在类中使用std :: mutex作为成员变量 [英] Using std::mutex as member variable in a class
问题描述
我定义了一个以std::mutex my_mutex
作为其私有成员变量的类.但是,当我尝试在不同线程调用的成员函数中使用lock_guard
来使用它时,编译器会抛出很多错误.如果我将此互斥锁保留在课堂之外,那么它将起作用.代码如下
I have defined a class that has std::mutex my_mutex
as its private member variable. But when I try to use it using lock_guard
in a member function which is called from different threads, the compiler throws up a lots of errors. If I keep this mutex outside the class it works. The code is as follows
class ThreadClass
{
std::mutex my_mutex;
public:
void addToList(int max, int interval)
{
std::lock_guard<std::mutex> guard(my_mutex);
for (int i = 0; i < max; i++)
{
// Some operation
}
}
};
int main()
{
std::thread ct(&ThreadClass::addToList,ThreadClass(),100,1);
std::thread ct2(&ThreadClass::addToList,ThreadClass(),100,10);
std::thread ct3(&ThreadClass::print,ThreadClass());
ct.join();
ct2.join();
ct3.join();
}
如果将同一个my_mutex
保留在类之外,则可以正常工作.因此,当同一个变量在类中并在线程作用于成员函数中调用时,它是否像静态成员一样对待?
If the same my_mutex
is kept out of the class then it works fine. So when the same variable is within the class and called within the member function acted on by a thread, does it treat like a static member?
推荐答案
std::thread
构造函数复制传递给执行函数的参数.但是std::mutex
是不可复制的,因此ThreadClass
如果具有这样的成员,则是不可复制的.
The std::thread
constructor copies the arguments that are passed to the executed function. But std::mutex
is non-copyable and so ThreadClass
is non-copyable if it has such a member.
您要将一个临时ThreadClass
对象传递给std::thread
,但是您可能想在所有线程中使用同一对象.您可以使用std::ref
传递现有对象的引用.以下代码可在GCC 7.1.0上编译:
You are passing a temporary ThreadClass
object to std::thread
, but you probably want to use the same object in all your threads. You can use std::ref
to pass a reference of an existing object. The following code compiles on GCC 7.1.0:
#include <thread>
#include <mutex>
class ThreadClass
{
std::mutex my_mutex;
public:
void addToList(int max, int interval)
{
std::lock_guard<std::mutex> guard(my_mutex);
// ...
}
void print()
{
// ...
}
};
int main()
{
ThreadClass obj;
std::thread ct(&ThreadClass::addToList, std::ref(obj), 100, 1);
std::thread ct2(&ThreadClass::addToList, std::ref(obj), 100, 10);
std::thread ct3(&ThreadClass::print, std::ref(obj));
ct.join();
ct2.join();
ct3.join();
}
将指针传递给对象而不是引用也应该起作用:
Passing a pointer to the object instead of a reference should also work:
std::thread ct(&ThreadClass::addToList, &obj, 100, 1);
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