packaged_task(); | (1) | (since C++11) |
template <class F> explicit packaged_task( F&& f ); | (2) | (since C++11) |
| (3) | ||
template <class F, class Allocator> explicit packaged_task( std::allocator_arg_t, const Allocator& a, F&& f ); | (since C++11) (until C++17) | |
template <class F, class Allocator> packaged_task( std::allocator_arg_t, const Allocator& a, F&& f ); | (since C++17) | |
| (4) | ||
packaged_task( packaged_task& ) = delete; | (since C++11) (until C++14) | |
packaged_task( const packaged_task& ) = delete; | (since C++14) | |
packaged_task( packaged_task&& rhs ); | (5) | (since C++11) |
Constructs a new std::packaged_task object.
1) Constructs a
std::packaged_task object with no task and no shared state. 2) Constructs a
std::packaged_task object with a shared state and a copy of the task, initialized with std::forward<F>(f). This constructor does not participate in overload resolution if std::decay<F>::type is the same type as std::packaged_task<R(ArgTypes...)>. 3) Constructs a
std::packaged_task object with a shared state and a copy of the task, initialized with std::forward<F>(f). Uses the provided allocator to allocate memory necessary to store the task. This constructor does not participate in overload resolution if std::decay<F>::type is the same type as std::packaged_task<R(ArgTypes...)>. 4) The copy constructor is deleted,
std::packaged_task is move-only. 5) Constructs a
std::packaged_task with the shared state and task formerly owned by rhs, leaving rhs with no shared state and a moved-from task.Parameters
| f | - | the callable target (function, member function, lambda-expression, functor) to execute |
| a | - | the allocator to use when storing the task |
| rhs | - | the std::packaged_task to move from |
Exceptions
1)
noexcept specification: noexcept 2-3) Any exceptions thrown by copy/move constructor of
f and possiblly std::bad_alloc if the allocation fails. 4) (none)
5)
noexcept specification: noexceptExample
#include <future>
#include <iostream>
#include <thread>
int fib(int n)
{
if (n < 3) return 1;
else return fib(n-1) + fib(n-2);
}
int main()
{
std::packaged_task<int(int)> fib_task(&fib);
std::cout << "starting task\n";
auto result = fib_task.get_future();
std::thread t(std::move(fib_task), 40);
std::cout << "waiting for task to finish...\n";
std::cout << result.get() << '\n';
std::cout << "task complete\n";
t.join();
}Output:
starting task waiting for task to finish... 102334155 task complete
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