实时性环境中JVM垃圾收集算法

提出一种适用于实时性环境的Java虚拟机垃圾收集算法。该算法通过对增量式收集器中堆空间划分方式和引用跟踪进行改进,以减少垃圾收集时带来的不确定性暂停,并且该算法可以指定用户在一个时间段内进行垃圾收集,以便使应用程序暂停时间达到最短,从而适用于实时性环境。实验结果表明,该算法能有效减少垃圾收集时暂停的频率和时长。     

基于嵌入式Java虚拟机的垃圾回收算法

阐述了一种适用于嵌入式Java虚拟机的垃圾回收算法。该算法对分代回收算法中代的划分方式,引用跟踪等方面进行改进,以降低对运行时间和内存空间的需求,从而使其适用于资源有限的嵌入式环境。试验结果表明,该算法有效提高了垃圾回收效率。     

FLSP:一个高效的系统级垃圾收集算法

垃圾收集是Java操作系统的核心功能,它直接影响到整个系统效率。现代Java操作系统中使用的垃圾收集算法普遍还是沿用应用程序级的垃圾收集算法。应用程序级垃圾收集算法的优化主要面向于普通的Java虚拟机。而Ja-va操作系统与Java虚拟机相比有更高的操作权限和更灵活的资源管理策略,如何利用这些特点和权限来提高垃圾收集算法的效率是以前的垃圾收集算法所没有考虑的。本文分析了操作系统下内存管理和垃圾收集的特点,在JUnicorn操作系统上,利用操作系统平台提供的便利,设计并实现了一个高效的系统级垃圾收集算法FLSP。测试数据表明,在操作系统级别,这种垃圾收集算法能够提高13%的系统性能,并且使垃圾收集的停顿时间缩短50%。     

Java虚拟机垃圾收集器的性能分析与调节

垃圾收集器是Jaya虚拟机(JVW)的核心组成部分之一,对Java虚拟机的性能有非常重要的影响。本文将介绍GC的工作原理以及对象回收算法,重点介绍JVM的分段回收技术;剖析JVM自带的GC性能分析工具;阐述如何通过命令行参数调节GC的运行,提高GC的效率。     

多核系统下并行节点复制垃圾收集算法

为了提高垃圾收集效率,减少用户程序等待时间,提出了一种在多核系统下基于LISP2算法的并行节点复制算法。该算法通过把LISP2算法的4个垃圾收集阶段分别并行化来实现并行垃圾收集。实验结果显示,该算法在多核系统下能有效提高垃圾收集效率。     

Reference count garbage collection

A garbage collection algorithm that permits a reference count storage reclamation scheme to collect circularly linked inaccessible structures is presented. The algorithm requires no additional information beyond that required by a reference count scheme. In particular, it does not require the garbage collector to be able to find pointers outside the heap. The algorithm is most useful for augmenting reference count storage reclamation systems and for implementing storage management systems on top of languages that do not provide their own. It is, however, considerably less efficient in space and time than conventional garbage collection systems.     

Global garbage collection for distributed heap storage systems

We present a garbage-collection algorithm, suitable for loosely-coupled multiprocessor systems, in which the processing elements (PEs) share only the communication medium. The algorithm is global, i.e., it involves all the PEs in the system. It allows space compaction, and it uses a system-wide marking phase to mark all accessible objects where a combination of parallel breadth-first/depth-first strategies is used for tracing the object-graphs according to a decentralized credit mechanism that regulates the number of garbage collection messages in the system. The credit mechanism is crucial for determining the space requirement of the garbage-collection messages. Also a variation of this algorithm is presented for systems with high locality of reference. It allows each PE to perform first its local garbage collection and only invokes the global garbage collection when the freed space by the local collector is insufficient.     

