1 files changed, 61 insertions, 0 deletions
diff --git a/chromium/v8/src/heap/progress-bar.h b/chromium/v8/src/heap/progress-bar.h
new file mode 100644
index 00000000000..b00558b684c
--- /dev/null
+++ b/chromium/v8/src/heap/progress-bar.h
@@ -0,0 +1,61 @@
+// Copyright 2021 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef V8_HEAP_PROGRESS_BAR_H_
+#define V8_HEAP_PROGRESS_BAR_H_
+
+#include <atomic>
+#include <cstdint>
+
+#include "src/base/logging.h"
+
+namespace v8 {
+namespace internal {
+
+// The progress bar allows for keeping track of the bytes processed of a single
+// object. The progress bar itself must be enabled before it's used.
+//
+// Only large objects use the progress bar which is stored in their page header.
+// These objects are scanned in increments and will be kept black while being
+// scanned. Even if the mutator writes to them they will be kept black and a
+// white to grey transition is performed in the value.
+//
+// The progress bar starts as disabled. After enabling (through `Enable()`), it
+// can never be disabled again.
+class ProgressBar final {
+ public:
+  void Initialize() { value_ = kDisabledSentinel; }
+  void Enable() { value_ = 0; }
+  bool IsEnabled() const {
+    return value_.load(std::memory_order_acquire) != kDisabledSentinel;
+  }
+
+  size_t Value() const {
+    DCHECK(IsEnabled());
+    return value_.load(std::memory_order_acquire);
+  }
+
+  bool TrySetNewValue(size_t old_value, size_t new_value) {
+    DCHECK(IsEnabled());
+    DCHECK_NE(kDisabledSentinel, new_value);
+    return value_.compare_exchange_strong(old_value, new_value,
+                                          std::memory_order_acq_rel);
+  }
+
+  void ResetIfEnabled() {
+    if (IsEnabled()) {
+      value_.store(0, std::memory_order_release);
+    }
+  }
+
+ private:
+  static constexpr size_t kDisabledSentinel = SIZE_MAX;
+
+  std::atomic<size_t> value_;
+};
+
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_HEAP_PROGRESS_BAR_H_