Move all crates into a crates directory (#1940)

crates/epaint/src/mutex.rs

@@ -0,0 +1,337 @@
+//! Helper module that wraps some Mutex types with different implementations.
+
+// ----------------------------------------------------------------------------
+
+#[cfg(not(target_arch = "wasm32"))]
+#[cfg(not(debug_assertions))]
+mod mutex_impl {
+    /// Provides interior mutability.
+    ///
+    /// Uses `parking_lot` crate on native targets, and `atomic_refcell` on `wasm32` targets.
+    #[derive(Default)]
+    pub struct Mutex<T>(parking_lot::Mutex<T>);
+
+    /// The lock you get from [`Mutex`].
+    pub use parking_lot::MutexGuard;
+
+    impl<T> Mutex<T> {
+        #[inline(always)]
+        pub fn new(val: T) -> Self {
+            Self(parking_lot::Mutex::new(val))
+        }
+
+        #[inline(always)]
+        pub fn lock(&self) -> MutexGuard<'_, T> {
+            self.0.lock()
+        }
+    }
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+#[cfg(debug_assertions)]
+mod mutex_impl {
+    /// Provides interior mutability.
+    ///
+    /// Uses `parking_lot` crate on native targets, and `atomic_refcell` on `wasm32` targets.
+    #[derive(Default)]
+    pub struct Mutex<T>(parking_lot::Mutex<T>);
+
+    /// The lock you get from [`Mutex`].
+    pub struct MutexGuard<'a, T>(parking_lot::MutexGuard<'a, T>, *const ());
+
+    #[derive(Default)]
+    struct HeldLocks(Vec<*const ()>);
+
+    impl HeldLocks {
+        #[inline(always)]
+        fn insert(&mut self, lock: *const ()) {
+            // Very few locks will ever be held at the same time, so a linear search is fast
+            assert!(
+                !self.0.contains(&lock),
+                "Recursively locking a Mutex in the same thread is not supported"
+            );
+            self.0.push(lock);
+        }
+
+        #[inline(always)]
+        fn remove(&mut self, lock: *const ()) {
+            self.0.retain(|&ptr| ptr != lock);
+        }
+    }
+
+    thread_local! {
+        static HELD_LOCKS_TLS: std::cell::RefCell<HeldLocks> = Default::default();
+    }
+
+    impl<T> Mutex<T> {
+        #[inline(always)]
+        pub fn new(val: T) -> Self {
+            Self(parking_lot::Mutex::new(val))
+        }
+
+        pub fn lock(&self) -> MutexGuard<'_, T> {
+            // Detect if we are recursively taking out a lock on this mutex.
+
+            // use a pointer to the inner data as an id for this lock
+            let ptr = (&self.0 as *const parking_lot::Mutex<_>).cast::<()>();
+
+            // Store it in thread local storage while we have a lock guard taken out
+            HELD_LOCKS_TLS.with(|held_locks| {
+                held_locks.borrow_mut().insert(ptr);
+            });
+
+            MutexGuard(self.0.lock(), ptr)
+        }
+    }
+
+    impl<T> Drop for MutexGuard<'_, T> {
+        fn drop(&mut self) {
+            let ptr = self.1;
+            HELD_LOCKS_TLS.with(|held_locks| {
+                held_locks.borrow_mut().remove(ptr);
+            });
+        }
+    }
+
+    impl<T> std::ops::Deref for MutexGuard<'_, T> {
+        type Target = T;
+
+        #[inline(always)]
+        fn deref(&self) -> &Self::Target {
+            &self.0
+        }
+    }
+
+    impl<T> std::ops::DerefMut for MutexGuard<'_, T> {
+        #[inline(always)]
+        fn deref_mut(&mut self) -> &mut Self::Target {
+            &mut self.0
+        }
+    }
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+#[cfg(not(feature = "deadlock_detection"))]
+mod rw_lock_impl {
+    /// The lock you get from [`RwLock::read`].
