Memory ordering needs barriers

Ensure proper memory ordering in concurrent code by using appropriate memory barriers and atomic operations based on the access pattern. When implementing release-store semantics, place the store fence before the actual store to prevent instruction reordering:

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Ensure proper memory ordering in concurrent code by using appropriate memory barriers and atomic operations based on the access pattern. When implementing release-store semantics, place the store fence before the actual store to prevent instruction reordering:

// INCORRECT - barrier after store
value.store(newValue);
storeFence();  // Too late!

// CORRECT - barrier before store
storeFence();  // Prevents reordering of previous stores
value.store(newValue);

Key guidelines:

  • Use volatile for single-writer scenarios requiring visibility
  • For performance-critical paths with single-threaded access, prefer lazySet() over volatile writes
  • When implementing custom concurrent data structures, consider using unpadded variants for better memory efficiency
  • Place state updates before notification in producer-consumer patterns to ensure proper visibility

This approach prevents subtle race conditions while maintaining performance in concurrent systems.

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