Delay initialization of free list in SkTLList until first use of list

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2138043002

Review-Url: https://codereview.chromium.org/2138043002

1 files changed, 32 insertions, 15 deletions

diff --git a/src/core/SkTLList.h b/src/core/SkTLList.h
index 48e81bdac1..58fa3f4aac 100644
--- a/src/core/SkTLList.h
+++ b/src/core/SkTLList.h
@@ -38,14 +38,10 @@ private:
 public:
     class Iter;
 
-    SkTLList() : fCount(0) {
-        fFirstBlock.fNodesInUse = 0;
-        for (unsigned int i = 0; i < N; ++i) {
-            fFreeList.addToHead(fFirstBlock.fNodes + i);
-            fFirstBlock.fNodes[i].fBlock = &fFirstBlock;
-        }
-        this->validate();
-    }
+    // Having fCount initialized to -1 indicates that the first time we attempt to grab a free node
+    // all the nodes in the pre-allocated first block need to be inserted into the free list. This
+    // allows us to skip that loop in instances when the list is never populated.
+    SkTLList() : fCount(-1) {}
 
     ~SkTLList() {
         this->validate();
@@ -148,18 +144,19 @@ public:
             this->remove(iter.get());
             iter = next;
         }
-        SkASSERT(0 == fCount);
+        SkASSERT(0 == fCount || -1 == fCount);
         this->validate();
     }
 
-    int count() const { return fCount; }
-    bool isEmpty() const { this->validate(); return 0 == fCount; }
+    int count() const { return SkTMax(fCount ,0); }
+    bool isEmpty() const { this->validate(); return 0 == fCount || -1 == fCount; }
 
     bool operator== (const SkTLList& list) const {
         if (this == &list) {
             return true;
         }
-        if (fCount != list.fCount) {
+        // Call count() rather than use fCount because an empty list may have fCount = 0 or -1.
+        if (this->count() != list.count()) {
             return false;
         }
         for (Iter a(*this, Iter::kHead_IterStart), b(list, Iter::kHead_IterStart);
@@ -223,7 +220,21 @@ private:
         Node fNodes[N];
     };
 
+    void delayedInit() {
+        SkASSERT(-1 == fCount);
+        fFirstBlock.fNodesInUse = 0;
+        for (unsigned int i = 0; i < N; ++i) {
+            fFreeList.addToHead(fFirstBlock.fNodes + i);
+            fFirstBlock.fNodes[i].fBlock = &fFirstBlock;
+        }
+        fCount = 0;
+        this->validate();
+    }
+
     Node* createNode() {
+        if (-1 == fCount) {
+            this->delayedInit();
+        }
         Node* node = fFreeList.head();
         if (node) {
             fFreeList.remove(node);
@@ -270,11 +281,17 @@ private:
 
     void validate() const {
 #ifdef SK_DEBUG
-        SkASSERT((0 == fCount) == fList.isEmpty());
-        if (0 == fCount) {
+        bool isEmpty = false;
+        if (-1 == fCount) {
+            // We should not yet have initialized the free list.
+            SkASSERT(fFreeList.isEmpty());
+            isEmpty = true;
+        } else if (0 == fCount) {
             // Should only have the nodes from the first block in the free list.
             SkASSERT(fFreeList.countEntries() == N);
+            isEmpty = true;
         }
+        SkASSERT(isEmpty == fList.isEmpty());
         fList.validate();
         fFreeList.validate();
         typename NodeList::Iter iter;
@@ -318,7 +335,7 @@ private:
             SkASSERT(activeCnt == block->fNodesInUse);
             activeNode = iter.next();
         }
-        SkASSERT(count == fCount);
+        SkASSERT(count == fCount || (0 == count && -1 == fCount));
 #endif
     }