Goals

Modern CPU

Modern CPUs

• Not only x64. ARMs are coming!
• More cores, same speed, sad Moore :(
• Optimizations

Modern CPUs

• registries
• caches (L1, L2, L3)
• prefetcher
• predictor
• pipeline
• write buffer

Atomicity

Atomicity

• Do it in one step
• Lock'n'roll
• Claim and work.

Atomicity - Interlocked

• Atomic operations on CPU level
• They are frequently translated to one ASM instruction

Atomicity - Interlocked adding

• Interlocked.Add(ref counter, value)
• Interlocked.Increment(ref counter)
• Interlocked.Decrement(ref counter)

Atomicity - Interlocked swapping

• Interlocked.Exchange(ref location, newValue)
• Swaps value in the location with the newValue
• Returns old value

Atomicity - Interlocked conditional swapping

• Interlocked.CompareExchange(ref location, newValue, valueToCompare)
• Swaps value in the location with the newValue conditionally
• Returns old value

Memory models

Memory models

• Consider two virtual operations: LOAD & STORE
• Four possible combinations:
  • LOAD-LOAD
  • LOAD-STORE
  • STORE-STORE
  • STORE-LOAD

Memory models - barriers

• Inserted between two LOAD/STORE operations.
• A memory barrier is a simple mechanism that disables some reorderings
• A full memory barrier prohibits ANY reorderings
• A full memory barrier is emitted by:
  • lock (obj)
  • Interlocked.Add/Exchange
  • when using high level constructs like WaitHandle

Memory models - barriers

• Aquire fence
  • Volatile.Read
  • Prohibits LOAD-LOAD
  • Prohibits LOAD-STORE
• Release fence
  • Volatile.Write
  • Prohibits STORE-LOAD
  • Prohibits STORE-STORE

Memory models - allowed reorderings

Summary

Summary

• You can write ultra performant code in .NET
• You can go low level with Volatile, Interlocked
• It's all there waiting for YOUR app to be performant!