUsize, ordering: Ordering) {
         let prev: Self = state.fetch_xor(ALLOCATED | QUEUED, ordering).into();
 
         debug_assert!(prev.is_queued());
diff --git a/tokio-threadpool/src/task/mod.rs b/tokio-threadpool/src/task/mod.rs
index 86348f42c4f..0477dd517d2 100644
--- a/tokio-threadpool/src/task/mod.rs
+++ b/tokio-threadpool/src/task/mod.rs
@@ -134,12 +134,12 @@ impl Task {
 
             let mut g = Guard(fut, true);
 
-            let mut waker = arc_waker::waker(Arc::new(Waker {
+            let waker = arc_waker::waker(Arc::new(Waker {
                 task: me.clone(),
                 pool: pool.clone(),
             }));
 
-            let mut cx = Context::from_waker(&mut waker);
+            let mut cx = Context::from_waker(&waker);
 
             let ret = g.0.as_mut().unwrap().as_mut().poll(&mut cx);
 
@@ -239,7 +239,7 @@ impl Task {
     pub fn schedule(me: &Arc<Self>, pool: &Arc<Pool>) {
         if me.schedule2() {
             let task = me.clone();
-            let _ = pool.submit(task, &pool);
+            pool.submit(task, &pool);
         }
     }
 
diff --git a/tokio-threadpool/src/task/state.rs b/tokio-threadpool/src/task/state.rs
index 3e00f89bc53..89430a9e728 100644
--- a/tokio-threadpool/src/task/state.rs
+++ b/tokio-threadpool/src/task/state.rs
@@ -27,11 +27,11 @@ impl State {
     ///
     /// Tasks start in the scheduled state as they are immediately scheduled on
     /// creation.
-    pub fn new() -> State {
+    pub(crate) fn new() -> State {
         State::Scheduled
     }
 
-    pub fn stub() -> State {
+    pub(crate) fn stub() -> State {
         State::Idle
     }
 }
diff --git a/tokio-threadpool/src/thread_pool.rs b/tokio-threadpool/src/thread_pool.rs
index 11da99f9a2f..121b4dd5015 100644
--- a/tokio-threadpool/src/thread_pool.rs
+++ b/tokio-threadpool/src/thread_pool.rs
@@ -198,6 +198,12 @@ impl Drop for ThreadPool {
     }
 }
 
+impl Default for ThreadPool {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 /*
  * TODO: Bring back
 
diff --git a/tokio-threadpool/src/worker/mod.rs b/tokio-threadpool/src/worker/mod.rs
index 30910ca718f..34ce41b96f8 100644
--- a/tokio-threadpool/src/worker/mod.rs
+++ b/tokio-threadpool/src/worker/mod.rs
@@ -622,7 +622,7 @@ impl Worker {
 
                     // We obtained permission to push the worker into the
                     // sleeper queue.
-                    if let Err(_) = self.pool.push_sleeper(self.id.0) {
+                    if self.pool.push_sleeper(self.id.0).is_err() {
                         trace!("  sleeping -- push to stack failed; idx={}", self.id.0);
                         // The push failed due to the pool being terminated.
                         //
diff --git a/tokio-threadpool/src/worker/stack.rs b/tokio-threadpool/src/worker/stack.rs
index 2d02864a3b2..1d4dfad9df4 100644
--- a/tokio-threadpool/src/worker/stack.rs
+++ b/tokio-threadpool/src/worker/stack.rs
@@ -120,10 +120,7 @@ impl Stack {
         terminate: bool,
     ) -> Option<(usize, worker::State)> {
         // Figure out the empty value
-        let terminal = match terminate {
-            true => TERMINATED,
-            false => EMPTY,
-        };
+        let terminal = if terminate { TERMINATED } else { EMPTY };
 
         // If terminating, the max lifecycle *must* be `Signaled`, which is the
         // highest lifecycle. By passing the greatest possible lifecycle value,
@@ -215,7 +212,7 @@ impl State {
     }
 
