Dynamic Atomic Array Resizing via Compare-and-Swap
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Solution Overview
Problem
Standard dynamic arrays are not thread-safe and require locks for concurrent access, leading to processing overhead and priority inversion issues in multi-threaded environments, while atomic arrays are not dynamic and cannot grow or shrink.
Innovation Solution
A dynamic atomic array that is non-blocking, wait-free, and thread-safe, allowing resizing through a compare and swap operation, and using a COPIED indicator to ensure accurate element copying without locks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If locks are used for concurrent access to dynamic arrays, then thread safety is improved, but processing overhead and priority inversion issues occur
Solution Approach 1:
The array is divided into multiple independent segments or slots, each capable of being accessed independently by different threads. Instead of locking the entire array, individual segments can be accessed without mutual exclusion, reducing contention and overhead while maintaining thread safety through structured access patterns.
Solution Approach 2:
The mechanical locking system is replaced with an atomic compare-and-swap operation at the hardware level. This substitution eliminates the need for software-based locks and blocking mechanisms, providing thread safety through atomic instructions that operate without requiring thread suspension or context switching.
2Reliability
If locks are used for concurrent access to dynamic arrays, then thread safety is improved, but priority inversion occurs
Solution Approach 1:
The lock-based synchronization mechanism is replaced with atomic compare-and-swap operations that do not require thread blocking. This eliminates priority inversion by allowing threads to attempt access without being suspended by lower-priority threads holding locks, as the atomic operation completes in a single indivisible step.
Solution Approach 2:
The system provides self-service thread safety through atomic hardware instructions that inherently protect against concurrent access conflicts without requiring external lock management. Threads independently perform atomic operations on their target elements, and the hardware ensures mutual exclusion at the instruction level, eliminating the need for lock acquisition and release protocols.
3Adaptability or versatility
If atomic arrays are made dynamic with resizing capability, then adaptability is improved, but thread safety becomes difficult to maintain
Solution Approach 1:
A new array structure is pre-allocated and prepared before the resizing operation begins. The atomic compare-and-swap operation then atomically transitions from the old array to the pre-prepared new array, ensuring that no thread observes a partially resized state. This preliminary preparation eliminates the need for locking during the transition.
Solution Approach 2:
The array structure is made dynamic through atomic transitions between different array instances. Rather than modifying a single array in place (which would require locks), the system dynamically switches between array versions using atomic compare-and-swap on the array reference, allowing resizing without compromising thread safety.
4Productivity
If standard dynamic array techniques are used, then resizing is efficient, but thread safety is lost
Solution Approach 1:
The software-based locking mechanism is replaced with a hardware-level atomic compare-and-swap instruction. This substitution maintains resizing efficiency by operating at the hardware level in a single atomic step, while simultaneously providing thread safety that software locks cannot achieve without blocking other threads.
Data Source
AI summary
Embodiments of the present invention provide techniques, including systems, methods, and computer readable medium, for dynamic atomic arrays. A dynamic atomic array is a data structure that provides an array that can grow or shrink in size as required. The dynamic atomic array is non-blocking, wait-free, and thread-safe. The dynamic atomic array may be used to provide arrays of any primitive data type as well as complex types, such as objects.