diff --git a/lab5/demos/pthread_count_2_mutex.c b/lab5/demos/pthread_count_2_mutex.c
new file mode 100644
index 0000000..4423722
--- /dev/null
+++ b/lab5/demos/pthread_count_2_mutex.c
@@ -0,0 +1,68 @@
+/*
+ * This program ends up in a threadrace when the argument is around 1M
+ *
+ * We need synchronization primitives to help here!
+ */
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+struct args {
+    int max;
+    char letter;
+    pthread_mutex_t* mutex;
+};
+
+volatile int counter = 0;
+
+void* count_thread(void* arg) {
+    struct args* a = arg;
+
+    for (int i = 0; i < a->max; i++) {
+        pthread_mutex_lock(a->mutex);
+        counter = counter + 1;
+        pthread_mutex_unlock(a->mutex);
+    }
+
+    // // But given this process is pretty fast... this is better
+    // pthread_mutex_lock(a->mutex);
+    // for (int i = 0; i < a->max; i++) {
+    //     counter = counter + 1;
+    // }
+    // pthread_mutex_unlock(a->mutex);
+
+    printf("Thread %c: done with counter at %d\n", a->letter, counter);
+    return NULL;
+}
+
+void* make_args(int max, char letter, pthread_mutex_t* mutex) {
+    struct args* a = malloc(sizeof(struct args));
+    a->max = max;
+    a->letter = letter;
+    a->mutex = mutex;
+
+    return (void*) a;
+}
+
+int main(int argc, char* argv[]) {
+    if (argc != 2) {
+        exit(1);
+    }
+
+    int max = atoi(argv[1]);
+
+    pthread_mutex_t* mutex = malloc(sizeof(pthread_mutex_t));
+    pthread_mutex_init(mutex, NULL);
+
+    pthread_t p1, p2;
+    pthread_create(&p1, NULL, count_thread, make_args(max, 'A', mutex));
+    pthread_create(&p2, NULL, count_thread, make_args(max, 'B', mutex));
+
+    pthread_join(p1, NULL);
+    pthread_join(p2, NULL);
+
+    pthread_mutex_destroy(mutex);
+
+    printf("main: done\n [counter: %d]\n [should: %d]\n", counter, max * 2);
+    return 0;
+}