     #[inline]
-    fn head(&self) -> usize {
+    fn head(self) -> usize {
         self.0 & STACK_MASK
     }
 
diff --git a/tokio-threadpool/src/worker/state.rs b/tokio-threadpool/src/worker/state.rs
index 82789eb3d89..e8d35c332fc 100644
--- a/tokio-threadpool/src/worker/state.rs
+++ b/tokio-threadpool/src/worker/state.rs
@@ -35,7 +35,7 @@ pub(crate) enum Lifecycle {
 
 impl State {
     /// Returns true if the worker entry is pushed in the sleeper stack
-    pub fn is_pushed(&self) -> bool {
+    pub fn is_pushed(self) -> bool {
         self.0 & PUSHED_MASK == PUSHED_MASK
     }
 
@@ -43,7 +43,7 @@ impl State {
         self.0 |= PUSHED_MASK
     }
 
-    pub fn is_notified(&self) -> bool {
+    pub fn is_notified(self) -> bool {
         use self::Lifecycle::*;
 
         match self.lifecycle() {
@@ -52,7 +52,7 @@ impl State {
         }
     }
 
-    pub fn lifecycle(&self) -> Lifecycle {
+    pub fn lifecycle(self) -> Lifecycle {
         Lifecycle::from(self.0 & LIFECYCLE_MASK)
     }
 
@@ -60,7 +60,7 @@ impl State {
         self.0 = (self.0 & !LIFECYCLE_MASK) | (val as usize)
     }
 
-    pub fn is_signaled(&self) -> bool {
+    pub fn is_signaled(self) -> bool {
         self.lifecycle() == Lifecycle::Signaled
     }
 
diff --git a/tokio-timer/src/clock/clock.rs b/tokio-timer/src/clock/clock.rs
deleted file mode 100644
index 50efeb496cf..00000000000
--- a/tokio-timer/src/clock/clock.rs
+++ /dev/null
@@ -1,136 +0,0 @@
-use crate::clock::Now;
-use crate::timer;
-use std::cell::Cell;
-use std::fmt;
-use std::sync::Arc;
-use std::time::Instant;
-
-/// A handle to a source of time.
-///
-/// `Clock` instances return [`Instant`] values corresponding to "now". The source
-/// of these values is configurable. The default source is [`Instant::now`].
-///
-/// [`Instant`]: https://doc.rust-lang.org/std/time/struct.Instant.html
-/// [`Instant::now`]: https://doc.rust-lang.org/std/time/struct.Instant.html#method.now
-#[derive(Default, Clone)]
-pub struct Clock {
-    now: Option<Arc<dyn Now>>,
-}
-
-thread_local! {
-    /// Thread-local tracking the current clock
-    static CLOCK: Cell<Option<*const Clock>> = Cell::new(None)
-}
-
-/// Returns an `Instant` corresponding to "now".
-///
-/// This function delegates to the source of time configured for the current
-/// execution context. By default, this is `Instant::now()`.
-///
-/// Note that, because the source of time is configurable, it is possible to
-/// observe non-monotonic behavior when calling `now` from different
-/// executors.
-///
-/// See [module](index.html) level documentation for more details.
-///
-/// # Examples
-///
-/// ```
-/// # use tokio_timer::clock;
-/// let now = clock::now();
-/// ```
-pub fn now() -> Instant {
-    CLOCK.with(|current| match current.get() {
