std::launch
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runs a function asynchronously (potentially in a new thread) and returns a std::future that will hold the result
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launch
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Defined in header
<future>
enum class launch : /* unspecified */ {
(since C++11)
async = /* unspecified */,
deferred = /* unspecified */,
/* implementation-defined */
std::launch is a BitmaskType. It specifies the launch policy for a task executed by the std::async function.
[edit] Constants
The following constants denoting individual bits are defined by the standard library:
Enumerator
Meaning
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 .
[edit] 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 |
[edit] See also
(C++11)
(function template) [edit]