C++ 如何在成员函数上使用 std::async？
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How to use std::async on a member function?
提问by Avihai Marchiano
How can I operate std::async call on a member function?
如何在成员函数上操作 std::async 调用？
Example:
例子：
class Person{
public:
void sum(int i){
cout << i << endl;
}
};
int main(int argc, char **argv) {
Person person;
async(&Person::sum,&person,4);
}
I want to call to sum async.
我想调用 sum async。
Person p;
call async to p.sum(xxx)
I didnt figure out if i can do it with std::async. Dont want to use boost. Looking for a one line async call way.
我不知道我是否可以用 std::async 做到这一点。不想使用升压。寻找一种单线异步调用方式。
回答by juanchopanza
Something like this:
像这样的东西：
auto f = std::async(&Person::sum, &p, xxx);
or
或者
auto f = std::async(std::launch::async, &Person::sum, &p, xxx);
where pis a Personinstance and xxxis an int.
其中p是一个Person实例，xxx是int。
This simple demo works with GCC 4.6.3:
这个简单的演示适用于 GCC 4.6.3：
#include <future>
#include <iostream>
struct Foo
{
Foo() : data(0) {}
void sum(int i) { data +=i;}
int data;
};
int main()
{
Foo foo;
auto f = std::async(&Foo::sum, &foo, 42);
f.get();
std::cout << foo.data << "\n";
}
回答by Johan Lundberg
There are several ways, but I find it's most clear to use a lambda, like this:
有几种方法，但我发现使用 lambda 最清楚，如下所示：
int i=42;
Person p;
auto theasync=std::async([&p,i]{ return p.sum(i);});
This creates a std::future. For a complete example of this, I have a full example including a async-capable setup of mingw here:
这将创建一个std::future. 对于一个完整的例子，我有一个完整的例子，包括一个支持异步的 mingw 设置：
http://scrupulousabstractions.tumblr.com/post/36441490955/eclipse-mingw-builds
http://scrupulousabstractions.tumblr.com/post/36441490955/eclipse-mingw-builds
You need to make sure that p is thread safe and that the &p reference is valid until the async is joined. (You can also hold p with a shared pointer, or in c++14, a unique_ptr or even move p into the lambda.)
您需要确保 p 是线程安全的，并且 &p 引用在加入异步之前一直有效。（您也可以使用共享指针保存 p，或者在 c++14 中，使用 unique_ptr 甚至将 p 移动到 lambda 中。）
