1 files changed, 119 insertions, 0 deletions
diff --git a/gfx/2d/GenericRefCounted.h b/gfx/2d/GenericRefCounted.h
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+++ b/gfx/2d/GenericRefCounted.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 <type_traits>
+
+#include "mozilla/RefPtr.h"
+#include "mozilla/RefCounted.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() = default;
+
+ 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(); }
+
+#ifdef MOZ_REFCOUNTED_LEAK_CHECKING
+  virtual const char* typeName() const = 0;
+  virtual size_t typeSize() const = 0;
+#endif
+};
+
+namespace detail {
+
+template <RefCountAtomicity Atomicity>
+class GenericRefCounted : public GenericRefCountedBase {
+ protected:
+  GenericRefCounted() : refCnt(0) {}
+
+  virtual ~GenericRefCounted() { MOZ_ASSERT(refCnt == detail::DEAD); }
+
+ public:
+  virtual void AddRef() override {
+    // Note: this method must be thread safe for GenericAtomicRefCounted.
+    MOZ_ASSERT(int32_t(refCnt) >= 0);
+    MozRefCountType cnt = ++refCnt;
+    detail::RefCountLogger::logAddRef(this, cnt);
+  }
+
+  virtual void Release() override {
+    // Note: this method must be thread safe for GenericAtomicRefCounted.
+    MOZ_ASSERT(int32_t(refCnt) > 0);
+    detail::RefCountLogger::ReleaseLogger logger{this};
+    MozRefCountType cnt = --refCnt;
+    // Note: it's not safe to touch |this| after decrementing the refcount,
+    // except for below.
+    logger.logRelease(cnt);
+    if (0 == cnt) {
+      // Because we have atomically decremented the refcount above, only
+      // one thread can get a 0 count here, so as long as we can assume that
+      // everything else in the system is accessing this object through
+      // RefPtrs, it's safe to access |this| here.
+#ifdef DEBUG
+      refCnt = detail::DEAD;
+#endif
+      delete this;
+    }
+  }
+
+  MozRefCountType refCount() const { return refCnt; }
+  bool hasOneRef() const {
+    MOZ_ASSERT(refCnt > 0);
+    return refCnt == 1;
+  }
+
+ private:
+  std::conditional_t<Atomicity == AtomicRefCount, Atomic<MozRefCountType>,
+                     MozRefCountType>
+      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