System Software

This course is a KV (combined course consisting of lectures and project work) in which you will learn the concepts and the implementation of various system software components such as garbage collectors, linkers, loaders, debuggers and text editors. In addition to the principal algorithms the course will also discuss case studies of such programs. The course is given in English. It is part of the Major Subjects Software Engineering and Computational Engineering in the Computer Science Master programme.

The course is taught on campus. If you missed a lecture, you can watch the video recordings from a previous semester, but the content is gradually updated. Moodle may have recordings of this year's lectures, too, but it's not guaranteed. Therefore, we strongly recommend that you attend the lectures and use the interactive environment to ask questions.

Lecture Dates

Contents

1. Memory Management
   1.1 Overview
   1.2 Allocation and deallocation of memory
   1.3 Simple free list
   1.4 Multiple free lists
   1.5 Buddy system
   1.6 Memory fragmentation

2. Garbage Collection
   2.1 Motivation
   2.2 Basic techniques
       2.2.1 Reference Counting
       2.2.2 Mark & Sweep
       2.2.3 Stop & Copy
   2.3 Variants
       2.3.1 Mark & Compact
       2.3.2 Generation scavenging
   2.4 Incremental garbage collection
       2.4.1 Tricolor marking
       2.4.2 Train algorithm
   2.5 Finding root pointers
       2.5.1 Pointer tables
       2.5.2 Conservative garbage collection
   2.6 Garbage collection in multi-threaded systems
   2.7 Finalization
   2.8 Case study: Java Hotspot VM
   2.9 Case study: .NET

3. Linkers and Loaders
   3.1 Overview
   3.2 Case study: Oberon
       3.2.1 Run-time data structures
       3.2.2 Resolving external references
       3.2.3 Load algorithm
   3.3 Case study: Java
       3.3.1 Overview
       3.3.2 Class files
       3.3.3 Loading phases
       3.3.4 Example: custom class loader
   3.4 Linking/loading in C/C++

4. Debuggers
   4.1 Architecture
   4.2 Case study: Java Platform Debugger

5. Text Editors
   5.1 Data structures for texts
       5.1.1 SimpleText
       5.1.2 GapText
       5.1.3 PieceListText
   5.2 Text representation on the screen (case study)
       5.2.1 Line descriptors
       5.2.2 Positions
       5.2.3 Input handling
       5.2.4 Updating the view
       5.2.5 Scrolling

Exam

The written exam will be on Thursday, December 18, 2025. Please register via Kusss. The room(s) will be announced on December 17 on ssw.jku.at.

In order to pass the course, you will have to implement also the project. The final mark will be computed from the exam (90 points) and from the project (15 points).

Part of the course will be a project in which either a garbage collector, a debugger or a text editor has to be implemented.

The project is to be submitted on Moodle before January 21, 2026 23:59 Linz time. The project must also be presented on January 22, 2026 between 12:00 and 16:00. Later in the term, we'll ask you to register for a time slot to present your project. Specific time slots will be either in person, or on Zoom.

Downloads

• The slides can be downloaded from the Kusss page or the Moodle page of this course.
• Source code of the prototype editor

Literature

• Jones, R., Hosking, A., Moss, E.: The Garbage Collection Handbook. CRC Press, 2012
• Jones R., Lins R.: Garbage Collection. Algorithms for Automatic Dynamic Memory Management. Wiley, 1996.
• Venners B.: Inside the Java Virtual Machine. McGraw-Hill 1999. www.artima.com/insidejvm/ed2/
• Kokosa, K.: Pro .NET Memory Management. Apress 2018.
• Levine J.R.: Linkers & Loaders. Morgan Kaufmann, 2000.
• Rosenberg J.B.: How Debuggers Work. Algorithms, Data Structures, and Architecture. Wiley, 1996.

