c++ multithread help.

[KaiserBreath]

Hi all,
given the following code:

********************************
using ThreadVector = std::vector<std::thread>;
ThreadVector tv;

class MyThread
{
public:

struct MyData
{
MyData() bj(nullptr), done(true){}
Movement* obj;
bool done;
int gg = 10;
};


MyThread()
{
auto th = std::thread(&MyThread::Update, this, std::ref(myData));
tv.push_back(std::move(th));
}

void Update(MyData data)
{
while (1)
{
// Here still uses old values....
std::this_thread::sleep_for(std::chrono::seconds(2));
std::cout << myData.gg << std::endl;
}
}

bool Replace(Movement* theobj, int newNum)
{
if (myData.done)
{
myData.gg = newNum;
myData.obj = theobj;
myData.done = false;
return true;
}
return false;
}


MyData myData;
};
********************************************
There is a problem where std::ref is not working. When I call the Replace function from the main thread, running the Update function still uses the old default values. Any ideas?

Thanks.

 

[davidktw]

using ThreadVector = std::vector<std::thread>;
ThreadVector tv;

class MyThread
{
public:

	struct MyData
	{
		MyData() :obj(nullptr), done(true){}
		Movement* obj;
		bool done;
		int gg = 10;
	};


	MyThread()
	{
		auto th = std::thread(&MyThread::Update, this, std::ref(myData));
		tv.push_back(std::move(th));
	}

	void Update([COLOR="Yellow"][B]MyData data[/B][/COLOR]) //should it be [COLOR="Lime"][B]MyData &data[/B][/COLOR]
	{
		while (1)
		{
// Here still uses old values....
			std::this_thread::sleep_for(std::chrono::seconds(2));
			std::cout << myData.gg << std::endl;
		}
	}

	bool Replace(Movement* theobj, int newNum)
	{
		if (myData.done)
		{
			myData.gg = newNum;
			myData.obj = theobj;
			myData.done = false;
			return true;
		}
		return false;
	}

	
	MyData myData;
};

Do everyone a favour, next time, wrap your codes within the CODE tags.

Look at the codes in YELLOW

Run the following codes and you will understand better what went wrong

#include <iostream>

using namespace std;

class Complex {
public:
  int i;

  Complex() :i(123) {}
};

void func(Complex c) {
}

int main() {

  Complex c;

  cout << "Variable 'c' at memory location: " << &c;
  cout << ", Value of i = " << c.i << endl;

  Complex d  = ref(c);
  Complex &e = ref(c);

  cout << "Variable 'd' at memory location: " << &d;
  cout << ", Value of i = " << d.i << endl;
  cout << "Variable 'e' at memory location: " << &e;
  cout << ", Value of i = " << e.i << endl;

  d.i = 321;
  cout << "After variable 'd', member 'i' value is changed" << endl;
  e.i = 456;
  cout << "After variable 'e', member 'i' value is changed" << endl;

  cout << "Variable 'c' at memory location: " << &c;
  cout << ", Value of i = " << c.i << endl;
  cout << "Variable 'd' at memory location: " << &d;
  cout << ", Value of i = " << d.i << endl;
  cout << "Variable 'e' at memory location: " << &e;
  cout << ", Value of i = " << e.i << endl;

}

There is an implicit COPY operation that happened.

 

[invisible.hippo]

using ThreadVector = std::vector<std::thread>;
ThreadVector tv;

class MyThread
{
public:

	struct MyData
	{
		MyData() :obj(nullptr), done(true){}
		Movement* obj;
		bool done;
		int gg = 10;
	};


	MyThread()
	{
		auto th = std::thread(&MyThread::Update, this, std::ref(myData));
		tv.push_back(std::move(th));
	}

	void Update([COLOR="Yellow"][B]MyData data[/B][/COLOR]) //should it be [COLOR="Lime"][B]MyData &data[/B][/COLOR]
	{
		while (1)
		{
// Here still uses old values....
			std::this_thread::sleep_for(std::chrono::seconds(2));
			std::cout << myData.gg << std::endl;
		}
	}

	bool Replace(Movement* theobj, int newNum)
	{
		if (myData.done)
		{
			myData.gg = newNum;
			myData.obj = theobj;
			myData.done = false;
			return true;
		}
		return false;
	}

	
	MyData myData;
};

Do everyone a favour, next time, wrap your codes within the CODE tags.

Look at the codes in YELLOW

Run the following codes and you will understand better what went wrong

#include <iostream>

using namespace std;

class Complex {
public:
  int i;

  Complex() :i(123) {}
};

void func(Complex c) {
}

int main() {

  Complex c;

  cout << "Variable 'c' at memory location: " << &c;
  cout << ", Value of i = " << c.i << endl;

  Complex d  = ref(c);
  Complex &e = ref(c);

  cout << "Variable 'd' at memory location: " << &d;
  cout << ", Value of i = " << d.i << endl;
  cout << "Variable 'e' at memory location: " << &e;
  cout << ", Value of i = " << e.i << endl;

  d.i = 321;
  cout << "After variable 'd', member 'i' value is changed" << endl;
  e.i = 456;
  cout << "After variable 'e', member 'i' value is changed" << endl;

  cout << "Variable 'c' at memory location: " << &c;
  cout << ", Value of i = " << c.i << endl;
  cout << "Variable 'd' at memory location: " << &d;
  cout << ", Value of i = " << d.i << endl;
  cout << "Variable 'e' at memory location: " << &e;
  cout << ", Value of i = " << e.i << endl;

}

There is an implicit COPY operation that happened.

MyData() : obj(nullptr)
Is this inheritance?

 

[davidktw]

MyData() : obj(nullptr)
Is this inheritance?

Nope, this is C++ initializer list.
Please feel free to read up at http://en.cppreference.com/w/cpp/language/initializer_list