Merge pull request #131 from notgull/msrv

Add an MSRV policy

.github/workflows/rust.yml

@@ -32,6 +32,17 @@ jobs:
     - run: rustup target add thumbv7m-none-eabi
     - name: Ensure we don't depend on libstd
       run: cargo hack build --target thumbv7m-none-eabi --no-dev-deps --no-default-features
+
+  msrv:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        version: [1.38.0]
+    steps:
+    - uses: actions/checkout@v2
+    - name: Install Rust
+      run: rustup update ${{ matrix.version }} && rustup default ${{ matrix.version }}
+    - run: cargo build --all --all-features --all-targets
 
   miri:
     runs-on: ubuntu-latest

Cargo.toml

@@ -10,6 +10,7 @@ license = "MIT"
 repository = "https://github.com/mvdnes/spin-rs.git"
 keywords = ["spinlock", "mutex", "rwlock"]
 description = "Spin-based synchronization primitives"
+rust-version = "1.38"
 
 [dependencies]
 lock_api_crate = { package = "lock_api", version = "0.4", optional = true }

README.md

@@ -127,6 +127,11 @@ time for your crate's users. You can do this like so:
 spin = { version = "x.y", default-features = false, features = [...] }
 ```
 
+## Minimum Safe Rust Version (MSRV)
+
+This crate is guaranteed to compile on a Minimum Safe Rust Version (MSRV) of 1.38.0 and above.
+This version will not be changed without a minor version bump.
+
 ## License
 
 `spin` is distributed under the MIT License, (See `LICENSE`).

src/relax.rs

@@ -23,7 +23,10 @@ pub struct Spin;
 impl RelaxStrategy for Spin {
     #[inline(always)]
     fn relax() {
-        core::hint::spin_loop();
+        // Use the deprecated spin_loop_hint() to ensure that we don't get
+        // a higher MSRV than we need to.
+        #[allow(deprecated)]
+        core::sync::atomic::spin_loop_hint();
     }
 }
 

src/rwlock.rs

@@ -251,7 +251,7 @@ impl<T: ?Sized, R> RwLock<T, R> {
     // Acquire a read lock, returning the new lock value.
     fn acquire_reader(&self) -> usize {
         // An arbitrary cap that allows us to catch overflows long before they happen
-        const MAX_READERS: usize = usize::MAX / READER / 2;
+        const MAX_READERS: usize = core::usize::MAX / READER / 2;
 
         let value = self.lock.fetch_add(READER, Ordering::Acquire);