fixup! src: fix timing of snapshot serialize callback

Author: joyeecheung

test/parallel/test-buffer-alloc-unsafe-is-initialized-with-zero-fill-flag.js

@@ -0,0 +1,18 @@
+// Flags: --expose-internals --zero-fill-buffers
+// Verifies that Buffer.allocUnsafe() allocates initialized memory under --zero-fill-buffers by
+// checking the usage count of the relevant native allocator code path.
+'use strict';
+
+const common = require('../common');
+if (!common.isDebug) {
+  common.skip('Only works in debug mode');
+}
+const { internalBinding } = require('internal/test/binding');
+const { getGenericUsageCount } = internalBinding('debug');
+const assert = require('assert');
+
+const initialCount = getGenericUsageCount('NodeArrayBufferAllocator.Allocate.ZeroFilled');
+const buffer = Buffer.allocUnsafe(Buffer.poolSize + 1);
+assert.strictEqual(buffer.every((b) => b === 0), true);
+const newCount = getGenericUsageCount('NodeArrayBufferAllocator.Allocate.ZeroFilled');
+assert.notStrictEqual(newCount, initialCount);

test/parallel/test-buffer-alloc-unsafe-is-uninitialized.js

@@ -13,5 +13,8 @@ const assert = require('assert');
 
 const initialCount = getGenericUsageCount('NodeArrayBufferAllocator.Allocate.Uninitialized');
 Buffer.allocUnsafe(Buffer.poolSize + 1);
+// We can't reliably check the contents of the buffer here because the OS or memory allocator
+// used might zero-fill memory for us, or they might happen to return reused memory that was
+// previously used by a process that zero-filled it.
 const newCount = getGenericUsageCount('NodeArrayBufferAllocator.Allocate.Uninitialized');
 assert.notStrictEqual(newCount, initialCount);