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Rewrite PointerHolder as derived from std::shared_ptr
This commit is contained in:
Jay Berkenbilt
parent
ec21910066
commit
ae819b5318
@ -39,6 +39,8 @@
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# define POINTERHOLDER_TRANSITION 0
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#endif // !defined(POINTERHOLDER_TRANSITION)
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#if POINTERHOLDER_TRANSITION < 4
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// *** WHAT IS HAPPENING ***
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// In qpdf 11, PointerHolder will be replaced with std::shared_ptr
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@ -140,137 +142,48 @@
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// written code. If you are relying on the incorrect behavior, use
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// PointerHolder<T const> instead.
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// OLD DOCUMENTATION
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// This class is basically std::shared_ptr but predates that by
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// several years.
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// This class expects to be initialized with a dynamically allocated
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// object pointer. It keeps a reference count and deletes this once
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// the reference count goes to zero. PointerHolder objects are
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// explicitly safe for use in STL containers.
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// It is very important that a client who pulls the pointer out of
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// this holder does not let the holder go out of scope until it is
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// finished with the pointer. It is also important that exactly one
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// instance of this object ever gets initialized with a given pointer.
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// Otherwise, the pointer will be deleted twice, and before that, some
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// objects will be left with a pointer to a deleted object. In other
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// words, the only legitimate way for two PointerHolder objects to
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// contain the same pointer is for one to be a copy of the other.
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// Copy and assignment semantics are well-defined and essentially
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// allow you to use PointerHolder as a means to get pass-by-reference
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// semantics in a pass-by-value environment without having to worry
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// about memory management details.
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// Comparison (== and <) are defined and operate on the internally
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// stored pointers, not on the data. This makes it possible to store
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// PointerHolder objects in sorted lists or to find them in STL
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// containers just as one would be able to store pointers. Comparing
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// the underlying pointers provides a well-defined, if not
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// particularly meaningful, ordering.
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# include <cstddef>
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# include <memory>
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template <class T>
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class PointerHolder
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{
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private:
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class Data
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class PointerHolder: public std::shared_ptr<T>
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{
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public:
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Data(T* pointer, bool array) :
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pointer(pointer),
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array(array),
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refcount(0)
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# if POINTERHOLDER_TRANSITION >= 3
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[[deprecated("use std::shared_ptr<T> instead")]]
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# endif // POINTERHOLDER_TRANSITION >= 3
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PointerHolder(std::shared_ptr<T> other) :
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std::shared_ptr<T>(other)
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{
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}
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~Data()
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{
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if (array) {
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delete[] this->pointer;
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} else {
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delete this->pointer;
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}
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}
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T* pointer;
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bool array;
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int refcount;
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private:
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Data(Data const&) = delete;
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Data& operator=(Data const&) = delete;
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};
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public:
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# if POINTERHOLDER_TRANSITION >= 3
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[[deprecated("use std::shared_ptr<T> instead")]]
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# if POINTERHOLDER_TRANSITION >= 1
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explicit
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# endif // POINTERHOLDER_TRANSITION >= 1
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PointerHolder(T* pointer = 0)
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# endif // POINTERHOLDER_TRANSITION >= 3
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PointerHolder(T* pointer = 0) :
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std::shared_ptr<T>(pointer)
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{
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this->init(new Data(pointer, false));
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}
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// Special constructor indicating to free memory with delete []
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// instead of delete
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PointerHolder(bool, T* pointer)
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// Create a shared pointer to an array
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# if POINTERHOLDER_TRANSITION >= 3
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[[deprecated("use std::shared_ptr<T> instead")]]
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# endif // POINTERHOLDER_TRANSITION >= 3
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PointerHolder(bool, T* pointer) :
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std::shared_ptr<T>(pointer, std::default_delete<T[]>())
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{
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this->init(new Data(pointer, true));
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}
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PointerHolder(PointerHolder const& rhs)
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{
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this->copy(rhs);
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}
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PointerHolder&
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operator=(PointerHolder const& rhs)
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{
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if (this != &rhs) {
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this->destroy();
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this->copy(rhs);
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}
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return *this;
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}
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PointerHolder&
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operator=(decltype(nullptr))
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{
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this->operator=(PointerHolder<T>());
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return *this;
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}
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~PointerHolder()
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{
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this->destroy();
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}
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bool
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operator==(PointerHolder const& rhs) const
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{
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return this->data->pointer == rhs.data->pointer;
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}
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bool
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operator==(decltype(nullptr)) const
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{
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return this->data->pointer == nullptr;
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}
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bool
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operator<(PointerHolder const& rhs) const
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{
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return this->data->pointer < rhs.data->pointer;
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}
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// get() is for interface compatibility with std::shared_ptr
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T*
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get() const
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{
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return this->data->pointer;
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}
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virtual ~PointerHolder() = default;
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// NOTE: The pointer returned by getPointer turns into a pumpkin
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// when the last PointerHolder that contains it disappears.
