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diff --git a/src/google/protobuf/stubs/shared_ptr.h b/src/google/protobuf/stubs/shared_ptr.h
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+// Protocol Buffers - Google's data interchange format
+// Copyright 2014 Google Inc. All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+// * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+// * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// from google3/util/gtl/shared_ptr.h
+
+#ifndef GOOGLE_PROTOBUF_STUBS_SHARED_PTR_H__
+#define GOOGLE_PROTOBUF_STUBS_SHARED_PTR_H__
+
+#include <google/protobuf/stubs/atomicops.h>
+
+#include <algorithm> // for swap
+#include <stddef.h>
+#include <memory>
+
+namespace google {
+namespace protobuf {
+namespace internal {
+
+// Alias to std::shared_ptr for any C++11 platform,
+// and for any supported MSVC compiler.
+#if !defined(UTIL_GTL_USE_STD_SHARED_PTR) && \
+ (defined(COMPILER_MSVC) || defined(LANG_CXX11))
+#define UTIL_GTL_USE_STD_SHARED_PTR 1
+#endif
+
+#if defined(UTIL_GTL_USE_STD_SHARED_PTR) && UTIL_GTL_USE_STD_SHARED_PTR
+
+// These are transitional. They will be going away soon.
+// Please just #include <memory> and just type std::shared_ptr yourself, instead
+// of relying on this file.
+//
+// Migration doc: http://go/std-shared-ptr-lsc
+using std::enable_shared_from_this;
+using std::shared_ptr;
+using std::static_pointer_cast;
+using std::weak_ptr;
+
+#else // below, UTIL_GTL_USE_STD_SHARED_PTR not set or set to 0.
+
+// For everything else there is the google3 implementation.
+inline bool RefCountDec(volatile Atomic32 *ptr) {
+ return Barrier_AtomicIncrement(ptr, -1) != 0;
+}
+
+inline void RefCountInc(volatile Atomic32 *ptr) {
+ NoBarrier_AtomicIncrement(ptr, 1);
+}
+
+template <typename T> class shared_ptr;
+template <typename T> class weak_ptr;
+
+// This class is an internal implementation detail for shared_ptr. If two
+// shared_ptrs point to the same object, they also share a control block.
+// An "empty" shared_pointer refers to NULL and also has a NULL control block.
+// It contains all of the state that's needed for reference counting or any
+// other kind of resource management. In this implementation the control block
+// happens to consist of two atomic words, the reference count (the number
+// of shared_ptrs that share ownership of the object) and the weak count
+// (the number of weak_ptrs that observe the object, plus 1 if the
+// refcount is nonzero).
+//
+// The "plus 1" is to prevent a race condition in the shared_ptr and
+// weak_ptr destructors. We need to make sure the control block is
+// only deleted once, so we need to make sure that at most one
+// object sees the weak count decremented from 1 to 0.
+class SharedPtrControlBlock {
+ template <typename T> friend class shared_ptr;
+ template <typename T> friend class weak_ptr;
+ private:
+ SharedPtrControlBlock() : refcount_(1), weak_count_(1) { }
+ Atomic32 refcount_;
+ Atomic32 weak_count_;
+};
+
+// Forward declaration. The class is defined below.
+template <typename T> class enable_shared_from_this;
+
+template <typename T>
+class shared_ptr {
+ template <typename U> friend class weak_ptr;
+ public:
+ typedef T element_type;
+
+ shared_ptr() : ptr_(NULL), control_block_(NULL) {}
+
+ explicit shared_ptr(T* ptr)
+ : ptr_(ptr),
+ control_block_(ptr != NULL ? new SharedPtrControlBlock : NULL) {
+ // If p is non-null and T inherits from enable_shared_from_this, we
+ // set up the data that shared_from_this needs.
+ MaybeSetupWeakThis(ptr);
+ }
+
+ // Copy constructor: makes this object a copy of ptr, and increments
+ // the reference count.
+ template <typename U>
+ shared_ptr(const shared_ptr<U>& ptr)
+ : ptr_(NULL),
+ control_block_(NULL) {
+ Initialize(ptr);
+ }
+ // Need non-templated version to prevent the compiler-generated default
+ shared_ptr(const shared_ptr<T>& ptr)
+ : ptr_(NULL),
+ control_block_(NULL) {
+ Initialize(ptr);
+ }
+
+ // Assignment operator. Replaces the existing shared_ptr with ptr.
