std::call_once

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Defined in header <mutex>
template< class Function, class... Args> void call_once( std::once_flag& flag, Function&& f, Args&& args...);		(C++11 feature)

Executes the function f exactly once, even if called from several threads.

Each group of call_once invocations, which receives the same std::once_flag object, follows the following requirements:

• Exactly one execution of exactly one of the functions, passed as f to the invocations in the group, is performed. It is undefined which function will be selected for execution. The selected function runs in the same thread as call_once invocation it was passed to.

• No invocation in the group returns before the abovementioned execution of the selected function is completed successfully, that is doesn't exit via an exception.

• If the selected function exits via exception, it is propagated to the caller. Another function is selected and executed.

Contents 1 Parameters 2 Return value 3 Exceptions 4 Example 5 See also

[edit] Parameters

flag	-	an object, for which exactly one function gets executed
f	-	function to call
args...	-	arguments to pass to the function

[edit] Return value

(none)

[edit] Exceptions

This section is incomplete

[edit] Example

This section is incomplete

[edit] See also

once_flag (C++11)	helper object to ensure that call_once invokes the function only once (class)