Portable atomic (and portable atomic util)

Cargo.toml

@@ -25,10 +25,13 @@ std = ["alloc", "parking_lot"]
 alloc = []
 default = ["std"]
 static = []
+portable_atomic = []
 
 [dependencies]
 pin-project = "1"
 parking_lot = { version = "0.12", optional = true, default-features = false }
+portable-atomic = { version = "1.9.0", default-features = false, features = ["require-cas", "critical-section"] }
+portable-atomic-util = { version = "0.2.4", default-features = false, features = ["alloc"] }
 
 [dev-dependencies]
 tokio = { version = "1.14.0", features = ["rt", "rt-multi-thread", "macros", "sync"] }

src/loom.rs

@@ -205,13 +205,13 @@ mod inner {
     #![allow(dead_code)]
     pub(crate) mod sync {
         #[allow(unused_imports)]
-        pub use core::sync::*;
+        pub use portable_atomic as atomic;
 
-        #[cfg(feature = "alloc")]
+        #[cfg(all(feature = "alloc", not(feature = "portable_atomic")))]
         pub use alloc::sync::*;
     }
 
-    pub(crate) use core::sync::atomic;
+    pub(crate) use portable_atomic as atomic;
 
     #[cfg(feature = "std")]
     pub use std::thread;
@@ -221,7 +221,7 @@ mod inner {
         pub(crate) fn spin_loop() {
             // MSRV: std::hint::spin_loop() stabilized in 1.49.0
             #[allow(deprecated)]
-            super::atomic::spin_loop_hint()
+            core::sync::atomic::spin_loop_hint(); // Apparently portable_atomic doesn't have spin_loop_hint
         }
     }
 

src/mpsc/async_impl.rs

@@ -14,7 +14,14 @@ use errors::*;
 feature! {
     #![feature = "alloc"]
 
-    use crate::{MAX_CAPACITY, loom::sync::Arc};
+    use crate::{MAX_CAPACITY};
+
+    #[cfg(not(feature = "portable_atomic"))]
+    use crate::loom::sync::Arc;
+
+    #[cfg(feature = "portable_atomic")]
+    use portable_atomic_util::Arc;
+
     use alloc::boxed::Box;
 
     /// Returns a new asynchronous multi-producer, single consumer (MPSC)

src/recycling.rs

@@ -390,10 +390,16 @@ feature! {
     use alloc::{
         collections::{VecDeque, BinaryHeap},
         string::String,
-        sync::Arc,
         vec::Vec,
     };
 
+    #[cfg(all(feature = "alloc", not(feature = "portable_atomic")))]
+    use alloc::sync::Arc;
+
+    #[cfg(all(feature = "alloc", feature = "portable_atomic"))]
+    use portable_atomic_util::Arc;
+
+
     impl<T, R> Recycle<T> for Arc<R>
     where
         R: Recycle<T>,