syntax - C++11 thread调用对象的成员函数

Question

如果掉一个类的成员函数，大概是这样。

clientThread = std::thread(&Client::sendMessage,“message”);

但如果希望这个类的特定对象，执行这个操作，怎么处理？

Answer 1

std::thread 调用类的成员函数需要传递类的一个对象作为参数：

#include <thread>
#include <iostream>

class bar {
public:
  void foo() {
    std::cout << "hello from member function" << std::endl;
  }
};

int main()
{
  std::thread t(&bar::foo, bar());
  t.join();
}

如果是在类的成员函数中处理thread，传入 this 即可，如：

std::thread spawn() {
    return std::thread(&blub::test, this);
  }

参考：stackoverflow

Answer 2

参考C plus plus

Parameters
fn
A pointer to function, pointer to member, or any kind of move-constructible function object (i.e., an object whose class
defines operator(), including closures and function objects). The
return value (if any) is ignored.
args...
Arguments passed to the call to fn (if any). Their types shall be move-constructible. If fn is a member pointer, the first argument shall be an object for which that member is defined or a reference, or a pointer to it).
x
thread object whose state is moved to the constructed object.

// constructing threads
#include <iostream>       // std::cout
#include <atomic>         // std::atomic
#include <thread>         // std::thread
#include <vector>         // std::vector

std::atomic<int> global_counter (0);

void increase_global (int n) { for (int i=0; i<n; ++i) ++global_counter; }

void increase_reference (std::atomic<int>& variable, int n) { for (int i=0; i<n; ++i) ++variable; }

struct C : std::atomic<int> {
  C() : std::atomic<int>(0) {}
  void increase_member (int n) { for (int i=0; i<n; ++i) fetch_add(1); }
};

int main ()
{
  std::vector<std::thread> threads;

  std::cout << "increase global counter with 10 threads...\n";
  for (int i=1; i<=10; ++i)
    threads.push_back(std::thread(increase_global,1000));

  std::cout << "increase counter (foo) with 10 threads using reference...\n";
  std::atomic<int> foo(0);
  for (int i=1; i<=10; ++i)
    threads.push_back(std::thread(increase_reference,std::ref(foo),1000));

  std::cout << "increase counter (bar) with 10 threads using member...\n";
  C bar;
  for (int i=1; i<=10; ++i)
    threads.push_back(std::thread(&C::increase_member,std::ref(bar),1000));

  std::cout << "synchronizing all threads...\n";
  for (auto& th : threads) th.join();

  std::cout << "global_counter: " << global_counter << '\n';
  std::cout << "foo: " << foo << '\n';
  std::cout << "bar: " << bar << '\n';

  return 0;
}

类似这样 std::thread(&C::increase_member,std::ref(bar),1000)