Struggling to communicate between processes with signals - c

Question

I'm trying to create a game in C under linux terminal.
I need to create a tetris game that consists of two c files,
One C file create execute file (a.out) and the other create (draw.out).
The first program create a child process and execute the other.
I need to send signals to the other program, but I found it difficult.
The source code is:
the first file-
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdbool.h>
#include <termios.h>
#include <signal.h>
char getch();
int main()
{
int fd[2],pid;
char *args[] = { "./draw.out", NULL },tav;
pipe(fd);
pid=fork();
if(pid==0)
{
execve("draw.out", args, NULL);
}
else
{
while(true)
kill(0,SIGUSR2);
}
return 1;
//getchar();
}
char getch() {
char buf = 0;
struct termios old = {0};
if (tcgetattr(0, &old) < 0)
perror("tcsetattr()");
old.c_lflag &= ~ICANON;
old.c_lflag &= ~ECHO;
old.c_cc[VMIN] = 1;
old.c_cc[VTIME] = 0;
if (tcsetattr(0, TCSANOW, &old) < 0)
perror("tcsetattr ICANON");
if (read(0, &buf, 1) < 0)
perror ("read()");
old.c_lflag |= ICANON;
old.c_lflag |= ECHO;
if (tcsetattr(0, TCSADRAIN, &old) < 0)
perror ("tcsetattr ~ICANON");
return (buf);
}
the second file-
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdbool.h>
#include <signal.h>
typedef struct
{
int x;
int y;
}Point;
typedef struct
{
Point dots[3];
}Tool;
void drawBoard(int array[][20]);
void initBoard(int array[][20]);
Tool retrieveTool();
bool changeLocation(int array[][20],Tool* tool);
void my_handler(int signum);
int main()
{
bool nextTool=true;
Tool temp=retrieveTool();
int gameBoard[20][20];
signal(SIGUSR2, my_handler);
initBoard(gameBoard);
changeLocation(gameBoard,&temp);
drawBoard(gameBoard);
while(true)
{
signal(SIGUSR2, my_handler);
sleep(1);
system("clear");
if(!changeLocation(gameBoard,&temp))
temp=retrieveTool();
drawBoard(gameBoard);
}
return 1;
//getchar();
}
void initBoard(int array[][20])
{
bool isLast=false;
int i=0,j=0;
for(i=0;i<20;i++)
{
if(i==19)
isLast=true;
for(j=0;j<20;j++)
{
if((j==0)||(j==19)||(isLast))
array[i][j]=1;
else
array[i][j]=0;
}
}
}
void drawBoard(int symbols[][20])
{
int i=0,j=0;
for(i=0;i<20;i++)
{
for(j=0;j<20;j++)
if(symbols[i][j]==1)
printf("*");
else
if(symbols[i][j]==2)
printf("-");
else
printf(" ");
printf("\n");
}
}
Tool retrieveTool()
{
Tool temp;
int startX=0,startY=8,i=0;
for(i=0;i<3;i++)
{
temp.dots[i].x=startX;
temp.dots[i].y=startY;
startY++;
}
return temp;
}
bool changeLocation(int array[][20],Tool* tool)
{
int i=0;
for(i=0;i<3;i++)
{
if(array[tool->dots[i].x+1][tool->dots[i].y]!=0)
return false;
}
i=0;
for(i=0;i<3;i++)
{
array[tool->dots[i].x][tool->dots[i].y]=0;
if((tool->dots[i].x+1)==19)
tool->dots[i].x=-1;
tool->dots[i].x++;
array[tool->dots[i].x][tool->dots[i].y]=2;
}
return true;
}
void my_handler(int signum)
{
if (signum == SIGUSR2)
{
printf("Received SIGUSR1!\n");
}
}
The draw.out is the output file of the second file.
i created the signal handeler in the second file,
But the program still don't recieve the signal, what am i doing wrong?

Answer 1

This fragment:
while(true) kill(0,SIGUSR2);
has no sense. The kill should be used with the process id of the reveiver of SIGUSR2 (the child process in this case, identified by pid). Also note that an infinite loop sending signals to the child process is not what you want.
In the child process, you have an error in the print statement at signal handler:
printf("Received SIGUSR1!\n");
should be
printf("Received SIGUSR2!\n");
Depending on the OS version, you have to reinstall the signal handler once it gets called
Note: you are synchronizing processes, not threads