Add basic (untested) adder thread implementation

adder.c

@@ -0,0 +1,61 @@
+#include <stdbool.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <time.h>
+#include "adder.h"
+#include "mailbox.h"
+
+/**
+ * Read all of the values from the given mailbox id and then send it back to mailbox 0.
+ *
+ * @param raw_mailbox_id A ponter to an integer holding the mailbox id this thread should read from.
+ * @return void* Returns a pointer to a return code. -1 on error, 0 otherwise. Must be freed by caller.
+ */
+void *adder(void *raw_mailbox_id) {
+	int mailbox_id = *(int*)(raw_mailbox_id);
+	int *ret_val = malloc(sizeof(int));
+	// If we're thread 0, we shouldn't be running adder.
+	// Any thread id below 0 is invalid.
+	if (mailbox_id <= 0) {
+		*ret_val = -1;
+		return ret_val;
+	}
+
+	int num_messages = 0;
+	int total_value = 0;
+	int start_time = time(NULL);
+	struct msg message;
+	while (true) {
+		int recv_result = RecvMsg(mailbox_id, &message);
+		if (recv_result != 0) {
+			*ret_val = -1;
+			return ret_val;
+		}
+
+		// If we have a negative value, we're done receiving messages.
+		if (message.value < 0) {
+			break;
+		}
+
+		num_messages++;
+		total_value += message.value;
+		sleep(1);
+	}
+
+	int end_time = time(NULL);
+	struct msg res_mesage = {
+		.iFrom = mailbox_id,
+		.value = total_value,
+		.cnt = num_messages,
+		.tot = end_time - start_time,
+	};
+
+	int send_result = SendMsg(0, &res_mesage);
+	if (send_result <= 0) {
+		*ret_val = -1;
+		return ret_val;
+	}
+
+	*ret_val = 0;
+	return ret_val;
+}

adder.h

@@ -0,0 +1,7 @@
+#ifndef ADDER_H
+#define ADDER_H
+
+// silly name, but it's required...
+void *adder(void *raw_mailbox_id);
+
+#endif