C++ Library - <stdatomic>

Quiz

The <stdatomic> header in C++, provides a set of functions to perform atomic operations on shared variables, to enable thread-safe manipulation of data. This header is part of the concurrency support library.

The <stdatomic> header shall define the atomic_flag type as a structure type (provides the classic test-and-set functionality) having two states, set and clear.

Including <stdatomic> Header

To include the <stdatomic> header in your C++ program, you can use the following syntax.

#include <stdatomic>

Functions of <stdatomic> Header

Below is list of all functions from <stdatomic> header.

Path Manipulation Functions

This path manipulation functions operate on file paths to compose, convert or resolve them.

S.No	Functions & Description
1	atomic_is_lock_free This function checks if the atomic type's operations are lock-free.
2	atomic_store, atomic_store_explicit These functions atomically replaces the value of the atomic object with a non-atomic argument.
3	atomic_exchange, atomic_exchange_explicit These functions atomically replaces the value of the atomic object with non-atomic argument and returns the old value of the atomic.
4	atomic_fetch_add, atomic_fetch_add_explicit These functions adds a non-atomic value to an atomic object and obtains the previous value of the atomic.
5	atomic_fetch_sub, atomic_fetch_sub_explicit These functions replaces the atomic object with the result of bitwise AND with a non-atomic argument and obtains the previous value of the atomic.
6	atomic_fetch_or, atomic_fetch_or_explict These functions replaces the atomic object with the result of bitwise OR with a non-atomic argument and obtains the previous value of the atomic.
7	atomic_fetch_xor, atomic_fetch_xor_explict These functions replaces the atomic object with the result of bitwise XOR with a non-atomic argument and obtains the previous value of the atomic.
8	atomic_flag_test_and_set, atomic_flag_test_and_set_explicit These functions atomically sets the value of the flag to false.
9	atomic_thread_fence This function provides generic memory order-dependent fence synchronization primitive.
10	atomic_signal_fence This function fence between a thread and a signal handler executed in the same thread.

Checking if Operations are Lock-Free

In the below example we are going to use, atomic_is_lock_free to check if atomic operations on a specific atomic type are lock-free.

#include <iostream>
#include <atomic>
int main() {
    std::atomic<int> atomicInt;
    bool isLockFree = atomic_is_lock_free(&atomicInt);
    std::cout << "Is atomic operation lock-free? " << std::boolalpha << isLockFree << std::endl;
    return 0;
}

Output

If we run the above code it will generate the following output

Is atomic operation lock-free? true

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