The Tor Browser: comparison ipc/chromium/src/base/linked

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+:d34a0e87bc84
+// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+//
+// A "smart" pointer type with reference tracking.  Every pointer to a
+// particular object is kept on a circular linked list.  When the last pointer
+// to an object is destroyed or reassigned, the object is deleted.
+//
+// Used properly, this deletes the object when the last reference goes away.
+// There are several caveats:
+// - Like all reference counting schemes, cycles lead to leaks.
+// - Each smart pointer is actually two pointers (8 bytes instead of 4).
+// - Every time a pointer is released, the entire list of pointers to that
+//   object is traversed.  This class is therefore NOT SUITABLE when there
+//   will often be more than two or three pointers to a particular object.
+// - References are only tracked as long as linked_ptr<> objects are copied.
+//   If a linked_ptr<> is converted to a raw pointer and back, BAD THINGS
+//   will happen (double deletion).
+//
+// A good use of this class is storing object references in STL containers.
+// You can safely put linked_ptr<> in a vector<>.
+// Other uses may not be as good.
+//
+// Note: If you use an incomplete type with linked_ptr<>, the class
+// *containing* linked_ptr<> must have a constructor and destructor (even
+// if they do nothing!).
+//
+// Thread Safety:
+//   A linked_ptr is NOT thread safe. Copying a linked_ptr object is
+//   effectively a read-write operation.
+//
+// Alternative: to linked_ptr is shared_ptr, which
+//  - is also two pointers in size (8 bytes for 32 bit addresses)
+//  - is thread safe for copying and deletion
+//  - supports weak_ptrs
+#ifndef BASE_LINKED_PTR_H_
+#define BASE_LINKED_PTR_H_
+#include "base/logging.h"  // for CHECK macros
+// This is used internally by all instances of linked_ptr<>.  It needs to be
+// a non-template class because different types of linked_ptr<> can refer to
+// the same object (linked_ptr<Superclass>(obj) vs linked_ptr<Subclass>(obj)).
+// So, it needs to be possible for different types of linked_ptr to participate
+// in the same circular linked list, so we need a single class type here.
+//
+// DO NOT USE THIS CLASS DIRECTLY YOURSELF.  Use linked_ptr<T>.
+class linked_ptr_internal {
+public:
+// Create a new circle that includes only this instance.
+void join_new() {
+next_ = this;
+}
+// Join an existing circle.
+void join(linked_ptr_internal const* ptr) {
+next_ = ptr->next_;
+ptr->next_ = this;
+}
+// Leave whatever circle we're part of.  Returns true iff we were the
+// last member of the circle.  Once this is done, you can join() another.
+bool depart() {
+if (next_ == this) return true;
+linked_ptr_internal const* p = next_;
+while (p->next_ != this) p = p->next_;
+p->next_ = next_;
+return false;
+}
+private:
+mutable linked_ptr_internal const* next_;
+};
+template <typename T>
+class linked_ptr {
+public:
+typedef T element_type;
+// Take over ownership of a raw pointer.  This should happen as soon as
+// possible after the object is created.
+explicit linked_ptr(T* ptr = NULL) { capture(ptr); }
+~linked_ptr() { depart(); }
+// Copy an existing linked_ptr<>, adding ourselves to the list of references.
+template <typename U> linked_ptr(linked_ptr<U> const& ptr) { copy(&ptr); }
+linked_ptr(linked_ptr const& ptr) { DCHECK_NE(&ptr, this); copy(&ptr); }
+// Assignment releases the old value and acquires the new.
+template <typename U> linked_ptr& operator=(linked_ptr<U> const& ptr) {
+depart();
+copy(&ptr);
+return *this;
+}
+linked_ptr& operator=(linked_ptr const& ptr) {
+if (&ptr != this) {
+depart();
+copy(&ptr);
+}
+return *this;
+}
+// Smart pointer members.
+void reset(T* ptr = NULL) { depart(); capture(ptr); }
+T* get() const { return value_; }
+T* operator->() const { return value_; }
+T& operator*() const { return *value_; }
+// Release ownership of the pointed object and returns it.
+// Sole ownership by this linked_ptr object is required.
+T* release() {
+bool last = link_.depart();
+CHECK(last);
+T* v = value_;
+value_ = NULL;
+return v;
+}
+bool operator==(const T* p) const { return value_ == p; }
+bool operator!=(const T* p) const { return value_ != p; }
+template <typename U>
+bool operator==(linked_ptr<U> const& ptr) const {
+return value_ == ptr.get();
+}
+template <typename U>
+bool operator!=(linked_ptr<U> const& ptr) const {
+return value_ != ptr.get();
+}
+private:
+template <typename U>
+friend class linked_ptr;
+T* value_;
+linked_ptr_internal link_;
+void depart() {
+if (link_.depart()) delete value_;
+}
+void capture(T* ptr) {
+value_ = ptr;
+link_.join_new();
+}
+template <typename U> void copy(linked_ptr<U> const* ptr) {
+value_ = ptr->get();
+if (value_)
+link_.join(&ptr->link_);
+else
+link_.join_new();
+}
+};
+template<typename T> inline
+bool operator==(T* ptr, const linked_ptr<T>& x) {
+return ptr == x.get();
+}
+template<typename T> inline
+bool operator!=(T* ptr, const linked_ptr<T>& x) {
+return ptr != x.get();
+}
+// A function to convert T* into linked_ptr<T>
+// Doing e.g. make_linked_ptr(new FooBarBaz<type>(arg)) is a shorter notation
+// for linked_ptr<FooBarBaz<type> >(new FooBarBaz<type>(arg))
+template <typename T>
+linked_ptr<T> make_linked_ptr(T* ptr) {
+return linked_ptr<T>(ptr);
+}
+#endif  // BASE_LINKED_PTR_H_

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comparison: ipc/chromium/src/base/linked_ptr.h

ipc/chromium/src/base/linked_ptr.h