pthread and ncurses - why doesn't this lock work?

Question

I am learning c and ncurses and wrote a simple snake game with halfdelay(1) to semi-automate it. When I added threads it stopped working in that I couldn't get any input from the keyboard.

So I wrote a short program to try threads/ncurses and mutex locking. The code has 2 threads with their own functions (fn and fn2). When I run it with the wmove/wprint in the respective function calls it works (well, it prints to screen!) I tried to implement mutex locking and moved the code to another function called print_to_screen() and nothing happens.

I have added if(thread_id == pthread_self()) to switch between threads but still nothing happens. I have added a couple of commented out lines which show the 2 threads reaching the print_to_screen() function, but the code in the if loops is not running at all.

Please help me, I am at my wits end - I even tried reading usr/inc.ncurses.h and man was that ever unhelpful! Here is the code. If you comment out the wmove/wprint bits in the 2 functions and uncomment the print_to_screen() call you can see the difference. The ncurses setup is from the invisible-island tutorial, if anyone knows why he has put (void) in front of his ncurses calls please let me know. TIA for any help you can give.

#include <stdlib.h>
#include <curses.h>
#include <signal.h>
#include <string.h> 
#include <time.h>
#include <pthread.h>
#include <sys/types.h>
#include <unistd.h>

void *myfunction(void *);
void *myfunction2(void *);

void print_to_screen(void);
static void finish(int);

pthread_t thread1, thread2;
pthread_mutex_t mx = PTHREAD_MUTEX_INITIALIZER;

int thread1_id, thread2_id, count, count2;
int done;   
int ch;

WINDOW *mywin;

int main(void){

    (void) signal(SIGINT, finish);      /* arrange interrupts to terminate */

    (void) initscr();      /* initialize the curses library */
    keypad(stdscr, TRUE);  /* enable keyboard mapping */
    (void) nonl();         /* tell curses not to do NL->CR/NL on output */
    (void) cbreak();       /* take input chars one at a time, no wait for \n */
    (void) echo();         /* echo input - in color */

      if (has_colors())
        {
        start_color();

        /*
         * Simple color assignment, often all we need.  Color pair 0 cannot
         * be redefined.  This example uses the same value for the color
         * pair as for the foreground color, though of course that is not
         * necessary:
         */
        init_pair(1, COLOR_RED,     COLOR_BLACK);
        init_pair(2, COLOR_GREEN,   COLOR_BLACK);
        init_pair(3, COLOR_YELLOW,  COLOR_BLACK);
        init_pair(4, COLOR_BLUE,    COLOR_BLACK);
        init_pair(5, COLOR_CYAN,    COLOR_BLACK);
        init_pair(6, COLOR_MAGENTA, COLOR_BLACK);
        init_pair(7, COLOR_WHITE,   COLOR_BLACK);
    }
    count = count2 = 0;
    done = 0;

    mywin = newwin(LINES, COLS, 0,0);
    keypad(mywin, TRUE);

    pthread_create( &thread1, NULL, myfunction, NULL);
    pthread_create( &thread2, NULL, myfunction2, NULL);

    pthread_join(thread1,  NULL);
    pthread_join(thread2,  NULL);

    finish(0);
    exit(0);
}

void *myfunction(void *ptr){

    thread1_id =  pthread_self();
    halfdelay(-1);

    while(1){
        ch = getch();
        if(ch == 'q') break;

        wmove(mywin, 5,2);
        wprintw(mywin, "Thread 1 at print");
        wmove(mywin, 10,count);
        waddch(mywin, ch);
        wrefresh(mywin);

        //print_to_screen();
        if(count++ >70) count = 0;
        nanosleep((struct timespec[]){{0, 250000000}}, NULL);
    }
    done = 1;
}

void *myfunction2(void *ptr){
    thread2_id =  pthread_self();

    while(1){
        if(done == 1) break;
        if(count++ >24) count = 0;
        wmove(mywin, 6,2);
        wprintw(mywin, "Thread 2 at print");
        wmove(mywin, count, 10);
        wprintw(mywin, "hello from thread 2");
        wrefresh(mywin); 

        //print_to_screen();
        nanosleep((struct timespec[]){{0, 250000000}}, NULL);
    }
}

void print_to_screen(){
    pthread_mutex_lock(&mx);

    //printw("PTHREAD ID = %d : ", pthread_self());
    //printw("thread1_id = %d : thread2_id = %d\n", thread1_id, thread2_id);

    if(pthread_self() == thread1_id){
        wmove(mywin, 5,2);
        wprintw(mywin, "Thread 1 at print");
        wmove(mywin, 10,count);
        waddch(mywin, ch);
        wrefresh(mywin);
    }


    if(pthread_self() == thread2_id){
        wmove(mywin, 6,2);
        wprintw(mywin, "Thread 2 at print");
        wmove(mywin, count, 10);
        wprintw(mywin, "hello from thread 2");
        wrefresh(mywin);
    }

    pthread_mutex_unlock(&mx);
}

static void finish(int sig)
{
    endwin();
    /* do your non-curses wrapup here */
}

Answer 1

As a start:

int thread1_id, thread2_id, count, count2;

should be

int count, count2;
pthread_t thread1_id, thread2_id;

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Also print_to_screen() is never called.