std::launch

 

C++

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Technical Specifications

 

Thread support library

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hardware_destructive_interference_sizehardware_constructive_interference_size (C++17)(C++17)
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Futures
promise (C++11) future (C++11) shared_future (C++11) packaged_task (C++11) async (C++11)	launch (C++11) future_status (C++11) future_error (C++11) future_category (C++11) future_errc (C++11)

 

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

Specifies the launch policy for a task executed by the std::async function. std::launch is an enumeration used as BitmaskType.

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

Constant	Explanation
std::launch::async	a new thread is launched to execute the task asynchronously
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.

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)