fixup! test: add checkIfCollectable to test/common/gc.js

test/common/gc.js

@@ -22,7 +22,14 @@
 // Note that this can still produce false positives. When the test using
 // this function still crashes due to OOM, inspect the heap to confirm
 // if a leak is present (e.g. using heap snapshots).
-async function checkIfCollectable(fn, maxCount = 4096, logEvery = 128) {
+// The generateSnapshotAt parameter can be used to specify a count
+// interval to create the heap snapshot which may enforce a more thorough GC.
+// This can be tried for code paths that require it for the GC to catch up
+// with heap growth. However this type of forced GC can be in conflict with
+// other logic in V8 such as bytecode aging, and it can slow down the test
+// significantly, so it should be used scarcely and only as a last resort.
+async function checkIfCollectable(
+  fn, maxCount = 4096, generateSnapshotAt = Infinity, logEvery = 128) {
   let anyFinalized = false;
   let count = 0;
 
@@ -33,11 +40,25 @@ async function checkIfCollectable(fn, maxCount = 4096, logEvery = 128) {
   async function createObject() {
     const obj = await fn();
     f.register(obj);
-    if (count % logEvery === 1) {
-      console.log('Created', count);
-    }
     if (count++ < maxCount && !anyFinalized) {
-      setImmediate(createObject);
+      setImmediate(createObject, 1);
+    }
+    // This can force a more thorough GC, but can slow the test down
+    // significantly in a big heap. Use it with care.
+    if (count % generateSnapshotAt === 0) {
+      // XXX(joyeecheung): This itself can consume a bit of JS heap memory,
+      // but the other alternative writeHeapSnapshot can run into disk space
+      // not enough problems in the CI & be slower depending on file system.
+      // Just do this for now as long as it works and only invent some
+      // internal voodoo when we absolutely have no other choice.
+      require('v8').getHeapSnapshot().pause().read();
+      console.log(`Generated heap snapshot at ${count}`);
+    }
+    if (count % logEvery === 0) {
+      console.log(`Created ${count} objects`);
+    }
+    if (anyFinalized) {
+      console.log(`Found finalized object at ${count}, stop testing`);
     }
   }