thin-provisioning-tools/cache.h

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#ifndef CACHE_H
#define CACHE_H
#include <boost/intrusive/circular_list_algorithms.hpp>
#include <boost/intrusive/rbtree_algorithms.hpp>
#include <boost/optional.hpp>
#include <list>
#include <map>
#include <stdexcept>
//----------------------------------------------------------------
namespace base {
// FIXME: move somewhere more useful
template <typename T>
struct deleter {
void operator()(T *t) {
delete t;
}
};
// ValueTraits needs to define value_type, key_type and a get_key()
// static function. Commonly you will want value_type to be a
// shared_ptr, with any teardown specific stuff in the destructor.
template <typename ValueTraits>
class cache {
public:
typedef typename ValueTraits::value_type value_type;
typedef typename ValueTraits::key_type key_type;
cache(unsigned max_entries);
~cache();
void insert(value_type const &v);
boost::optional<value_type> get(key_type const &k);
void put(value_type const &k);
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template <typename T>
void iterate_unheld(T fn) const;
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private:
void make_space();
struct value_entry {
// FIXME: this means the cached object must have a
// default constructor also, which is a shame.
// so we can construct the headers.
value_entry()
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: ref_count_(1) {
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}
explicit value_entry(value_type v)
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: ref_count_(1),
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v_(v) {
}
struct {
value_entry *next_, *prev_;
} lru_;
struct {
value_entry *parent_, *left_, *right_;
int color_;
} lookup_;
unsigned ref_count_;
value_type v_;
};
struct value_ptr_cmp {
bool operator() (value_entry const *lhs, value_entry const *rhs) {
key_type k1 = ValueTraits::get_key(lhs->v_);
key_type k2 = ValueTraits::get_key(rhs->v_);
return k1 < k2;
}
};
struct key_value_ptr_cmp {
bool operator() (key_type const &k1, value_entry const *rhs) {
key_type k2 = ValueTraits::get_key(rhs->v_);
return k1 < k2;
}
bool operator() (value_entry const *lhs, key_type const &k2) {
key_type k1 = ValueTraits::get_key(lhs->v_);
return k1 < k2;
}
};
struct list_node_traits {
typedef value_entry node;
typedef value_entry *node_ptr;
typedef const value_entry *const_node_ptr;
static node_ptr get_next(const_node_ptr n) {
return n->lru_.next_;
}
static void set_next(node_ptr n, node_ptr next) {
n->lru_.next_ = next;
}
static node_ptr get_previous(const_node_ptr n) {
return n->lru_.prev_;
}
static void set_previous(node_ptr n, node_ptr prev) {
n->lru_.prev_ = prev;
}
};
struct rbtree_node_traits {
typedef value_entry node;
typedef value_entry *node_ptr;
typedef const value_entry * const_node_ptr;
typedef int color;
static node_ptr get_parent(const_node_ptr n) {
return n->lookup_.parent_;
}
static void set_parent(node_ptr n, node_ptr parent) {
n->lookup_.parent_ = parent;
}
static node_ptr get_left(const_node_ptr n) {
return n->lookup_.left_;
}
static void set_left(node_ptr n, node_ptr left) {
n->lookup_.left_ = left;
}
static node_ptr get_right(const_node_ptr n) {
return n->lookup_.right_;
}
static void set_right(node_ptr n, node_ptr right) {
n->lookup_.right_ = right;
}
static int get_color(const_node_ptr n) {
return n->lookup_.color_;
}
static void set_color(node_ptr n, color c) {
n->lookup_.color_ = c;
}
static color red() {
return 0;
}
static color black() {
return 1;
}
};
typedef boost::intrusive::circular_list_algorithms<list_node_traits> lru_algo;
typedef boost::intrusive::rbtree_algorithms<rbtree_node_traits> lookup_algo;
unsigned max_entries_;
unsigned current_entries_;
value_entry lru_header_;
value_entry lookup_header_;
};
template <typename ValueTraits>
cache<ValueTraits>::cache(unsigned max_entries)
: max_entries_(max_entries),
current_entries_(0) {
lru_algo::init_header(&lru_header_);
lookup_algo::init_header(&lookup_header_);
}
template <typename ValueTraits>
cache<ValueTraits>::~cache() {
deleter<value_entry> d;
lookup_algo::clear_and_dispose(&lookup_header_, d);
}
template <typename ValueTraits>
void
cache<ValueTraits>::insert(value_type const &v) {
make_space();
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// FIXME: use an auto_ptr to avoid the explicit try/catch
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value_entry *node = new value_entry(v);
try {
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value_ptr_cmp cmp;
lookup_algo::insert_equal(&lookup_header_, &lookup_header_, node, cmp);
current_entries_++;
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} catch (...) {
delete node;
throw;
}
}
template <typename ValueTraits>
boost::optional<typename ValueTraits::value_type>
cache<ValueTraits>::get(key_type const &k) {
key_value_ptr_cmp cmp;
value_entry *node = lookup_algo::find(&lookup_header_, k, cmp);
if (node == &lookup_header_)
return boost::optional<value_type>();
if (!node->ref_count_++)
lru_algo::unlink(node);
return boost::optional<value_type>(node->v_);
}
template <typename ValueTraits>
void
cache<ValueTraits>::put(value_type const &v) {
// FIXME: the lookup will go once we use a proper hook
key_value_ptr_cmp cmp;
key_type k = ValueTraits::get_key(v);
value_entry *node = lookup_algo::find(&lookup_header_, k, cmp);
if (node == &lookup_header_)
throw std::runtime_error("invalid put");
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if (node->ref_count_ == 0)
throw std::runtime_error("invalid put");
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if (!--node->ref_count_)
lru_algo::link_after(&lru_header_, node);
}
template <typename ValueTraits>
void
cache<ValueTraits>::make_space() {
if (current_entries_ == max_entries_) {
value_entry *node = lru_header_.lru_.prev_;
if (node == &lru_header_)
throw std::runtime_error("cache full");
lru_algo::unlink(node);
lookup_algo::unlink(node);
delete node;
current_entries_--;
}
}
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template <typename ValueTraits>
template <typename T>
void
cache<ValueTraits>::iterate_unheld(T fn) const {
value_entry *n = lru_header_.lru_.next_;
while (n != &lru_header_) {
fn(n->v_);
n = n->lru_.next_;
}
}
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}
//----------------------------------------------------------------
#endif