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Simplify 'List_model'

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This patch replaces the original policy-based 'update_from_xml' by a new
method that takes three functors for creating, destroying, and updating
elements as arguments. XML nodes are associated with their corresponding
internal data models by annotating the element type with the
'type_matches' class function and the 'matches' method.

The patch also improves safety by enforcing that list-model elements can
never be copied.

Fixes #4317
This commit is contained in:
Norman Feske 2023-10-27 16:01:23 +02:00 committed by Christian Helmuth
parent b7b74e62a0
commit b9b2a7de34
1 changed files with 87 additions and 157 deletions
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244
repos/base/include/util/list_model.h
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@ -4,13 +4,51 @@
* \date 2017-08-09 * \date 2017-08-09
* *
* The 'List_model' stores a component-internal representation of XML-node * The 'List_model' stores a component-internal representation of XML-node
* content. The XML information is imported according to an 'Update_policy', * content. The internal representation 'ELEM' carries two methods 'matches'
* which specifies how the elements of the data model are created, destroyed, * and 'type_matches' that define the relation of the elements to XML nodes.
* and updated. The elements are ordered according to the order of XML nodes. * E.g.,
*
* ! struct Item : List_model<Item>::Element
* ! {
* ! static bool type_matches(Xml_node const &);
* !
* ! bool matches(Xml_node const &) const;
* ! ...
* ! };
*
* The class function 'type_matches' returns true if the specified XML node
* matches the 'Item' type. It can thereby be used to control the creation
* of 'ELEM' nodes by responding to specific XML tags while ignoring unrelated
* XML tags.
*
* The 'matches' method returns true if the concrete element instance matches
* the given XML node. It is used to correlate existing 'ELEM' objects with
* new versions of XML nodes to update the 'ELEM' objects.
*
* The functor arguments 'create_fn', 'destroy_fn', and 'update_fn' for the
* 'update_from_xml' method define how objects are created, destructed, and
* updated. E.g.,
*
* ! _list_model.update_from_xml(node,
* !
* ! [&] (Xml_node const &node) -> Item & {
* ! return *new (alloc) Item(node); },
* !
* ! [&] (Item &item) { destroy(alloc, &item); },
* !
* ! [&] (Item &item, Xml_node const &node) { item.update(node); }
* ! );
*
* The elements are ordered according to the order of XML nodes.
*
* The list model is a container owning the elements. Before destructing a
* list model, its elements must be removed by calling 'update_from_xml'
* with an 'Xml_node("<empty/>")' as argument, which results in the call
* of 'destroy_fn' for each element.
*/ */
/* /*
* Copyright (C) 2017 Genode Labs GmbH * Copyright (C) 2017-2023 Genode Labs GmbH
* *
* This file is part of the Genode OS framework, which is distributed * This file is part of the Genode OS framework, which is distributed
* under the terms of the GNU Affero General Public License version 3. * under the terms of the GNU Affero General Public License version 3.
