CODEWITHSUNDEEP
c++multithreadingthread-safety
HuLu
HuLu

Reputation: 164

Do different objects of C++ interfere with each other in the thread?

I am trying to learn C++ native multithreading technology

The compiler I am using is g++ follow the C++ 14

The development tool I use is CodeBlock

I created 10 different objects and used them as the start of the thread

#include <iostream>       // std::cout
#include <thread>         // std::thread
#include <vector>         // std::vector
#include "TestClass.h"

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

  TestClass test[10];
  for (int i=1; i<=10; ++i){
    threads.push_back(std::thread(&TestClass::run,std::ref(test[i-1])));
  }

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

  for(int i=0;i<10;i++){
    std::cout << test[i].Getm_Counter() << std::endl;
  }
  return 0;
}

The thread content is as follows

#ifndef TESTCLASS_H
#define TESTCLASS_H


class TestClass
{
    public:
        TestClass();
        virtual ~TestClass();

        unsigned int Getm_Counter() { return m_Counter; }

        void run();

    protected:

    private:
        unsigned int m_Counter;
};

#endif // TESTCLASS_H

implement as follows

#include "TestClass.h"

TestClass::TestClass()
{
    //ctor
}

TestClass::~TestClass()
{
    //dtor
}

void TestClass::run(){
    for(int i=0;i<10;i++){
        m_Counter++;
    }
}

I expect that the count for each object is 10, but the result is not like this. Why? enter image description here

Upvotes: 0

Views: 122

Answers (1)

Gojita
Gojita

Reputation: 500

You did not initialize m_Counter (to 0 or any other value). So anything can be expected about its value at the end of your run (depending on the garbage value it may take).

Upvotes: 4

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