Bug 1570395: Add StaticLocalAutoPtr and StaticLocalRefPtr to XPCOM; r=froydnj

This patch adds smart pointers to be used for initializing objects as C++11
"magic statics" -- that is, they are able to take advantage of C++11's
guarantee of thread safety during initialization by atomically constructing
both the smart pointer itself as well as the object being pointed to.

Unlike Static{Auto,Ref}Ptr, they have non-trivial constructors, though they
must still have trivial destructors to prevent emission of atexit calls.

The new classes use the new `MOZ_STATIC_LOCAL_CLASS` annotation which ensures
their instantiations are static locals and prevents non-trivial destructors.

Differential Revision: https://phabricator.services.mozilla.com/D40092

--HG--
rename : xpcom/base/StaticPtr.h => xpcom/base/StaticLocalPtr.h
extra : moz-landing-system : lando

mfbt/RefPtr.h

@@ -24,6 +24,8 @@ namespace mozilla {
 template <class T>
 class OwningNonNull;
 template <class T>
+class StaticLocalRefPtr;
+template <class T>
 class StaticRefPtr;
 #if defined(XP_WIN)
 namespace mscom {
@@ -146,6 +148,10 @@ class MOZ_IS_REFPTR RefPtr {
   template <class U>
   MOZ_IMPLICIT RefPtr(const mozilla::OwningNonNull<U>& aOther);
 
+  // Defined in StaticLocalPtr.h
+  template <class U>
+  MOZ_IMPLICIT RefPtr(const mozilla::StaticLocalRefPtr<U>& aOther);
+
   // Defined in StaticPtr.h
   template <class U>
   MOZ_IMPLICIT RefPtr(const mozilla::StaticRefPtr<U>& aOther);
@@ -210,6 +216,10 @@ class MOZ_IS_REFPTR RefPtr {
   template <class U>
   RefPtr<T>& operator=(const mozilla::OwningNonNull<U>& aOther);
 
+  // Defined in StaticLocalPtr.h
+  template <class U>
+  RefPtr<T>& operator=(const mozilla::StaticLocalRefPtr<U>& aOther);
+
   // Defined in StaticPtr.h
   template <class U>
   RefPtr<T>& operator=(const mozilla::StaticRefPtr<U>& aOther);

