NAME¶

std::launch - std::launch

Synopsis¶

Defined in header <future>
enum class launch : /* unspecified */ {

async = /* unspecified */,
deferred = /* unspecified */, (since C++11)
/* implementation-defined */

};

std::launch is a BitmaskType. It specifies the launch policy for a task executed by
the std::async function.

The following constants denoting individual bits are defined by the standard
library:

Constant Explanation
std::launch::async the task is executed on a different thread, potentially by
creating and launching it first
std::launch::deferred the task is executed on the calling thread the first time its
result is requested (lazy evaluation)

In addition, implementations are allowed to:

* define additional bits and bitmasks to specify restrictions on task interactions
applicable to a subset of launch policies, and
* enable those additional bitmasks for the first (default) overload of std::async.

Defect reports

The following behavior-changing defect reports were applied retroactively to
previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 2102 C++11 std::launch was an it is not
implementation-defined type implementation-defined

See also¶

async runs a function asynchronously (potentially in a new thread) and returns a
(C++11) std::future that will hold the result
(function template)