# std::launch

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< cpp‎ | thread

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)

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