cs-3013-assignment-3/mailbox.c

#include "mailbox.h"
#include <semaphore.h>
#include <stdlib.h>
#include <string.h>

struct mailbox *mailboxes = NULL;
static int num_mailboxes = -1;

/**
 * Setup the mailboxes global variable
 *
 * @param n The number of mailboxes to initialize.
 *
 * @return int 1 if the mailboxes are already allocated, -1 on error, 0 otherwise.
 */
int init_mailboxes(int n) {
	if (mailboxes != NULL) {
		return 1;
	} else if (n <= 0) {
		return -1;
	}

	mailboxes = calloc(n, sizeof(struct mailbox));
	num_mailboxes = n;
	for (int i = 0; i < n; i++) {
		int sem_result = sem_init(&mailboxes[i].send_sem, 0, 1);
		if (sem_result != 0) {
			free(mailboxes);
			return -1;
		}

		sem_result = sem_init(&mailboxes[i].recv_sem, 0, 0);
		if (sem_result != 0) {
			free(mailboxes);
			sem_destroy(&mailboxes[i].send_sem);
			return -1;
		}
	}

	return 0;
}

/**
 * Free the mailboxes global variable.
 */
void free_mailboxes() {
	if (mailboxes == NULL) {
		return;
	}
	for (int i = 0; i < num_mailboxes; i++) {
		sem_destroy(&mailboxes[i].send_sem);
		sem_destroy(&mailboxes[i].recv_sem);
	}

	free(mailboxes);
	// Mark mailboxes as null so freeing is idempotent.
	mailboxes = NULL;
	num_mailboxes = -1;
}

/**
 * Send a message to the given mailbox. Blocks if the mailbox is full.
 *
 * @param dest The index of the mailbox to send to.
 * @param message The message to send to the mailbox. Will be copied into the mailbox.
 *
 * @reutrn int -1 on error, 0 otherwise.
 */
int SendMsg(int dest, struct msg *message) {
	if (dest >= num_mailboxes || dest < 0) {
		return -1;
	}

	struct mailbox *dest_mailbox = &mailboxes[dest];
	int wait_result = sem_wait(&dest_mailbox->send_sem);
	if (wait_result != 0) {
		return -1;
	}

	memcpy(&dest_mailbox->stored_message, message, sizeof(struct msg));
	// Signal that someone can recieve a message, now that it's stored.
	sem_post(&dest_mailbox->recv_sem);

	return 0;
}

/**
 * Send a message to the given mailbox. Returns immediately if the mailbox is full.
 *
 * @param dest The index of the mailbox to send to.
 * @param message The message to send to the mailbox. Will be copied into the mailbox.
 *
 * @reutrn int -1 on error, 0 otherwise. If the mailbox is full, errno will equal EAGAIN
 */
int NBSendMsg(int dest, struct msg *message) {
	if (dest >= num_mailboxes || dest < 0) {
		return -1;
	}

	struct mailbox *dest_mailbox = &mailboxes[dest];
	int wait_result = sem_trywait(&dest_mailbox->send_sem);
	if (wait_result != 0) {
		return -1;
	}

	memcpy(&dest_mailbox->stored_message, message, sizeof(struct msg));
	// Signal that someone can recieve a message, now that it's stored.
	sem_post(&dest_mailbox->recv_sem);

	return 0;
}

/**
 * Receive a message from the given mailbox.
 *
 * @param mailbox_index The index of the mailbox to receive from.
 * @param message A pointer to an already allocated message struct to store the recieved message in.
 * @return int -1 on error, 0 otherwise.
 */
int RecvMsg(int mailbox_index, struct msg *message) {
	if (mailbox_index >= num_mailboxes || mailbox_index < 0) {
		return -1;
	}

	struct mailbox *src_mailbox = &mailboxes[mailbox_index];
	int wait_result = sem_wait(&src_mailbox->recv_sem);
	if (wait_result != 0) {
		return -1;
	}

	memcpy(message, &src_mailbox->stored_message, sizeof(struct msg));
	// Signal that someone can send a message to this mailbox now that we've taken the message out.
	sem_post(&src_mailbox->send_sem);

	return 0;
}