# Swapping arrays for an interrupt, quickly **URL:** \ **Category:** Programming\ **Created:** [July 26, 2023, 10:11pm UTC](https://forum.arduino.cc/t/swapping-arrays-for-an-interrupt-quickly/1152089 "2023-07-26T22:11:05Z")\ **Posts on this page:** 1\ **Showing post:** 17
**Author:** ![PieterP](https://avatars.discourse-cdn.com/v4/letter/p/ecccb3/32.png) [@PieterP](https://forum.arduino.cc/u/PieterP)\ **Post date:** [August 8, 2023, 5:58pm UTC](https://forum.arduino.cc/t/swapping-arrays-for-an-interrupt-quickly/1152089/17 "2023-08-08T17:58:29Z")
> [@J-M-L](#): > > `__sync_synchronize()` This might be okay on AVR, since `__sync_synchronize()` is only a compile-time fence (in the absence of caches, out-of-order execution, multiple cores, etc.). However, on non-AVR targets, you should use the standard library atomics and fences, e.g. [std::atomic\_signal\_fence - cppreference.com](https://en.cppreference.com/w/cpp/atomic/atomic_signal_fence). This is because C++ has a well-defined memory model, and rigorously defines the behavior and synchronization and memory order guarantees for all atomic operations and fences. A full memory fence like `__sync_synchronize()` is serious overkill: for interrupt handlers, you should only need compile-time barriers. (\*) Even for multithreaded applications, you only need atomic exchange/load-acquire and store-release operations to implement a mutex, not full barriers. See e.g. [Correctly Implementing a Spinlock in C++ | Erik Rigtorp](https://rigtorp.se/spinlock/) In the context of interrupts, a mutex is essentially useless, because the ISR cannot possibly acquire it without deadlocking. * * * (\*) Since both the access of the volatile variable `mutexFlag` and the call to `(no)interrupts()` (access of a volatile register) have observable side effects, you don't need any additional ordering constraints in this case. However, `volatile` does not guarantee any memory order, so it cannot be used for multithreaded applications. --- _[View the full topic](https://forum.arduino.cc/t/swapping-arrays-for-an-interrupt-quickly/1152089)._