xpcom/base/StaticLocalPtr.h

@@ -0,0 +1,242 @@
+/* -*- 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 https://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_StaticLocalPtr_h
+#define mozilla_StaticLocalPtr_h
+
+#include "mozilla/AlreadyAddRefed.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/RefPtr.h"
+
+namespace mozilla {
+
+/**
+ * StaticLocalAutoPtr and StaticLocalRefPtr are like nsAutoPtr and nsRefPtr,
+ * except they are suitable for use as "magic static" local variables -- that
+ * is, they are able to take advantage of C++11's guarantee of thread safety
+ * during initialization by atomically constructing both the smart pointer
+ * itself as well as the object being pointed to.
+ *
+ * A static local instance of StaticLocal{Auto,Ref}Ptr does not cause the
+ * compiler to emit any atexit calls. In order to accomplish this,
+ * StaticLocal{Auto,Ref}Ptr must have a trivial destructor. As a consequence,
+ * it does not delete/release its raw pointer upon destruction.
+ *
+ * The clang plugin, run as part of our "static analysis" builds, makes it a
+ * compile-time error to use StaticLocal{Auto,Ref}Ptr as anything except a
+ * static local variable.
+ *
+ * StaticLocal{Auto,Ref}Ptr have a limited interface as compared to
+ * ns{Auto,Ref}Ptr; this is intentional, since their range of acceptable uses is
+ * smaller.
+ */
+
+template <typename T>
+class MOZ_STATIC_LOCAL_CLASS StaticLocalAutoPtr final {
+ public:
+  explicit StaticLocalAutoPtr(T* aRawPtr) : mRawPtr(aRawPtr) {}
+
+  StaticLocalAutoPtr(StaticLocalAutoPtr<T>&& aOther) : mRawPtr(aOther.mRawPtr) {
+    aOther.mRawPtr = nullptr;
+  }
+
+  T* get() const { return mRawPtr; }
+
+  operator T*() const { return get(); }
+
+  T* operator->() const {
+    MOZ_ASSERT(mRawPtr);
+    return get();
+  }
+
+  T& operator*() const { return *get(); }
+
+  T* forget() {
+    T* temp = mRawPtr;
+    mRawPtr = nullptr;
+    return temp;
+  }
+
+ private:
+  StaticLocalAutoPtr(const StaticLocalAutoPtr<T>& aOther) = delete;
+
+  // We do not allow assignment as the intention of this class is to only
+  // assign to mRawPtr during construction.
+  StaticLocalAutoPtr& operator=(const StaticLocalAutoPtr<T>& aOther) = delete;
+  StaticLocalAutoPtr& operator=(StaticLocalAutoPtr<T>&&) = delete;
+
+  void Assign(T* aNewPtr) {
+    MOZ_ASSERT(!aNewPtr || mRawPtr != aNewPtr);
+    T* oldPtr = mRawPtr;
+    mRawPtr = aNewPtr;
+    delete oldPtr;
+  }
+
+  T* mRawPtr;
+};
+
+template <typename T>
+class MOZ_STATIC_LOCAL_CLASS StaticLocalRefPtr final {
+ public:
+  explicit StaticLocalRefPtr(T* aRawPtr) : mRawPtr(nullptr) {
+    AssignWithAddref(aRawPtr);
+  }
+
+  explicit StaticLocalRefPtr(already_AddRefed<T>& aPtr) : mRawPtr(nullptr) {
+    AssignAssumingAddRef(aPtr.take());
+  }
+
+  explicit StaticLocalRefPtr(already_AddRefed<T>&& aPtr) : mRawPtr(nullptr) {
+    AssignAssumingAddRef(aPtr.take());
+  }
+
+  StaticLocalRefPtr(const StaticLocalRefPtr<T>& aPtr)
+      : StaticLocalRefPtr(aPtr.mRawPtr) {}
+
+  StaticLocalRefPtr(StaticLocalRefPtr<T>&& aPtr) : mRawPtr(aPtr.mRawPtr) {
+    aPtr.mRawPtr = nullptr;
+  }
+
+  already_AddRefed<T> forget() {
+    T* temp = mRawPtr;
+    mRawPtr = nullptr;
+    return already_AddRefed<T>(temp);
+  }
+
+  T* get() const { return mRawPtr; }
+
+  operator T*() const { return get(); }
+
+  T* operator->() const {
+    MOZ_ASSERT(mRawPtr);
+    return get();
+  }
+
+  T& operator*() const { return *get(); }
+
+ private:
+  // We do not allow assignment as the intention of this class is to only
+  // assign to mRawPtr during construction.
+  StaticLocalRefPtr<T>& operator=(const StaticLocalRefPtr<T>& aRhs) = delete;
+  StaticLocalRefPtr<T>& operator=(StaticLocalRefPtr<T>&& aRhs) = delete;
+
+  void AssignWithAddref(T* aNewPtr) {
+    if (aNewPtr) {
+      aNewPtr->AddRef();
+    }
+    AssignAssumingAddRef(aNewPtr);
+  }
+
+  void AssignAssumingAddRef(T* aNewPtr) {
+    T* oldPtr = mRawPtr;
+    mRawPtr = aNewPtr;
+    if (oldPtr) {
+      oldPtr->Release();
+    }
+  }
+
