bendns' repos / mindus
mindustry logic execution, map- and schematic- parsing and rendering
Diffstat (limited to 'src/utils/lazy.rs')
-rw-r--r--src/utils/lazy.rs45
1 files changed, 45 insertions, 0 deletions
diff --git a/src/utils/lazy.rs b/src/utils/lazy.rs
new file mode 100644
index 0000000..268a81c
--- /dev/null
+++ b/src/utils/lazy.rs
@@ -0,0 +1,45 @@
+//! [LazyLock] copy
+use std::cell::UnsafeCell;
+use std::mem::ManuallyDrop;
+use std::panic::{RefUnwindSafe, UnwindSafe};
+
+union Data<T, F> {
+ value: ManuallyDrop<T>,
+ f: ManuallyDrop<F>,
+}
+
+pub struct Lock<T, F = fn() -> T> {
+ data: UnsafeCell<Data<T, F>>,
+}
+
+impl<T, F: FnOnce() -> T> Lock<T, F> {
+ #[inline]
+ pub const fn new(f: F) -> Lock<T, F> {
+ Lock {
+ data: UnsafeCell::new(Data {
+ f: ManuallyDrop::new(f),
+ }),
+ }
+ }
+
+ #[inline]
+ // SAFETY: CALL ONLY ONCE! NOT CHECKED
+ pub unsafe fn load(this: &Lock<T, F>) {
+ let data = &mut *this.data.get();
+ let f = ManuallyDrop::take(&mut data.f);
+ let value = f();
+ data.value = ManuallyDrop::new(value);
+ }
+}
+
+impl<T, F> Lock<T, F> {
+ #[inline]
+ // SAFETY: CALL [load] FIRST!
+ pub unsafe fn get(&self) -> &T {
+ &*(*self.data.get()).value
+ }
+}
+
+unsafe impl<T: Sync + Send, F: Send> Sync for Lock<T, F> {}
+impl<T: RefUnwindSafe + UnwindSafe, F: UnwindSafe> RefUnwindSafe for Lock<T, F> {}
+impl<T: UnwindSafe, F: UnwindSafe> UnwindSafe for Lock<T, F> {}