@ -20,27 +58,16 @@
#define _INCLUDE__UTIL__LIST_MODEL_H_ #define _INCLUDE__UTIL__LIST_MODEL_H_
/* Genode includes */ /* Genode includes */
#include <util/noncopyable.h>
#include <util/xml_node.h> #include <util/xml_node.h>
#include <util/list.h> #include <util/list.h>
#include <base/log.h> #include <base/log.h>
#include <base/exception.h>
namespace Genode { namespace Genode { template <typename> class List_model; }
template <typename> class List_model;
template <typename CREATE_FN, typename DESTROY_FN, typename UPDATE_FN,
typename NODE = decltype(CREATE_FN())>
static inline void update_list_model_from_xml(List_model<NODE> &,
Xml_node const &,
CREATE_FN const &,
DESTROY_FN const &,
UPDATE_FN const &);
}
template <typename ELEM> template <typename ELEM>
class Genode::List_model class Genode::List_model : Noncopyable
{ {
private: private:
@ -60,8 +87,16 @@ class Genode::List_model
ELEM *_next() const { return List<ELEM>::Element::next(); } ELEM *_next() const { return List<ELEM>::Element::next(); }
/**
* Noncopyable
*/
Element(Element const &) = delete;
Element & operator = (Element const &) = delete;
public: public:
Element() { };
/** /**
* Return the element's neighbor if present, otherwise nullptr * Return the element's neighbor if present, otherwise nullptr
*/ */
@ -77,12 +112,12 @@ class Genode::List_model
} }
/** /**
* Update data model according to XML structure 'node' * Update data model according to the given XML node
*
* \throw Unknown_element_type
*/ */
template <typename POLICY> inline void update_from_xml(Xml_node const &,
inline void update_from_xml(POLICY &policy, Xml_node node); auto const &create_fn,
auto const &destroy_fn,
auto const &update_fn);
/** /**
* Call functor 'fn' for each const element * Call functor 'fn' for each const element
@ -121,83 +156,58 @@ class Genode::List_model
if (Element const *e = _elements.first()) if (Element const *e = _elements.first())
fn(static_cast<ELEM const &>(*e)); fn(static_cast<ELEM const &>(*e));
} }
/**
* Remove all elements from the data model
*
* This method should be called at the destruction time of the
* 'List_model'.
*
* List-model elements are not implicitly destroyed by the destructor
* because the 'policy' needed to destruct elements is not kept as
* member of the list model (multiple policies may applied to the same
* list model).
*/
template <typename POLICY>
void destroy_all_elements(POLICY &policy)
{
Element *next = nullptr;
for (Element *e = _elements.first(); e; e = next) {
next = e->_next();
ELEM &elem = static_cast<ELEM &>(*e);
_elements.remove(&elem);
policy.destroy_element(elem);
}
}
}; };
template <typename ELEM> template <typename ELEM>
template <typename POLICY> void Genode::List_model<ELEM>::update_from_xml(Xml_node const &node,
void Genode::List_model<ELEM>::update_from_xml(POLICY &policy, Xml_node node) auto const &create_fn,
auto const &destroy_fn,
auto const &update_fn)
{ {
typedef typename POLICY::Element Element; List<ELEM> updated_list;
List<Element> updated_list; ELEM *last_updated = nullptr; /* used for appending to 'updated_list' */
Element *last_updated = nullptr; /* used for appending to 'updated_list' */
node.for_each_sub_node([&] (Xml_node sub_node) { node.for_each_sub_node([&] (Xml_node sub_node) {
/* skip XML nodes that are unrelated to the data model */ /* skip XML nodes that are unrelated to the data model */
if (!policy.node_is_element(sub_node)) if (!ELEM::type_matches(sub_node))
return; return;
/* check for duplicates, which must not exist in the list model */ /* check for duplicates, which must not exist in the list model */
for (Element *dup = updated_list.first(); dup; dup = dup->_next()) { for (ELEM *dup = updated_list.first(); dup; dup = dup->_next()) {
/* update existing element with information from later node */ /* update existing element with information from later node */
if (policy.element_matches_xml_node(*dup, sub_node)) { if (dup->matches(sub_node)) {
policy.update_element(*dup, sub_node); update_fn(*dup, sub_node);
return; return;
} }
} }
/* look up corresponding element in original list */ /* look up corresponding element in original list */
Element *curr = _elements.first(); ELEM *curr = _elements.first();
while (curr && !policy.element_matches_xml_node(*curr, sub_node)) while (curr && !curr->matches(sub_node))
curr = curr->_next(); curr = curr->_next();
/* consume existing element or create new one */ /* consume existing element or create new one */
if (curr) { if (curr)
_elements.remove(curr); _elements.remove(curr);
} else { else
/* \throw Unknown_element_type */ curr = &create_fn(sub_node);
curr = &policy.create_element(sub_node);
}
/* append current element to 'updated_list' */ /* append current element to 'updated_list' */
updated_list.insert(curr, last_updated); updated_list.insert(curr, last_updated);
last_updated = curr; last_updated = curr;
policy.update_element(*curr, sub_node); update_fn(*curr, sub_node);
}); });
/* remove stale elements */ /* remove stale elements */
Element *next = nullptr; ELEM *next = nullptr;
for (Element *e = _elements.first(); e; e = next) { for (ELEM *e = _elements.first(); e; e = next) {
next = e->_next(); next = e->_next();
policy.destroy_element(*e); destroy_fn(*e);
} }
/* use 'updated_list' list new data model */ /* use 'updated_list' list new data model */
@ -205,98 +215,18 @@ void Genode::List_model<ELEM>::update_from_xml(POLICY &policy, Xml_node node)
} }
/** namespace Genode {
* Policy interface to be supplied to 'List_model::update_from_xml'
*
* \param ELEM element type, must be a list element
*
* This class template is merely a blue print of a policy to document the
* interface.