+    pub use parking_lot::MappedRwLockReadGuard as RwLockReadGuard;
+
+    /// The lock you get from [`RwLock::write`].
+    pub use parking_lot::MappedRwLockWriteGuard as RwLockWriteGuard;
+
+    /// Provides interior mutability.
+    ///
+    /// Uses `parking_lot` crate on native targets, and `atomic_refcell` on `wasm32` targets.
+    #[derive(Default)]
+    pub struct RwLock<T>(parking_lot::RwLock<T>);
+
+    impl<T> RwLock<T> {
+        #[inline(always)]
+        pub fn new(val: T) -> Self {
+            Self(parking_lot::RwLock::new(val))
+        }
+
+        #[inline(always)]
+        pub fn read(&self) -> RwLockReadGuard<'_, T> {
+            parking_lot::RwLockReadGuard::map(self.0.read(), |v| v)
+        }
+
+        #[inline(always)]
+        pub fn write(&self) -> RwLockWriteGuard<'_, T> {
+            parking_lot::RwLockWriteGuard::map(self.0.write(), |v| v)
+        }
+    }
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+#[cfg(feature = "deadlock_detection")]
+mod rw_lock_impl {
+    /// The lock you get from [`RwLock::read`].
+    pub use parking_lot::MappedRwLockReadGuard as RwLockReadGuard;
+
+    /// The lock you get from [`RwLock::write`].
+    pub use parking_lot::MappedRwLockWriteGuard as RwLockWriteGuard;
+
+    /// Provides interior mutability.
+    ///
+    /// Uses `parking_lot` crate on native targets, and `atomic_refcell` on `wasm32` targets.
+    #[derive(Default)]
+    pub struct RwLock<T> {
+        lock: parking_lot::RwLock<T>,
+        last_lock: parking_lot::Mutex<backtrace::Backtrace>,
+    }
+
+    impl<T> RwLock<T> {
+        pub fn new(val: T) -> Self {
+            Self {
+                lock: parking_lot::RwLock::new(val),
+                last_lock: Default::default(),
+            }
+        }
+
+        pub fn read(&self) -> RwLockReadGuard<'_, T> {
+            assert!(
+                !self.lock.is_locked_exclusive(),
+                "{} DEAD-LOCK DETECTED! Previous lock held at:\n{}\n\n",
+                std::any::type_name::<Self>(),
+                format_backtrace(&mut self.last_lock.lock())
+            );
+
+            *self.last_lock.lock() = make_backtrace();
+            parking_lot::RwLockReadGuard::map(self.lock.read(), |v| v)
+        }
+
+        pub fn write(&self) -> RwLockWriteGuard<'_, T> {
+            assert!(
+                !self.lock.is_locked(),
+                "{} DEAD-LOCK DETECTED! Previous lock held at:\n{}\n\n",
+                std::any::type_name::<Self>(),
+                format_backtrace(&mut self.last_lock.lock())
+            );
+
+            *self.last_lock.lock() = make_backtrace();
+            parking_lot::RwLockWriteGuard::map(self.lock.write(), |v| v)
+        }
+    }
+
+    fn make_backtrace() -> backtrace::Backtrace {
+        backtrace::Backtrace::new_unresolved()
+    }
+
+    fn format_backtrace(backtrace: &mut backtrace::Backtrace) -> String {
+        backtrace.resolve();
+
+        let stacktrace = format!("{:?}", backtrace);
+
+        // Remove irrelevant parts of the stacktrace:
+        let end_offset = stacktrace
+            .find("std::sys_common::backtrace::__rust_begin_short_backtrace")
+            .unwrap_or(stacktrace.len());
+        let stacktrace = &stacktrace[..end_offset];
+
+        let first_interesting_function = "epaint::mutex::rw_lock_impl::make_backtrace\n";
+        if let Some(start_offset) = stacktrace.find(first_interesting_function) {
+            stacktrace[start_offset + first_interesting_function.len()..].to_owned()
+        } else {
+            stacktrace.to_owned()
+        }
+    }
+}
+
+// ----------------------------------------------------------------------------
+
+#[cfg(target_arch = "wasm32")]
+mod mutex_impl {
+    // `atomic_refcell` will panic if multiple threads try to access the same value
+
+    /// Provides interior mutability.
