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 <stdio.h> // printf() #include <stdlib.h> // atoi(), exit(), ... #include <string.h> // strtok(), strcmp(), ... #include <pthread.h> // 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, " \n"); while(token != NULL){ line_sum += atoi(token); token = strtok(NULL, " \n"); } // 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\n"); 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\n", sum); fclose(file); pthread_mutex_destroy(&sum_mutex); // destroys the mutex variable pthread_exit(NULL); // destroys main thread }

The value that needs to be synchronized with the sum_mutex variable is the global sum variable. This…

Answered: 1) What value needs to be synchronized…

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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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 <stdio.h> // printf()
	#include <stdlib.h> // atoi(), exit(), ...
	#include <string.h> // strtok(), strcmp(), ...
	#include <pthread.h> // 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, " \n");
	while(token != NULL){
	line_sum += atoi(token);
	token = strtok(NULL, " \n");
	}
	// 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\n");
	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\n", sum);
	fclose(file);
	pthread_mutex_destroy(&sum_mutex); // destroys the mutex variable
	pthread_exit(NULL); // destroys main thread
	}

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