std::packaged_task
Defined in header <future> | ? | ? |
|---|---|---|
template< class > class packaged_task; //not defined | (1) | (since C++11) |
template< class R, class ...Args > class packaged_task<R(Args...)>; | (2) | (since C++11) |
类模板std::packaged_task包任何Callable目标%28函数、lambda表达式、绑定表达式或其他函数对象%29，以便可以异步调用它。其返回值或抛出的异常以共享状态存储，可通过std::future物品。
就像std::function，，，std::packaged_task是一个多态的、分配器感知的容器：存储的可调用目标可以在堆上分配，也可以用提供的分配器分配。
成员函数
(constructor) | constructs the task object (public member function) |
|---|---|
(destructor) | destructs the task object (public member function) |
operator= | moves the task object (public member function) |
valid | checks if the task object has a valid function (public member function) |
swap | swaps two task objects (public member function) |
得到结果
弄到[医]返回一个std：：未来与承诺的结果%28公共成员函数%29相关联
执行
操作符%28%29执行函数%28公共成员函数%29
制造[医]准备好了[医]在[医]螺纹[医]Exit执行该函数，确保只在当前线程退出%28公共成员函数%29时才准备好结果。
重置重置状态，放弃以前执行的任何存储结果%28公共成员函数%29
非会员职能
std::swap(std::packaged_task) (C++11) | specializes the std::swap algorithm (function template) |
|---|
帮助者类
std::uses_allocator<std::packaged_task> (C++11)(until C++17) | specializes the std::uses_allocator type trait (class template specialization) |
|---|
例
二次
#include <iostream>
#include <cmath>
#include <thread>
#include <future>
#include <functional>
// unique function to avoid disambiguating the std::pow overload set
int f(int x, int y) { return std::pow(x,y); }
void task_lambda()
{
std::packaged_task<int(int,int)> task([](int a, int b) {
return std::pow(a, b);
});
std::future<int> result = task.get_future();
task(2, 9);
std::cout << "task_lambda:\t" << result.get() << '\n';
}
void task_bind()
{
std::packaged_task<int()> task(std::bind(f, 2, 11));
std::future<int> result = task.get_future();
task();
std::cout << "task_bind:\t" << result.get() << '\n';
}
void task_thread()
{
std::packaged_task<int(int,int)> task(f);
std::future<int> result = task.get_future();
std::thread task_td(std::move(task), 2, 10);
task_td.join();
std::cout << "task_thread:\t" << result.get() << '\n';
}
int main()
{
task_lambda();
task_bind();
task_thread();
}二次
产出：
二次
task_lambda: 512
task_bind: 2048
task_thread: 1024二次
另见
future (C++11) | waits for a value that is set asynchronously (class template) |
|---|
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