Add basic SendMsg routine

mailbox.c

@@ -1,7 +1,10 @@
 #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
@@ -13,9 +16,12 @@ struct mailbox *mailboxes = NULL;
 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) {
@@ -45,4 +51,31 @@ void free_mailboxes() {
 	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;
 }

mailbox.h

@@ -28,5 +28,7 @@ struct mailbox {
 
 int init_mailboxes(int n);
 void free_mailboxes();
+// God I hate the caps, but this is the required definition.
+int SendMsg(int dest, struct msg *message);
 
 #endif