1 files changed, 210 insertions, 0 deletions
diff --git a/mfbt/RefCounted.h b/mfbt/RefCounted.h
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index 000000000..ae05f1e0f
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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/. */
+
+/* CRTP refcounting templates.  Do not use unless you are an Expert. */
+
+#ifndef mozilla_RefCounted_h
+#define mozilla_RefCounted_h
+
+#include "mozilla/AlreadyAddRefed.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Atomics.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/Move.h"
+#include "mozilla/RefCountType.h"
+#include "mozilla/TypeTraits.h"
+
+#if defined(MOZILLA_INTERNAL_API)
+#include "nsXPCOM.h"
+#endif
+
+#if defined(MOZILLA_INTERNAL_API) && \
+    (defined(DEBUG) || defined(FORCE_BUILD_REFCNT_LOGGING))
+#define MOZ_REFCOUNTED_LEAK_CHECKING
+#endif
+
+namespace mozilla {
+
+/**
+ * RefCounted<T> is a sort of a "mixin" for a class T.  RefCounted
+ * manages, well, refcounting for T, and because RefCounted is
+ * parameterized on T, RefCounted<T> can call T's destructor directly.
+ * This means T doesn't need to have a virtual dtor and so doesn't
+ * need a vtable.
+ *
+ * RefCounted<T> is created with refcount == 0.  Newly-allocated
+ * RefCounted<T> must immediately be assigned to a RefPtr to make the
+ * refcount > 0.  It's an error to allocate and free a bare
+ * RefCounted<T>, i.e. outside of the RefPtr machinery.  Attempts to
+ * do so will abort DEBUG builds.
+ *
+ * Live RefCounted<T> have refcount > 0.  The lifetime (refcounts) of
+ * live RefCounted<T> are controlled by RefPtr<T> and
+ * RefPtr<super/subclass of T>.  Upon a transition from refcounted==1
+ * to 0, the RefCounted<T> "dies" and is destroyed.  The "destroyed"
+ * state is represented in DEBUG builds by refcount==0xffffdead.  This
+ * state distinguishes use-before-ref (refcount==0) from
+ * use-after-destroy (refcount==0xffffdead).
+ *
+ * Note that when deriving from RefCounted or AtomicRefCounted, you
+ * should add MOZ_DECLARE_REFCOUNTED_TYPENAME(ClassName) to the public
+ * section of your class, where ClassName is the name of your class.
+ */
+namespace detail {
+const MozRefCountType DEAD = 0xffffdead;
+
+// When building code that gets compiled into Gecko, try to use the
+// trace-refcount leak logging facilities.
+#ifdef MOZ_REFCOUNTED_LEAK_CHECKING
+class RefCountLogger
+{
+public:
+  static void logAddRef(const void* aPointer, MozRefCountType aRefCount,
+                        const char* aTypeName, uint32_t aInstanceSize)
+  {
+    MOZ_ASSERT(aRefCount != DEAD);
+    NS_LogAddRef(const_cast<void*>(aPointer), aRefCount, aTypeName,
+                 aInstanceSize);
+  }
+
+  static void logRelease(const void* aPointer, MozRefCountType aRefCount,
+                         const char* aTypeName)
+  {
+    MOZ_ASSERT(aRefCount != DEAD);
+    NS_LogRelease(const_cast<void*>(aPointer), aRefCount, aTypeName);
+  }
+};
+#endif
+
+// This is used WeakPtr.h as well as this file.
+enum RefCountAtomicity
+{
+  AtomicRefCount,
+  NonAtomicRefCount
+};
+
+template<typename T, RefCountAtomicity Atomicity>
+class RefCounted
+{
+protected:
+  RefCounted() : mRefCnt(0) {}
+  ~RefCounted() { MOZ_ASSERT(mRefCnt == detail::DEAD); }
+
+public:
+  // Compatibility with nsRefPtr.
+  void AddRef() const
+  {
+    // Note: this method must be thread safe for AtomicRefCounted.
