Fast implementation of QuadTree

src/core/SkTObjectPool.h

+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkFreeList_DEFINED
+#define SkFreeList_DEFINED
+
+#include "SkTInternalSList.h"
+
+/**
+ * An implementation of a self growing pool of objects.
+ * It maintains a pool of fully initialized objects. If an attempt is made to
+ * acquire one, and there are none left, it makes some more.
+ * It does not automatically reclaim them, they have to be given back to it.
+ * Constructors will be called on objects allocated by the pool at allocation
+ * time.
+ * All allocated objects will be destroyed and memory will be reclaimed when
+ * the pool is destroyed, so the pool must survive longer than you are using
+ * any item taken from it.
+ */
+template<typename T, int numItemsPerBlock = 4096/sizeof(T)> class SkTObjectPool {
+public:
+    SkTObjectPool() {}
+    ~SkTObjectPool() {
+        while (!fBlocks.isEmpty()) {
+            SkDELETE(fBlocks.pop());
+        }
+    }
+
+    /**
+     * Get an item from the pool.
+     * If the pool has no free items, it will allocate and construct some more.
+     * The returned item is only valid as long as the pool has not been
+     * destroyed, at that point all memory allocated by grow will have been
+     * reclaimed.
+     * This method is *not* thread safe.
+     */
+    T* acquire() {
+        if (fAvailable.isEmpty()) {
+            grow();
+        }
+        return fAvailable.pop();
+    }
+
+    /**
+     * Release an item into the pool.
+     * The item does not have to have come from the pool, but if it did not
+     * it must have a lifetime greater than the pool does.
+     * This method is *not* thread safe.
+     */
+    void release(T* entry) {
+        fAvailable.push(entry);
+    }
+
+    /**
+     * Takes all the items from an SkTInternalSList and adds them back to this
+     * pool. The other list will be left empty.
+     */
+    void releaseAll(SkTInternalSList<T>* other) {
+        fAvailable.pushAll(other);
+    }
+
+    /**
+     * Returns the number of items immediately available without having to
+     * construct any new ones.
+     */
+    int available() const { return fAvailable.getCount(); }
+
+    /**
+     * Returns the number of blocks of items the pool has allocated so far.
+     */
+    int blocks() const { return fBlocks.getCount(); }
+
+private:
+    /**
+     * The type for a new block of entries for the list.
+     */
+    struct Block {
+        T entries[numItemsPerBlock];
+        SK_DECLARE_INTERNAL_SLIST_INTERFACE(Block);
+    };
+    SkTInternalSList<Block> fBlocks;
+    SkTInternalSList<T> fAvailable;
+
+    /**
+     * When the free list runs out of items, this method is called to allocate
+     * a new block of them.
+     * It calls the constructors and then pushes the nodes into the available
+     * list.
+     */
+    void grow() {
+        Block* block = SkNEW(Block);
+        fBlocks.push(block);
+        for(int index = 0; index < numItemsPerBlock; ++index) {
+            fAvailable.push(&block->entries[index]);
+        }
+    }
+
+};
+
+#endif