std::launch

 

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Defined in header <future>
enum class launch : /* unspecified */ {     async =    /* unspecified */,     deferred = /* unspecified */,     /* implementation-defined */ };		(since C++11)

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

Constants

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

Name	Explanation
async	the task is executed on a different thread, potentially by creating and launching it first
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 implementation-defined type	it is not implementation-defined

See also

async (C++11)

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