C++ Atomic Library - exchange

Description

It automically replaces the value of the atomic object with non-atomic argument and returns the old value of the atomic.

Declaration

Following is the declaration for std::atomic_exchange.

template< class T >
T atomic_exchange( std::atomic<T>* obj, T desr );

C++11

template< class T >
T atomic_exchange( volatile std::atomic<T>* obj, T desr );

Parameters

• obj − It is used in pointer to the atomic object to modify.

• desr − It is used to store the value in the atomic object.

• order − It is used to synchronise the memory ordering for this operation.

Return Value

It returns the value held previously by the atomic object pointed to by obj.

Exceptions

No-noexcept − this member function never throws exceptions.

Example

In below example for std::atomic_exchange.

#include <thread>
#include <vector>
#include <iostream>
#include <atomic>

std::atomic<bool> lock(false);

void f(int n) {
   for (int cnt = 0; cnt < 100; ++cnt) {
      while(std::atomic_exchange_explicit(&lock, true, std::memory_order_acquire))
             ;
        std::cout << "Output from thread " << n << '\n';
        std::atomic_store_explicit(&lock, false, std::memory_order_release);
   }
}
int main() {
   std::vector<std::thread> v;
   for (int n = 0; n < 10; ++n) {
      v.emplace_back(f, n);
   }
   for (auto& t : v) {
      t.join();
   }
}

The output should be like this −

Output from thread 0
Output from thread 1
Output from thread 0
Output from thread 1
Output from thread 0
Output from thread 1
Output from thread 0
Output from thread 1
.....................