feedback-arc-set/generator.c

/**
 * @file generator.c
 * @date 2018-05-21
 *
 * @brief Client program which generates solutions and submits them.
 */

#include "common.h"
#include <time.h>

/**
 * @details Global variable for the program name.
 */
static const char *pname;

/**
 * @details Global struct for shared memory.
 */
static struct circ_buf *shared;

/**
 * @details Global file descriptor for shared memory.
 */
static int shmfd;

/**
 * @details Semaphore for tracking the used space in shared memory.
 */
static sem_t *sUsedSpace;

/**
 * @details Semaphore for tracking the free space in shared memory.
 */
static sem_t *sFreeSpace;

/**
 * @details Semaphore for exclusive access to shared memory for generators.
 */
static sem_t *sWriteEnd;

/**
 * @details Struct for signal handler.
 */
static struct sigaction sa;

/**
 * @details struct which stores a node in an adjacency list.
 */
struct AdjListNode {
	int dest;
	struct AdjListNode *next;
};

/**
 * @details Struct which respresents an adjacency list. Stores a pointer to
 *          the first element.
 */
struct AdjList {
	struct AdjListNode *head;
};

/**
 * @details Struct which stores a graph made up of the count of nodes and an
 *          array for the adjacency lists.
 */
struct Graph {
	int V;
	struct AdjList *array;
};

/**
 * @details Global graph which gets populated by parse().
 */
struct Graph graph;

/**
 * @details Variable which gets set on signal received.
 */
static volatile sig_atomic_t quit = 0;

/**
 * @details Signal handler.
 * @param signum The number of the received signal.
 * @return This function has no return value.
 */
static void sig_handler(int signum)
{
	quit = 1;
}

/**
 * @details Prints the synopsis.
 * @param void This function takes no parameters.
 * @return Always non-zero.
 */
static void usage(void)
{
	fprintf(stderr, "SYNOPSIS\n"
			"\tgenerator EDGE1...\n"
			"EXAMPLE\n"
			"\tgenerator 0-1 1-2 1-3 1-4 2-4 3-6 4-3 4-5 6-0\n");
	exit(EXIT_FAILURE);
}

/**
 * @details Function which creates a new adjacency list node.
 * @param dest The value of the node.
 * @return Returns the new node.
 */
static struct AdjListNode *newAdjListNode(int dest)
{
	struct AdjListNode *newNode = malloc(sizeof(struct AdjListNode));
	newNode->dest = dest;
	newNode->next = NULL;
	return newNode;
}

/**
 * @details Function which creates a new graph.
 * @param V The number of nodes in the new graph.
 * @return This function has no return value.
 */
static void createGraph(int V)
{
	graph.V = V;

	graph.array = malloc(V * sizeof(struct AdjList));

	for (int i = 0; i < V; i++)
		graph.array[i].head = NULL;
}

/**
 * @details This function adds a new edge from src to dest.
 * @param src The source node of the edge.
 * @param dest The destination node of the edge.
 * @return This function has no return value.
 */
static void addEdge(int src, int dest)
{
	struct AdjListNode *newNode = newAdjListNode(dest);
	newNode->next = graph.array[src].head;
	graph.array[src].head = newNode;
}

/**
 * @details Function which safely converts a string to an integer.
 * @param str The string to be converted.
 * @return -2 if out of range (long). -1 if out of range (int). Converted value
 *         on success.
 */
static int strToInt(char *str)
{
	char *endptr;
	long val;

	errno = 0;
	val = strtol(str, &endptr, 10);
	if ((errno == ERANGE && (val == LONG_MAX || val == LONG_MIN)) ||
	    (errno != 0)) {
		perror("[./generator] strtol");
		return -2;
	}
	if (val < INT_MIN || val > INT_MAX) {
		fprintf(stderr, "[%s] Please choose a smaller node: ", pname);
		return -1;
	}

	return (int) val;
}

/**
 * @details Function which parses the commandline arguments and populates the graph.
 * @param argc The number of supplied commandline arguments.
 * @param argv The array of supplied commandline arguments.
 * @return This function has no return value.
 */
static void parse(int argc, char *argv[])
{
	char *token;
	int V = 0;
	int src;
	int dest;
	int edges_counter = 0;
	int edges[(argc - 1) * 2];

	for (int i = 1; i < argc; i++) {
		char const *edge = argv[i];
		char *str, *orig_copy;
		str = orig_copy = strdup(edge);
		int count = 0;
		while ((token = strsep(&str, "-"))) {
			if (strcmp(token, edge) == 0 && str == NULL) {
				fprintf(stderr, "[%s] An edge consists of two "
						"nodes separated  by a dash\n", pname);
				free(orig_copy);
				return;
			}
			if (count == 0) {
				src = strToInt(token);
				edges[edges_counter] = src;
				edges_counter++;
				if (src > V)
					V = src;
			}
			if (count == 1) {
				dest = strToInt(token);
				edges[edges_counter] = dest;
				edges_counter++;
				if (dest > V)
					V = dest;
			}
			if (count > 1) {
				fprintf(stderr, "[%s] An edge consists of two "
						"nodes separated by a dash\n", pname);
				free(orig_copy);
				return;
			}
			switch (src) {
			case -2:
				free(orig_copy);
				return;
				break;
			case -1:
				fprintf(stderr, "%s\n", edge);
				free(orig_copy);
				return;
				break;
			default:
				break;
			}

			count++;
		}
		free(orig_copy);
	}

	createGraph(V+1);
	for (int i = 0; i < (sizeof(edges) / sizeof(int)); i+=2) {
		addEdge(edges[i], edges[i+1]);
	}
}