+  T* MOZ_OWNING_REF mRawPtr;
+};
+
+namespace StaticLocalPtr_internal {
+class Zero;
+}  // namespace StaticLocalPtr_internal
+
+#define REFLEXIVE_EQUALITY_OPERATORS(type1, type2, eq_fn, ...) \
+  template <__VA_ARGS__>                                       \
+  inline bool operator==(type1 lhs, type2 rhs) {               \
+    return eq_fn;                                              \
+  }                                                            \
+                                                               \
+  template <__VA_ARGS__>                                       \
+  inline bool operator==(type2 lhs, type1 rhs) {               \
+    return rhs == lhs;                                         \
+  }                                                            \
+                                                               \
+  template <__VA_ARGS__>                                       \
+  inline bool operator!=(type1 lhs, type2 rhs) {               \
+    return !(lhs == rhs);                                      \
+  }                                                            \
+                                                               \
+  template <__VA_ARGS__>                                       \
+  inline bool operator!=(type2 lhs, type1 rhs) {               \
+    return !(lhs == rhs);                                      \
+  }
+
+// StaticLocalAutoPtr (in)equality operators
+
+template <class T, class U>
+inline bool operator==(const StaticLocalAutoPtr<T>& aLhs,
+                       const StaticLocalAutoPtr<U>& aRhs) {
+  return aLhs.get() == aRhs.get();
+}
+
+template <class T, class U>
+inline bool operator!=(const StaticLocalAutoPtr<T>& aLhs,
+                       const StaticLocalAutoPtr<U>& aRhs) {
+  return !(aLhs == aRhs);
+}
+
+REFLEXIVE_EQUALITY_OPERATORS(const StaticLocalAutoPtr<T>&, const U*,
+                             lhs.get() == rhs, class T, class U)
+
+REFLEXIVE_EQUALITY_OPERATORS(const StaticLocalAutoPtr<T>&, U*, lhs.get() == rhs,
+                             class T, class U)
+
+// Let us compare StaticLocalAutoPtr to 0.
+REFLEXIVE_EQUALITY_OPERATORS(const StaticLocalAutoPtr<T>&,
+                             StaticLocalPtr_internal::Zero*,
+                             lhs.get() == nullptr, class T)
+
+// StaticLocalRefPtr (in)equality operators
+
+template <class T, class U>
+inline bool operator==(const StaticLocalRefPtr<T>& aLhs,
+                       const StaticLocalRefPtr<U>& aRhs) {
+  return aLhs.get() == aRhs.get();
+}
+
+template <class T, class U>
+inline bool operator!=(const StaticLocalRefPtr<T>& aLhs,
+                       const StaticLocalRefPtr<U>& aRhs) {
+  return !(aLhs == aRhs);
+}
+
+REFLEXIVE_EQUALITY_OPERATORS(const StaticLocalRefPtr<T>&, const U*,
+                             lhs.get() == rhs, class T, class U)
+
+REFLEXIVE_EQUALITY_OPERATORS(const StaticLocalRefPtr<T>&, U*, lhs.get() == rhs,
+                             class T, class U)
+
+// Let us compare StaticLocalRefPtr to 0.
+REFLEXIVE_EQUALITY_OPERATORS(const StaticLocalRefPtr<T>&,
+                             StaticLocalPtr_internal::Zero*,
+                             lhs.get() == nullptr, class T)
+
+#undef REFLEXIVE_EQUALITY_OPERATORS
+
+}  // namespace mozilla
+
+// Declared in mozilla/RefPtr.h
+template <class T>
+template <class U>
+RefPtr<T>::RefPtr(const mozilla::StaticLocalRefPtr<U>& aOther)
+    : RefPtr(aOther.get()) {}
+
+template <class T>
+template <class U>
+RefPtr<T>& RefPtr<T>::operator=(const mozilla::StaticLocalRefPtr<U>& aOther) {
+  return operator=(aOther.get());
+}
+
+template <class T>
+inline already_AddRefed<T> do_AddRef(
+    const mozilla::StaticLocalRefPtr<T>& aObj) {
+  RefPtr<T> ref(aObj);
+  return ref.forget();
+
+#endif  // mozilla_StaticLocalPtr_h

xpcom/base/moz.build

@@ -126,6 +126,7 @@ EXPORTS.mozilla += [
     'NSPRLogModulesParser.h',
     'OwningNonNull.h',
     'SizeOfState.h',
+    'StaticLocalPtr.h',
     'StaticMonitor.h',
     'StaticMutex.h',
     'StaticPtr.h',