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# if POINTERHOLDER_TRANSITION >= 2
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[[deprecated("use PointerHolder<T>::get() instead of getPointer()")]]
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# endif // POINTERHOLDER_TRANSITION >= 2
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T*
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getPointer()
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{
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return this->data->pointer;
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return this->get();
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}
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# if POINTERHOLDER_TRANSITION >= 2
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[[deprecated("use PointerHolder<T>::get() instead of getPointer()")]]
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@ -278,73 +191,45 @@ class PointerHolder
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T const*
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getPointer() const
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{
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return this->data->pointer;
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return this->get();
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}
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# if POINTERHOLDER_TRANSITION >= 2
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[[deprecated("use use_count() instead of getRefcount()")]]
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[[deprecated("use PointerHolder<T>::get() instead of getPointer()")]]
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# endif // POINTERHOLDER_TRANSITION >= 2
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int
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getRefcount() const
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{
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return this->data->refcount;
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return static_cast<int>(this->use_count());
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}
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// use_count() is for compatibility with std::shared_ptr
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long
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use_count()
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PointerHolder&
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operator=(decltype(nullptr))
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{
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return static_cast<long>(this->data->refcount);
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std::shared_ptr<T>::operator=(nullptr);
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return *this;
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}
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T const&
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operator*() const
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{
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return *this->data->pointer;
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return *(this->get());
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}
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T&
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operator*()
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{
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return *this->data->pointer;
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return *(this->get());
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}
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T const*
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operator->() const
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{
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return this->data->pointer;
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return this->get();
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}
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T*
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operator->()
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{
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return this->data->pointer;
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return this->get();
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}
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private:
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void
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init(Data* data)
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{
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this->data = data;
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++this->data->refcount;
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}
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void
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copy(PointerHolder const& rhs)
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{
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this->init(rhs.data);
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}
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void
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destroy()
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{
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bool gone = false;
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{
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if (--this->data->refcount == 0) {
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gone = true;
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}
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}
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if (gone) {
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delete this->data;
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}
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}
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Data* data;
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};
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template <typename T, typename... _Args>
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@ -361,4 +246,5 @@ make_array_pointer_holder(size_t n)
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return PointerHolder<T>(true, new T[n]);
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}
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#endif // POINTERHOLDER_TRANSITION < 4
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#endif // POINTERHOLDER_HH
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@ -65,8 +65,8 @@ callHelloWithGet(ObjectHolder const& oh)
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(*oh).hello();
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}
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int
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main(int argc, char* argv[])
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void
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test_ph()
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{
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std::list<ObjectHolder> ol1;
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@ -111,5 +111,135 @@ main(int argc, char* argv[])
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std::cout << "array" << std::endl;
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PointerHolder<Object> o_arr1_ph(true, new Object[2]);
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std::cout << "goodbye" << std::endl;
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}
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PointerHolder<Object>
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make_object_ph()
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{
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return new Object;
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}
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std::shared_ptr<Object>
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make_object_sp()
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{
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return std::make_shared<Object>();
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}
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PointerHolder<Object const>
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make_object_const_ph()
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{
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return new Object;
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}
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std::shared_ptr<Object const>
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make_object_const_sp()
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{
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return std::make_shared<Object const>();
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}
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void
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hello_ph(PointerHolder<Object> o)
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{
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o->hello();
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}
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void
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hello_sp(std::shared_ptr<Object> o)
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{
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o->hello();
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}
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void
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hello_ph_const(PointerHolder<Object const> o)
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{
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o->hello();
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}
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void
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hello_sp_const(std::shared_ptr<Object const> o)
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{
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o->hello();
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}
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void
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ph_sp_compat()
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{
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// Ensure bidirectional compatibility between PointerHolder and
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// shared_ptr.
