< cpp‎ | thread
Defined in header <mutex>
class once_flag;
(since C++11)

The class std::once_flag is a helper structure for std::call_once.

An object of type std::once_flag that is passed to multiple calls to std::call_once allows those calls to coordinate with each other such that only one of the calls will actually run to completion.

std::once_flag is neither copyable nor movable.

Member functions


constexpr once_flag() noexcept;

Constructs an once_flag object. The internal state is set to indicate that no function has been called yet.



See also

invokes a function only once even if called from multiple threads
(function template)