From 2a472af7b842edb6647a832bdf2581d304fa5364 Mon Sep 17 00:00:00 2001
From: ridiculousfish <corydoras@ridiculousfish.com>
Date: Mon, 30 Jan 2017 12:59:01 -0800
Subject: [PATCH] Add sanity checking to LRU cache

---
 src/fish_tests.cpp |  2 ++
 src/lru.h          | 39 ++++++++++++++++++++++++++++++++++++++-
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/src/fish_tests.cpp b/src/fish_tests.cpp
index 8a0040fc0..f06a2997a 100644
--- a/src/fish_tests.cpp
+++ b/src/fish_tests.cpp
@@ -1170,9 +1170,11 @@ static void test_lru(void) {
         while (expected_values.size() > test_lru_t::test_capacity) {
             expected_values.erase(expected_values.begin());
         }
+        cache.check_sanity();
     }
     do_test(cache.evicted == expected_evicted);
     do_test(cache.values() == expected_values);
+    cache.check_sanity();
 
     // Stable-sort ints in reverse order
     // This a/2 check ensures that some different ints compare the same
diff --git a/src/lru.h b/src/lru.h
index 83b770f50..4dcc1f314 100644
--- a/src/lru.h
+++ b/src/lru.h
@@ -242,7 +242,9 @@ class lru_cache_t {
     }
 
     // Number of entries
-    size_t size() { return this->node_map.size(); }
+    size_t size() const {
+        return this->node_map.size();
+    }
 
     // Sorting support
     // Given a binary function F implementing less-than on the contents, place the nodes in sorted order
@@ -296,6 +298,41 @@ class lru_cache_t {
 
     iterator begin() const { return iterator(mouth.prev); };
     iterator end() const { return iterator(&mouth); };
+
+    void check_sanity() const {
+        // Check linked list sanity
+        size_t expected_count = this->size();
+        const lru_link_t *prev = &mouth;
+        const lru_link_t *cursor = mouth.next;
+
+        size_t max = 1024 * 1024 * 64;
+        size_t count = 0;
+        while (cursor != &mouth) {
+            if (cursor->prev != prev) {
+                assert(0 && "Node busted previous link");
+            }
+            prev = cursor;
+            cursor = cursor->next;
+            if (count++ > max) {
+                assert(0 && "LRU cache unable to re-reach the mouth - not circularly linked?");
+            }
+        }
+        if (mouth.prev != prev) {
+            assert(0 && "mouth.prev does not connect to last node");
+        }
+        if (count != expected_count) {
+            assert(0 && "Linked list count mismatch from map count");
+        }
+
+        // Count iterators
+        size_t iter_dist = 0;
+        for (const auto &p : *this) {
+            iter_dist++;
+        }
+        if (iter_dist != count) {
+            assert(0 && "Linked list iterator mismatch from map count");
+        }
+    }
 };
 
 #endif