近年來，隨著軟體系統的持續演進和複雜化，如何進行高效且有效的重構已
成為重要的研究議題。同時，確保軟體系統的高可用性和強大的穩健性仍然是
我們關注的重點。針對此議題，本論文進行了一項全面的研究，探討如何透過
軟體系統的重構來提升虛擬化基礎的容錯能力。我們特別針對Cuju 進行研究和
應用，Cuju 是一個開源專案，其主要實現了一種針對虛擬化基礎容錯的時代同
步技術。
Cuju 採用了許多性能優化技術，包括非停機/流水線連續遷移、客戶端虛擬
內存/虛擬設備狀態的追蹤紀錄，以及消除QEMU 和KVM 之間的數據傳輸。然
而，通過將基於內核的虛擬機（KVM）從Linux 內核4.15 升級到5.4，我們擴大
了Cuju 的能力，為我們的研究內容提供了更好的穩定性。
本研究的主要目標是深入探討如何充分利用Cuju 的這些能力，並透過有效
的重構方法來提高軟體系統的容錯能力。我們首先識別和劃分出最常見的重構
技術，以及那些對系統容錯性具有重大負面影響的程式碼。接著，我們將這些
重構技術適用到一組開源軟體系統中，並透過與Cuju 的整合來實現更高的系統
容錯能力。
我們的初步研究結果顯示，透過有效的軟體重構，可以降低系統故障的發
生，同時，Cuju 的虛擬化基礎容錯機制也能提供無縫的系統恢復功能。當這兩
者結合在一起時，將有望提升軟體系統的韌性和可靠性。我們相信，這個研究
的結果將有助於開發和維護軟體系統，尤其是在容錯能力方面，提供了新的思
維和方法。

The constant evolution of software systems requires effective and efficient refactoring techniques to increase their robustness and reliability. One critical area is
the improvement of virtualization-based fault tolerance. In this research, we focus
on Cuju, an open source project that implements an epoch-based synchronization
technique that provides virtualization-based fault tolerance.
Cuju employs numerous performance optimization techniques, including nonstop/pipelined continuous migration, dirty tracking for guest virtual memory/virtual
device status, and elimination of data transfer between QEMU and KVM. Moreover, Cuju’s capabilities are enhanced by upgrading the kernel-based virtual machine (KVM) from Linux kernel 4.15 to 5.4, providing a robust platform for our
research.
The goal of this study is to determine how Cuju’s capabilities, enhanced by
the improved KVM, can improve the fault tolerance of software systems through
effective refactoring. We start by identifying and categorizing the most common
refactoring techniques and code smells that negatively impact the fault tolerance
ability. These techniques are then adapted and applied to a set of open source
software systems and integrated with Cuju for fault tolerance.
Our initial findings suggest that effective software refactoring can reduce the
occurrence of bugs, while Cuju’s virtualization-based fault-tolerance mechanism
can provide seamless system recovery. These combined strategies promise to significantly improve the robustness and reliability of software systems

Contents
Abstract (Chinese) I
Abstract II
Contents III
List of Figures V
1 Introduction 1
2 Related Works 4
2.1 QEMU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 KVM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.3 Cuju . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.4 Software Refactoring . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.5 VMware Workstation Player . . . . . . . . . . . . . . . . . . . . . . 6
3 Design and Implementation 8
3.1 Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1.1 Software Refactoring for Code Quality Improvement . . . . . 8
3.1.2 Integration with Cuju . . . . . . . . . . . . . . . . . . . . . 9
3.2 Tools for Code Improvement . . . . . . . . . . . . . . . . . . . . . . 9
3.2.1 Code Analysis Tools . . . . . . . . . . . . . . . . . . . . . . 9
III
3.3 Improvement Categories . . . . . . . . . . . . . . . . . . . . . . . . 10
3.3.1 Cleanliness of Code . . . . . . . . . . . . . . . . . . . . . . . 10
3.3.2 Performance Enhancements . . . . . . . . . . . . . . . . . . 11
3.3.3 Security Enhancements . . . . . . . . . . . . . . . . . . . . . 11
3.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4 Experimentation 13
4.1 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.2 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.2.1 Cleanliness of Code . . . . . . . . . . . . . . . . . . . . . . . 15
4.2.2 Performance Enhancements . . . . . . . . . . . . . . . . . . 16
4.2.3 Security Enhancements . . . . . . . . . . . . . . . . . . . . . 18
5 Conclusion and Future Work 19
Bibliography 21

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