+ // Increment ptr's reference count and decrement the one being replaced.
+ template <typename U>
+ shared_ptr<T>& operator=(const shared_ptr<U>& ptr) {
+ if (ptr_ != ptr.ptr_) {
+ shared_ptr<T> me(ptr); // will hold our previous state to be destroyed.
+ swap(me);
+ }
+ return *this;
+ }
+
+ // Need non-templated version to prevent the compiler-generated default
+ shared_ptr<T>& operator=(const shared_ptr<T>& ptr) {
+ if (ptr_ != ptr.ptr_) {
+ shared_ptr<T> me(ptr); // will hold our previous state to be destroyed.
+ swap(me);
+ }
+ return *this;
+ }
+
+ // TODO(austern): Consider providing this constructor. The draft C++ standard
+ // (20.8.10.2.1) includes it. However, it says that this constructor throws
+ // a bad_weak_ptr exception when ptr is expired. Is it better to provide this
+ // constructor and make it do something else, like fail with a CHECK, or to
+ // leave this constructor out entirely?
+ //
+ // template <typename U>
+ // shared_ptr(const weak_ptr<U>& ptr);
+
+ ~shared_ptr() {
+ if (ptr_ != NULL) {
+ if (!RefCountDec(&control_block_->refcount_)) {
+ delete ptr_;
+
+ // weak_count_ is defined as the number of weak_ptrs that observe
+ // ptr_, plus 1 if refcount_ is nonzero.
+ if (!RefCountDec(&control_block_->weak_count_)) {
+ delete control_block_;
+ }
+ }
+ }
+ }
+
+ // Replaces underlying raw pointer with the one passed in. The reference
+ // count is set to one (or zero if the pointer is NULL) for the pointer
+ // being passed in and decremented for the one being replaced.
+ //
+ // If you have a compilation error with this code, make sure you aren't
+ // passing NULL, nullptr, or 0 to this function. Call reset without an
+ // argument to reset to a null ptr.
+ template <typename Y>
+ void reset(Y* p) {
+ if (p != ptr_) {
+ shared_ptr<T> tmp(p);
+ tmp.swap(*this);
+ }
+ }
+
+ void reset() {
+ reset(static_cast<T*>(NULL));
+ }
+
+ // Exchanges the contents of this with the contents of r. This function
+ // supports more efficient swapping since it eliminates the need for a
+ // temporary shared_ptr object.
+ void swap(shared_ptr<T>& r) {
+ using std::swap; // http://go/using-std-swap
+ swap(ptr_, r.ptr_);
+ swap(control_block_, r.control_block_);
+ }
+
+ // The following function is useful for gaining access to the underlying
+ // pointer when a shared_ptr remains in scope so the reference-count is
+ // known to be > 0 (e.g. for parameter passing).
+ T* get() const {
+ return ptr_;
+ }
+
+ T& operator*() const {
+ return *ptr_;
+ }
+
+ T* operator->() const {
+ return ptr_;
+ }
+
+ long use_count() const {
+ return control_block_ ? control_block_->refcount_ : 1;
+ }
+
+ bool unique() const {
+ return use_count() == 1;
+ }
+
+ private:
+ // If r is non-empty, initialize *this to share ownership with r,
+ // increasing the underlying reference count.
+ // If r is empty, *this remains empty.
+ // Requires: this is empty, namely this->ptr_ == NULL.
+ template <typename U>
+ void Initialize(const shared_ptr<U>& r) {
+ // This performs a static_cast on r.ptr_ to U*, which is a no-op since it
+ // is already a U*. So initialization here requires that r.ptr_ is
+ // implicitly convertible to T*.
+ InitializeWithStaticCast<U>(r);
+ }
+
+ // Initializes *this as described in Initialize, but additionally performs a
+ // static_cast from r.ptr_ (V*) to U*.
+ // NOTE(gfc): We'd need a more general form to support const_pointer_cast and
+ // dynamic_pointer_cast, but those operations are sufficiently discouraged
+ // that supporting static_pointer_cast is sufficient.
