Advanced Topic 41 of 51 Concurrency & Parallelism
False Sharing
Performance loss when threads modify data on one cache line.
How it works
Threads writing different variables on the same cache line force the line to bounce between cores, slowing programs drastically; pad or align data to 64 bytes.
Where it is used
Per-thread counters in arrays.
Common pitfall
Invisible in code; detect with perf and cache profilers.
Where it fits in the course
False Sharing is topic 41 of 51 in Concurrency & Parallelism, rated Advanced. It follows Load Balancing in Parallel Programs. The next topic is NUMA.
Practice and explore
- Open the interactive lesson, with a mini quiz.
- Take the Concurrency & Parallelism quiz.
How to study this topic
- Read the explanation above and restate the definition in your own words.
- Open the interactive lesson and answer its mini quiz.
- Read the common pitfall, then write a short example that avoids it.
- Check your understanding in the Concurrency & Parallelism quiz, and revisit the topic if you miss a question.
Frequently asked questions
What is False Sharing?
Performance loss when threads modify data on one cache line. It belongs to Concurrency & Parallelism and is an advanced-level topic.
Where do people use False Sharing?
Per-thread counters in arrays.
What is the most common mistake with False Sharing?
Invisible in code; detect with perf and cache profilers.
What should I learn before this topic?
Start with Load Balancing in Parallel Programs, the topic just before it in Concurrency & Parallelism.
How can I practice it?
Answer the mini quiz in the interactive lesson, then take the Concurrency & Parallelism quiz.
Is False Sharing hard to learn?
It is an Advanced topic. Expect to read the explanation more than once and to connect it with earlier topics. Working through a small example by hand helps most.
How long does it take to learn False Sharing?
Most learners can read the explanation and finish the interactive lesson in under an hour. Fluency comes from applying the idea, so plan a few short practice sessions with the quiz.
Which topics are related to False Sharing?
Load Balancing in Parallel Programs, NUMA, Parallel Sorting are closely connected. The full list is in the related topics section of this page.
What should I study after False Sharing?
Continue with NUMA, the next topic in Concurrency & Parallelism.
Related topics
- Load Balancing in Parallel Programs (Concurrency & Parallelism)
- NUMA (Concurrency & Parallelism)
- Parallel Sorting (Concurrency & Parallelism)
- Parallel Graph Algorithms (Concurrency & Parallelism)