/**
 * @details Cleanup function which frees memory and closes shared memory and
 *          semaphores.
 * @param void This function takes no parameters.
 * @return 0 on success, non-zero on failure.
 */
static void cleanup(void)
{
	sem_post(sWriteEnd);
	sem_post(sFreeSpace);
	for (int v = 0; v < graph.V; v++) {
		struct AdjListNode *pCrawl = graph.array[v].head;
		struct AdjListNode *tmp;
		while (pCrawl) {
			tmp = pCrawl;
			pCrawl = pCrawl->next;
			free(tmp);
		}
	}
	free(graph.array);

	if (munmap(shared, sizeof(*shared)) == -1) {
		perror("munmap");
		exit(EXIT_FAILURE);
	}

	close(shmfd);

	sem_close(sUsedSpace);
	sem_close(sFreeSpace);
	sem_close(sWriteEnd);

	exit(EXIT_SUCCESS);
}

/**
 * @details Custom sem_wait function which listens for signals.
 * @param sem Semaphore to be decremented.
 * @return This function has no return value.
 */
static void wait_sem(sem_t *sem)
{
	while (sem_wait(sem) == -1) { // interrupted by syscall? 
		if (errno == EINTR) {
			if (quit == 1) {
				cleanup();
				exit(EXIT_SUCCESS);
			}
			else continue;
		}
		cleanup();
		exit(EXIT_FAILURE);
	}
	return;
}

/**
 * @details Function which writes a solution to the shared memory buffer.
 * @param solution The solution to be written to shared memory.
 * @return This function has no return value.
 */
static void putSolution(int *solution)
{
	wait_sem(sWriteEnd);

	if (shared->quit == 1) {
		quit = 1;
		cleanup();
	}

	for (int i = 0; i < MAX_ITEMS; i++) {
		wait_sem(sFreeSpace);
		if (shared->quit == 1) {
			quit = 1;
			cleanup();
		}

		shared->data[shared->tail] = solution[i];
		shared->tail = (shared->tail + 1) % MAX_ITEMS;
		sem_post(sUsedSpace);
	}

	sem_post(sWriteEnd);
}

/**
 * @details Function which finds the index of a specific value in an array.
 * @param array The array in which the desired value resides.
 * @param value The value to search for.
 * @param size The size of the array.
 * @return -1 if value not found in array. The index of value if found.
 */
static int findIndex(int array[], int value, int size)
{
	int index = 0;
	while (index < size && array[index] != value)
		index++;

	return (index == size ? -1 : index);
}

/**
 * @details Function which receives a random permutation of the nodes and finds
 *          a random set of edges which - if removed - leave an acyclic graph.
 * @param permutation The random permutation of the nodes.
 * @param V The number of nodes in the graph.
 * @param solution Contains the solution of edges at the end.
 * @return This function has no return value.
 */
static void genSolution(int permutation[], int V, int *solution)
{
	if (shared->quit == 1) {
		quit = 1;
		cleanup();
	}

	int r;

	// initialize array to indices
	for (int i = 0; i < V; i++) {
		permutation[i] = i;
	}

	// loop from end to start, choose random and switch
	// with number at current index.
	for (int i = (V - 1); i > 0; i--) {
		r = rand() % (i+1);
		int tmp = permutation[r];
		permutation[r] = permutation[i];
		permutation[i] = tmp;
	}

	int count = 0;
	for (int i = 0; i < MAX_ITEMS; i++) {
		solution[i] = -1;
	}

	for (int u = 0; u < V; u++) {
		int idx = findIndex(permutation, u, V);
		struct AdjListNode *pCrawl = graph.array[u].head;
		while (pCrawl) {
			int idx_v = findIndex(permutation, pCrawl->dest, V);
			if (idx > idx_v) {
				solution[count++] = u;
				solution[count++] = pCrawl->dest;
				if (count > MAX_ITEMS)
					return;
				break;
			}
			pCrawl = pCrawl->next;
		}
	}
}

/**
 * The main entry point of the program.
 * @details Sets up signal handler, shared memory and semaphores, parses the
 *          commandline arguments and periodically generates a new solution and
 *          submits it to the shared memory.
 * @param argc The number of commandline arguments.
 * @param argv The array of commandline arguments.
 * @return 0 on success, non-zero on failure.
 */
int main(int argc, char *argv[])
{
	if (argc == 1)
		usage();
	pname = argv[0];

	struct sigaction sa;
	memset(&sa, 0, sizeof(sa));
	sa.sa_handler = &sig_handler;
	sigaction(SIGINT, &sa, NULL);
	sigaction(SIGTERM, &sa, NULL);

	shmfd = shm_open(SHM_NAME, O_RDWR, PERMISSION);
	if (shmfd == -1) {
		perror("[./generator] shm_open");
		exit(EXIT_FAILURE);
	}

	shared = mmap(NULL, sizeof(*shared), PROT_READ | PROT_WRITE, MAP_SHARED, shmfd, 0);
	if (shared == MAP_FAILED) {
		perror("[./generator] mmap");
		exit(EXIT_FAILURE);
	}

	sFreeSpace = sem_open(SEM_FREE_SPACE, 0);
	sUsedSpace = sem_open(SEM_USED_SPACE, 0);
	sWriteEnd = sem_open(SEM_WRITE_END, 0);
	if (sFreeSpace == SEM_FAILED ||
	    sUsedSpace == SEM_FAILED ||
	    sWriteEnd == SEM_FAILED) {
		perror("[./generator] sem_open");
		exit(EXIT_FAILURE);
	}

	parse(argc, argv);

	// seed differently for each process
	srand(time(NULL) * getpid());

	int permutation[graph.V];

	while (quit == 0) {
		if (shared->quit == 1)
			break;

		int solution[MAX_ITEMS];
		genSolution(permutation, graph.V, solution);
		putSolution(solution);
	}

	cleanup();

	return 0;
}