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#pragma once
#include <yql/essentials/utils/yql_panic.h>
#include <util/generic/hash.h>
#include <util/generic/maybe.h>
#include <util/generic/vector.h>
#include <stdexcept>
#include <algorithm>
namespace NYql {
// TCheckpointHashMap - hash table with checkpoint/rollback support
//
// This class behaves like a regular THashMap but provides the ability
// to create checkpoints of the current state and rollback to them.
//
// Key methods:
// - Checkpoint() - creates a savepoint of the current state
// - Rollback() - reverts all changes back to the last checkpoint
// - Set(key, value) - sets value for the given key
// - Get(key) - gets value by key (throws exception if key doesn't exist)
// - erase(key) - removes element by key
// - find(key) - finds element, returns const_iterator
//
// Usage example:
// TCheckpointHashMap<int, string> map;
// map.Set(1, "hello");
// map.Checkpoint();
// map.Set(2, "world");
// map.Set(1, "modified");
// map.Rollback(); // map now contains only {1: "hello"}
//
// Alternative with TCheckpointGuard (RAII):
// {
// TCheckpointGuard guard(map);
// map.Set(2, "temp");
// } // automatic rollback when leaving scope
//
// WARNING: This class is NOT exception-safe!
// - Internal state corruption is possible during exceptions
template <typename TKey, typename TValue>
class TCheckpointHashMap {
public:
using key_type = typename THashMap<TKey, TValue>::key_type;
using mapped_type = typename THashMap<TKey, TValue>::mapped_type;
using value_type = typename THashMap<TKey, TValue>::value_type;
using size_type = typename THashMap<TKey, TValue>::size_type;
using const_iterator = typename THashMap<TKey, TValue>::const_iterator;
using TUnderlyingMap = THashMap<TKey, TValue>;
TCheckpointHashMap()
: CurrentCheckpointId_(0)
{
}
TCheckpointHashMap(const TCheckpointHashMap& other) = delete;
TCheckpointHashMap(TCheckpointHashMap&& other) = delete;
TCheckpointHashMap& operator=(const TCheckpointHashMap& other) = delete;
TCheckpointHashMap& operator=(TCheckpointHashMap&& other) = delete;
void Checkpoint() {
++CurrentCheckpointId_;
}
void Rollback() {
YQL_ENSURE(CurrentCheckpointId_ != 0, "Cannot rollback without checkpoint");
auto it = Commands_.rbegin();
while (it != Commands_.rend() && it->first == CurrentCheckpointId_) {
const auto& cmd = it->second;
if (cmd.OldValue.Defined()) {
Map_[cmd.Key] = *cmd.OldValue;
} else {
Map_.erase(cmd.Key);
}
++it;
}
auto eraseFrom = it.base();
Commands_.erase(eraseFrom, Commands_.end());
--CurrentCheckpointId_;
}
void Set(const TKey& key, const TValue& value) {
typename TUnderlyingMap::insert_ctx ctx = nullptr;
auto it = Map_.find(key, ctx);
if (CurrentCheckpointId_ != 0) {
if (it == Map_.end()) {
Commands_.emplace_back(CurrentCheckpointId_, TUpdateCommand(key, Nothing()));
} else {
Commands_.emplace_back(CurrentCheckpointId_, TUpdateCommand(key, it->second));
}
}
if (it == Map_.end()) {
Map_.emplace_direct(ctx, key, value);
} else {
it->second = value;
}
}
const TValue& Get(const TKey& key) const {
return Map_.at(key);
}
size_type erase(const TKey& key) {
auto it = Map_.find(key);
if (it != Map_.end()) {
if (CurrentCheckpointId_ != 0) {
Commands_.emplace_back(CurrentCheckpointId_, TUpdateCommand(key, it->second));
}
Map_.erase(it);
return 1;
}
return 0;
}
const_iterator find(const TKey& key) const {
return Map_.find(key);
}
size_type count(const TKey& key) const {
return Map_.count(key);
}
bool contains(const TKey& key) const {
return Map_.find(key) != Map_.end();
}
const_iterator begin() const {
return Map_.begin();
}
const_iterator cbegin() const {
return Map_.cbegin();
}
const_iterator end() const {
return Map_.end();
}
const_iterator cend() const {
return Map_.cend();
}
bool empty() const {
return Map_.empty();
}
size_type size() const {
return Map_.size();
}
size_type max_size() const {
return Map_.max_size();
}
bool operator==(const TCheckpointHashMap& other) const {
return Map_ == other.Map_;
}
bool operator!=(const TCheckpointHashMap& other) const {
return !(*this == other);
}
const THashMap<TKey, TValue>& GetUnderlyingMap() const {
return Map_;
}
size_t GetCommandCount() const {
return Commands_.size();
}
private:
struct TUpdateCommand {
TKey Key;
TMaybe<TValue> OldValue;
TUpdateCommand(TKey key, TMaybe<TValue> oldVal)
: Key(std::move(key))
, OldValue(std::move(oldVal))
{
}
};
using TCommand = TUpdateCommand;
TUnderlyingMap Map_;
TVector<std::pair<size_t, TCommand>> Commands_;
size_t CurrentCheckpointId_;
};
template <typename TKey, typename TValue>
class TCheckpointGuard {
public:
explicit TCheckpointGuard(TCheckpointHashMap<TKey, TValue>& map)
: Map_(map)
{
Map_.Checkpoint();
}
~TCheckpointGuard() {
Map_.Rollback();
}
private:
TCheckpointHashMap<TKey, TValue>& Map_;
};
} // namespace NYql
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