-        Some(ptr) => unsafe { (*ptr).now() },
-        None => Instant::now(),
-    })
-}
-
-impl Clock {
-    /// Return a new `Clock` instance that uses the current execution context's
-    /// source of time.
-    pub fn new() -> Clock {
-        CLOCK.with(|current| match current.get() {
-            Some(ptr) => unsafe { (*ptr).clone() },
-            None => Clock::system(),
-        })
-    }
-
-    /// Return a new `Clock` instance that uses `now` as the source of time.
-    pub fn new_with_now<T: Now>(now: T) -> Clock {
-        Clock {
-            now: Some(Arc::new(now)),
-        }
-    }
-
-    /// Return a new `Clock` instance that uses [`Instant::now`] as the source
-    /// of time.
-    ///
-    /// [`Instant::now`]: https://doc.rust-lang.org/std/time/struct.Instant.html#method.now
-    pub fn system() -> Clock {
-        Clock { now: None }
-    }
-
-    /// Returns an instant corresponding to "now" by using the instance's source
-    /// of time.
-    pub fn now(&self) -> Instant {
-        match self.now {
-            Some(ref now) => now.now(),
-            None => Instant::now(),
-        }
-    }
-}
-
-#[allow(deprecated)]
-impl timer::Now for Clock {
-    fn now(&mut self) -> Instant {
-        Clock::now(self)
-    }
-}
-
-impl fmt::Debug for Clock {
-    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
-        fmt.debug_struct("Clock")
-            .field("now", {
-                if self.now.is_some() {
-                    &"Some(Arc<Now>)"
-                } else {
-                    &"None"
-                }
-            })
-            .finish()
-    }
-}
-
-/// Set the default clock for the duration of the closure.
-///
-/// # Panics
-///
-/// This function panics if there already is a default clock set.
-pub fn with_default<F, R>(clock: &Clock, f: F) -> R
-where
-    F: FnOnce() -> R,
-{
-    CLOCK.with(|cell| {
-        assert!(
-            cell.get().is_none(),
-            "default clock already set for execution context"
-        );
-
-        // Ensure that the clock is removed from the thread-local context
-        // when leaving the scope. This handles cases that involve panicking.
-        struct Reset<'a>(&'a Cell<Option<*const Clock>>);
-
-        impl<'a> Drop for Reset<'a> {
-            fn drop(&mut self) {
-                self.0.set(None);
-            }
-        }
-
-        let _reset = Reset(cell);
-
-        cell.set(Some(clock as *const Clock));
-
-        f()
-    })
-}
diff --git a/tokio-timer/src/clock/mod.rs b/tokio-timer/src/clock/mod.rs
index 1791bc75859..bcae9ddaad0 100644
--- a/tokio-timer/src/clock/mod.rs
+++ b/tokio-timer/src/clock/mod.rs
@@ -16,8 +16,142 @@
 //! [`Instant::now`]: https://doc.rust-lang.org/std/time/struct.Instant.html#method.now
 //! [`with_default`]: fn.with_default.html
 
