Parallel Computing in the Computer Science Curriculum > Modules > Concurrent Access to Data Structures

Concurrent Access to Data Structures

Professor Libby Shoop, Macalester College

Summary

This module enables students to experiment with creating a task-parallel solution to the problem of crawling the web by using Java threads and thread-safe data structures available in the java.util.concurrent package. We provide enough code for a sequential solution, which the students can use as the basis for creating a task-parallel threaded solution. We provide some code to get them started with the threaded solution, because in our case this is the first threaded program they try.

Module Characteristics

Languages Supported: Java
Relevant Parallel Computing Concepts: Shared Memory
Recommended Teaching Level: Introductory/Intermediate, perhaps in a data structures or algorithms course.

Learning Goals

Context for Use

This module is best implemented in an introductory (2nd course) or intermediate-level Java-based course. It can be taught around the time in which the concepts of threads and thread-safe data structures are introduced. An instructor could go through the materials (handout, slideshow presentation) in class and assign exercises as a lab or homework.

Description and Teaching Materials

You can visit the module in your browser:
Concurrent Access to Data Structures

or you can download the module in either PDF format or latex format.
PDF Format: Concurrent Access to Data Structures.pdf.
Latex Format: Concurrent Access to Data Structures.tar.gz.
Word Format: Concurrent Access to Data Structures.docx.

Teaching Notes and Tips


This module utilizes the java.util.concurrent package.
In the code archive:

The concept of the lab/homework is that students should have worked out a sequential version of the Spider already. You could do this by explaining it to them, or by having them work on that first. We have used this in the past by staging assignments so that they get some parts of the code and then must complete to make a working spider. What is provided here is the already working sequential version.

You may feel like using different data structures for parts of this assignment- we realize there are other ways to hold the information kept by the crawler. However, we are pretty sure that the concurrent data structures that we chose for the threaded version likely are the proper ones from the java.util.concurrent library. We'd welcome comments or suggestion on this.

The lecture/class materials present the concepts of using multiple threads that share data structures in memory. Since the intended audience is introductory to intermediate students, there is not a deep conversation about race conditions, rather we intended a gentle introduction to this issue when data is shared, and an explanation of how the designers of the data structures in the java.util.concurrent library build them to ensure atomic operations by multiple therads (i.e. they are thread-safe).

Assessment


References and Resources

Java 1.6 Documentation of java.util.concurrent
Java 1.5 Documentation of java.util.concurrent

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Concurrent Access to Data Structures --Discussion  

I have used this module in the object-oriented computing and data structures course at Macalester College. During a lab section, I went over the introductory material on the slides for 15-20 minutes. During the rest of the 2-hour lab, the students completed the code fragments they were given. This was the first time they used threads. --Libby Shoop

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