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std::cout << "compat" << std::endl;
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PointerHolder<Object> ph_from_ph = make_object_ph();
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std::shared_ptr<Object> sp_from_ph = make_object_ph();
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PointerHolder<Object> ph_from_sp = make_object_sp();
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std::shared_ptr<Object> sp_from_sp = make_object_sp();
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hello_sp(ph_from_ph);
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hello_ph(sp_from_ph);
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hello_sp(ph_from_sp);
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hello_ph(sp_from_sp);
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PointerHolder<Object const> ph_const_from_ph = make_object_const_ph();
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std::shared_ptr<Object const> sp_const_from_ph = make_object_const_ph();
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PointerHolder<Object const> ph_const_from_sp = make_object_const_sp();
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std::shared_ptr<Object const> sp_const_from_sp = make_object_const_sp();
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hello_sp_const(ph_const_from_ph);
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hello_ph_const(sp_const_from_ph);
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hello_sp_const(ph_const_from_sp);
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hello_ph_const(sp_const_from_sp);
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PointerHolder<Object> arr1_ph;
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{
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std::cout << "initialize ph array from shared_ptr" << std::endl;
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std::shared_ptr<Object> arr1(
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new Object[2], std::default_delete<Object[]>());
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arr1_ph = arr1;
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}
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std::cout << "delete ph array" << std::endl;
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arr1_ph = nullptr;
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std::shared_ptr<Object> arr2_sp;
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{
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std::cout << "initialize sp array from PointerHolder" << std::endl;
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PointerHolder<Object> arr2(true, new Object[2]);
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arr2_sp = arr2;
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}
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std::cout << "delete sp array" << std::endl;
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arr2_sp = nullptr;
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std::cout << "end compat" << std::endl;
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}
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std::list<PointerHolder<Object>>
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get_ph_list()
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{
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std::list<PointerHolder<Object>> l = {
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make_object_sp(),
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make_object_ph(),
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};
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return l;
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}
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std::list<std::shared_ptr<Object>>
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get_sp_list()
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{
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std::list<std::shared_ptr<Object>> l = {
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make_object_sp(),
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make_object_ph(),
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};
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return l;
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}
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void
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ph_sp_containers()
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{
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std::cout << "containers" << std::endl;
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// Demonstrate that using auto makes it easy to switch interfaces
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// from using a container of one shared pointer type to a
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// container of the other.
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auto phl1 = get_ph_list();
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auto phl2 = get_sp_list();
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std::cout << "end containers" << std::endl;
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}
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int
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main(int argc, char* argv[])
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{
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test_ph();
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ph_sp_compat();
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ph_sp_containers();
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return 0;
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}
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@ -30,3 +30,51 @@ destroyed Object, id 6
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destroyed Object, id 5
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destroyed Object, id 3
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destroyed Object, id 1
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compat
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created Object, id 7
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created Object, id 8
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created Object, id 9
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created Object, id 10
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calling Object::hello for 7
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calling Object::hello for 8
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calling Object::hello for 9
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calling Object::hello for 10
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created Object, id 11
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created Object, id 12
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created Object, id 13
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created Object, id 14
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calling Object::hello const for 11
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calling Object::hello const for 12
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calling Object::hello const for 13
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calling Object::hello const for 14
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initialize ph array from shared_ptr
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created Object, id 15
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created Object, id 16
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delete ph array
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destroyed Object, id 16
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destroyed Object, id 15
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initialize sp array from PointerHolder
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created Object, id 17
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created Object, id 18
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delete sp array
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destroyed Object, id 18
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destroyed Object, id 17
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end compat
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destroyed Object, id 14
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destroyed Object, id 13
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destroyed Object, id 12
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destroyed Object, id 11
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destroyed Object, id 10
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destroyed Object, id 9
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destroyed Object, id 8
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destroyed Object, id 7
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containers
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created Object, id 19
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created Object, id 20
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created Object, id 21
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created Object, id 22
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end containers
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destroyed Object, id 21
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destroyed Object, id 22
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destroyed Object, id 19
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destroyed Object, id 20
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