+    MOZ_ASSERT(int32_t(mRefCnt) >= 0);
+#ifndef MOZ_REFCOUNTED_LEAK_CHECKING
+    ++mRefCnt;
+#else
+    const char* type = static_cast<const T*>(this)->typeName();
+    uint32_t size = static_cast<const T*>(this)->typeSize();
+    const void* ptr = static_cast<const T*>(this);
+    MozRefCountType cnt = ++mRefCnt;
+    detail::RefCountLogger::logAddRef(ptr, cnt, type, size);
+#endif
+  }
+
+  void Release() const
+  {
+    // Note: this method must be thread safe for AtomicRefCounted.
+    MOZ_ASSERT(int32_t(mRefCnt) > 0);
+#ifndef MOZ_REFCOUNTED_LEAK_CHECKING
+    MozRefCountType cnt = --mRefCnt;
+#else
+    const char* type = static_cast<const T*>(this)->typeName();
+    const void* ptr = static_cast<const T*>(this);
+    MozRefCountType cnt = --mRefCnt;
+    // Note: it's not safe to touch |this| after decrementing the refcount,
+    // except for below.
+    detail::RefCountLogger::logRelease(ptr, cnt, type);
+#endif
+    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
+      mRefCnt = detail::DEAD;
+#endif
+      delete static_cast<const T*>(this);
+    }
+  }
+
+  // Compatibility with wtf::RefPtr.
+  void ref() { AddRef(); }
+  void deref() { Release(); }
+  MozRefCountType refCount() const { return mRefCnt; }
+  bool hasOneRef() const
+  {
+    MOZ_ASSERT(mRefCnt > 0);
+    return mRefCnt == 1;
+  }
+
+private:
+  mutable typename Conditional<Atomicity == AtomicRefCount,
+                               Atomic<MozRefCountType>,
+                               MozRefCountType>::Type mRefCnt;
+};
+
+#ifdef MOZ_REFCOUNTED_LEAK_CHECKING
+// Passing override for the optional argument marks the typeName and
+// typeSize functions defined by this macro as overrides.
+#define MOZ_DECLARE_REFCOUNTED_VIRTUAL_TYPENAME(T, ...) \
+  virtual const char* typeName() const __VA_ARGS__ { return #T; } \
+  virtual size_t typeSize() const __VA_ARGS__ { return sizeof(*this); }
+#else
+#define MOZ_DECLARE_REFCOUNTED_VIRTUAL_TYPENAME(T, ...)
+#endif
+
+// Note that this macro is expanded unconditionally because it declares only
+// two small inline functions which will hopefully get eliminated by the linker
+// in non-leak-checking builds.
+#define MOZ_DECLARE_REFCOUNTED_TYPENAME(T) \
+  const char* typeName() const { return #T; } \
+  size_t typeSize() const { return sizeof(*this); }
+
+} // namespace detail
+
+template<typename T>
+class RefCounted : public detail::RefCounted<T, detail::NonAtomicRefCount>
+{
+public:
+  ~RefCounted()
+  {
+    static_assert(IsBaseOf<RefCounted, T>::value,
+                  "T must derive from RefCounted<T>");
+  }
+};
+
+namespace external {
+
+/**
+ * AtomicRefCounted<T> is like RefCounted<T>, with an atomically updated
+ * reference counter.
+ *
+ * NOTE: Please do not use this class, use NS_INLINE_DECL_THREADSAFE_REFCOUNTING
+ * instead.
+ */
+template<typename T>
+class AtomicRefCounted :
+  public mozilla::detail::RefCounted<T, mozilla::detail::AtomicRefCount>
+{
+public:
+  ~AtomicRefCounted()
+  {
+    static_assert(IsBaseOf<AtomicRefCounted, T>::value,
+                  "T must derive from AtomicRefCounted<T>");
+  }
+};
+
+} // namespace external
+
+} // namespace mozilla
+
+#endif // mozilla_RefCounted_h