+ template <typename U, typename V>
+ void InitializeWithStaticCast(const shared_ptr<V>& r) {
+ if (r.control_block_ != NULL) {
+ RefCountInc(&r.control_block_->refcount_);
+
+ ptr_ = static_cast<U*>(r.ptr_);
+ control_block_ = r.control_block_;
+ }
+ }
+
+ // Helper function for the constructor that takes a raw pointer. If T
+ // doesn't inherit from enable_shared_from_this<T> then we have nothing to
+ // do, so this function is trivial and inline. The other version is declared
+ // out of line, after the class definition of enable_shared_from_this.
+ void MaybeSetupWeakThis(enable_shared_from_this<T>* ptr);
+ void MaybeSetupWeakThis(...) { }
+
+ T* ptr_;
+ SharedPtrControlBlock* control_block_;
+
+#ifndef SWIG
+ template <typename U>
+ friend class shared_ptr;
+
+ template <typename U, typename V>
+ friend shared_ptr<U> static_pointer_cast(const shared_ptr<V>& rhs);
+#endif
+};
+
+// Matches the interface of std::swap as an aid to generic programming.
+template <typename T> void swap(shared_ptr<T>& r, shared_ptr<T>& s) {
+ r.swap(s);
+}
+
+template <typename T, typename U>
+shared_ptr<T> static_pointer_cast(const shared_ptr<U>& rhs) {
+ shared_ptr<T> lhs;
+ lhs.template InitializeWithStaticCast<T>(rhs);
+ return lhs;
+}
+
+// See comments at the top of the file for a description of why this
+// class exists, and the draft C++ standard (as of July 2009 the
+// latest draft is N2914) for the detailed specification.
+template <typename T>
+class weak_ptr {
+ template <typename U> friend class weak_ptr;
+ public:
+ typedef T element_type;
+
+ // Create an empty (i.e. already expired) weak_ptr.
+ weak_ptr() : ptr_(NULL), control_block_(NULL) { }
+
+ // Create a weak_ptr that observes the same object that ptr points
+ // to. Note that there is no race condition here: we know that the
+ // control block can't disappear while we're looking at it because
+ // it is owned by at least one shared_ptr, ptr.
+ template <typename U> weak_ptr(const shared_ptr<U>& ptr) {
+ CopyFrom(ptr.ptr_, ptr.control_block_);
+ }
+
+ // Copy a weak_ptr. The object it points to might disappear, but we
+ // don't care: we're only working with the control block, and it can't
+ // disappear while we're looking at because it's owned by at least one
+ // weak_ptr, ptr.
+ template <typename U> weak_ptr(const weak_ptr<U>& ptr) {
+ CopyFrom(ptr.ptr_, ptr.control_block_);
+ }
+
+ // Need non-templated version to prevent default copy constructor
+ weak_ptr(const weak_ptr& ptr) {
+ CopyFrom(ptr.ptr_, ptr.control_block_);
+ }
+
+ // Destroy the weak_ptr. If no shared_ptr owns the control block, and if
+ // we are the last weak_ptr to own it, then it can be deleted. Note that
+ // weak_count_ is defined as the number of weak_ptrs sharing this control
+ // block, plus 1 if there are any shared_ptrs. We therefore know that it's
+ // safe to delete the control block when weak_count_ reaches 0, without
+ // having to perform any additional tests.
+ ~weak_ptr() {
+ if (control_block_ != NULL &&
+ !RefCountDec(&control_block_->weak_count_)) {
+ delete control_block_;
+ }
+ }
+
+ weak_ptr& operator=(const weak_ptr& ptr) {
+ if (&ptr != this) {
+ weak_ptr tmp(ptr);
+ tmp.swap(*this);
+ }
+ return *this;
+ }
+ template <typename U> weak_ptr& operator=(const weak_ptr<U>& ptr) {
+ weak_ptr tmp(ptr);
+ tmp.swap(*this);
+ return *this;
+ }
+ template <typename U> weak_ptr& operator=(const shared_ptr<U>& ptr) {
+ weak_ptr tmp(ptr);
+ tmp.swap(*this);
+ return *this;
+ }
+
+ void swap(weak_ptr& ptr) {
+ using std::swap; // http://go/using-std-swap
+ swap(ptr_, ptr.ptr_);
+ swap(control_block_, ptr.control_block_);
+ }
+
+ void reset() {
+ weak_ptr tmp;
+ tmp.swap(*this);
+ }
+
+ // Return the number of shared_ptrs that own the object we are observing.
