tomwalters@123: // Copyright (c) 2003 Google Inc.
tomwalters@123: //
tomwalters@123: // Permission is hereby granted, free of charge, to any person or organization
tomwalters@123: // obtaining a copy of the software and accompanying documentation covered by
tomwalters@123: // this license (the "Software") to use, reproduce, display, distribute,
tomwalters@123: // execute, and transmit the Software, and to prepare derivative works of the
tomwalters@123: // Software, and to permit third-parties to whom the Software is furnished to
tomwalters@123: // do so, all subject to the following:
tomwalters@123: //
tomwalters@123: // The copyright notices in the Software and this entire statement, including
tomwalters@123: // the above license grant, this restriction and the following disclaimer,
tomwalters@123: // must be included in all copies of the Software, in whole or in part, and
tomwalters@123: // all derivative works of the Software, unless such copies or derivative
tomwalters@123: // works are solely in the form of machine-executable object code generated by
tomwalters@123: // a source language processor.
tomwalters@123: //
tomwalters@123: // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
tomwalters@123: // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
tomwalters@123: // FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
tomwalters@123: // SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
tomwalters@123: // FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
tomwalters@123: // ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
tomwalters@123: // DEALINGS IN THE SOFTWARE.
tomwalters@123: //
tomwalters@123: // linked_ptr.h
tomwalters@123: // Author: Dan Egnor
tomwalters@123: //
tomwalters@123: // A "smart" pointer type with reference tracking.  Every pointer to a
tomwalters@123: // particular object is kept on a circular linked list.  When the last pointer
tomwalters@123: // to an object is destroyed or reassigned, the object is deleted.
tomwalters@123: //
tomwalters@123: // Used properly, this deletes the object when the last reference goes away.
tomwalters@123: // There are several caveats:
tomwalters@123: // - Like all reference counting schemes, cycles lead to leaks.
tomwalters@123: // - Each smart pointer is actually two pointers (8 bytes instead of 4).
tomwalters@123: // - Every time a pointer is assigned, the entire list of pointers to that
tomwalters@123: //   object is traversed.  This class is therefore NOT SUITABLE when there
tomwalters@123: //   will often be more than two or three pointers to a particular object.
tomwalters@123: // - References are only tracked as long as linked_ptr<> objects are copied.
tomwalters@123: //   If a linked_ptr<> is converted to a raw pointer and back, BAD THINGS
tomwalters@123: //   will happen (double deletion).
tomwalters@123: //
tomwalters@123: // A good use of this class is storing object references in STL containers.
tomwalters@123: // You can safely put linked_ptr<> in a vector<>.
tomwalters@123: // Other uses may not be as good.
tomwalters@123: //
tomwalters@123: // Note: If you use an incomplete type with linked_ptr<>, the class
tomwalters@123: // *containing* linked_ptr<> must have a constructor and destructor (even
tomwalters@123: // if they do nothing!).
tomwalters@123: //
tomwalters@123: // Bill Gibbons suggested we use something like this.  Yonat Sharon has
tomwalters@123: // a different (less useful IMHO) implementation at ootips.org.
tomwalters@123: //
tomwalters@123: // Thread Safety:
tomwalters@123: //   A linked_ptr is NOT thread safe. Copying a linked_ptr object is
tomwalters@123: //   effectively a read-write operation.
tomwalters@123: 
tomwalters@123: #ifndef UTIL_GTL_LINKED_PTR_H__
tomwalters@123: #define UTIL_GTL_LINKED_PTR_H__
tomwalters@123: 
tomwalters@123: #include <assert.h>
tomwalters@123: 
tomwalters@123: // This is used internally by all instances of linked_ptr<>.  It needs to be
tomwalters@123: // a non-template class because different types of linked_ptr<> can refer to
tomwalters@123: // the same object (linked_ptr<Superclass>(obj) vs linked_ptr<Subclass>(obj)).
tomwalters@123: // So, it needs to be possible for different types of linked_ptr to participate
tomwalters@123: // in the same circular linked list, so we need a single class type here.
tomwalters@123: //
tomwalters@123: // DO NOT USE THIS CLASS DIRECTLY YOURSELF.  Use linked_ptr<T>.
tomwalters@123: class linked_ptr_internal {
tomwalters@123:  public:
tomwalters@123:   // Create a new circle that includes only this instance.
tomwalters@123:   void join_new() {
tomwalters@123:     next_ = this;
tomwalters@123:   }
tomwalters@123: 
tomwalters@123:   // Join an existing circle.
tomwalters@123:   void join(linked_ptr_internal const* ptr) {
tomwalters@123:     linked_ptr_internal const* p = ptr;
tomwalters@123:     while (p->next_ != ptr) p = p->next_;
tomwalters@123:     p->next_ = this;
tomwalters@123:     next_ = ptr;
tomwalters@123:   }
tomwalters@123: 
tomwalters@123:   // Leave whatever circle we're part of.  Returns true iff we were the
tomwalters@123:   // last member of the circle.  Once this is done, you can join() another.
