Remove SignleUseCell

It's no longer used, so we don't need it anymore.

Signed-off-by: Joe Richey <[email protected]>

Author: josephlr

src/lib.rs

@@ -11,9 +11,6 @@
 #![deny(missing_debug_implementations)]
 #![deny(unsafe_op_in_unsafe_fn)]
 
-use core::cell::UnsafeCell;
-use core::sync::atomic::{AtomicBool, Ordering};
-
 pub use crate::addr::{align_down, align_up, PhysAddr, VirtAddr};
 
 pub mod addr;
@@ -66,60 +63,3 @@ impl PrivilegeLevel {
         }
     }
 }
-
-/// A wrapper that can be used to safely create one mutable reference `&'static mut T` from a static variable.
-///
-/// `SingleUseCell` is safe because it ensures that it only ever gives out one reference.
-///
-/// ``SingleUseCell<T>` is a safe alternative to `static mut` or a static `UnsafeCell<T>`.
-#[derive(Debug)]
-pub struct SingleUseCell<T> {
-    used: AtomicBool,
-    value: UnsafeCell<T>,
-}
-
-impl<T> SingleUseCell<T> {
-    /// Construct a new SingleUseCell.
-    pub const fn new(value: T) -> Self {
-        Self {
-            used: AtomicBool::new(false),
-            value: UnsafeCell::new(value),
-        }
-    }
-
-    /// Try to acquire a mutable reference to the wrapped value.
-    /// This will only succeed the first time the function is
-    /// called and fail on all following calls.
-    ///
-    /// ```
-    /// use x86_64::SingleUseCell;
-    ///
-    /// static FOO: SingleUseCell<i32> = SingleUseCell::new(0);
-    ///
-    /// // Call `try_get_mut` for the first time and get a reference.
-    /// let first: &'static mut i32 = FOO.try_get_mut().unwrap();
-    /// assert_eq!(first, &0);
-    ///
-    /// // Calling `try_get_mut` again will return `None`.
-    /// assert_eq!(FOO.try_get_mut(), None);
-    /// ```
-    pub fn try_get_mut(&self) -> Option<&mut T> {
-        let already_used = self.used.swap(true, Ordering::AcqRel);
-        if already_used {
-            None
-        } else {
-            Some(unsafe {
-                // SAFETY: no reference has been given out yet and we won't give out another.
-                &mut *self.value.get()
-            })
-        }
-    }
-}
-
-// SAFETY: Sharing a `SingleUseCell<T>` between threads is safe regardless of whether `T` is `Sync`
-// because we only expose the inner value once to one thread. The `T: Send` bound makes sure that
-// sending a unique reference to another thread is safe.
-unsafe impl<T: Send> Sync for SingleUseCell<T> {}
-
-// SAFETY: It's safe to send a `SingleUseCell<T>` to another thread if it's safe to send `T`.
-unsafe impl<T: Send> Send for SingleUseCell<T> {}

testing/src/gdt.rs

@@ -1,7 +1,7 @@
 use lazy_static::lazy_static;
 use x86_64::structures::gdt::{Descriptor, GlobalDescriptorTable, SegmentSelector};
 use x86_64::structures::tss::TaskStateSegment;
-use x86_64::{SingleUseCell, VirtAddr};
+use x86_64::VirtAddr;
 
 pub const DOUBLE_FAULT_IST_INDEX: u16 = 0;
 
@@ -18,12 +18,12 @@ lazy_static! {
         };
         tss
     };
-    static ref GDT: (SingleUseCell<GlobalDescriptorTable>, Selectors) = {
+    static ref GDT: (GlobalDescriptorTable, Selectors) = {
         let mut gdt = GlobalDescriptorTable::new();
         let code_selector = gdt.append(Descriptor::kernel_code_segment());
         let tss_selector = gdt.append(Descriptor::tss_segment(&TSS));
         (
-            SingleUseCell::new(gdt),
+            gdt,
             Selectors {
                 code_selector,
                 tss_selector,
@@ -41,7 +41,7 @@ pub fn init() {
     use x86_64::instructions::segmentation::{Segment, CS};
     use x86_64::instructions::tables::load_tss;
 
-    GDT.0.try_get_mut().unwrap().load();
+    GDT.0.load();
     unsafe {
         CS::set_reg(GDT.1.code_selector);
         load_tss(GDT.1.tss_selector);