+ // Note that this number can be 0 (if this pointer has expired).
+ long use_count() const {
+ return control_block_ != NULL ? control_block_->refcount_ : 0;
+ }
+
+ bool expired() const { return use_count() == 0; }
+
+ // Return a shared_ptr that owns the object we are observing. If we
+ // have expired, the shared_ptr will be empty. We have to be careful
+ // about concurrency, though, since some other thread might be
+ // destroying the last owning shared_ptr while we're in this
+ // function. We want to increment the refcount only if it's nonzero
+ // and get the new value, and we want that whole operation to be
+ // atomic.
+ shared_ptr<T> lock() const {
+ shared_ptr<T> result;
+ if (control_block_ != NULL) {
+ Atomic32 old_refcount;
+ do {
+ old_refcount = control_block_->refcount_;
+ if (old_refcount == 0)
+ break;
+ } while (old_refcount !=
+ NoBarrier_CompareAndSwap(
+ &control_block_->refcount_, old_refcount,
+ old_refcount + 1));
+ if (old_refcount > 0) {
+ result.ptr_ = ptr_;
+ result.control_block_ = control_block_;
+ }
+ }
+
+ return result;
+ }
+
+ private:
+ void CopyFrom(T* ptr, SharedPtrControlBlock* control_block) {
+ ptr_ = ptr;
+ control_block_ = control_block;
+ if (control_block_ != NULL)
+ RefCountInc(&control_block_->weak_count_);
+ }
+
+ private:
+ element_type* ptr_;
+ SharedPtrControlBlock* control_block_;
+};
+
+template <typename T> void swap(weak_ptr<T>& r, weak_ptr<T>& s) {
+ r.swap(s);
+}
+
+// See comments at the top of the file for a description of why this class
+// exists, and section 20.8.10.5 of the draft C++ standard (as of July 2009
+// the latest draft is N2914) for the detailed specification.
+template <typename T>
+class enable_shared_from_this {
+ friend class shared_ptr<T>;
+ public:
+ // Precondition: there must be a shared_ptr that owns *this and that was
+ // created, directly or indirectly, from a raw pointer of type T*. (The
+ // latter part of the condition is technical but not quite redundant; it
+ // rules out some complicated uses involving inheritance hierarchies.)
+ shared_ptr<T> shared_from_this() {
+ // Behavior is undefined if the precondition isn't satisfied; we choose
+ // to die with a CHECK failure.
+ CHECK(!weak_this_.expired()) << "No shared_ptr owns this object";
+ return weak_this_.lock();
+ }
+ shared_ptr<const T> shared_from_this() const {
+ CHECK(!weak_this_.expired()) << "No shared_ptr owns this object";
+ return weak_this_.lock();
+ }
+
+ protected:
+ enable_shared_from_this() { }
+ enable_shared_from_this(const enable_shared_from_this& other) { }
+ enable_shared_from_this& operator=(const enable_shared_from_this& other) {
+ return *this;
+ }
+ ~enable_shared_from_this() { }
+
+ private:
+ weak_ptr<T> weak_this_;
+};
+
+// This is a helper function called by shared_ptr's constructor from a raw
+// pointer. If T inherits from enable_shared_from_this<T>, it sets up
+// weak_this_ so that shared_from_this works correctly. If T does not inherit
+// from weak_this we get a different overload, defined inline, which does
+// nothing.
+template<typename T>
+void shared_ptr<T>::MaybeSetupWeakThis(enable_shared_from_this<T>* ptr) {
+ if (ptr) {
+ CHECK(ptr->weak_this_.expired()) << "Object already owned by a shared_ptr";
+ ptr->weak_this_ = *this;
+ }
+}
+
+#endif // UTIL_GTL_USE_STD_SHARED_PTR
+
+} // internal
+} // namespace protobuf
+} // namespace google
+
+#endif // GOOGLE_PROTOBUF_STUBS_SHARED_PTR_H__