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

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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