C# Dev for Beginners #20: Thread-Safe Collections - ConcurrentDictionary, BlockingCollection, etc.
List and Dictionary will betray you. Under concurrent access, they corrupt data silently. .NET has better options built specifically for multithreading.
What you'll learn:
• Why List and Dictionary fail with threads
• System.Collections.Concurrent namespace
• ConcurrentDictionary - the thread-safe workhorse
• TryAdd, TryGetValue, TryRemove patterns
• GetOrAdd - atomic check-and-add
• AddOrUpdate - atomic modifications
• ConcurrentBag for unordered collections
• ConcurrentQueue (FIFO) and ConcurrentStack (LIFO)
• BlockingCollection for producer-consumer
• The Lazy pattern for expensive factories
Key insights:
• Regular collections + threads = silent corruption
• Concurrent collections handle locking internally
• Try methods never throw on missing keys
• GetOrAdd factory might run multiple times
• Use Lazy when factory is expensive
• BlockingCollection coordinates producers/consumers
• CompleteAdding signals no more items coming
• Still need locks for multi-operation atomicity
We'll build:
• Thread-safe cache with ConcurrentDictionary
• GetOrAdd caching pattern
• Producer-consumer file processor
• Multi-threaded word frequency counter
Previous Video: Introduction to Multithreading
Next Video: Tasks - Modern Multithreading
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0:00 Thread-Safe Collections
1:17 Regular Collections Will Betray You
1:44 List Under Pressure
2:30 The Concurrent Collection Family
3:25 ConcurrentDictionary Basics
4:10 GetOrAdd - The Atomic Pattern
4:32 GetOrAdd - Caching Pattern
4:57 AddOrUpdate - Modify Atomically
5:47 ConcurrentBag - Unordered and Fast
6:33 ConcurrentQueue and ConcurrentStack
6:58 BlockingCollection - Producer/Consumer
7:43 Complete Producer-Consumer Example
8:14 Common Mistakes
9:09 Lazy Factory Pattern
9:29 Choosing the Right Collection
10:23 Q: When Should I Still Use Locks?
11:05 Key Takeaways
12:01 Practice Challenge