Execute a task asynchronously
12345678910111213141516171819 | #include <future>
int func()
{
int some_value = 0;
// Do work...
return some_value;
}
int main()
{
std::future<int> result_future = std::async(func);
// Do something...
int result = result_future.get();
} |
This pattern is licensed under the CC0 Public Domain Dedication.
Intent
High-level asynchronous execution of tasks.
Description
std::async provides a high-level way to
accomplish asynchronous execution of tasks, abstracting over
std::thread and
std::promise.
On line 14, we call std::async, passing func as the function to
execute asynchronously. Arguments to func can be passed as
additional arguments to std::async. The return value is a
std::future<int>, representing an int
value that will be returned from the task at some point in the
future.
By default, std::async will decide whether to execute the task
concurrently or to wait until we request the result and then
execute the task. If we want to specifically request one of these
behaviours, we can use a flag as the first argument. To request
concurrent execution, if possible, we use
std::launch::async. To request that the task
is executed only when the result is needed, we use
std::launch::deferred.
On line 18, we use the std::future’s get member function to get
the result of the asynchronous task. This blocks until the result
is available.
Note: It is important that we capture the future returned by
std::async. If we do not, then the call will always block.
