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// 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_
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