使用make_shared <std :: thread>创建shared_ptr <std :: thread>的实例

Question

Consider the following code:

class A
{
    ....
    shared_ptr<std::thread> mThread;
    void Step();
    void LaunchTrhead();
}

void A::LaunchThread()
{
    ...
    mThread=make_shared<std::thread>(Step); // This line gives an error
    ...
}

void A::Step()
{
    ...
}

I'm trying to initialise the shared pointer mThread so that it calls the function Step . However, the compiler gives me the error " invalid initialization of reference of type ... from expression of type 'unresolved overloaded function type' ". Obviously I'm doing something stupid, but I can't put my finger on it. Can anybody help? Thanks in advance!

Answer 1

Step() is a non-static member function, so it has an implicit first parameter of type A* . You need to bind the current instance of A when invoking it.

mThread = std::make_shared<std::thread>(std::bind(&A::Step, this));

You can also use a lambda instead of bind

mThread = std::make_shared<std::thread>([this]{ Step(); });

As @Casey points out in the comments, std::thread 's constructor has special treatment for pointer to member functions, and will assume the first following argument is a pointer or reference to the instance on which to call the member function. This means you can avoid bind and directly pass this as the second argument.

mThread = std::make_shared<std::thread>(&A::Step, this);

Answer 2

Try (use labda instead of the free function):

mThread=make_shared<std::thread>([this](){ Step(); }); 

The way it is, you're not passing a reference to this to the constructor inspite of it being a member function.

This solution uses a lambda to create a function-object that takes no parameters but has a reference to this.

If you want to use the global function do this instead, and move void Step() to before it's usage:

mThread=make_shared<std::thread>(::Step()); 

the :: removes the ambiguity over the scope of the function.

Answer 3

您应该使用shared_from_this()替换它