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// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
// vim: ts=8 sw=2 smarttab
/*
* Ceph - scalable distributed file system
*
* Copyright (C) 2013 Inktank Storage, Inc.
*
* This is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License version 2.1, as published by the Free Software
* Foundation. See file COPYING.
*
*/
#ifndef MAPCACHER_H
#define MAPCACHER_H
#include "include/Context.h"
#include "common/sharedptr_registry.hpp"
namespace MapCacher {
/**
* Abstraction for ordering key updates
*/
template<typename K, typename V>
class Transaction {
public:
/// Std::set keys according to map
virtual void set_keys(
const std::map<K, V> &keys ///< [in] keys/values to std::set
) = 0;
/// Remove keys
virtual void remove_keys(
const std::set<K> &to_remove ///< [in] keys to remove
) = 0;
/// Add context to fire when data is readable
virtual void add_callback(
Context *c ///< [in] Context to fire on readable
) = 0;
virtual ~Transaction() {}
};
/**
* Abstraction for fetching keys
*/
template<typename K, typename V>
class StoreDriver {
public:
/// Returns requested key values
virtual int get_keys(
const std::set<K> &keys, ///< [in] keys requested
std::map<K, V> *got ///< [out] values for keys obtained
) = 0; ///< @return error value
/// Returns next key
virtual int get_next(
const K &key, ///< [in] key after which to get next
std::pair<K, V> *next ///< [out] first key after key
) = 0; ///< @return 0 on success, -ENOENT if there is no next
virtual int get_next_or_current(
const K &key, ///< [in] key at-which-or-after to get
std::pair<K, V> *next_or_current
) = 0; ///< @return 0 on success, -ENOENT if there is no next
virtual ~StoreDriver() {}
};
/**
* Uses SharedPtrRegistry to cache objects of in progress writes
* allowing the user to read/write a consistent view of the map
* without flushing writes.
*/
template<typename K, typename V>
class MapCacher {
private:
StoreDriver<K, V> *driver;
SharedPtrRegistry<K, boost::optional<V> > in_progress;
typedef typename SharedPtrRegistry<K, boost::optional<V> >::VPtr VPtr;
typedef ContainerContext<std::set<VPtr> > TransHolder;
public:
MapCacher(StoreDriver<K, V> *driver) : driver(driver) {}
/// Fetch first key/value std::pair after specified key
int get_next(
K key, ///< [in] key after which to get next
std::pair<K, V> *next ///< [out] next key
) {
while (true) {
std::pair<K, boost::optional<V> > cached;
std::pair<K, V> store;
bool got_cached = in_progress.get_next(key, &cached);
bool got_store = false;
int r = driver->get_next(key, &store);
if (r < 0 && r != -ENOENT) {
return r;
} else if (r == 0) {
got_store = true;
}
if (!got_cached && !got_store) {
return -ENOENT;
} else if (
got_cached &&
(!got_store || store.first >= cached.first)) {
if (cached.second) {
if (next)
*next = make_pair(cached.first, cached.second.get());
return 0;
} else {
key = cached.first;
continue; // value was cached as removed, recurse
}
} else {
if (next)
*next = store;
return 0;
}
}
ceph_abort(); // not reachable
return -EINVAL;
} ///< @return error value, 0 on success, -ENOENT if no more entries
/// Adds operation setting keys to Transaction
void set_keys(
const std::map<K, V> &keys, ///< [in] keys/values to std::set
Transaction<K, V> *t ///< [out] transaction to use
) {
std::set<VPtr> vptrs;
for (auto i = keys.begin(); i != keys.end(); ++i) {
VPtr ip = in_progress.lookup_or_create(i->first, i->second);
*ip = i->second;
vptrs.insert(ip);
}
t->set_keys(keys);
t->add_callback(new TransHolder(vptrs));
}
/// Adds operation removing keys to Transaction
void remove_keys(
const std::set<K> &keys, ///< [in]
Transaction<K, V> *t ///< [out] transaction to use
) {
std::set<VPtr> vptrs;
for (auto i = keys.begin(); i != keys.end(); ++i) {
boost::optional<V> empty;
VPtr ip = in_progress.lookup_or_create(*i, empty);
*ip = empty;
vptrs.insert(ip);
}
t->remove_keys(keys);
t->add_callback(new TransHolder(vptrs));
}
/// Gets keys, uses cached values for unstable keys
int get_keys(
const std::set<K> &keys_to_get, ///< [in] std::set of keys to fetch
std::map<K, V> *got ///< [out] keys gotten
) {
std::set<K> to_get;
std::map<K, V> _got;
for (auto i = keys_to_get.begin();
i != keys_to_get.end();
++i) {
VPtr val = in_progress.lookup(*i);
if (val) {
if (*val)
got->insert(make_pair(*i, val->get()));
//else: value cached is empty, key doesn't exist
} else {
to_get.insert(*i);
}
}
int r = driver->get_keys(to_get, &_got);
if (r < 0)
return r;
for (auto i = _got.begin(); i != _got.end(); ++i) {
got->insert(*i);
}
return 0;
} ///< @return error value, 0 on success
};
} // namespace
#endif
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