發(fā)布時(shí)間：2018-01-12 01:08

  本文關(guān)鍵詞：Dalvik虛擬機(jī)垃圾回收算法的分析與性能優(yōu)化　出處：《東南大學(xué)》2015年碩士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： Android Dalvik虛擬機(jī) 垃圾回收算法 增量標(biāo)記 分代算法

【摘要】：Dalvik虛擬機(jī)是Android系統(tǒng)的核心模塊,它執(zhí)行Java程序的速度直接影響Android系統(tǒng)的性能。Java語(yǔ)言采用自動(dòng)垃圾回收機(jī)制,這使得程序員的工作量大大降低,并在很大程度上避免了內(nèi)存泄漏問(wèn)題。然而,該機(jī)制也給系統(tǒng)帶來(lái)了性能下降、響應(yīng)延遲等問(wèn)題。本文主要對(duì)Dalvik原生垃圾回收算法進(jìn)行了詳細(xì)地分析并對(duì)其性能進(jìn)行了優(yōu)化。本文通過(guò)分析Dalvik虛擬機(jī)原生垃圾回收算法,找出了性能瓶頸。首先,針對(duì)并發(fā)GC初始標(biāo)記階段時(shí)間較長(zhǎng)的特點(diǎn)設(shè)計(jì)了增量標(biāo)記算法,將標(biāo)記根集階段劃分成兩次進(jìn)行,每次先標(biāo)記一部分根集再并發(fā)地標(biāo)記這部分根集的引用,避免了長(zhǎng)時(shí)間的暫停：其次,根據(jù)對(duì)象在生存時(shí)間和空間上的局部性,實(shí)現(xiàn)了按年齡大小分代的垃圾回收算法,通過(guò)在堆資源中添加年齡位圖對(duì)對(duì)象年齡進(jìn)行統(tǒng)計(jì),當(dāng)對(duì)象年齡達(dá)到老年代閾值時(shí)將其提升為老年代。同時(shí),將大對(duì)象直接看作老年代,避免對(duì)它們的頻繁操作。只有當(dāng)回收年輕代不能滿足應(yīng)用程序需求時(shí)再進(jìn)行全部收集,通過(guò)這種回收策略,本文將垃圾收集的工作主要放在對(duì)年輕代對(duì)象的收集上,減少了系統(tǒng)的暫停時(shí)間。本文通過(guò)Oxbenchmark測(cè)試軟件在Nexus3手機(jī)上對(duì)改進(jìn)后的算法進(jìn)行測(cè)試,結(jié)果表明：在增量標(biāo)記算法和原生算法整體花費(fèi)時(shí)間持平的情況下,沒(méi)有出現(xiàn)并發(fā)GC中長(zhǎng)時(shí)間暫停的情況,長(zhǎng)時(shí)間暫停的次數(shù)由12次減少為0次；在Oxbenchmark對(duì)系統(tǒng)的整體性能的測(cè)試中,按年齡大小分代算法最快耗時(shí)4093ms,較原生算法提升了36.97%,平均用時(shí)4497.85ms,提升了35.25%；在創(chuàng)建不同深度二叉樹(shù)測(cè)試用時(shí)上,按年齡大小分代算法相對(duì)原生算法在垃圾回收性能的得分上提升了36%。
[Abstract]:Dalvik virtual machine is the core module of Android system. The speed of executing Java programs directly affects the performance of Android system. Java language adopts automatic garbage collection mechanism, which greatly reduces the workload of programmers. And to a large extent, the memory leak problem is avoided. However, this mechanism also brings the performance degradation to the system. This paper mainly analyzes the native garbage collection algorithm of Dalvik and optimizes its performance. This paper analyzes the native garbage collection algorithm of Dalvik virtual machine. The performance bottleneck is found. Firstly, the incremental marking algorithm is designed for the long time of concurrent GC initial marking phase, and the label root set stage is divided into two stages. A part of the root set is marked first at a time and then the reference of that part of the root set is labeled concurrently, thus avoiding a long pause: secondly, based on the locality of the object in time and space. A garbage collection algorithm based on age is implemented. The age bitmap is added to the heap resource to calculate the age of the object, and the age of the object is raised to the old age when the age reaches the threshold. At the same time. Treat large objects directly as older, avoiding frequent manipulation of them. Collect all objects only when the younger generation of recycling fails to meet the requirements of the application, through this recycling strategy. In this paper, the work of garbage collection is mainly focused on the collection of younger generation objects. This paper uses Oxbenchmark software to test the improved algorithm on Nexus3 mobile phone. The results show that when the whole time of incremental marking algorithm and native algorithm is equal, there is no long time pause in concurrent GC, and the number of long time pause is reduced from 12 times to 0 times. In the testing of the overall performance of the system by Oxbenchmark, the age generation algorithm can take 4093 Ms as the fastest time, which is 36.97% higher than the original algorithm. The average time used was 4497.85ms, which increased 35.25ms. In the test time of creating binary tree with different depth, the age generation algorithm improved the garbage collection performance by 36 points compared with the native algorithm.
【學(xué)位授予單位】：東南大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：X705

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