1 files changed, 102 insertions, 0 deletions
diff --git a/src/util.rs b/src/util.rs
new file mode 100644
index 0000000..d84e37d
--- /dev/null
+++ b/src/util.rs
@@ -0,0 +1,102 @@
+//! This module is full of hackery and dark magic.
+//! Either spend a day fixing it and quietly submit a PR or don't mention it to anybody.
+use core::cell::UnsafeCell;
+use core::{mem, ptr};
+
+pub const fn ptr_size_bits() -> usize {
+    mem::size_of::<usize>() * 8
+}
+
+pub fn map_in_place_2<T, U, F: FnOnce(U, T) -> T>((k, v): (U, &mut T), f: F) {
+    unsafe {
+        // # Safety
+        //
+        // If the closure panics, we must abort otherwise we could double drop `T`
+        let _promote_panic_to_abort = AbortOnPanic;
+
+        ptr::write(v, f(k, ptr::read(v)));
+    }
+}
+
+/// # Safety
+///
+/// Requires that you ensure the reference does not become invalid.
+/// The object has to outlive the reference.
+pub unsafe fn change_lifetime_const<'a, 'b, T>(x: &'a T) -> &'b T {
+    &*(x as *const T)
+}
+
+/// # Safety
+///
+/// Requires that you ensure the reference does not become invalid.
+/// The object has to outlive the reference.
+pub unsafe fn change_lifetime_mut<'a, 'b, T>(x: &'a mut T) -> &'b mut T {
+    &mut *(x as *mut T)
+}
+
+/// A simple wrapper around `T`
+///
+/// This is to prevent UB when using `HashMap::get_key_value`, because
+/// `HashMap` doesn't expose an api to get the key and value, where
+/// the value is a `&mut T`.
+///
+/// See [#10](https://github.com/xacrimon/dashmap/issues/10) for details
+///
+/// This type is meant to be an implementation detail, but must be exposed due to the `Dashmap::shards`
+#[repr(transparent)]
+pub struct SharedValue<T> {
+    value: UnsafeCell<T>,
+}
+
+impl<T: Clone> Clone for SharedValue<T> {
+    fn clone(&self) -> Self {
+        let inner = self.get().clone();
+
+        Self {
+            value: UnsafeCell::new(inner),
+        }
+    }
+}
+
+unsafe impl<T: Send> Send for SharedValue<T> {}
+
+unsafe impl<T: Sync> Sync for SharedValue<T> {}
+
+impl<T> SharedValue<T> {
+    /// Create a new `SharedValue<T>`
+    pub const fn new(value: T) -> Self {
+        Self {
+            value: UnsafeCell::new(value),
+        }
+    }
+
+    /// Get a shared reference to `T`
+    pub fn get(&self) -> &T {
+        unsafe { &*self.value.get() }
+    }
+
+    /// Get an unique reference to `T`
+    pub fn get_mut(&mut self) -> &mut T {
+        unsafe { &mut *self.value.get() }
+    }
+
+    /// Unwraps the value
+    pub fn into_inner(self) -> T {
+        self.value.into_inner()
+    }
+
+    /// Get a mutable raw pointer to the underlying value
+    pub(crate) fn as_ptr(&self) -> *mut T {
+        self.value.get()
+    }
+}
+
+struct AbortOnPanic;
+
+impl Drop for AbortOnPanic {
+    fn drop(&mut self) {
+        if std::thread::panicking() {
+            std::process::abort()
+        }
+    }
+}