1 files changed, 82 insertions, 0 deletions
diff --git a/js/src/jit-test/tests/atomics/mutual-exclusion.js b/js/src/jit-test/tests/atomics/mutual-exclusion.js
new file mode 100644
index 0000000000..ccf4b1789e
--- /dev/null
+++ b/js/src/jit-test/tests/atomics/mutual-exclusion.js
@@ -0,0 +1,82 @@
+// |jit-test| skip-if: helperThreadCount() === 0 || getBuildConfiguration("arm64-simulator") === true
+
+// Let a few threads hammer on memory with atomics to provoke errors
+// in exclusion work.  This test is not 100% fail-safe: the test may
+// pass despite a bug, but this is unlikely.
+
+// Map an Int32Array on shared memory.  The first location is used as
+// a counter, each worker counts up on exit and the main thread will
+// wait until the counter reaches the number of workers.  The other
+// elements are contended accumulators where we count up and down very
+// rapidly and for a long time, any failure in mutual exclusion should
+// lead to errors in the result.  (For example, the test fails almost
+// immediately when I disable simulation of mutual exclusion in the
+// ARM simulator.)
+
+const numWorkers = 4;           // You're not meant to change this
+const iterCount = 255;          // Nor this
+const sabLength = 1024;         // Nor this
+
+const oddResult = (function () {
+    var v = 0;
+    for ( var j=0 ; j < numWorkers ; j++ )
+        v |= (iterCount << (8 * j));
+    return v;
+})();
+
+const evenResult = 0;
+
+const sab = new SharedArrayBuffer(sabLength);
+
+setSharedObject(sab);
+
+const iab = new Int32Array(sab);
+
+function testRun(limit) {
+    console.log("Limit = " + limit);
+
+    // Fork off workers to hammer on memory.
+    for ( var i=0 ; i < numWorkers ; i++ ) {
+        evalInWorker(`
+                     const iab = new Int32Array(getSharedObject());
+                     const v = 1 << (8 * ${i});
+                     for ( var i=0 ; i < ${limit} ; i++ ) {
+                         for ( var k=0 ; k < ${iterCount} ; k++ ) {
+                             if (i & 1) {
+                                 for ( var j=1 ; j < iab.length ; j++ )
+                                     Atomics.sub(iab, j, v);
+                             }
+                             else {
+                                 for ( var j=1 ; j < iab.length ; j++ )
+                                     Atomics.add(iab, j, v);
+                             }
+                         }
+                     }
+                     Atomics.add(iab, 0, 1);
+                     `);
+    }
+
+    // Wait...
+    while (Atomics.load(iab, 0) != numWorkers)
+        ;
+    Atomics.store(iab, 0, 0);
+
+    // Check the results and clear the array again.
+    const v = (limit & 1) ? oddResult : evenResult;
+    for ( var i=1 ; i < iab.length ; i++ ) {
+        assertEq(iab[i], v);
+        iab[i] = 0;
+    }
+}
+
+// Under some configurations the test can take a while to run (and may
+// saturate the CPU since it runs four workers); try not to time out.
+
+var then = new Date();
+testRun(1);
+if (new Date() - then < 20000) {
+    testRun(2);
+    if (new Date() - then < 30000) {
+	testRun(3);
+    }
+}