Remove mutexes around boxed services (#2947)

6 files changed, 17 insertions, 119 deletions

diff --git a/axum/clippy.toml b/axum/clippy.toml
deleted file mode 100644
index 291e8cd5..00000000
--- a/axum/clippy.toml
+++ /dev/null
@@ -1,3 +0,0 @@
-disallowed-types = [
-    { path = "std::sync::Mutex", reason = "Use our internal AxumMutex instead" },
-]
diff --git a/axum/src/boxed.rs b/axum/src/boxed.rs
index 6347de58..0d65b2d3 100644
--- a/axum/src/boxed.rs
+++ b/axum/src/boxed.rs
@@ -1,7 +1,6 @@
 use std::{convert::Infallible, fmt};
 
 use crate::extract::Request;
-use crate::util::AxumMutex;
 use tower::Service;
 
 use crate::{
@@ -10,7 +9,7 @@ use crate::{
     Router,
 };
 
-pub(crate) struct BoxedIntoRoute<S, E>(AxumMutex<Box<dyn ErasedIntoRoute<S, E>>>);
+pub(crate) struct BoxedIntoRoute<S, E>(Box<dyn ErasedIntoRoute<S, E>>);
 
 impl<S> BoxedIntoRoute<S, Infallible>
 where
@@ -21,10 +20,10 @@ where
         H: Handler<T, S>,
         T: 'static,
     {
-        Self(AxumMutex::new(Box::new(MakeErasedHandler {
+        Self(Box::new(MakeErasedHandler {
             handler,
             into_route: |handler, state| Route::new(Handler::with_state(handler, state)),
-        })))
+        }))
     }
 }
 
@@ -36,20 +35,20 @@ impl<S, E> BoxedIntoRoute<S, E> {
         F: FnOnce(Route<E>) -> Route<E2> + Clone + Send + Sync + 'static,
         E2: 'static,
     {
-        BoxedIntoRoute(AxumMutex::new(Box::new(Map {
-            inner: self.0.into_inner().unwrap(),
+        BoxedIntoRoute(Box::new(Map {
+            inner: self.0,
             layer: Box::new(f),
-        })))
+        }))
     }
 
     pub(crate) fn into_route(self, state: S) -> Route<E> {
-        self.0.into_inner().unwrap().into_route(state)
+        self.0.into_route(state)
     }
 }
 
 impl<S, E> Clone for BoxedIntoRoute<S, E> {
     fn clone(&self) -> Self {
-        Self(AxumMutex::new(self.0.lock().unwrap().clone_box()))
+        Self(self.0.clone_box())
     }
 }
 
diff --git a/axum/src/routing/route.rs b/axum/src/routing/route.rs
index 71349ba6..da1e848a 100644
--- a/axum/src/routing/route.rs
+++ b/axum/src/routing/route.rs
@@ -2,7 +2,6 @@ use crate::{
     body::{Body, HttpBody},
     box_clone_service::BoxCloneService,
     response::Response,
-    util::AxumMutex,
 };
 use axum_core::{extract::Request, response::IntoResponse};
 use bytes::Bytes;
@@ -29,7 +28,7 @@ use tower_service::Service;
 ///
 /// You normally shouldn't need to care about this type. It's used in
 /// [`Router::layer`](super::Router::layer).
-pub struct Route<E = Infallible>(AxumMutex<BoxCloneService<Request, Response, E>>);
+pub struct Route<E = Infallible>(BoxCloneService<Request, Response, E>);
 
 impl<E> Route<E> {
     pub(crate) fn new<T>(svc: T) -> Self
@@ -38,16 +37,16 @@ impl<E> Route<E> {
         T::Response: IntoResponse + 'static,
         T::Future: Send + 'static,
     {
-        Self(AxumMutex::new(BoxCloneService::new(
+        Self(BoxCloneService::new(
             svc.map_response(IntoResponse::into_response),
-        )))
+        ))
     }
 
     pub(crate) fn oneshot_inner(
         &mut self,
         req: Request,
     ) -> Oneshot<BoxCloneService<Request, Response, E>, Request> {
-        self.0.get_mut().unwrap().clone().oneshot(req)
+        self.0.clone().oneshot(req)
     }
 
     pub(crate) fn layer<L, NewError>(self, layer: L) -> Route<NewError>
@@ -73,7 +72,7 @@ impl<E> Route<E> {
 impl<E> Clone for Route<E> {
     #[track_caller]
     fn clone(&self) -> Self {
-        Self(AxumMutex::new(self.0.lock().unwrap().clone()))
+        Self(self.0.clone())
     }
 }
 
