S.c

// 2019 ARP assignment V2.0
// Andrea Pitto - S3942710
// 10 - 07 - 2020

// This is the process that is used to communicate with the others. It is the only one that interfaces with the terminal.
// It can receive and handle 3 different commands: start, pause, log.
// In order to use it, you have to type e.g. "kill -18 22961", where the first number is the signal chosen, whilst the second
// is the PID of the node S itself. This process then communicates with P, spreading user commands through all the children of main

#include "def.h"

// These 3 flags are stored as global variables because you cannot pass any argument of choice to the signal handlers
int start_flag = 0;
int stop_flag = 0;
int log_flag = 0;

// This handler is devoted to resuming token computation, as well as all other tasks in all the nodes
void start_handler(int signum)
{
	start_flag = 1;
}

// This handler is devoted to manage pause the execution of the nodes
void stop_handler(int signum)
{
	stop_flag = 1;
}

// This handler issues the opening of the log file
void log_handler(int signum)
{
	log_flag = 1;
}

int main(int argc, char *argv[])
{
	close(atoi(argv[0]));
	close(atoi(argv[2]));
	close(atoi(argv[3]));
	close(atoi(argv[4]));
	close(atoi(argv[5]));

	pid_t Spid = getpid();
	printf("S: my PID is %d\n", Spid);
	pid_t Parpid = getppid(); // get process ID of parent (i.e. main)

	// Creation of Input Terminal welcome message, including dynamic Spid injection
	char welcome0[1] = "";
	char welcome1[148] = "[This is the Input Terminal, through which you can send signals to the running processes. "
						 "Please also check the Output Terminal to inspect outputs]";
	char welcome2[20] = "Available commands:";
	char command1[30] = "kill -10 ";
	char command2[30] = "kill -12 ";
	char command3[30] = "kill -18 ";
	char Spid_array[20];
	sprintf(Spid_array, "%d", Spid);
	strncat(command1, Spid_array, (sizeof(command1) - strlen(command1)));
	strncat(command2, Spid_array, (sizeof(command2) - strlen(command2)));
	strncat(command3, Spid_array, (sizeof(command3) - strlen(command3)));
	char welcome3[99] = "10 is to open the log file, 12 to pause, 18 to resume. To end, press Ctrl+C in the Output Terminal";
	// Set Input Terminal variables as environmental ones (which can be accessed, by the creator process only, via getenv())
	setenv("welcome0", welcome0, 1);
	setenv("welcome1", welcome1, 1);
	setenv("welcome2", welcome2, 1);
	setenv("welcome3", welcome3, 1);
	setenv("command1", command1, 1);
	setenv("command2", command2, 1);
	setenv("command3", command3, 1);

	// Launch a new terminal (Input Terminal) that allows the user to send signals to the running processes
	// while welcoming the user with useful information
	int exit_status = system("gnome-terminal -- sh -c \"echo $welcome0; echo $welcome1; echo $welcome0; "
							 "echo $welcome2; echo $welcome0; echo $command1; echo $command2; echo $command3; "
							 "echo $welcome0; echo $welcome3; echo $welcome0; exec bash\"");

	signal(SIGCONT, start_handler); // reacts to "kill -18 Spid"
	signal(SIGUSR2, stop_handler);	// reacts to "kill -12 Spid"
	signal(SIGUSR1, log_handler);	// reacts to "kill -10 Spid"

	// Comment on SIGCONT:
	// As other processes never actually stop (only token computation is halted),
	// the SIGCONT signal does not have any effect, but is useful here as
	// a third custom signal which also does not produce undesired side effects

	while (1)
	{
		// If main is dead, end the process
		if (getppid() != Parpid)
		{
			unsetenv("welcome0");
			unsetenv("welcome1");
			unsetenv("welcome2");
			unsetenv("welcome3");
			unsetenv("command1");
			unsetenv("command2");
			unsetenv("command3");
			close(atoi(argv[1]));
			return 0;
		}

		if (start_flag)
		{
			write(atoi(argv[1]), &(int){1}, sizeof(int)); // state = 0: P and G communication stopped
			start_flag = 0;
			printf("\n\n\t\t\tReceived start command by user\n\n");
		}
		if (stop_flag)
		{
			write(atoi(argv[1]), &(int){0}, sizeof(int)); // state = 1: P and G communication resumed/in progress
			stop_flag = 0;
			printf("\n\n\t\t\tReceived stop command by user\n\n");
		}
		if (log_flag)
		{
			write(atoi(argv[1]), &(int){3}, sizeof(int)); // state = 3: send open log file request (and pause computations)
			log_flag = 0;
			printf("\n\n\t\tReceived open log command by user (computation paused)\n\n");
		}
	}
}