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Diffstat (limited to 'src/google/protobuf/stubs/shared_ptr.h')
| -rw-r--r-- | src/google/protobuf/stubs/shared_ptr.h | 470 |
1 files changed, 470 insertions, 0 deletions
diff --git a/src/google/protobuf/stubs/shared_ptr.h b/src/google/protobuf/stubs/shared_ptr.h new file mode 100644 index 0000000..c659307 --- /dev/null +++ b/src/google/protobuf/stubs/shared_ptr.h @@ -0,0 +1,470 @@ +// Protocol Buffers - Google's data interchange format +// Copyright 2014 Google Inc. All rights reserved. +// http://code.google.com/p/protobuf/ +// +// 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__ |