c ++线程问题

Question

我正在尝试使用以下代码在c ++中创建一个线程:

pthread_t mythread;
void* f (void*) = MyClass::myfunction;
pthread_create(&mythread, NULL, &f, NULL);

它不起作用.知道什么是错的吗？

myfunction的类型:

void* MyClass::myfunction(void* argv);

返回的错误是:

error: declaration of ‘void* Class::f(void*)’ has ‘extern’ and is initialized

error: invalid pure specifier (only ‘= 0’ is allowed) before ‘::’ token

error: function ‘void* Class::f(void*)’ is initialized like a variable

Answer 1

您将声明f为函数而不是函数指针.它应该是:

void* (*f) (void*) = &MyClass::myfunction;
      ^^^^

pthread_create(&mythread, NULL, f, NULL);
                                ^ no & since it's already a pointer

这也只有在myfunction静态时才有效,因为你不能将指向成员函数的指针转换为指向函数的指针.

如果你确实需要线程来对特定对象执行非静态成员函数,那么一种方法是编写一个静态包装器,将对象作为参数:

class MyClass {
public:
    void start_thread() {
        // Pass "this" to the thread we're creating
        pthread_create(&mythread, NULL, &MyClass::thread_entry, this);
    }
private:
    static void * thread_entry(void * object) {
        // Call the member function on the object passed to the thread
        return static_cast<MyClass*>(object)->thread();
    }
    void * thread() {
        // do the interesting stuff, with access to the member variables
    }
};

当然,这些天有一个标准的线程库,不需要这种舞蹈:

std::thread thread(&MyClass::thread, this);