Concurrency

Concurrency is a decoupling strategy; decoupling what gets done from when it gets done.

Can sometimes improve performance.
Design is remarkably difference from single-threaded systems.
Correct concurrency is complex, even for simple problems.

Concurrency Defense Principles

Single Responsibility Principle

Limit the Scope of Data
Use Copies of Data
Threads Should be as Independent as Possible

Then ...

Know the Library
Know the Execution Models
Beware Dependency Between Synchronized Methods
Keep Synchronized Sections Small
Writing Correct Shutdown Code Is Hard
Test Threaded Code