tomwalters@123:   bool depart() {
tomwalters@123:     if (next_ == this) return true;
tomwalters@123:     linked_ptr_internal const* p = next_;
tomwalters@123:     while (p->next_ != this) p = p->next_;
tomwalters@123:     p->next_ = next_;
tomwalters@123:     return false;
tomwalters@123:   }
tomwalters@123: 
tomwalters@123:  private:
tomwalters@123:   mutable linked_ptr_internal const* next_;
tomwalters@123: };
tomwalters@123: 
tomwalters@123: template <typename T>
tomwalters@123: class linked_ptr {
tomwalters@123:  public:
tomwalters@123:   typedef T element_type;
tomwalters@123: 
tomwalters@123:   // Take over ownership of a raw pointer.  This should happen as soon as
tomwalters@123:   // possible after the object is created.
tomwalters@123:   explicit linked_ptr(T* ptr = NULL) { capture(ptr); }
tomwalters@123:   ~linked_ptr() { depart(); }
tomwalters@123: 
tomwalters@123:   // Copy an existing linked_ptr<>, adding ourselves to the list of references.
tomwalters@123:   template <typename U> linked_ptr(linked_ptr<U> const& ptr) { copy(&ptr); }
tomwalters@123:   linked_ptr(linked_ptr const& ptr) { assert(&ptr != this); copy(&ptr); }
tomwalters@123: 
tomwalters@123:   // Assignment releases the old value and acquires the new.
tomwalters@123:   template <typename U> linked_ptr& operator=(linked_ptr<U> const& ptr) {
tomwalters@123:     depart();
tomwalters@123:     copy(&ptr);
tomwalters@123:     return *this;
tomwalters@123:   }
tomwalters@123: 
tomwalters@123:   linked_ptr& operator=(linked_ptr const& ptr) {
tomwalters@123:     if (&ptr != this) {
tomwalters@123:       depart();
tomwalters@123:       copy(&ptr);
tomwalters@123:     }
tomwalters@123:     return *this;
tomwalters@123:   }
tomwalters@123: 
tomwalters@123:   // Smart pointer members.
tomwalters@123:   void reset(T* ptr = NULL) { depart(); capture(ptr); }
tomwalters@123:   T* get() const { return value_; }
tomwalters@123:   T* operator->() const { return value_; }
tomwalters@123:   T& operator*() const { return *value_; }
tomwalters@123:   // Release ownership of the pointed object and returns it.
tomwalters@123:   // Sole ownership by this linked_ptr object is required.
tomwalters@123:   T* release() {
tomwalters@123:     // !! GOOGLE Gears specific modification !!
tomwalters@123:     // GCC emits a warning for not using last in a opt build.
tomwalters@123:     // Warnings are treated as errors.
tomwalters@123: #ifdef DEBUG
tomwalters@123:     bool last = link_.depart();
tomwalters@123:     assert(last);
tomwalters@123: #else
tomwalters@123:     link_.depart();
tomwalters@123: #endif
tomwalters@123:     T* v = value_;
tomwalters@123:     value_ = NULL;
tomwalters@123:     return v;
tomwalters@123:   }
tomwalters@123: 
tomwalters@123:   bool operator==(T* p) const { return value_ == p; }
tomwalters@123:   bool operator!=(T* p) const { return value_ != p; }
tomwalters@123:   template <typename U>
tomwalters@123:   bool operator==(linked_ptr<U> const& ptr) const {
tomwalters@123:     return value_ == ptr.get();
tomwalters@123:   }
tomwalters@123:   template <typename U>
tomwalters@123:   bool operator!=(linked_ptr<U> const& ptr) const {
tomwalters@123:     return value_ != ptr.get();
tomwalters@123:   }
tomwalters@123: 
tomwalters@123:  private:
tomwalters@123:   template <typename U>
tomwalters@123:   friend class linked_ptr;
tomwalters@123: 
tomwalters@123:   T* value_;
tomwalters@123:   linked_ptr_internal link_;
tomwalters@123: 
tomwalters@123:   void depart() {
tomwalters@123:     if (link_.depart()) delete value_;
tomwalters@123:   }
tomwalters@123: 
tomwalters@123:   void capture(T* ptr) {
tomwalters@123:     value_ = ptr;
tomwalters@123:     link_.join_new();
tomwalters@123:   }
tomwalters@123: 
tomwalters@123:   template <typename U> void copy(linked_ptr<U> const* ptr) {
tomwalters@123:     value_ = ptr->get();
tomwalters@123:     if (value_)
tomwalters@123:       link_.join(&ptr->link_);
tomwalters@123:     else
tomwalters@123:       link_.join_new();
tomwalters@123:   }
tomwalters@123: };
tomwalters@123: 
tomwalters@123: template<typename T> inline
tomwalters@123: bool operator==(T* ptr, const linked_ptr<T>& x) {
tomwalters@123:   return ptr == x.get();
tomwalters@123: }
tomwalters@123: 
tomwalters@123: template<typename T> inline
tomwalters@123: bool operator!=(T* ptr, const linked_ptr<T>& x) {
tomwalters@123:   return ptr != x.get();
tomwalters@123: }
tomwalters@123: 
tomwalters@123: // A function to convert T* into linked_ptr<T>
tomwalters@123: // Doing e.g. make_linked_ptr(new FooBarBaz<type>(arg)) is a shorter notation
tomwalters@123: // for linked_ptr<FooBarBaz<type> >(new FooBarBaz<type>(arg))
tomwalters@123: template <typename T>
tomwalters@123: linked_ptr<T> make_linked_ptr(T* ptr) {
tomwalters@123:   return linked_ptr<T>(ptr);
tomwalters@123: }
tomwalters@123: 
tomwalters@123: #endif // UTIL_GTL_LINKED_PTR_H__