From c5735552a2b0f14708b934577b190209c9a6e5b5 Mon Sep 17 00:00:00 2001
From: Nick Krichevsky <nick@ollien.com>
Date: Sun, 22 Sep 2019 15:05:12 -0400
Subject: [PATCH] Add basic RecvMsg routine

---
 mailbox.c | 25 +++++++++++++++++++++++++
 mailbox.h |  1 +
 2 files changed, 26 insertions(+)

diff --git a/mailbox.c b/mailbox.c
index ed8b544..39b7de2 100644
--- a/mailbox.c
+++ b/mailbox.c
@@ -77,5 +77,30 @@ int SendMsg(int dest, struct msg *message) {
 	// 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;
 }
\ No newline at end of file
diff --git a/mailbox.h b/mailbox.h
index b30a543..44caa4b 100644
--- a/mailbox.h
+++ b/mailbox.h
@@ -30,5 +30,6 @@ 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);
+int RecvMsg(int mailbox_index, struct msg *message);
 
 #endif
\ No newline at end of file