Merge #800

800: Use wrapping addition for JEC r=cuviper a=cuviper

32-bit targets only have 12 bits in the atomic counters to represent the Jobs Event Counter (JEC). This should be fine with wrapping addition, but commit a0efb4a changed from wrapping `fetch_add` to a plain `+`, which is a checked addition in debug builds. We simply need to make this an explicit `wrapping_add` instead.

In theory, 64-bit targets had a problem too, but 44 bits for JEC is pretty good headroom in debug mode.

Fixes #797.

Co-authored-by: Josh Stone <cuviper@gmail.com>

.github/workflows/ci.yaml

@@ -71,7 +71,7 @@ jobs:
         rust: [stable, nightly]
     steps:
       - name: Checkout
-        uses: actions/checkout@v1
+        uses: actions/checkout@v2
       - name: Install
         uses: actions-rs/toolchain@v1
         with:
@@ -90,13 +90,45 @@ jobs:
           command: test
           args: --verbose --package rayon-demo
 
+  i686:
+    name: Test (ubuntu-latest, stable-i686)
+    runs-on: ubuntu-latest
+    steps:
+      - name: System install
+        run: |
+          sudo apt-get update
+          sudo apt-get install gcc-multilib
+      - name: Rust install
+        uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable-i686-unknown-linux-gnu
+          profile: minimal
+          override: true
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Build
+        uses: actions-rs/cargo@v1
+        with:
+          command: build
+          args: --verbose
+      - name: Test rayon
+        uses: actions-rs/cargo@v1
+        with:
+          command: test
+          args: --verbose --package rayon
+      - name: Test rayon-core
+        uses: actions-rs/cargo@v1
+        with:
+          command: test
+          args: --verbose --package rayon-core
+
   # wasm won't actually work without threading, but it builds
   wasm:
     name: WebAssembly
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v1
+        uses: actions/checkout@v2
       - name: Install
         uses: actions-rs/toolchain@v1
         with:

Cargo.toml

@@ -19,7 +19,7 @@ members = ["rayon-demo", "rayon-core"]
 exclude = ["ci"]
 
 [dependencies]
-rayon-core = { version = "1.8.0", path = "rayon-core" }
+rayon-core = { version = "1.8.1", path = "rayon-core" }
 crossbeam-deque = "0.7.2"
 
 # This is a public dependency!

RELEASES.md

@@ -1,3 +1,9 @@
+# Release rayon-core 1.8.1 (2020-09-17)
+
+- Fixed an overflow panic on high-contention workloads, for a counter that was
+  meant to simply wrap. This panic only occurred with debug assertions enabled,
+  and was much more likely on 32-bit targets.
+
 # Release rayon 1.4.0 / rayon-core 1.8.0 (2020-08-24)
 
 - Implemented a new thread scheduler, [RFC 5], which uses targeted wakeups for

bors.toml

@@ -1,6 +1,7 @@
 status = [
   "Check (1.31.0)",
   "Test (ubuntu-latest, stable)",
+  "Test (ubuntu-latest, stable-i686)",
   "Test (ubuntu-latest, beta)",
   "Test (ubuntu-latest, nightly)",
   "Test (windows-latest, stable)",