Item 16. Lazy Optimization, Part 4: Multithreaded Environments

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Difficulty: 8

In this final chapter of the miniseries, we consider the effects of thread safety on copy-on-write strings. Is lazy copy really an optimization? The answer may surprise you.

1. Why is Optimized::String (from Item 15) not thread-safe? Give examples.

2. Demonstrate how to make Optimized::String thread-safe:

   1. assuming there are atomic operations to get, set, and compare integer values; and

   2. assuming there aren't.

3. What are the effects on performance? Discuss.

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