Add ability to setup/destroy mailboxes

mailbox.c

@@ -0,0 +1,48 @@
+#include "mailbox.h"
+#include <stdlib.h>
+
+struct mailbox *mailboxes = NULL;
+
+/**
+ * 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;
+	}
+
+	mailboxes = calloc(n, sizeof(struct mailbox));
+	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;
+	}
+
+	free(mailboxes);
+	// Mark mailboxes as null so freeing is idempotent.
+	mailboxes = NULL;
+}

mailbox.h

@@ -3,6 +3,8 @@
 
 #include <semaphore.h>
 
+extern struct mailbox *mailboxes;
+
 struct msg {
 	// index of thread that sent the message
 	// if iFrom is -1, then the message is considered invalid.
@@ -24,4 +26,7 @@ struct mailbox {
 	sem_t recv_sem;
 };
 
+int init_mailboxes(int n);
+void free_mailboxes();
+
 #endif