-mod clock;
 mod now;
 
-pub use self::clock::{now, with_default, Clock};
 pub use self::now::Now;
+
+use crate::timer;
+use std::cell::Cell;
+use std::fmt;
+use std::sync::Arc;
+use std::time::Instant;
+
+/// A handle to a source of time.
+///
+/// `Clock` instances return [`Instant`] values corresponding to "now". The source
+/// of these values is configurable. The default source is [`Instant::now`].
+///
+/// [`Instant`]: https://doc.rust-lang.org/std/time/struct.Instant.html
+/// [`Instant::now`]: https://doc.rust-lang.org/std/time/struct.Instant.html#method.now
+#[derive(Default, Clone)]
+pub struct Clock {
+    now: Option<Arc<dyn Now>>,
+}
+
+thread_local! {
+    /// Thread-local tracking the current clock
+    static CLOCK: Cell<Option<*const Clock>> = Cell::new(None)
+}
+
+/// Returns an `Instant` corresponding to "now".
+///
+/// This function delegates to the source of time configured for the current
+/// execution context. By default, this is `Instant::now()`.
+///
+/// Note that, because the source of time is configurable, it is possible to
+/// observe non-monotonic behavior when calling `now` from different
+/// executors.
+///
+/// See [module](index.html) level documentation for more details.
+///
+/// # Examples
+///
+/// ```
+/// # use tokio_timer::clock;
+/// let now = clock::now();
+/// ```
+pub fn now() -> Instant {
+    CLOCK.with(|current| match current.get() {
+        Some(ptr) => unsafe { (*ptr).now() },
+        None => Instant::now(),
+    })
+}
+
+impl Clock {
+    /// Return a new `Clock` instance that uses the current execution context's
+    /// source of time.
+    pub fn new() -> Clock {
+        CLOCK.with(|current| match current.get() {
+            Some(ptr) => unsafe { (*ptr).clone() },
+            None => Clock::system(),
+        })
+    }
+
+    /// Return a new `Clock` instance that uses `now` as the source of time.
+    pub fn new_with_now<T: Now>(now: T) -> Clock {
+        Clock {
+            now: Some(Arc::new(now)),
+        }
+    }
+
+    /// Return a new `Clock` instance that uses [`Instant::now`] as the source
+    /// of time.
+    ///
+    /// [`Instant::now`]: https://doc.rust-lang.org/std/time/struct.Instant.html#method.now
+    pub fn system() -> Clock {
+        Clock { now: None }
+    }
+
+    /// Returns an instant corresponding to "now" by using the instance's source
+    /// of time.
+    pub fn now(&self) -> Instant {
+        match self.now {
+            Some(ref now) => now.now(),
+            None => Instant::now(),
+        }
+    }
+}
+
+#[allow(deprecated)]
+impl timer::Now for Clock {
+    fn now(&mut self) -> Instant {
+        Clock::now(self)
+    }
+}
+
+impl fmt::Debug for Clock {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("Clock")
+            .field("now", {
+                if self.now.is_some() {
+                    &"Some(Arc<Now>)"
+                } else {
+                    &"None"
+                }
+            })
+            .finish()
+    }
+}
+
+/// Set the default clock for the duration of the closure.
+///
+/// # Panics
+///
+/// This function panics if there already is a default clock set.
+pub fn with_default<F, R>(clock: &Clock, f: F) -> R
+where
+    F: FnOnce() -> R,
+{
+    CLOCK.with(|cell| {
+        assert!(
+            cell.get().is_none(),
+            "default clock already set for execution context"
+        );
+
+        // Ensure that the clock is removed from the thread-local context
+        // when leaving the scope. This handles cases that involve panicking.
+        struct Reset<'a>(&'a Cell<Option<*const Clock>>);
+
+        impl<'a> Drop for Reset<'a> {
+            fn drop(&mut self) {
+                self.0.set(None);
+            }
+        }
+
+        let _reset = Reset(cell);
+
+        cell.set(Some(clock as *const Clock));
+
+        f()
+    })
+}
diff --git a/tokio-timer/src/delay_queue.rs b/tokio-timer/src/delay_queue.rs
index d9d0f36cb2c..32ae1c26ece 100644
--- a/tokio-timer/src/delay_queue.rs
+++ b/tokio-timer/src/delay_queue.rs
@@ -370,6 +370,8 @@ impl<T> DelayQueue<T> {
     }
 
     /// TODO: Dox... also is the fn signature correct?
+    #[allow(clippy::needless_lifetimes)] // false positive: https://github.com/rust-lang/rust-clippy/issues/3988
+    #[allow(clippy::should_implement_trait)] // false positive : https://github.com/rust-lang/rust-clippy/issues/4290
     pub async fn next(&mut self) -> Option<Result<Expired<T>, Error>> {
         use async_util::future::poll_fn;
 
diff --git a/tokio-timer/src/interval.rs b/tokio-timer/src/interval.rs
index f04486403b9..2d37647c593 100644
--- a/tokio-timer/src/interval.rs
+++ b/tokio-timer/src/interval.rs
@@ -72,6 +72,8 @@ impl Interval {
     }
 
     /// TODO: dox
+    #[allow(clippy::needless_lifetimes)] // false positive: https://github.com/rust-lang/rust-clippy/issues/3988
+    #[allow(clippy::should_implement_trait)] // false positive : https://github.com/rust-lang/rust-clippy/issues/4290
     pub async fn next(&mut self) -> Option<Instant> {
         use async_util::future::poll_fn;
 
diff --git a/tokio-timer/src/lib.rs b/tokio-timer/src/lib.rs
index 36449472ce3..52e7e6c6ca7 100644
--- a/tokio-timer/src/lib.rs
+++ b/tokio-timer/src/lib.rs
@@ -81,11 +81,11 @@ fn ms(duration: Duration, round: Round) -> u64 {
     // Round up.
     let millis = match round {
         Round::Up => (duration.subsec_nanos() + NANOS_PER_MILLI - 1) / NANOS_PER_MILLI,
-        Round::Down => duration.subsec_nanos() / NANOS_PER_MILLI,
+        Round::Down => duration.subsec_millis(),
     };
 