Garbage collection in a distributed object-oriented system

An algorithm for garbage collection in distributed systems with object sharing across processor boundaries is described. The algorithm allows local garbage collection at each node in the system to proceed independently of local collection at the other nodes. It requires no global synchronization or knowledge of the global state of the system and exhibits the capability for graceful degradation. The concept of a specialized dump node is proposed to facilitate the collection of inaccessible circular structures. An experimental evaluation of the algorithm is also described. The algorithm is compared with a corresponding scheme that requires global synchronization. The results show that the algorithm works well in distributed processing environments even when the locality of object references is low     

Schedulable garbage collection in CLI virtual execution system

Virtual software execution environment, known as Virtual Machine (VM), has been gaining popularity through Java Virtual Machine (JVM) and Common Language Infrastructure (CLI). Given their advantages in portability, productivity, and safety, etc., applying VM to real-time embedded systems can leverage production cost, fast time-to-market, and software integrity. However, this approach can only become practical once the VM operations and application tasks are made schedulable jointly. In this paper, we present a schedulable garbage collection algorithm applicable on real-time applications in CLI virtual machine environment. To facilitate the scheduling of real-time applications and garbage collection operations, we make the pause time due to garbage collection controllable, and the invocation of garbage collection predictable. To demonstrate the approach, a prototype for a schedulable garbage collection has been implemented in CLI execution environment. The garbage collection is carried out by a concurrent thread while meeting a targeted pause time and satisfying the memory requests of applications. A cost model of garbage collection is established based on measured WCET such that the execution time and overhead of garbage collection operations can be predicted. Finally, we illustrate a joint scheduling algorithm to meet the time and memory constraints of real-time systems.     

分代算法在KVM中的实现

在嵌入式系统中，需要分析什么样的垃圾回收机制能够适应嵌入式系统的特点，满足系统对于稳定性和性能的要求，分析了嵌入式Java虚拟机KVM垃圾回收机制的特点，所采用的垃圾收集算法，以及垃圾收集器在KVM中是如何工作的，找出存在的缺陷和不足，并在mark-sweep-compact算法的基础上实现了分代算法。     

The measured cost of conservative garbage collection

Because dynamic memory management is an important part of a large class of computer programs, high-performance algorithms for dynamic memory management have been, and will continue to be, of considerable interest. Experience indicates that for many programs, dynamic storage allocation is so important that programmers feel compelled to write and use their own domain-specific allocators to avoid the overhead of system libraries. As an alternative to explicit storage management techniques, conservative garbage collection has been suggested as an important algorithm for dynamic storage management in C programs. In this paper, I evaluate the costs of different dynamic storage management algorithms, including domain-specific allocators, widely-used general-purpose allocators, and a publicly available conservative garbage collection algorithm. Surprisingly, I find that programmer enhancements often have little effect on program performance. I also find that the true cost of conservative garbage collection is not the CPU overhead, but the memory system overhead of the algorithm. I conclude that conservative garbage collection is a promising alternative to explicit storage management and that the performance of conservative collection is likely to improve in the future. C programmers should now seriously consider using conservative garbage collection instead of explicitly calling free in programs they write.     

一种改进的增量式JVM垃圾收集算法

非增量式Java虚拟机(JVM)垃圾回收算法的内存开销较大。为此,提出一种基于栈式分配策略的JVM增量式垃圾收集算法。对Java栈帧进行改造使其支持存储对象,改进增量式收集器中堆空间的划分、引用跟踪方式,以减少垃圾收集带来的不确定性暂停。实验结果表明,该算法能有效减少暂停的频率和时长,提高运行速度。     

基于长生命周期对象的混合垃圾收集

Java语言因其在软件工程上的优势而被广泛地用来进行服务器应用的开发.这些应用中通常存在着大量的长生命周期的对象.单一的经典的垃圾收集算法不能够有效地减少对长生命周期对象的重复处理.一种基于长生命周期对象的混合垃圾收集算法(LLH)被设计和实现.该算法结合了缩并,复制和分代收集的特点,通过这些经典算法的动态切换与协作来解决这一问题.实验结果表明,与经典的分代垃圾收集相比,LLH收集算法能够使SPECjbb 2005的Throughput分值提高3%～25%.     