diff --git a/axum/src/routing/tests/mod.rs b/axum/src/routing/tests/mod.rs
index e9ab56e1..20e27493 100644
--- a/axum/src/routing/tests/mod.rs
+++ b/axum/src/routing/tests/mod.rs
@@ -12,7 +12,6 @@ use crate::{
         tracing_helpers::{capture_tracing, TracingEvent},
         *,
     },
-    util::mutex_num_locked,
     BoxError, Extension, Json, Router, ServiceExt,
 };
 use axum_core::extract::Request;
@@ -1068,35 +1067,3 @@ async fn impl_handler_for_into_response() {
     assert_eq!(res.status(), StatusCode::CREATED);
     assert_eq!(res.text().await, "thing created");
 }
-
-#[crate::test]
-async fn locks_mutex_very_little() {
-    let (num, app) = mutex_num_locked(|| async {
-        Router::new()
-            .route("/a", get(|| async {}))
-            .route("/b", get(|| async {}))
-            .route("/c", get(|| async {}))
-            .with_state::<()>(())
-            .into_service::<Body>()
-    })
-    .await;
-    // once for `Router::new` for setting the default fallback and 3 times, once per route
-    assert_eq!(num, 4);
-
-    for path in ["/a", "/b", "/c"] {
-        // calling the router should only lock the mutex once
-        let (num, _res) = mutex_num_locked(|| async {
-            // We cannot use `TestClient` because it uses `serve` which spawns a new task per
-            // connection and `mutex_num_locked` uses a task local to keep track of the number of
-            // locks. So spawning a new task would unset the task local set by `mutex_num_locked`
-            //
-            // So instead `call` the service directly without spawning new tasks.
-            app.clone()
-                .oneshot(Request::builder().uri(path).body(Body::empty()).unwrap())
-                .await
-                .unwrap()
-        })
-        .await;
-        assert_eq!(num, 1);
-    }
-}
diff --git a/axum/src/test_helpers/tracing_helpers.rs b/axum/src/test_helpers/tracing_helpers.rs
index 96abe510..09800f8f 100644
--- a/axum/src/test_helpers/tracing_helpers.rs
+++ b/axum/src/test_helpers/tracing_helpers.rs
@@ -1,10 +1,9 @@
-use crate::util::AxumMutex;
 use std::{
     future::{Future, IntoFuture},
     io,
     marker::PhantomData,
     pin::Pin,
-    sync::Arc,
+    sync::{Arc, Mutex},
 };
 
 use serde::{de::DeserializeOwned, Deserialize};
@@ -87,12 +86,12 @@ where
 }
 
 struct TestMakeWriter {
-    write: Arc<AxumMutex<Option<Vec<u8>>>>,
+    write: Arc<Mutex<Option<Vec<u8>>>>,
 }
 
 impl TestMakeWriter {
     fn new() -> (Self, Handle) {
-        let write = Arc::new(AxumMutex::new(Some(Vec::<u8>::new())));
+        let write = Arc::new(Mutex::new(Some(Vec::<u8>::new())));
 
         (
             Self {
@@ -134,7 +133,7 @@ impl<'a> io::Write for Writer<'a> {
 }
 
 struct Handle {
-    write: Arc<AxumMutex<Option<Vec<u8>>>>,
+    write: Arc<Mutex<Option<Vec<u8>>>>,
 }
 
 impl Handle {
diff --git a/axum/src/util.rs b/axum/src/util.rs
index bae803db..7c9b7864 100644
--- a/axum/src/util.rs
+++ b/axum/src/util.rs
@@ -1,8 +1,6 @@
 use pin_project_lite::pin_project;
 use std::{ops::Deref, sync::Arc};
 
-pub(crate) use self::mutex::*;
-
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub(crate) struct PercentDecodedStr(Arc<str>);
 
@@ -57,64 +55,3 @@ fn test_try_downcast() {
     assert_eq!(try_downcast::<i32, _>(5_u32), Err(5_u32));
     assert_eq!(try_downcast::<i32, _>(5_i32), Ok(5_i32));
 }
-
-// `AxumMutex` is a wrapper around `std::sync::Mutex` which, in test mode, tracks the number of
-// times it's been locked on the current task. That way we can write a test to ensure we don't
-// accidentally introduce more locking.
-//
-// When not in test mode, it is just a type alias for `std::sync::Mutex`.
-#[cfg(not(test))]
-mod mutex {
-    #[allow(clippy::disallowed_types)]
-    pub(crate) type AxumMutex<T> = std::sync::Mutex<T>;
-}
-
-#[cfg(test)]
-#[allow(clippy::disallowed_types)]
-mod mutex {
-    use std::sync::{
-        atomic::{AtomicUsize, Ordering},
-        LockResult, Mutex, MutexGuard,
-    };
-
-    tokio::task_local! {
-        pub(crate) static NUM_LOCKED: AtomicUsize;
-    }
-
-    pub(crate) async fn mutex_num_locked<F, Fut>(f: F) -> (usize, Fut::Output)
-    where
-        F: FnOnce() -> Fut,
-        Fut: std::future::IntoFuture,
-    {
-        NUM_LOCKED
-            .scope(AtomicUsize::new(0), async move {
-                let output = f().await;
-                let num = NUM_LOCKED.with(|num| num.load(Ordering::SeqCst));
-                (num, output)
-            })
-            .await
-    }
-
-    pub(crate) struct AxumMutex<T>(Mutex<T>);
-
-    impl<T> AxumMutex<T> {
-        pub(crate) fn new(value: T) -> Self {
-            Self(Mutex::new(value))
-        }
-
-        pub(crate) fn get_mut(&mut self) -> LockResult<&mut T> {
-            self.0.get_mut()
-        }
-
-        pub(crate) fn into_inner(self) -> LockResult<T> {
-            self.0.into_inner()
-        }
-
-        pub(crate) fn lock(&self) -> LockResult<MutexGuard<'_, T>> {
-            _ = NUM_LOCKED.try_with(|num| {
-                num.fetch_add(1, Ordering::SeqCst);
-            });
-            self.0.lock()
-        }
-    }
-}