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Unified Diff: third_party/bar/shared_ptr.h

Issue 624713003: Keep only base/extractor.[cc|h]. (Closed) Base URL: https://chromium.googlesource.com/external/omaha.git@master
Patch Set: Created 6 years, 2 months ago
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Index: third_party/bar/shared_ptr.h
diff --git a/third_party/bar/shared_ptr.h b/third_party/bar/shared_ptr.h
deleted file mode 100644
index 5f7038853a20d0ccec35c6685288d857e309382a..0000000000000000000000000000000000000000
--- a/third_party/bar/shared_ptr.h
+++ /dev/null
@@ -1,438 +0,0 @@
-// Copyright 2006 and onwards Google Inc.
-// Author: Michael Ellman (with suggestions from jrvb, m3b, toddw, jwray)
-//
-// A simple reference counted pointer implementation. It is a subset
-// of the boost/tr1 shared_ptr class, which is expected to be part of
-// the next C++ standard. See section 20.8.10 [util.smartptr] of the
-// draft standard for a full description of the standard interface.
-//
-// Standard features that have been omitted from this implementation include:
-// - no custom deallocators - uses delete
-// - shared_ptr<T>'s constructor isn't templated: its argument is just T*.
-// - no support for smart pointer casts
-// - no support for unowned pointers
-// - no support for variadic templates or rvalue references
-// - no integration with auto_ptr or unique_ptr
-// - not exception-safe
-// - no overloaded comparison operators (e.g. operator<). They're
-// convenient, but they can be explicitly defined outside the class.
-//
-// It's usually the case that when you want to share an object, there
-// is a clear owner that outlives the other users. If that's the case,
-// the owner can use scoped_ptr and the rest can use a raw pointer.
-//
-// A somewhat common design pattern that doesn't have a clear object
-// owner is when there is a shared container in which older versions
-// of an object are replaced with newer versions. The objects should be
-// deleted only when (a) they are replaced with a new version and (b)
-// there are no outside users of the old version. Replacing raw pointers
-// in the implementation with shared_ptr's ensures that the accounting
-// and object lifetimes are handled appropriately.
-//
-// The typical usage is as follows.
-//
-// 1. Functions using shared_ptr's should declare shared_ptr parameters to
-// be of type const reference since the caller will still have its own
-// shared_ptr for the entire call.
-//
-// void foo(const shared_ptr<T>& param)
-//
-// 2. Functions setting shared_ptr's should declare shared_ptr parameters
-// to be of pointer type.
-//
-// typedef map<Key, shared_ptr<Value> > MyMap;
-// void GetAndSharedObject(const Key& key, shared_ptr<Value>* value) {
-// ReaderMutexLock l(&lock_);
-// MyMap::iterator iter = shared_container.find(key);
-// *value = iter->second;
-// }
-//
-// Thread Safety:
-// Once constructed, a shared_ptr has the same thread-safety as built-in
-// types. In particular, it is safe to read a shared object simultaneously
-// from multiple threads.
-//
-// Weak ptrs
-// The weak_ptr auxiliary class (see clause 20.8.10.3 of the draft standard)
-// is used to break ownership cycles. A weak_ptr points to an object that's
-// owned by a shared_ptr, but the weak_ptr is an observer, not an owner. When
-// the last shared_ptr that points to the object disappears, the weak_ptr
-// expires, at which point the expired() member function will return true.
-//
-// You can't directly get a raw pointer from weak_ptr, i.e. it has no get()
-// or operator*() member function. (These features were intentionally left out
-// to avoid the risk of dangling pointers.) To access a weak_ptr's pointed-to
-// object, use lock() to obtain a temporary shared_ptr.
-//
-// enable_shared_from_this
-// A user-defined class T can inherit from enable_shared_from_this<T> (see
-// clause 20.8.10.5 of the draft standard) to inherit T::shared_from_this(),
-// which returns a shared_ptr pointing to *this. It is similar to weak_ptr in
-// that there must already be at least one shared_ptr instance that owns
-// *this.
-
-#ifndef BAR_COMMON_SHARED_PTR_H_
-#define BAR_COMMON_SHARED_PTR_H_
-
-#include <windows.h>
-#include <algorithm> // for swap
-
-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) { }
- LONG refcount_;
- LONG 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;
-
- explicit shared_ptr(T* ptr = NULL)
- : 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 (::InterlockedDecrement(&control_block_->refcount_) == 0) {
- delete ptr_;
-
- // weak_count_ is defined as the number of weak_ptrs that observe
- // ptr_, plus 1 if refcount_ is nonzero.
- if (::InterlockedDecrement(&control_block_->weak_count_) == 0) {
- 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.
- void reset(T* p = NULL) {
- if (p != ptr_) {
- shared_ptr<T> tmp(p);
- tmp.swap(*this);
- }
- }
-
- // 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) {
- std::swap(ptr_, r.ptr_);
- std::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) {
- if (r.control_block_ != NULL) {
- ::InterlockedIncrement(&r.control_block_->refcount_);
-
- ptr_ = 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_;
-
- template <typename U>
- friend class shared_ptr;
-};
-
-// 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);
-}
-
-// 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 &&
- ::InterlockedDecrement(&control_block_->weak_count_) == 0) {
- 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) {
- std::swap(ptr_, ptr.ptr_);
- std::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) {
- LONG old_refcount;
- do {
- old_refcount = control_block_->refcount_;
- if (old_refcount == 0)
- break;
- } while (old_refcount !=
- ::InterlockedCompareExchange(
- &control_block_->refcount_, old_refcount + 1,
- old_refcount));
- 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)
- ::InterlockedIncrement(&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 an access violation exception.
-#if DEBUG
- if (weak_this_.expired()) {
- // No shared_ptr owns this object.
- *static_cast<int*>(NULL) = 0;
- }
-#endif
- return weak_this_.lock();
- }
- shared_ptr<const T> shared_from_this() const {
-#if DEBUG
- if (weak_this_.expired()) {
- // No shared_ptr owns this object.
- *static_cast<int*>(NULL) = 0;
- }
-#endif
- 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)
- ptr->weak_this_ = *this;
-}
-
-#endif // BAR_COMMON_SHARED_PTR_H_
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