Pattern-Oriented Software Architecture, Volume 2, Patterns for Concurrent and Networked Objects

Chapter 5

Concurrency Patterns

“You look at where you’re going and where you are and it never makes sense, but then you look back at where you’ve been and a pattern seems to emerge. And if you project forward from that pattern, then sometimes you can come up with something.”

Robert M. Pirsig

This chapter presents five patterns that address various types of concurrency architecture and design issues for components, subsystems, and applications: Active Object, Monitor Object, Half-Sync/Half-Async, Leader/Followers, and Thread-Specific Storage.

The choice of concurrency architecture has a significant impact on the design and performance of multi-threaded networking middleware and applications. No single concurrency architecture is suitable for all workload conditions and hardware and software platforms. The patterns in this chapter therefore collectively provide solutions to a variety of concurrency problems.

The first two patterns in this chapter specify designs for sharing resources among multiple threads or processes:

• The Active Object design pattern (369) decouples method execution from method invocation. Its purpose is to enhance concurrency and simplify synchronized access to objects that reside in their own threads of control
• The Monitor Object design pattern (399) synchronizes concurrent method execution to ensure that only one method at a time runs within an object. It also allows an object’s methods to schedule their execution sequences cooperatively.

Both patterns can ...