Add ability to spawn adder threads

main.c

@@ -1,8 +1,11 @@
 #include <errno.h>
+#include <pthread.h>
+#include <signal.h>
 #include <stdbool.h>
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
+#include "adder.h"
 #include "mailbox.h"
 #include "main.h"
 
@@ -71,6 +74,31 @@ static int get_input(int num_threads, struct input **res) {
 	return input_index;
 }
 
+/**
+ * Start the adder threads
+ *
+ * @param thread_ids An array of all of the thread ids to spawn, in order.
+ * @param num_threads The number of threads to spawn
+ * @param threads A pre-allocated array to hold the spawned threads.
+ *
+ * @return int -1 on error, 0 otherwise.
+ */
+static int start_adder_threads(int *thread_ids, int num_threads, pthread_t *threads) {
+	for (int i = 0; i < num_threads; i++) {
+		int create_result = pthread_create(&threads[i], NULL, adder, &thread_ids[i]);
+		if (create_result != 0) {
+			// Clean up all of the threads that have started if we have an error.
+			for (int j = 0; j < i; j++) {
+				pthread_kill(threads[i], SIGKILL);
+			}
+
+			return -1;
+		}
+	}
+
+	return 0;
+}
+
 int main(int argc, char *argv[]) {
 	struct input *inputs = NULL;
 	if (argc < 2 || argc > 3) {
@@ -100,5 +128,20 @@ int main(int argc, char *argv[]) {
 		return 1;
 	}
 
+	// Must allocate an array of the ids to prevent a race condition when adder starts
+	// We don't want the thread id to be deallocated.
+	// We don't want to allocate an id for thread id 0, so we store all of the others.
+	int mailbox_ids[num_threads];
+	for (int i = 0; i < num_threads; i++) {
+		mailbox_ids[i] = i + 1;
+	}
+	pthread_t threads[num_threads];
+	int start_result = start_adder_threads(mailbox_ids, num_threads, threads);
+	if (start_result != 0) {
+		printf("Failed to start adder threads. (%s)\n", strerror(errno));
+		free_mailboxes();
+		return 1;
+	}
+
 	free_mailboxes();
 }