[VM] Introduce ListQueue class

TEST=list_queue_test.cc

Change-Id: Ie85055475f35a9fdc4f31e61d5f1f5d04eb707a8
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/420220
Reviewed-by: Ben Konyi <[email protected]>
Commit-Queue: Derek Xu <[email protected]>

Author: derekxu16

runtime/bin/builtin_impl_sources.gni

@@ -64,6 +64,7 @@ builtin_impl_tests = [
   "eventhandler_test.cc",
   "file_test.cc",
   "hashmap_test.cc",
+  "list_queue_test.cc",
   "priority_heap_test.cc",
   "snapshot_utils_test.cc",
   "test_utils.cc",

runtime/bin/list_queue_test.cc

@@ -0,0 +1,69 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#include <vector>
+
+#include "platform/list_queue.h"
+#include "vm/unit_test.h"
+
+namespace dart {
+
+void ExpectContentsToBe(const ListQueue<intptr_t>& actual,
+                        const std::vector<intptr_t>& expected) {
+  intptr_t i = 0;
+  actual.ForEach([&expected, &i](intptr_t actual_element) {
+    EXPECT(actual_element == expected[i]);
+    ++i;
+  });
+}
+
+VM_UNIT_TEST_CASE(ListQueue_PublicMethods) {
+  ListQueue<intptr_t> l;
+  intptr_t front = -1;
+
+  l.PushBack(1);
+  ExpectContentsToBe(l, {1});
+  EXPECT(l.Length() == 1);
+
+  front = l.PopFront();
+  EXPECT(front == 1);
+  ExpectContentsToBe(l, {});
+  EXPECT(l.Length() == 0);
+
+  l.PushBack(2);
+  ExpectContentsToBe(l, {2});
+  EXPECT(l.Length() == 1);
+
+  l.PushBack(3);
+  ExpectContentsToBe(l, {2, 3});
+  EXPECT(l.Length() == 2);
+
+  front = l.PopFront();
+  EXPECT(front == 2);
+  ExpectContentsToBe(l, {3});
+  EXPECT(l.Length() == 1);
+
+  l.PushBack(4);
+  ExpectContentsToBe(l, {3, 4});
+  EXPECT(l.Length() == 2);
+}
+
+VM_UNIT_TEST_CASE(ListQueue_Grow) {
+  const intptr_t kInitialCapacity = ListQueue<intptr_t>::kInitialCapacity;
+
+  ListQueue<intptr_t> l;
+  l.PushBack(1);
+  ExpectContentsToBe(l, {1});
+  l.PopFront();
+  ExpectContentsToBe(l, {});
+
+  // Force |l| to grow by adding more than |kInitialCapacity| elements to it.
+  for (intptr_t i = 0; i <= kInitialCapacity + 3; ++i) {
+    l.PushBack(123);
+  }
+
+  ExpectContentsToBe(l, std::vector<intptr_t>(kInitialCapacity + 4, 123));
+}
+
+}  // namespace dart

runtime/platform/list_queue.h

@@ -0,0 +1,80 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#ifndef RUNTIME_PLATFORM_LIST_QUEUE_H_
+#define RUNTIME_PLATFORM_LIST_QUEUE_H_
+
+#include <functional>
+#include <memory>
+#include <utility>
+
+#include "platform/assert.h"
+#include "platform/globals.h"
+
+// A queue backed by a circular buffer similar to dart:collection's ListQueue.
+template <typename T>
+class ListQueue {
+ public:
+  static constexpr intptr_t kInitialCapacity = 64;
+
+  ListQueue()
+      : buffer_(std::make_unique<T[]>(kInitialCapacity)),
+        capacity_(kInitialCapacity) {}
+
+  void PushBack(T&& element) {
+    buffer_[tail_] = std::move(element);
+    tail_ = (tail_ + 1) % capacity_;
+    if (head_ == tail_) {
+      Grow();
+    }
+    ++length_;
+  }
+
+  T&& PopFront() {
+    ASSERT(head_ != tail_);
+    T&& element = std::move(buffer_[head_]);
+    head_ = (head_ + 1) % capacity_;
+    --length_;
+    return std::move(element);
+  }
+
+  // The number of elements currently in the queue.
+  intptr_t Length() { return length_; }
+
+  void ForEach(std::function<void(const T&)> callback) const {
+    for (intptr_t i = head_; i != tail_; i = (i + 1) % capacity_) {
+      callback(buffer_[i]);
+    }
+  }
+
+ private:
+  std::unique_ptr<T[]> buffer_;
+  intptr_t capacity_;
+  intptr_t length_ = 0;
+  intptr_t head_ = 0;
+  intptr_t tail_ = 0;
+
+  void Grow() {
+    intptr_t split = capacity_ - head_;
+
+    intptr_t new_capacity = capacity_ << 1;
+    std::unique_ptr<T[]> new_buffer = std::make_unique<T[]>(new_capacity);
+
+    for (intptr_t i = 0; i < split; ++i) {
+      new_buffer[i] = std::move(buffer_[head_ + i]);
+    }
+    for (intptr_t i = split; i < split + head_; ++i) {
+      new_buffer[i] = std::move(buffer_[i - split]);
+    }
+
+    head_ = 0;
+    tail_ = capacity_;
+    buffer_.swap(new_buffer);
+    capacity_ = new_capacity;
+  }
+
+  DISALLOW_COPY_AND_ASSIGN(ListQueue);
+};
+
+#endif  // RUNTIME_PLATFORM_LIST_QUEUE_H_

runtime/platform/platform_sources.gni

@@ -18,6 +18,7 @@ platform_sources = [
   "growable_array.h",
   "hashmap.cc",
   "hashmap.h",
+  "list_queue.h",
   "lockers.h",
   "memory_sanitizer.h",
   "safe_stack.h",