Consider this example: #include <iostream> #include <atomic> #include <thread> #include <chrono> #include <cassert> int main(){ std::atomic<int> v = 0; std::at...

Consider this example: #include <iostream> #include <atomic> #include <thread> struct SpinLock{ std::atomic<bool> state; void lock(){ bool expected = false; while(!stat...

#include <memory> #include <atomic> #include <iostream> #include <thread> #include <cassert> int main() { std::atomic<bool> flag = {false}; std::atomic<int&...

Consider this example: std::atomic<int> v = {0}; // thread 1: for(int i = 0; i<999999;i++) v.load(memory_order::seq_cst); // #1 v.exchange(2,memory_order::seq_cst); // #2 //thread 2: ...

Consider this example: #include <iostream> #include <atomic> #include <random> #include <thread> int need_close(){ random_device rd; std::mt19937 gen(rd()); uniform_int_d...

I want to implement a sequence lock in C++23. If possible, it should not rely on non-standard extensions or undefined behavior. There is the proposal P1478R8: Byte-wise atomic memcpy, which covers ...

I need a function to atomically add float32 values in Go. This is what came up with based on some C code I found: package atomic import ( "sync/atomic" "unsafe" "math" ) func AddFloat32(addr ...

Generally _Atomic does not imply semantics of volatile, i.e. operations on the atomic object are not observable side effects that the compiler needs to preserve. As a consequence the compiler can o...

I'm trying to understand memory fences in c++11, I know there are better ways to do this, atomic variables and so on, but wondered if this usage was correct. I realize that this program doesn't do ...

Consider the following code: #include <atomic> #include <thread> #include <cassert> #include <memory> int i = 0; std::atomic_int a{0}; int main() { std::thread thr1{[] {...

C++20 std::atomic has wait and notify_* member functions, but no wait_for/wait_until. The Microsoft STL implementation for std::atomic uses WaitOnAddress (when the OS is new enough to has it). And ...

Are C/C++ fundamental types, like int, double, etc., atomic, e.g. threadsafe? Are they free from data races; that is, if one thread writes to an object of such a type while another thread reads fr...

In the ARM documentation, it mentions that The Cortex-M4 processor supports ARMv7 unaligned accesses, and performs all accesses as single, unaligned accesses. They are converted into two or mo...

atomic_flag_test_and_set Yes! atomic_flag_clear Yes! atomic_flag_test_and_clear nope atomic_flag_set nope If you wanted to do something like set a flag on a event in some context, and in some oth...

The standard technique to enforce atomic access to volatile variables shared with ISRs, via "atomic access guards" or "interrupt guards", in particular when running a bare metal...

I would like to generate identifiers for a class named order in a thread-safe manner. The code below does not compile. I know that the atomic types do not have copy constructors, and I assume that ...

As the title says, are procedures atomic in MySQL? i.e. would something like for (..) <check_if_row_has_flag> for (..) <update_row> work atomically? Interestingly, I couldn't find mu...

Is a PostgreSQL function such as the following automatically transactional? CREATE OR REPLACE FUNCTION refresh_materialized_view(name) RETURNS integer AS $BODY$ DECLARE _table_name ALIAS FOR $1...

Let's consider this trivial code: #include <atomic> std::atomic<int> a; void f(){ for(int k=0;k<100;++k) a.load(std::memory_order_relaxed); } MSVC, Clang and GCC all perform 10...

Can somebody explain the usage of WRITE_ONCE and READ_ONCE? And internally WRITE_ONCE uses a volatile qualifier. Why? How does WRITE_ONCE and READ_ONCE solve cache coherency problem? Difference bet...

std::array< std::atomic_size_t, 10 > A; // ... std::atomic_init(A, {0}); // error A = {ATOMIC_VAR_INIT(0)}; // error How would you initialize an array of std::atomic to 0s? Even for loops up...

In GCC atomic built-in I found that __atomic_exchange function does have a third parameter int memorder, which could take one of the values __ATOMIC_RELAXED, __ATOMIC_SEQ_CST, __ATOMIC_ACQUIRE, __A...

In this comment under a CWG issue, Jens Maurer says The read-compare-write is a single, indivisible operation ("atomically"). However, as discussed in For purposes of ordering, is ato...

I wanted to replace the pthread_spinlock_t example with my own spinlock implementation. However, my implementation's result is literally far lower than the pthread_spinlock_t performance. While the...

While porting some Windows C++ code to iOS, I need to provide an implementation of Win32's long InterlockedIncrement(long *p) call. This is easy enough using the functions defined in <libkern/OS...