May 8, 2015 · "An operation acting on shared memory is atomic if it completes in a single step relative to other threads. When an atomic store is performed on a shared memory, no other thread can observe the modification half-complete. When an atomic load is performed on a shared variable, it reads the entire value as it appeared at a single moment in time."

Aug 13, 2015 · std::atomic<> wraps operations that, in pre-C++ 11 times, had to be performed using (for example) interlocked functions with MSVC or atomic bultins in case of GCC. Also, std::atomic<> gives you more control by allowing various memory orders that specify synchronization and ordering constraints. If you want to read more about C++ 11 atomics and ...

Sep 6, 2018 · Here, each upsert is atomic: the first one left count at 2, the second one left it at 3. Everything works. Note that "atomic" is contextual: in this case, the upsert operation only needs to be atomic with respect to operations on the answers table in the database; the computer can be free to do other things as long as they don't affect (or are ...

Jun 4, 2014 · The definition of atomic is hazy; a value that is atomic in one application could be non-atomic in another. For a general guideline, a value is non-atomic if the application deals with only a part of the value. Eg: The current Wikipedia article on First NF (Normal Form) section Atomicity actually quotes from the introductory parts above.

Aug 10, 2012 · Generally I would suggest that one confine use of them to small methods like "atomic increment" and such, which could easily be rewritten if needed to use other approaches (e.g. on the Cortex-M0, they'd be implemented by temporarily disabling interrupts). –

Feb 27, 2015 · Atomic Operations. If, as in the example above, our critical section is a single assignment, OpenMP provides a potentially more efficient way of protecting this. OpenMP provides an atomic directive which, like critical, specifies the next statement must be done by one thread at a time: #pragma omp atomic global_data++; Unlike a critical directive:

Sep 18, 2023 · std::atomic<int> id{0}; int create_id() { id++; return id.load(); } But I assume it's possible for that function to return the same value twice, right? For example, thread A calls the function, increments the value, but then halts while thread B comes in and also increments the value, finally A and B both return the same value.

Or for static storage like in the question, even just std::atomic<int> data; works; static storage is zero-initialized by default, and this is sufficient for std::atomic or C _Atomic to work correctly (C17 required that and deprecated ATOMIC_VAR_INIT). –

Mar 27, 2013 · Atomic Operations on the other hand are usually associated with low-level programming with regards to multi-processing or multi-threading applications and are similar to Critical Sections. For example, if two threads both access and modify the same variable, each thread goes through the following steps:

Atomic operations leverage processor support (compare and swap instructions) and don't use locks at all, whereas locks are more OS-dependent and perform differently on, for example, Win and Linux. Locks actually suspend thread execution, freeing up cpu resources for other tasks, but incurring in obvious context-switching overhead when stopping ...