class
<atomic>

std::atomic_flag

struct atomic_flag;
Atomic flag
Atomic flags are boolean atomic objects that support two operations: test-and-set and clear.

Atomic flags are lock-free (this is the only type guaranteed to be lock-free on all library implementations).

Member functions

(constructor)
Construct atomic flag (public member function )
test_and_set
Test and set flag (public member function )
clear
Clear flag (public member function )
operator= is deleted (non-copyable/moveable).

Example

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// using atomic_flag as a lock
#include <iostream>       // std::cout
#include <atomic>         // std::atomic_flag
#include <thread>         // std::thread
#include <vector>         // std::vector
#include <sstream>        // std::stringstream

std::atomic_flag lock_stream = ATOMIC_FLAG_INIT;
std::stringstream stream;

void append_number(int x) {
  while (lock_stream.test_and_set()) {}
  stream << "thread #" << x << '\n';
  lock_stream.clear();
}

int main ()
{
  std::vector<std::thread> threads;
  for (int i=1; i<=10; ++i) threads.push_back(std::thread(append_number,i));
  for (auto& th : threads) th.join();

  std::cout << stream.str();
  return 0;
}


Possible output (order of lines may vary):
thread #1
thread #2
thread #3
thread #4
thread #5
thread #6
thread #7
thread #8
thread #9
thread #10

C++