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SHM Cache Locks

Problem Statement

The SHM (Shared Memory) cache backend in Hazaar MVC currently lacks a mechanism to prevent race conditions and ensure data consistency when multiple processes attempt to read from or write to the cache simultaneously. Implementing cache locks using semaphores will help synchronize access to the shared memory cache, preventing data corruption and ensuring reliable caching behavior in concurrent environments.

Who will benefit?

Developers using the SHM cache backend in Hazaar MVC, particularly those working in multi-threaded or multi-process environments, will benefit from this feature. It will ensure that cache operations are atomic and that data integrity is maintained across all processes.

Benefits and risks

Benefits

  • Prevents race conditions by ensuring that only one process can access or modify a cache entry at a time.
  • Enhances the reliability and consistency of the SHM cache backend, especially in high-concurrency scenarios.
  • Improves overall application stability by avoiding potential data corruption in the cache.

Risks

  • Potential performance overhead due to the additional locking and unlocking operations.
  • Increased complexity in the cache backend code, which may require careful testing and validation to avoid deadlocks or other synchronization issues.

Proposed solution

  1. Semaphore Implementation:

    • Introduce semaphores to control access to the SHM cache. Before a cache entry is read or written, a semaphore will be acquired to lock the cache. Once the operation is complete, the semaphore will be released.

  2. Locking Mechanism:

    • Implement a locking mechanism that uses PHP’s sem_acquire() and sem_release() functions to manage semaphore operations.
    • Ensure that the semaphore is initialized and destroyed properly during the cache backend lifecycle to avoid resource leaks.

  3. Integration with Cache Operations:

    • Modify existing cache read/write operations to include the semaphore locking logic.
    • Ensure that all critical sections of code that access shared memory are protected by the semaphore.

  4. Testing and Optimization:

    • Test the semaphore implementation in various scenarios, including high-concurrency environments, to ensure that it works correctly without introducing deadlocks.
    • Optimize the performance of the semaphore operations to minimize any impact on cache access times.

Examples

N/A

Priority/Severity

  • High (This will bring a huge increase in performance/productivity/usability/legislative cover)
  • Medium (This will bring a good increase in performance/productivity/usability)
  • Low (anything else e.g., trivial, minor improvements)