std::atomic_flag (3) - Linux Manuals
std::atomic_flag: std::atomic_flag
Command to display std::atomic_flag
manual in Linux: $ man 3 std::atomic_flag
NAME
std::atomic_flag - std::atomic_flag
Synopsis
Defined in header <atomic>
class atomic_flag; (since C++11)
std::atomic_flag is an atomic boolean type. Unlike all specializations of std::atomic, it is guaranteed to be lock-free. Unlike std::atomic<bool>, std::atomic_flag does not provide load or store operations.
Member functions
constructs an atomic_flag
constructor (public member function)
the assignment operator
operator= (public member function)
atomically sets flag to false
clear (public member function)
atomically sets the flag to true and obtains its previous value
test_and_set (public member function)
Example
A spinlock mutex can be implemented in userspace using an atomic_flag
// Run this code
#include <thread>
#include <vector>
#include <iostream>
#include <atomic>
std::atomic_flag lock = ATOMIC_FLAG_INIT;
void f(int n)
{
for (int cnt = 0; cnt < 100; ++cnt) {
while (lock.test_and_set(std::memory_order_acquire)) // acquire lock
; // spin
std::cout << "Output from thread " << n << '\n';
lock.clear(std::memory_order_release); // release lock
}
}
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();
}
}
Output:
Output from thread 2
Output from thread 6
Output from thread 7
...<exactly 1000 lines>...
See also
atomic_flag_test_and_set
atomic_flag_test_and_set_explicit atomically sets the flag to true and returns its previous value
(function)
(C++11)
(C++11)
atomic_flag_clear
atomic_flag_clear_explicit atomically sets the value of the flag to false
(function)
(C++11)
(C++11)
ATOMIC_FLAG_INIT initializes an std::atomic_flag to false
(macro constant)
(C++11)
Pages related to std::atomic_flag
- std::atomic_flag::atomic_flag (3) - std::atomic_flag::atomic_flag
- std::atomic_flag::clear (3) - std::atomic_flag::clear
- std::atomic_flag::operator= (3) - std::atomic_flag::operator=
- std::atomic_flag::test_and_set (3) - std::atomic_flag::test_and_set
- std::atomic_flag_clear,std::atomic_flag_clear_explicit (3) - std::atomic_flag_clear,std::atomic_flag_clear_explicit
- std::atomic_flag_test_and_set,std::atomic_flag_test_and_set_explicit (3) - std::atomic_flag_test_and_set,std::atomic_flag_test_and_set_explicit
- std::atomic_fetch_add,std::atomic_fetch_add_explicit (3) - std::atomic_fetch_add,std::atomic_fetch_add_explicit
- std::atomic_fetch_and,std::atomic_fetch_and_explicit (3) - std::atomic_fetch_and,std::atomic_fetch_and_explicit
- std::atomic_fetch_or,std::atomic_fetch_or_explicit (3) - std::atomic_fetch_or,std::atomic_fetch_or_explicit
- std::atomic_fetch_sub,std::atomic_fetch_sub_explicit (3) - std::atomic_fetch_sub,std::atomic_fetch_sub_explicit
- std::atomic_fetch_xor,std::atomic_fetch_xor_explicit (3) - std::atomic_fetch_xor,std::atomic_fetch_xor_explicit
- std::atomic_...<std::shared_ptr> (3) - std::atomic_...<std::shared_ptr>
- std::atomic_bool (3)
- std::atomic_compare_exchange_weak,std::atomic_compare_exchange_strong, (3) - std::atomic_compare_exchange_weak,std::atomic_compare_exchange_strong,
- std::atomic_compare_exchange_weak,std::atomic_compare_exchange_strong,std::atomic_compare_exchange_weak_explicit,std::atomic_compare_exchange_strong_explicit (3) - std::atomic_compare_exchange_weak,std::atomic_compare_exchange_strong,std::atomic_compare_exchange_weak_explicit,std::atomic_compare_exchange_strong_explicit
- std::atomic_exchange,std::atomic_exchange_explicit (3) - std::atomic_exchange,std::atomic_exchange_explicit