基于关键引用验证的分布式实时垃圾搜集器*

提出了一种新的分布式垃圾搜集器（GC）机制,即基于关键引用验证的分布式GC。性能分析说明,与以往的分布式GC相比,该算法能以最短的时间延迟回收循环垃圾。尽管该算法为保留引用列表和验证过程需要额外的一些存储空间,但具有一定的实时性和较好的容错性,综合性能较好,适用于大规模分布式系统。     

基于数据更新间隔的NAND闪存垃圾回收算法

闪存因具有速度快、体积小等优点而广泛应用于数据存储领域,为提高NAND闪存的垃圾回收效率、延长闪存使用寿命,提出一种基于数据更新间隔的垃圾回收算法UIGC。计算闪存中空闲页的分散度,将其作为垃圾回收触发条件。从垃圾回收效率和磨损均衡效果2个方面出发,综合考虑块中无效页年龄累计和以及块中有效页比例,使用动态回收块选择和静态回收块选择相结合的策略来选择目标回收块,根据回收块中有效页数据更新间隔判断有效页热度,同时提出数据更新稳定性的概念来划分有效页的数据更新状态,将具有不同热度和更新状态的有效页数据分别存储在不同的空闲块中,从而提高块中数据的同步更新概率。实验结果表明,UIGC算法相较于CAT、FaGC等现有垃圾回收算法具有更优的垃圾回收效率和磨损均衡效果,并能有效延长闪存使用寿命。     

弱一致性模型下的分布式垃圾回收算法RRDGC

垃圾回收有效地减轻了编程人员的负担、优化了程序的设计,在基于弱一致性模型的分布式共享存储系统中进行自动垃圾回收是非常困难的和低效的,本文提出了一种基于跟踪策略的实时分布式垃圾回收算法--RRDGC，使得各节点回收进程可以和应用程序并发执行，同时有效减少了弱一致性模型下额外的通信开销，降低了程序的响应时间．算法确保了垃圾回收的正确性和有效性，体现了增量和实时性的特点．最后通过仿真实验对比论证了该算法的正确性和高效性．     

基于类型的运行时环境存储管理算法

基于类型进行分类管理堆空间的垃圾回收算法通过废弃对象复用来降低运行时环境创建对象所需时间开销,同时还通过线程缓存、租赁等技术进一步增强运行时系统的存储管理效率.运行实验表明,该算法能够在回收线程和工作线程之间实现细粒度的并行性并缩短对象申请和回收时间,进而能够减少工作线程的停顿现象,增加服务器应用的平滑性以及提高堆空间的使用效率.     

Mark scan garbage collection on a distributed architecture

In any computer architecture designed for the evaluation of declarative languages, efficient reclamation of redundant (garbage) storage is essential. High performance, exploiting the inherent parallelism of such languages, is now typically achieved by parallel architectures, computational graphs thus being distributed across many processing elements.This paper describes a real-time mark-scan garbage collection algorithm for a distributed machine with local store. The algorithm allows collection on a per-process basis, and several collections may run concurrently and asynchronously. Both non real-time and real-time versions are provided.It is hoped to publish implementation results for the algorithm when such are available.     

A parallel asynchronous garbage collection algorithm fordistributed systems

The problem of distributed garbage collection is discussed. An algorithm for parallel distributed asynchronous garbage collection is presented. The liveness and safety properties of this method are demonstrated. The algorithm does not require a global clock, complex termination detection methods, or distributed synchronization techniques. A new color code is introduced to distinguish between local cells (black) and those that are exclusively accessible from the remote pointers (gray). The mutator operation is revised to handle a multiple mutator scheme on a given local memory. Simulation results show that the developed distributed and parallel algorithm performs much better than the sequential method as tested on a Balance 8000 computer