*/
template <typename ELEM>
struct Genode::List_model<ELEM>::Update_policy
{
typedef List_model<ELEM>::Unknown_element_type Unknown_element_type;
/* template <typename CREATE_FN, typename DESTROY_FN, typename UPDATE_FN,
* Type that needs to be supplied by the policy implementation typename NODE = decltype(CREATE_FN())>
*/ static inline void update_list_model_from_xml(List_model<NODE> &model,
typedef ELEM Element; Xml_node const &node,
CREATE_FN const &create_fn,
/** DESTROY_FN const &destroy_fn,
* Destroy element UPDATE_FN const &update_fn)
*
* When this function is called, the element is no longer contained
* in the model's list.
*/
void destroy_element(ELEM &elem);
/**
* Create element of the type given in the 'elem_node'
*
* \throw List_model::Unknown_element_type
*/
ELEM &create_element(Xml_node elem_node);
/**
* Import element properties from XML node
*/
void update_element(ELEM &elem, Xml_node elem_node);
/**
* Return true if element corresponds to XML node
*/
static bool element_matches_xml_node(Element const &, Xml_node);
/**
* Return true if XML node should be imported
*
* This method allows the policy to disregard certain XML node types from
* building the data model.
*/
static bool node_is_element(Xml_node) { return true; }
};
template <typename CREATE_FN, typename DESTROY_FN, typename UPDATE_FN, typename NODE>
void Genode::update_list_model_from_xml(List_model<NODE> &model,
Xml_node const &xml,
CREATE_FN const &create,
DESTROY_FN const &destroy,
UPDATE_FN const &update)
{
struct Model_update_policy : List_model<NODE>::Update_policy
{ {
CREATE_FN const &_create_fn; model.update_from_xml(node, create_fn, destroy_fn, update_fn);
DESTROY_FN const &_destroy_fn; }
UPDATE_FN const &_update_fn;
Model_update_policy(CREATE_FN const &create_fn,
DESTROY_FN const &destroy_fn,
UPDATE_FN const &update_fn)
:
_create_fn(create_fn), _destroy_fn(destroy_fn), _update_fn(update_fn)
{ }
void destroy_element(NODE &node) { _destroy_fn(node); }
NODE &create_element(Xml_node xml) { return _create_fn(xml); }
void update_element(NODE &node, Xml_node xml) { _update_fn(node, xml); }
static bool element_matches_xml_node(NODE const &node, Xml_node xml)
{
return node.matches(xml);
}
static bool node_is_element(Xml_node node)
{
return NODE::type_matches(node);
}
} policy(create, destroy, update);
model.update_from_xml(policy, xml);
} }
#endif /* _INCLUDE__UTIL__LIST_MODEL_H_ */ #endif /* _INCLUDE__UTIL__LIST_MODEL_H_ */