Pull new version of protobuf sources.

third_party/protobuf/src/google/protobuf/stubs/shared_ptr.h

Index: third_party/protobuf/src/google/protobuf/stubs/shared_ptr.h
diff --git a/third_party/protobuf/src/google/protobuf/stubs/shared_ptr.h b/third_party/protobuf/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__