Refactor CI scripts to improve thread management for Rust builds and tests

- Renamed thread variables for clarity, changing `$Threads` to `$BuildThreads` and introducing `$TestThreads` to cap test execution at 8 threads to prevent resource exhaustion.
- Updated `cargo` commands in both PowerShell and shell scripts to utilize the new thread management variables, ensuring consistent behavior across CI environments.
- Added comments to clarify the rationale behind capping test threads, enhancing maintainability and understanding of the CI process.

These changes aim to optimize resource usage during CI runs and improve the reliability of Rust builds and tests.

scripts/ci.ps1

@@ -6,7 +6,11 @@ param(
 )
 
 $RbxDom = -not $NoRbxDom
-$Threads = [Environment]::ProcessorCount
+$BuildThreads = [Environment]::ProcessorCount
+# Cap test threads: two_way_sync tests spawn child processes (atlas serve)
+# with file watchers, HTTP servers, and temp dirs. Running too many in
+# parallel (e.g. 32) exhausts OS resources and causes spurious failures.
+$TestThreads = [Math]::Min([Environment]::ProcessorCount, 8)
 
 $ErrorActionPreference = "Continue"
 $failures = @()
@@ -57,9 +61,9 @@ $selene = $LASTEXITCODE
 Record-Result "Selene" $selene
 
 Write-Step 6 "Rust Linting (Clippy) - Auto-fix"
-cargo clippy -j $Threads --fix --allow-dirty --allow-staged 2>&1 | Out-Null
+cargo clippy -j $BuildThreads --fix --allow-dirty --allow-staged 2>&1 | Out-Null
 Write-Host "Verifying..." -ForegroundColor Yellow
-cargo clippy -j $Threads --all-targets --all-features 2>&1
+cargo clippy -j $BuildThreads --all-targets --all-features 2>&1
 $clippy = $LASTEXITCODE
 Record-Result "Clippy" $clippy
 
@@ -69,7 +73,7 @@ $build = $LASTEXITCODE
 Record-Result "Build" $build
 
 Write-Step 8 "Run ALL Rust Tests"
-$testOutput = cargo test --locked --all-features -- --test-threads=$Threads 2>&1
+$testOutput = cargo test --locked --all-features -- --test-threads=$TestThreads 2>&1
 $rustTests = $LASTEXITCODE
 $testOutput | Write-Host
 Record-Result "Rust Tests" $rustTests
@@ -107,9 +111,9 @@ if ($RbxDom) {
 
     Write-Step 13 "Rust Linting (Clippy) for rbx-dom - Auto-fix"
     Push-Location rbx-dom
-    cargo clippy -j $Threads --fix --allow-dirty --allow-staged 2>&1 | Out-Null
+    cargo clippy -j $BuildThreads --fix --allow-dirty --allow-staged 2>&1 | Out-Null
     Write-Host "Verifying..." -ForegroundColor Yellow
-    cargo clippy -j $Threads --all-targets --all-features -- -D warnings 2>&1
+    cargo clippy -j $BuildThreads --all-targets --all-features -- -D warnings 2>&1
     $clippyRbxDom = $LASTEXITCODE
     Pop-Location
     Record-Result "Clippy (rbx-dom)" $clippyRbxDom
@@ -126,9 +130,9 @@ if ($RbxDom) {
 
     Write-Step 15 "Run ALL rbx-dom Rust Tests"
     Push-Location rbx-dom
-    cargo test --verbose -- --test-threads=$Threads
+    cargo test --verbose -- --test-threads=$TestThreads
     $testsRbxDom = $LASTEXITCODE
-    cargo test --all-features --verbose -- --test-threads=$Threads
+    cargo test --all-features --verbose -- --test-threads=$TestThreads
     $testsRbxDomAll = $LASTEXITCODE
     Pop-Location
     Record-Result "Tests (rbx-dom)" $testsRbxDom

scripts/ci.sh

@@ -11,7 +11,12 @@ for arg in "$@"; do
     esac
 done
 
-THREADS=$(nproc 2>/dev/null || sysctl -n hw.logicalcpu 2>/dev/null || echo 4)
+BUILD_THREADS=$(nproc 2>/dev/null || sysctl -n hw.logicalcpu 2>/dev/null || echo 4)
+# Cap test threads: two_way_sync tests spawn child processes (atlas serve)
+# with file watchers, HTTP servers, and temp dirs. Running too many in
+# parallel (e.g. 32) exhausts OS resources and causes spurious failures.
+_cpu_count=$(nproc 2>/dev/null || sysctl -n hw.logicalcpu 2>/dev/null || echo 4)
+TEST_THREADS=$(( _cpu_count < 8 ? _cpu_count : 8 ))
 
 failures=()
 
@@ -57,9 +62,9 @@ selene_exit=$?
 record "Selene" $selene_exit
 
 step 6 "Rust Linting (Clippy) - Auto-fix"
-cargo clippy -j $THREADS --fix --allow-dirty --allow-staged >/dev/null 2>&1
+cargo clippy -j $BUILD_THREADS --fix --allow-dirty --allow-staged >/dev/null 2>&1
 echo "Verifying..."
-cargo clippy -j $THREADS --all-targets --all-features 2>&1
+cargo clippy -j $BUILD_THREADS --all-targets --all-features 2>&1
 clippy_exit=$?
 record "Clippy" $clippy_exit
 
@@ -69,7 +74,7 @@ build_exit=$?
 record "Build" $build_exit
 
 step 8 "Run ALL Rust Tests"
-cargo test --locked --all-features -- --test-threads=$THREADS 2>&1
+cargo test --locked --all-features -- --test-threads=$TEST_THREADS 2>&1
 rust_tests=$?
 record "Rust Tests" $rust_tests
 
@@ -103,9 +108,9 @@ if [ "$RBX_DOM" = true ]; then
     record "Selene (rbx_dom_lua)" $selene_rbxdom
 
     step 13 "Rust Linting (Clippy) for rbx-dom - Auto-fix"
-    (cd rbx-dom && cargo clippy -j $THREADS --fix --allow-dirty --allow-staged >/dev/null 2>&1)
+    (cd rbx-dom && cargo clippy -j $BUILD_THREADS --fix --allow-dirty --allow-staged >/dev/null 2>&1)
     echo "Verifying..."
-    (cd rbx-dom && cargo clippy -j $THREADS --all-targets --all-features -- -D warnings 2>&1)
+    (cd rbx-dom && cargo clippy -j $BUILD_THREADS --all-targets --all-features -- -D warnings 2>&1)
     clippy_rbxdom=$?
     record "Clippy (rbx-dom)" $clippy_rbxdom
 
@@ -118,9 +123,9 @@ if [ "$RBX_DOM" = true ]; then
     record "Build (rbx-dom all-features)" $build_rbxdom_all
 
     step 15 "Run ALL rbx-dom Rust Tests"
-    (cd rbx-dom && cargo test --verbose -- --test-threads=$THREADS)
+    (cd rbx-dom && cargo test --verbose -- --test-threads=$TEST_THREADS)
     tests_rbxdom=$?
-    (cd rbx-dom && cargo test --all-features --verbose -- --test-threads=$THREADS)
+    (cd rbx-dom && cargo test --all-features --verbose -- --test-threads=$TEST_THREADS)
     tests_rbxdom_all=$?
     record "Tests (rbx-dom)" $tests_rbxdom
     record "Tests (rbx-dom all-features)" $tests_rbxdom_all