     duration
         .as_secs()
         .saturating_mul(MILLIS_PER_SEC)
-        .saturating_add(millis as u64)
+        .saturating_add(u64::from(millis))
 }
diff --git a/tokio-timer/src/timer/atomic_stack.rs b/tokio-timer/src/timer/atomic_stack.rs
index c248c20a1c7..6e091cbd90e 100644
--- a/tokio-timer/src/timer/atomic_stack.rs
+++ b/tokio-timer/src/timer/atomic_stack.rs
@@ -115,7 +115,7 @@ impl Iterator for AtomicStackEntries {
 
 impl Drop for AtomicStackEntries {
     fn drop(&mut self) {
-        while let Some(entry) = self.next() {
+        for entry in self {
             // Flag the entry as errored
             entry.error();
         }
diff --git a/tokio-timer/src/timer/entry.rs b/tokio-timer/src/timer/entry.rs
index dc8288cf125..5d4d9808992 100644
--- a/tokio-timer/src/timer/entry.rs
+++ b/tokio-timer/src/timer/entry.rs
@@ -125,8 +125,9 @@ impl Entry {
     }
 
     /// Only called by `Registration`
-    pub fn time_mut(&self) -> &mut Time {
-        unsafe { &mut *self.time.get() }
+    #[allow(clippy::mut_from_ref)] // https://github.com/rust-lang/rust-clippy/issues/4281
+    pub unsafe fn time_mut(&self) -> &mut Time {
+        &mut *self.time.get()
     }
 
     /// Returns `true` if the `Entry` is currently associated with a timer
diff --git a/tokio-timer/src/timer/registration.rs b/tokio-timer/src/timer/registration.rs
index d7604c86815..5e379d2353c 100644
--- a/tokio-timer/src/timer/registration.rs
+++ b/tokio-timer/src/timer/registration.rs
@@ -38,7 +38,9 @@ impl Registration {
     }
 
     pub fn reset(&mut self, deadline: Instant) {
-        self.entry.time_mut().deadline = deadline;
+        unsafe {
+            self.entry.time_mut().deadline = deadline;
+        }
         Entry::reset(&mut self.entry);
     }
 
@@ -46,7 +48,9 @@ impl Registration {
     #[cfg(feature = "async-traits")]
     pub fn reset_timeout(&mut self) {
         let deadline = crate::clock::now() + self.entry.time_ref().duration;
-        self.entry.time_mut().deadline = deadline;
+        unsafe {
+            self.entry.time_mut().deadline = deadline;
+        }
         Entry::reset(&mut self.entry);
     }
 
diff --git a/tokio-tls/src/lib.rs b/tokio-tls/src/lib.rs
index f2730e2843a..b16f047363b 100644
--- a/tokio-tls/src/lib.rs
+++ b/tokio-tls/src/lib.rs
@@ -149,8 +149,7 @@ impl<S> TlsStream<S> {
     {
         self.0.get_mut().context = ctx as *mut _ as *mut ();
         let g = Guard(self);
-        let r = f(&mut (g.0).0);
-        r
+        f(&mut (g.0).0)
     }
 }
 
