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Defined in header <atomic> | ||
bool atomic_flag_test_and_set(volatilestd::atomic_flag* obj)noexcept; | (1) | (since C++11) |
bool atomic_flag_test_and_set(std::atomic_flag* obj)noexcept; | (2) | (since C++11) |
bool atomic_flag_test_and_set_explicit(volatilestd::atomic_flag* obj, std::memory_order order)noexcept; | (3) | (since C++11) |
bool atomic_flag_test_and_set_explicit(std::atomic_flag* obj, std::memory_order order)noexcept; | (4) | (since C++11) |
Atomically changes the state of astd::atomic_flag pointed to byobj to set (true) and returns the value it held before.
Contents |
| obj | - | pointer tostd::atomic_flag to access |
| order | - | the memory synchronization order |
The value previously held by the flag pointed to byobj.
std::atomic_flag_test_and_set andstd::atomic_flag_test_and_set_explicit can be implemented asobj->test_and_set() andobj->test_and_set(order) respectively.
A spinlock mutex can be implemented in userspace using anstd::atomic_flag.
#include <atomic>#include <iostream>#include <thread>#include <vector> std::atomic_flag lock=ATOMIC_FLAG_INIT; void f(int n){for(int cnt=0; cnt<100;++cnt){while(std::atomic_flag_test_and_set_explicit(&lock,std::memory_order_acquire));// spin until the lock is acquiredstd::cout<<"Output from thread "<< n<<'\n';std::atomic_flag_clear_explicit(&lock,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();}
Output:
Output from thread 2Output from thread 6Output from thread 7...<exactly 1000 lines>...
(C++11) | the lock-free boolean atomic type (class)[edit] |
(C++11)(C++11) | atomically sets the value of the flag tofalse (function)[edit] |
(C++11) | defines memory ordering constraints for the given atomic operation (enum)[edit] |
C documentation foratomic_flag_test_and_set,atomic_flag_test_and_set_explicit | |
