fix: circular dependency in qlist

fixes #4294 Signed-off-by: Roman Gershman <[email protected]>
dragonflydb · Dec 12, 2024 · a4d1bff · a4d1bff
1 parent b37287b
commit a4d1bff
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Showing 2 changed files with 14 additions and 1 deletion.
diff --git a/src/core/qlist.cc b/src/core/qlist.cc
@@ -371,6 +371,7 @@ string QList::Pop(Where where) {
 
   /* The head and tail should never be compressed */
   DCHECK(node->encoding != QUICKLIST_NODE_ENCODING_LZF);
+  DCHECK(head_->prev->next == nullptr);
 
   string res;
   if (ABSL_PREDICT_FALSE(QL_NODE_IS_PLAIN(node))) {
@@ -390,6 +391,7 @@ string QList::Pop(Where where) {
     }
     DelPackedIndex(node, pos);
   }
+  DCHECK(head_->prev->next == nullptr);
   return res;
 }
 
@@ -479,11 +481,13 @@ bool QList::PushSentinel(string_view value, Where where) {
     if (len_ == 1) {  // sanity check
       DCHECK_EQ(malloc_size_, orig->sz);
     }
+    DCHECK(head_->prev->next == nullptr);
     return false;
   }
 
   quicklistNode* node = CreateFromSV(QUICKLIST_NODE_CONTAINER_PACKED, value);
   InsertNode(orig, node, opt);
+  DCHECK(head_->prev->next == nullptr);
   return true;
 }
 
@@ -837,7 +841,7 @@ quicklistNode* QList::ListpackMerge(quicklistNode* a, quicklistNode* b) {
 void QList::DelNode(quicklistNode* node) {
   if (node->next)
     node->next->prev = node->prev;
-  if (node->prev)
+  if (node != head_)  // For head, node->prev is tail, and its next should point to NULL.
     node->prev->next = node->next;
 
   if (node == head_) {

diff --git a/src/core/qlist_test.cc b/src/core/qlist_test.cc
@@ -282,6 +282,15 @@ TEST_F(QListTest, CompressionPlain) {
   EXPECT_EQ(500, i);
 }
 
+TEST_F(QListTest, LargeValues) {
+  string val(100000, 'a');
+  ql_.Push(val, QList::HEAD);
+  ql_.Push(val, QList::HEAD);
+  ql_.Pop(QList::HEAD);
+  auto items = ToItems();
+  EXPECT_THAT(items, ElementsAre(val));
+}
+
 using FillCompress = tuple<int, unsigned>;
 
 class PrintToFillCompress {