@@ -193,8 +192,8 @@ where
     fn poll_shutdown(mut self: Pin<&mut Self>, ctx: &mut Context<'_>) -> Poll<io::Result<()>> {
         match self.with_context(ctx, |s| s.shutdown()) {
             Ok(()) => Poll::Ready(Ok(())),
-            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => return Poll::Pending,
-            Err(e) => return Poll::Ready(Err(e)),
+            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => Poll::Pending,
+            Err(e) => Poll::Ready(Err(e)),
         }
     }
 }
@@ -289,6 +288,7 @@ impl TlsAcceptor {
     /// This is typically used after a new socket has been accepted from a
     /// `TcpListener`. That socket is then passed to this function to perform
     /// the server half of accepting a client connection.
+    #[allow(clippy::needless_lifetimes)] // false positive: https://github.com/rust-lang/rust-clippy/issues/3988
     pub async fn accept<S>(&self, stream: S) -> Result<TlsStream<S>, Error>
     where
         S: AsyncRead + AsyncWrite + Unpin,
diff --git a/tokio-udp/src/socket.rs b/tokio-udp/src/socket.rs
index 9779004f040..5a3c94e8925 100644
--- a/tokio-udp/src/socket.rs
+++ b/tokio-udp/src/socket.rs
@@ -407,8 +407,8 @@ impl UdpSocket {
     /// address of the local interface with which the system should join the
     /// multicast group. If it's equal to `INADDR_ANY` then an appropriate
     /// interface is chosen by the system.
-    pub fn join_multicast_v4(&self, multiaddr: &Ipv4Addr, interface: &Ipv4Addr) -> io::Result<()> {
-        self.io.get_ref().join_multicast_v4(multiaddr, interface)
+    pub fn join_multicast_v4(&self, multiaddr: Ipv4Addr, interface: Ipv4Addr) -> io::Result<()> {
+        self.io.get_ref().join_multicast_v4(&multiaddr, &interface)
     }
 
     /// Executes an operation of the `IPV6_ADD_MEMBERSHIP` type.
@@ -425,8 +425,8 @@ impl UdpSocket {
     /// For more information about this option, see [`join_multicast_v4`].
     ///
     /// [`join_multicast_v4`]: #method.join_multicast_v4
-    pub fn leave_multicast_v4(&self, multiaddr: &Ipv4Addr, interface: &Ipv4Addr) -> io::Result<()> {
-        self.io.get_ref().leave_multicast_v4(multiaddr, interface)
+    pub fn leave_multicast_v4(&self, multiaddr: Ipv4Addr, interface: Ipv4Addr) -> io::Result<()> {
+        self.io.get_ref().leave_multicast_v4(&multiaddr, &interface)
     }
 
     /// Executes an operation of the `IPV6_DROP_MEMBERSHIP` type.
diff --git a/tokio/src/codec/length_delimited.rs b/tokio/src/codec/length_delimited.rs
index e319ba46150..b4822802b10 100644
--- a/tokio/src/codec/length_delimited.rs
+++ b/tokio/src/codec/length_delimited.rs
@@ -494,7 +494,7 @@ impl LengthDelimitedCodec {
         // payload
         src.reserve(n);
 
-        return Ok(Some(n));
+        Ok(Some(n))
     }
 
     fn decode_data(&self, n: usize, src: &mut BytesMut) -> io::Result<Option<BytesMut>> {
@@ -584,6 +584,12 @@ impl Encoder for LengthDelimitedCodec {
     }
 }
 
+impl Default for LengthDelimitedCodec {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 // ===== impl Builder =====
 
 impl Builder {
@@ -930,6 +936,12 @@ impl Builder {
     }
 }
 
+impl Default for Builder {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 // ===== impl FrameTooBig =====
 
 impl fmt::Debug for FrameTooBig {
diff --git a/tokio/src/runtime/current_thread/builder.rs b/tokio/src/runtime/current_thread/builder.rs
index ff8550f83ce..31a2ec3c818 100644
--- a/tokio/src/runtime/current_thread/builder.rs
+++ b/tokio/src/runtime/current_thread/builder.rs
@@ -82,3 +82,9 @@ impl Builder {
         Ok(runtime)
     }
 }
+
+impl Default for Builder {
+    fn default() -> Self {
+        Self::new()
+    }
+}
diff --git a/tokio/src/runtime/threadpool/builder.rs b/tokio/src/runtime/threadpool/builder.rs
index 54c37691dea..f6b06b7d2fa 100644
--- a/tokio/src/runtime/threadpool/builder.rs
+++ b/tokio/src/runtime/threadpool/builder.rs
@@ -374,3 +374,9 @@ impl Builder {
         })
     }
 }
+
+impl Default for Builder {
+    fn default() -> Self {
+        Self::new()
+    }
+}