Bug 882561 - Add a GenericRefCounted base class to moz2d, will allow moz2d to hold strong references to external objects without adding a dependency r=jwalden

gfx/2d/GenericRefCounted.h

@@ -0,0 +1,102 @@
+/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// This header provides virtual, non-templated alternatives to MFBT's RefCounted<T>.
+// It intentionally uses MFBT coding style with the intention of moving there
+// should there be other use cases for it.
+
+#ifndef MOZILLA_GENERICREFCOUNTED_H_
+#define MOZILLA_GENERICREFCOUNTED_H_
+
+#include "mozilla/RefPtr.h"
+
+namespace mozilla {
+
+/**
+ * Common base class for GenericRefCounted and GenericAtomicRefCounted.
+ *
+ * Having this shared base class, common to both the atomic and non-atomic
+ * cases, allows to have RefPtr's that don't care about whether the
+ * objects they're managing have atomic refcounts or not.
+ */
+class GenericRefCountedBase
+{
+  protected:
+    virtual ~GenericRefCountedBase() {};
+
+  public:
+    // AddRef() and Release() method names are for compatibility with nsRefPtr.
+    virtual void AddRef() = 0;
+
+    virtual void Release() = 0;
+
+    // ref() and deref() method names are for compatibility with wtf::RefPtr.
+    // No virtual keywords here: if a subclass wants to override the refcounting
+    // mechanism, it is welcome to do so by overriding AddRef() and Release().
+    void ref() { AddRef(); }
+    void deref() { Release(); }
+};
+
+namespace detail {
+
+template<RefCountAtomicity Atomicity>
+class GenericRefCounted : public GenericRefCountedBase
+{
+  protected:
+    GenericRefCounted() : refCnt(0) { }
+
+    virtual ~GenericRefCounted() {
+      MOZ_ASSERT(refCnt == detail::DEAD);
+    }
+
+  public:
+    virtual void AddRef() {
+      MOZ_ASSERT(refCnt >= 0);
+      ++refCnt;
+    }
+
+    virtual void Release() {
+      MOZ_ASSERT(refCnt > 0);
+      if (0 == --refCnt) {
+#ifdef DEBUG
+        refCnt = detail::DEAD;
+#endif
+        delete this;
+      }
+    }
+
+    int refCount() const { return refCnt; }
+    bool hasOneRef() const {
+      MOZ_ASSERT(refCnt > 0);
+      return refCnt == 1;
+    }
+
+  private:
+    typename Conditional<Atomicity == AtomicRefCount, Atomic<int>, int>::Type refCnt;
+};
+
+} // namespace detail
+
+/**
+ * This reference-counting base class is virtual instead of
+ * being templated, which is useful in cases where one needs
+ * genericity at binary code level, but comes at the cost
+ * of a moderate performance and size overhead, like anything virtual.
+ */
+class GenericRefCounted : public detail::GenericRefCounted<detail::NonAtomicRefCount>
+{
+};
+
+/**
+ * GenericAtomicRefCounted is like GenericRefCounted, with an atomically updated
+ * reference counter.
+ */
+class GenericAtomicRefCounted : public detail::GenericRefCounted<detail::AtomicRefCount>
+{
+};
+
+} // namespace mozilla
+
+#endif

gfx/2d/moz.build

@@ -6,6 +6,10 @@
 
 MODULE = 'gfx2d'
 
+EXPORTS.mozilla += [
+    'GenericRefCounted.h',
+]
+
 EXPORTS.mozilla.gfx += [
     '2D.h',
     'BaseMargin.h',