Stop MemoryTest hanging CI on macOS

.github/workflows/ci.yaml

@@ -9,6 +9,8 @@ jobs:
   ci:
     name: CI
     runs-on: ${{ matrix.os }}
+    # a hung test fails in an hour instead of at GitHub's 6 hour default
+    timeout-minutes: 60
     continue-on-error: true
     strategy:
       fail-fast: false

runtime/src/test/java/run/endive/runtime/MemoryTest.java

@@ -6,6 +6,7 @@
 
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.Executors;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.Supplier;
@@ -285,25 +286,30 @@ public void waitAndNotifyWithAtomicsOnSameWord(String name, Supplier<Memory> mem
         memory.atomicWriteInt(addr, 0);
 
         var stop = new AtomicBoolean();
+        // not the common pool: on a 3-core runner it can leave the waiter queued behind adds
+        var threads = Executors.newFixedThreadPool(2);
         var adds =
                 CompletableFuture.runAsync(
                         () -> {
                             while (!stop.get()) {
                                 memory.atomicAddInt(0, 1);
                             }
-                        });
+                        },
+                        threads);
         try {
             for (int round = 0; round < 100; round++) {
                 var waiter =
                         CompletableFuture.supplyAsync(
-                                () -> memory.atomicWait(addr, 0, TimeUnit.SECONDS.toNanos(30)));
+                                () -> memory.atomicWait(addr, 0, TimeUnit.SECONDS.toNanos(30)),
+                                threads);
                 while (memory.atomicNotify(addr, 1) == 0 && !waiter.isDone()) {
                     Thread.onSpinWait();
                 }
                 assertEquals(0, waiter.get(30, TimeUnit.SECONDS), "round " + round);
             }
         } finally {
             stop.set(true);
+            threads.shutdown();
         }
         adds.get(30, TimeUnit.SECONDS);
     }