230 lines
7.5 KiB
C++
230 lines
7.5 KiB
C++
/*
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* Copyright (c) 2002-2005 The Regents of The University of Michigan
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are
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* met: redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer;
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* redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution;
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* neither the name of the copyright holders nor the names of its
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* contributors may be used to endorse or promote products derived from
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* this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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* Authors: Nathan Binkert
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*/
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#ifndef __BASE_REFCNT_HH__
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#define __BASE_REFCNT_HH__
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/**
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* @file base/refcnt.hh
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*
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* Classes for managing reference counted objects.
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*/
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/**
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* Derive from RefCounted if you want to enable reference counting of
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* this class. If you want to use automatic reference counting, you
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* should use RefCountingPtr<T> instead of regular pointers.
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*/
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class RefCounted
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{
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private:
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// The reference count is mutable because one may want to
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// reference count a const pointer. This really is OK because
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// const is about logical constness of the object not really about
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// strictly disallowing an object to change.
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mutable int count;
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private:
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// Don't allow a default copy constructor or copy operator on
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// these objects because the default operation will copy the
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// reference count as well and we certainly don't want that.
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RefCounted(const RefCounted &);
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RefCounted &operator=(const RefCounted &);
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public:
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/**
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* We initialize the reference count to zero and the first object
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* to take ownership of it must increment it to one.
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*
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* @attention A memory leak will occur if you never assign a newly
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* constructed object to a reference counting pointer.
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*/
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RefCounted() : count(0) {}
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/**
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* We make the destructor virtual because we're likely to have
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* virtual functions on reference counted objects.
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*
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* @todo Even if this were true, does it matter? Shouldn't the
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* derived class indicate this? This only matters if we would
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* ever choose to delete a "RefCounted *" which I doubt we'd ever
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* do. We don't ever delete a "void *".
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*/
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virtual ~RefCounted() {}
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/// Increment the reference count
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void incref() { ++count; }
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/// Decrement the reference count and destroy the object if all
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/// references are gone.
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void decref() { if (--count <= 0) delete this; }
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};
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/**
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* If you want a reference counting pointer to a mutable object,
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* create it like this:
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* @code
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* typedef RefCountingPtr<Foo> FooPtr;
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* @endcode
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*
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* @attention Do not use "const FooPtr"
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* To create a reference counting pointer to a const object, use this:
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* @code
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* typedef RefCountingPtr<const Foo> ConstFooPtr;
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* @endcode
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*
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* These two usages are analogous to iterator and const_iterator in the stl.
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*/
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template <class T>
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class RefCountingPtr
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{
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protected:
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/// The stored pointer.
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/// Arguably this should be private.
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T *data;
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/**
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* Copy a new pointer value and increment the reference count if
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* it is a valid pointer. Note, this does not delete the
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* reference any existing object.
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* @param d Pointer to store.
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*/
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void
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copy(T *d)
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{
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data = d;
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if (data)
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data->incref();
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}
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/**
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* Delete the reference to any existing object if it is non NULL.
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* @attention this doesn't clear the pointer value, so a double
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* decref could happen if not careful.
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*/
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void
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del()
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{
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if (data)
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data->decref();
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}
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/**
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* Drop the old reference and change it to something new.
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*/
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void
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set(T *d)
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{
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// Need to check if we're actually changing because otherwise
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// we could delete the last reference before adding the new
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// reference.
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if (data != d) {
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del();
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copy(d);
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}
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}
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public:
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/// Create an empty reference counting pointer.
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RefCountingPtr() : data(0) {}
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/// Create a new reference counting pointer to some object
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/// (probably something newly created). Adds a reference.
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RefCountingPtr(T *data) { copy(data); }
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/// Create a new reference counting pointer by copying another
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/// one. Adds a reference.
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RefCountingPtr(const RefCountingPtr &r) { copy(r.data); }
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/// Destroy the pointer and any reference it may hold.
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~RefCountingPtr() { del(); }
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// The following pointer access functions are const because they
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// don't actually change the pointer, though the user could change
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// what is pointed to. This is analagous to a "Foo * const".
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/// Access a member variable.
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T *operator->() const { return data; }
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/// Dereference the pointer.
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T &operator*() const { return *data; }
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/// Directly access the pointer itself without taking a reference.
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T *get() const { return data; }
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/// Assign a new value to the pointer
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const RefCountingPtr &operator=(T *p) { set(p); return *this; }
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/// Copy the pointer from another RefCountingPtr
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const RefCountingPtr &operator=(const RefCountingPtr &r)
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{ return operator=(r.data); }
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/// Check if the pointer is empty
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bool operator!() const { return data == 0; }
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/// Check if the pointer is non-empty
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operator bool() const { return data != 0; }
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};
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/// Check for equality of two reference counting pointers.
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template<class T>
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inline bool operator==(const RefCountingPtr<T> &l, const RefCountingPtr<T> &r)
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{ return l.get() == r.get(); }
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/// Check for equality of of a reference counting pointers and a
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/// regular pointer
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template<class T>
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inline bool operator==(const RefCountingPtr<T> &l, const T *r)
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{ return l.get() == r; }
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/// Check for equality of of a reference counting pointers and a
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/// regular pointer
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template<class T>
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inline bool operator==(const T *l, const RefCountingPtr<T> &r)
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{ return l == r.get(); }
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/// Check for inequality of two reference counting pointers.
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template<class T>
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inline bool operator!=(const RefCountingPtr<T> &l, const RefCountingPtr<T> &r)
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{ return l.get() != r.get(); }
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/// Check for inequality of of a reference counting pointers and a
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/// regular pointer
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template<class T>
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inline bool operator!=(const RefCountingPtr<T> &l, const T *r)
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{ return l.get() != r; }
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/// Check for inequality of of a reference counting pointers and a
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/// regular pointer
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template<class T>
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inline bool operator!=(const T *l, const RefCountingPtr<T> &r)
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{ return l != r.get(); }
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#endif // __BASE_REFCNT_HH__
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