• General
• Wilson P.R.:. Uniprocessor Garbage Collection Techniques. Technical Report, University of Texas, 1994. ftp://ftp.cs.utexas.edu/pub/garbage/bigsurv.ps
• Reference counting
• Collins, G. E: A method for overlapping and erasure of lists. Communications of the ACM 3, 12 (Dec 1960), 655-657
• Mark & Sweep
• McCarthy, J.: Recursive functions of symbolic expressions and their computation by machine. Communications of the ACM 3 (1960), 184-195.
• Schorr, Waite: An efficient machine-independent procedure for garbage collection in various list structures. Communications of the ACM (August 1967), 501-505
• Stop & Copy
• Cheney C.J.: A Nonrecursive List Compacting Algorithm. Communications of the ACM, 13(119):677-678, November 1970
• Generation Scavenging
• Ungar, D.: Generation scavenging: A nondisruptive high performance storage reclamation algorithm. ACM SIGPLAN Notices 19, 5 (May 1984) and ACM Software Engineering Notes 9, 3 (May 1984).
• Appel A.W.: Simple Generational Garbage Collection and Fast Allocation. Software Practice and Experience, 1988
• Ungar, D., Jackson, F.: An adaptive tenuring policy for generation scavengers. ACM Transactions on Programming Languages and Systems 1, 1 (January 1992), 1-27
• Pointer tables and conservative garbage collection
• Agesen O., Detlefs D.L.: Finding References in Java Stacks. OOPSLA’97 Garbage Collection and Memory Management Workshop. Atlanta, GA, October 1997. citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.47.6924.
• Boehm H.J., Weiser M.: 1988. Garbage collection in an uncooperative environment. Software -- Practice and Experience. 18(9):807-820
• Diwan A., Moss E., Hudson R.: Compiler Support for Garbage Collection in a Statically Typed Language. Proceedings PLDI'92, p. 273-282, San Francisco, CA, June 1992.
• Safepoints
• Agesen O.: GC points in a threaded environment. Technical report, Sun Microsystems, 1998. citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.44.2891
• Miscellaneous
• Detlefs D., Printezis T.: A Generational Mostly-Concurrent Garbage Collector. Intl. Symp. on Memory Management (ISMM), 2000, 143-154. dl.acm.org/citation.cfm?id=362480
• Deutsch, L P., Bobrow, D. G.: An efficient incremental automatic garbage collector. Communications of the ACM 19,9 (Sept. 1976),522-526.
• Lieberman, H, Hewitt, C. A real-time garbage collector based on the lifetimes of objects. Communications of the ACM 26, 6 (June 1983), 419-429.

• Lindholm T., Yellin F.: The Java Virtual Machine Specification https://docs.oracle.com/javase/specs/jls/se12/html/
• Venners B.: Inside the Java Virtual Machine. McGraw-Hill 1999. www.artima.com/insidejvm/ed2/
• Liang S., Bracha G.: Dynamic Class Loading in the Java Virtual Machine. Proceedings of OOPSLA'98, 36-44. dl.acm.org/citation.cfm?id=286945
• The Java class loader architecture: www.securingjava.com/chapter-two/chapter-two-7.html
• Gutknecht J., Wirth N.: Project Oberon - The Design of an Operating System and Compiler. ACM Press, 1992
• Franz M.: Dynamic Linking of Software Components. IEEE Computer 30(3): 74-81, March 1997.
• Presser L., White J.R.: Linkers and Loaders. Computing Surveys 4(3): 149-167, September 1972.

• The Java Platform Debugger Architecture (JPDA): docs.oracle.com/javase/8/docs/technotes/guides/jpda/
• Debugger dbx: en.wikipedia.org/wiki/Dbx_(debugger)

• Wiki with links to text editor resources: texteditors.org/cgi-bin/wiki.pl?DesigningTextEditors
• Gutknecht J.: Concepts of the Text Editor Lara. Communications of the ACM 28(9): 942-960, Sept. 1985.
• Bruce C.: Design and Implementation of an Advanced Text Editor. mclauchlan.site.net.au/scott/C=Hacking/C-Hacking11/zedace.html
• Finseth C.A.: The Craft of Text Editing. www.finseth.com/craft/
• Various text editor implementations from the GNU Free Software Foundation: https://directory.fsf.org/wiki/Category/Use/editing
• Hansen W.J.: Data Structures in a Bit-Mapped Text Editor. BYTE: 183-190, January 1987.