CSC/ECE 506 Spring 2012/ch5a ja

Chapter 5a CSC/ECE 506 Spring 2012 / ch5a

An exploration and summary of concurrency issues as it relates to linked-list based data structures such as hash tables, trees, and graphs. This topic examines concurrency problems related to each type and possible solutions to allow for parallelization.

Introduction to Linked-List Parallel Programming

In determining opportunities for parallel programming in your software design, many programmers will focus exclusively on loop or array structures, rather than also considering the possibilities that linked-list pointer-based structures could also provide.

For example, one parallel technique used in array processing is the copy-scan technique. Take the following grid:

The basic process for copy-scan would be to:

 a) Copy row 1 to row 2.
 b) Copy row 1 to row 3, row 2 to row 4, etc on the next run.
 c) Continue in this manner until all rows have been copied in a log(n) fashion.

Similarly, in the linked list world, there is the concept of pointer doubling.

 a) Each processor will make a copy of the pointer it holds to it's neighbor.
 b) Next, each processor will make a pointer to the processor 2 steps away.
 c) This continues in logarithmic fashion until each processor has a pointer to the end of the chain.

In this chapter, we will explore 3 linked-list based data structures and the concurrency issues they present: hash tables, trees, and graphs.