Multitask-Process in C++ with Windows Form and Winsock

I have to write a program which includes communication using TCP/IP and which is controlable through a Windows form. Therefore i have written a multithread-program using "pthread.h". The one thread is for windows-form, the other for the winsock-stuff.

    int main(int argc, char* argv[])
{
    pthread_t t1, t2; // declare 2 threads.
    pthread_create(&t1, NULL, RunTCPIP, NULL); // create a thread running TCP-Communication
    pthread_create(&t2, NULL, RunForms, NULL); // create a thread running Windows Forms
    pthread_exit(NULL);
    return 0;
}

void * RunForms(void * argument)
{
//  //run GUI
    Application::EnableVisualStyles();
    Application::SetCompatibleTextRenderingDefault(false);
    Server_C_GUI::Mainform form;
    Application::Run(%form);
    return 0;
}

void * RunTCPIP(void * argument)
{
    //Winsock-stuff....
    return 0;
}

There are some variables which i have to use in both threads. And that´s my problem. I have created "globals.h" where i have defined my global variables.

#include <string>
using namespace std;

#ifndef EXTERN
#define EXTERN extern
#endif

//Variables for OperatingMode & GUI
EXTERN const string szServerResponse;
EXTERN char cPlay;
EXTERN char cBreak;
EXTERN char cQuit;

I have included "globals.h" in the main.cpp - There it works. But when i try to include "globals.h" in "MyForm.h" - the header of my CLR-windows-form - several failures arise.

In "MyForm.h" i'd like for example to write the following code:

private: System::Void btnQuit_Click(System::Object^  sender, System::EventArgs^  e)
    {
        cQuit = 0; //cQuit = global variable
    } 

How can i use global variables in a multithread program with winsock and clr windows forms? What am i doing wrong?