1 files changed, 115 insertions, 0 deletions
diff --git a/testing/web-platform/tests/js/builtins/weakrefs/gc-has-one-chance-to-call-cleanupCallback-queueMicrotaskMutationObserver.optional.window.js b/testing/web-platform/tests/js/builtins/weakrefs/gc-has-one-chance-to-call-cleanupCallback-queueMicrotaskMutationObserver.optional.window.js
new file mode 100644
index 0000000000..7b29f00943
--- /dev/null
+++ b/testing/web-platform/tests/js/builtins/weakrefs/gc-has-one-chance-to-call-cleanupCallback-queueMicrotaskMutationObserver.optional.window.js
@@ -0,0 +1,115 @@
+// META: script=/common/gc.js
+// META: script=resources/maybe-garbage-collect.js
+// ├──> maybeGarbageCollectAndCleanupAsync
+// ├──> maybeGarbageCollectAsync
+// └──> resolveGarbageCollection
+/*---
+esid: sec-finalization-registry-target
+info: |
+  FinalizationRegistry ( cleanupCallback )
+
+  FinalizationRegistry.prototype.cleanupSome ( [ callback ] )
+
+  ...
+  4. If callback is not undefined and IsCallable(callback) is false, throw a TypeError exception.
+  5. Perform ? CleanupFinalizationRegistry(finalizationRegistry, callback).
+  6. Return undefined.
+
+  Execution
+
+  At any time, if an object obj is not live, an ECMAScript implementation may perform the following steps atomically:
+
+  1. For each WeakRef ref such that ref.[[Target]] is obj,
+    a. Set ref.[[Target]] to empty.
+  2. For each FinalizationRegistry finalizationRegistry such that finalizationRegistry.[[Cells]] contains cell, such that cell.[[Target]] is obj,
+    a. Set cell.[[Target]] to empty.
+    b. Optionally, perform ! HostCleanupFinalizationRegistry(finalizationRegistry).
+---*/
+
+
+let cleanupCallback = 0;
+let holdings = [];
+function cb(holding) {
+  holdings.push(holding);
+}
+
+let finalizationRegistry = new FinalizationRegistry(function() {
+  cleanupCallback += 1;
+});
+
+function emptyCells() {
+  let target = {};
+  finalizationRegistry.register(target, 'a');
+
+  let prom = maybeGarbageCollectAndCleanupAsync(target);
+  target = null;
+
+  return prom;
+}
+
+function queueMicrotaskByMutationObserver(callback) {
+  const textNode = document.createTextNode('');
+  new MutationObserver(callback).observe(textNode, { characterData: true });
+  textNode.data = 1;
+}
+
+promise_test(() => {
+  return (async () => {
+    assert_implements(
+      typeof FinalizationRegistry.prototype.cleanupSome === 'function',
+      'FinalizationRegistry.prototype.cleanupSome is not implemented.'
+    );
+
+    assert_implements(
+      typeof MutationObserver === 'function',
+      'MutationObserver is not implemented.'
+    );
+
+    let ticks = 0;
+    await emptyCells();
+    await queueMicrotaskByMutationObserver(() => ticks++);
+
+    finalizationRegistry.cleanupSome(cb);
+
+    // cleanupSome will be invoked if there are empty cells left. If the
+    // cleanupCallback already ran, then cb won't be called.
+    let expectedCalled = cleanupCallback === 1 ? 0 : 1;
+    // This asserts the registered object was emptied in the previous GC.
+    assert_equals(holdings.length, expectedCalled, 'cleanupSome callback for the first time');
+
+    // At this point, we can't assert if cleanupCallback was called, because it's
+    // optional. Although, we can finally assert it's not gonna be called anymore
+    // for the other executions of the Garbage Collector.
+    // The chance of having it called only happens right after the
+    // cell.[[Target]] is set to empty.
+    assert_true(cleanupCallback >= 0, 'cleanupCallback might be 0');
+    assert_true(cleanupCallback <= 1, 'cleanupCallback might be 1');
+
+    // Restoring the cleanupCallback variable to 0 will help us asserting the
+    // finalizationRegistry callback is not called again.
+    cleanupCallback = 0;
+
+    await maybeGarbageCollectAsync();
+    await queueMicrotaskByMutationObserver(() => ticks++);
+
+    finalizationRegistry.cleanupSome(cb);
+
+    assert_equals(holdings.length, expectedCalled, 'cleanupSome callback is not called anymore, no empty cells');
+    assert_equals(cleanupCallback, 0, 'cleanupCallback is not called again #1');
+
+    await maybeGarbageCollectAsync();
+    await queueMicrotaskByMutationObserver(() => ticks++);
+
+    finalizationRegistry.cleanupSome(cb);
+
+    assert_equals(holdings.length, expectedCalled, 'cleanupSome callback is not called again #2');
+    assert_equals(cleanupCallback, 0, 'cleanupCallback is not called again #2');
+    assert_equals(ticks, 3, 'ticks is 3');
+
+    if (holdings.length) {
+      assert_array_equals(holdings, ['a']);
+    }
+
+    await maybeGarbageCollectAsync();
+  })().catch(resolveGarbageCollection);
+}, 'cleanupCallback has only one optional chance to be called for a GC that cleans up a registered target.');