Need help with the following questions:

1) What value needs to be synchronized with the sum_mutex variable? Why?

2) If you remove the pthread_mutex_lock and pthread_mutex_unlock statement from the program, does it still produce a correct output? Why or why not?

Program:

#include // printf()
	#include // atoi(), exit(), ...
	#include // strtok(), strcmp(), ...
	#include // pthread types and functions
	#define MAX_LINE_LENGTH 100
	#define NUM_THREADS 4
	int sum = 0;
	pthread_mutex_t sum_mutex; // Mutex variables help keep the threads synchronized
	void *add_line_numbers(void *arg) {
	char *line = (char *) arg;
	int line_sum = 0;
	// TODO Break down the line and add every number
	char *token = strtok(line, " ");
	while(token != NULL){
	line_sum += atoi(token);
	token = strtok(NULL, " ");
	}
	// What does pthread_mutex_lock/unlock do?
	// It ensures the section between this lock/unlock statements can only be executed by 1 process,
	// if another needs access it must wait until the first runs the unlock statement
	pthread_mutex_lock(&sum_mutex);
	// TODO Add the result of the line to the global sum
	int x = sum;
	x += line_sum;
	sum = x;
	pthread_mutex_unlock(&sum_mutex);
	pthread_exit(NULL);
	}
	int main() {
	FILE *file;
	char line[MAX_LINE_LENGTH];
	pthread_t threads[NUM_THREADS];
	pthread_mutex_init(&sum_mutex, NULL);
	file = fopen("numbers.txt", "r");
	if (file == NULL) {
	printf("Error: cannot open file ");
	exit(EXIT_FAILURE);
	}
	int line_count = 0;
	while (fgets(line, MAX_LINE_LENGTH, file) != NULL) {
	// TODO Create your threads with the given line (remember sharing address locations is not good with threads)
	char *thread_line = (char*)malloc(MAX_LINE_LENGTH);
	strncpy(thread_line,line,MAX_LINE_LENGTH);
	pthread_create(&threads[line_count],NULL,add_line_numbers,(void*)thread_line);
	line_count++;
	}
	int i;
	for (i = 0; i < NUM_THREADS; i++) {
	// TODO Wait until all threads finish reading the lines
	pthread_join(threads[i],0);
	}
	printf("Sum of all numbers in the file is %d ", sum);
	fclose(file);
	pthread_mutex_destroy(&sum_mutex); // destroys the mutex variable
	pthread_exit(NULL); // destroys main thread
	}