cppreference

All atomic types except for std::atomic_flag may be implemented using mutexes or other locking operations, rather than using the lock-free atomic CPU instructions. Atomic types are also allowed to be sometimes lock-free, e.g. if only aligned memory accesses are naturally atomic on a given architecture, misaligned objects of the same type have to use locks.

Author: wintel2014

C++/C++11/LockFree/Makefile

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+BIN = lockfree
+
+$(BIN): $(BIN).cpp
+	g++ $^ -o $@ -latomic -std=c++11

C++/C++11/LockFree/lockfree.cpp

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+#include <iostream>
+#include <utility>
+#include <atomic>
+ 
+struct A { int a[100]; };
+struct B { int x, y; };
+struct C { int x, y, z; };
+int main()
+{
+    std::cout << std::boolalpha
+              << "std::atomic<A> is lock free? "
+              << std::atomic<A>{}.is_lock_free() << '\n'
+              << "std::atomic<B> is lock free? "
+              << std::atomic<B>{}.is_lock_free() << '\n'
+              << "std::atomic<C> is lock free? "
+              << std::atomic<C>{}.is_lock_free() << '\n';
+
+    std::cout << "std::atomic<bool> is lock free? "
+              << std::atomic<bool>{}.is_lock_free() << '\n';
+}