+    ///
+    /// Uses `parking_lot` crate on native targets, and `atomic_refcell` on `wasm32` targets.
+    #[derive(Default)]
+    pub struct Mutex<T>(atomic_refcell::AtomicRefCell<T>);
+
+    /// The lock you get from [`Mutex`].
+    pub use atomic_refcell::AtomicRefMut as MutexGuard;
+
+    impl<T> Mutex<T> {
+        #[inline(always)]
+        pub fn new(val: T) -> Self {
+            Self(atomic_refcell::AtomicRefCell::new(val))
+        }
+
+        /// Panics if already locked.
+        #[inline(always)]
+        pub fn lock(&self) -> MutexGuard<'_, T> {
+            self.0.borrow_mut()
+        }
+    }
+}
+
+#[cfg(target_arch = "wasm32")]
+mod rw_lock_impl {
+    // `atomic_refcell` will panic if multiple threads try to access the same value
+
+    /// The lock you get from [`RwLock::read`].
+    pub use atomic_refcell::AtomicRef as RwLockReadGuard;
+
+    /// The lock you get from [`RwLock::write`].
+    pub use atomic_refcell::AtomicRefMut as RwLockWriteGuard;
+
+    /// Provides interior mutability.
+    ///
+    /// Uses `parking_lot` crate on native targets, and `atomic_refcell` on `wasm32` targets.
+    #[derive(Default)]
+    pub struct RwLock<T>(atomic_refcell::AtomicRefCell<T>);
+
+    impl<T> RwLock<T> {
+        #[inline(always)]
+        pub fn new(val: T) -> Self {
+            Self(atomic_refcell::AtomicRefCell::new(val))
+        }
+
+        #[inline(always)]
+        pub fn read(&self) -> RwLockReadGuard<'_, T> {
+            self.0.borrow()
+        }
+
+        /// Panics if already locked.
+        #[inline(always)]
+        pub fn write(&self) -> RwLockWriteGuard<'_, T> {
+            self.0.borrow_mut()
+        }
+    }
+}
+
+// ----------------------------------------------------------------------------
+
+pub use mutex_impl::{Mutex, MutexGuard};
+pub use rw_lock_impl::{RwLock, RwLockReadGuard, RwLockWriteGuard};
+
+impl<T> Clone for Mutex<T>
+where
+    T: Clone,
+{
+    fn clone(&self) -> Self {
+        Self::new(self.lock().clone())
+    }
+}
+
+// ----------------------------------------------------------------------------
+
+#[cfg(test)]
+mod tests {
+    use crate::mutex::Mutex;
+    use std::time::Duration;
+
+    #[test]
+    fn lock_two_different_mutexes_single_thread() {
+        let one = Mutex::new(());
+        let two = Mutex::new(());
+        let _a = one.lock();
+        let _b = two.lock();
+    }
+
+    #[test]
+    #[should_panic]
+    fn lock_reentry_single_thread() {
+        let one = Mutex::new(());
+        let _a = one.lock();
+        let _a2 = one.lock(); // panics
+    }
+
+    #[test]
+    fn lock_multiple_threads() {
+        use std::sync::Arc;
+        let one = Arc::new(Mutex::new(()));
+        let our_lock = one.lock();
+        let other_thread = {
+            let one = Arc::clone(&one);
+            std::thread::spawn(move || {
+                let _ = one.lock();
+            })
+        };
+        std::thread::sleep(Duration::from_millis(200));
+        drop(our_lock);
+        other_thread.join().unwrap();
+    }
+}