Add an AtomicCell abstraction

Author: Zoxc

Cargo.lock

@@ -2780,6 +2780,7 @@ name = "rustc_data_structures"
 version = "0.0.0"
 dependencies = [
  "cfg-if 0.1.8 (registry+https://github.com/rust-lang/crates.io-index)",
+ "crossbeam-utils 0.6.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "ena 0.13.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "graphviz 0.0.0",
  "indexmap 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",

src/librustc_data_structures/Cargo.toml

@@ -19,6 +19,7 @@ rustc_cratesio_shim = { path = "../librustc_cratesio_shim" }
 serialize = { path = "../libserialize" }
 graphviz = { path = "../libgraphviz" }
 cfg-if = "0.1.2"
+crossbeam-utils = { version = "0.6.5", features = ["nightly"] }
 stable_deref_trait = "1.0.0"
 rayon = { version = "0.2.0", package = "rustc-rayon" }
 rayon-core = { version = "0.2.0", package = "rustc-rayon-core" }

src/librustc_data_structures/sync.rs

@@ -67,6 +67,59 @@ cfg_if! {
         use std::ops::Add;
         use std::panic::{resume_unwind, catch_unwind, AssertUnwindSafe};
 
+        #[derive(Debug)]
+        pub struct AtomicCell<T: Copy>(Cell<T>);
+
+        impl<T: Copy> AtomicCell<T> {
+            #[inline]
+            pub fn new(v: T) -> Self {
+                AtomicCell(Cell::new(v))
+            }
+        }
+
+        impl<T: Copy> AtomicCell<T> {
+            pub fn into_inner(self) -> T {
+                self.0.into_inner()
+            }
+
+            #[inline]
+            pub fn load(&self) -> T {
+                self.0.get()
+            }
+
+            #[inline]
+            pub fn store(&self, val: T) {
+                self.0.set(val)
+            }
+
+            pub fn swap(&self, val: T) -> T {
+                self.0.replace(val)
+            }
+        }
+
+        impl<T: Copy + PartialEq> AtomicCell<T> {
+            pub fn compare_exchange(&self,
+                                    current: T,
+                                    new: T)
+                                    -> Result<T, T> {
+                let read = self.0.get();
+                if read == current {
+                    self.0.set(new);
+                    Ok(read)
+                } else {
+                    Err(read)
+                }
+            }
+        }
+
+        impl<T: Add<Output=T> + Copy> AtomicCell<T> {
+            pub fn fetch_add(&self, val: T) -> T {
+                let old = self.0.get();
+                self.0.set(old + val);
+                old
+            }
+        }
+
         #[derive(Debug)]
         pub struct Atomic<T: Copy>(Cell<T>);
 
@@ -77,7 +130,7 @@ cfg_if! {
             }
         }
 
-        impl<T: Copy + PartialEq> Atomic<T> {
+        impl<T: Copy> Atomic<T> {
             pub fn into_inner(self) -> T {
                 self.0.into_inner()
             }
@@ -95,7 +148,9 @@ cfg_if! {
             pub fn swap(&self, val: T, _: Ordering) -> T {
                 self.0.replace(val)
             }
+        }
 
+        impl<T: Copy + PartialEq> Atomic<T> {
             pub fn compare_exchange(&self,
                                     current: T,
                                     new: T,
@@ -271,6 +326,8 @@ cfg_if! {
 
         pub use std::sync::atomic::{AtomicBool, AtomicUsize, AtomicU32, AtomicU64};
 
+        pub use crossbeam_utils::atomic::AtomicCell;
+
         pub use std::sync::Arc as Lrc;
         pub use std::sync::Weak as Weak;