Merge bitcoin/bitcoin#22481: mempool: apply rule of 5 to epochguard.h, fix compiler warnings

7b3a20b mempool: apply rule of 5 to epochguard.h, fix compiler warnings (Jon Atack)

Pull request description:

  Apply the rule of five to `src/util/epochguard.h::{Epoch, Marker}` for safety, which also nicely fixes the `-Wdeprecated-copy` compiler warnings with Clang 13.

  References:

  - https://en.cppreference.com/w/cpp/language/rule_of_three
  - https://www.stroustrup.com/C++11FAQ.html#default
  - https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Rc-five

  <details><summary>Compiler warnings fixed</summary><p>

  ```bash
  In file included from policy/rbf.cpp:5:
  In file included from ./policy/rbf.h:8:
  In file included from ./txmempool.h:24:
  ./util/epochguard.h:53:17: warning: definition of implicit copy constructor for 'Marker' is deprecated because it has a user-declared copy assignment operator [-Wdeprecated-copy]
          Marker& operator=(const Marker&) = delete;
                  ^
  ./txmempool.h:81:7: note: in implicit copy constructor for 'Epoch::Marker' first required here
  class CTxMemPoolEntry
        ^
  policy/rbf.cpp:29:29: note: in implicit copy constructor for 'CTxMemPoolEntry' first required here
      CTxMemPoolEntry entry = *pool.mapTx.find(tx.GetHash());
  ```

  ```bash
  In file included from txmempool.cpp:6:
  In file included from ./txmempool.h:24:
  ./util/epochguard.h:53:17: warning: definition of implicit copy constructor for 'Marker' is deprecated because it has a user-declared copy assignment operator [-Wdeprecated-copy]
          Marker& operator=(const Marker&) = delete;
                  ^
  ./txmempool.h:81:7: note: in implicit copy constructor for 'Epoch::Marker' first required here
  class CTxMemPoolEntry
        ^
  /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/ext/new_allocator.h:150:23: note: in implicit copy constructor for 'CTxMemPoolEntry' first required here
          { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
                               ^
  /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/bits/alloc_traits.h:512:8: note: in instantiation of function template specialization '__gnu_cxx::new_allocator<boost::multi_index::detail::hashed_index_node<boost::multi_index::detail::hashed_index_node<boost::multi_index::detail::ordered_index_node<boost::multi_index::detail::null_augment_policy, boost::multi_index::detail::ordered_index_node<boost::multi_index::detail::null_augment_policy, boost::multi_index::detail::ordered_index_node<boost::multi_index::detail::null_augment_policy, boost::multi_index::detail::index_node_base<CTxMemPoolEntry, std::allocator<CTxMemPoolEntry>>>>>>>>::construct<CTxMemPoolEntry, const CTxMemPoolEntry &>' requested here
            __a.construct(__p, std::forward<_Args>(__args)...);
                ^
  /usr/include/boost/multi_index_container.hpp:655:24: note: in instantiation of function template specialization 'std::allocator_traits<std::allocator<boost::multi_index::detail::hashed_index_node<boost::multi_index::detail::hashed_index_node<boost::multi_index::detail::ordered_index_node<boost::multi_index::detail::null_augment_policy, boost::multi_index::detail::ordered_index_node<boost::multi_index::detail::null_augment_policy, boost::multi_index::detail::ordered_index_node<boost::multi_index::detail::null_augment_policy, boost::multi_index::detail::index_node_base<CTxMemPoolEntry, std::allocator<CTxMemPoolEntry>>>>>>>>>::construct<CTxMemPoolEntry, const CTxMemPoolEntry &>' requested here
      node_alloc_traits::construct(
                         ^
  /usr/include/boost/multi_index/detail/index_base.hpp:108:15: note: in instantiation of member function 'boost::multi_index::multi_index_container<CTxMemPoolEntry, boost::multi_index::indexed_by<boost::multi_index::hashed_unique<mempoolentry_txid, SaltedTxidHasher>, boost::multi_index::hashed_unique<boost::multi_index::tag<index_by_wtxid>, mempoolentry_wtxid, SaltedTxidHasher>, boost::multi_index::ordered_non_unique<boost::multi_index::tag<descendant_score>, boost::multi_index::identity<CTxMemPoolEntry>, CompareTxMemPoolEntryByDescendantScore>, boost::multi_index::ordered_non_unique<boost::multi_index::tag<entry_time>, boost::multi_index::identity<CTxMemPoolEntry>, CompareTxMemPoolEntryByEntryTime>, boost::multi_index::ordered_non_unique<boost::multi_index::tag<ancestor_score>, boost::multi_index::identity<CTxMemPoolEntry>, CompareTxMemPoolEntryByAncestorFee>>>::construct_value' requested here
        final().construct_value(x,v);
                ^
  /usr/include/boost/multi_index/detail/ord_index_impl.hpp:770:33: note: (skipping 5 contexts in backtrace; use -ftemplate-backtrace-limit=0 to see all)
      final_node_type* res=super::insert_(v,x,variant);
                                  ^
  /usr/include/boost/multi_index_container.hpp:693:33: note: in instantiation of function template specialization 'boost::multi_index::detail::hashed_index<mempoolentry_txid, SaltedTxidHasher, std::equal_to<uint256>, boost::multi_index::detail::nth_layer<1, CTxMemPoolEntry, boost::multi_index::indexed_by<boost::multi_index::hashed_unique<mempoolentry_txid, SaltedTxidHasher>, boost::multi_index::hashed_unique<boost::multi_index::tag<index_by_wtxid>, mempoolentry_wtxid, SaltedTxidHasher>, boost::multi_index::ordered_non_unique<boost::multi_index::tag<descendant_score>, boost::multi_index::identity<CTxMemPoolEntry>, CompareTxMemPoolEntryByDescendantScore>, boost::multi_index::ordered_non_unique<boost::multi_index::tag<entry_time>, boost::multi_index::identity<CTxMemPoolEntry>, CompareTxMemPoolEntryByEntryTime>, boost::multi_index::ordered_non_unique<boost::multi_index::tag<ancestor_score>, boost::multi_index::identity<CTxMemPoolEntry>, CompareTxMemPoolEntryByAncestorFee>>, std::allocator<CTxMemPoolEntry>>, boost::mpl::vector0<>, boost::multi_index::detail::hashed_unique_tag>::insert_<boost::multi_index::detail::lvalue_tag>' requested here
      final_node_type* res=super::insert_(v,x,variant);
                                  ^
  /usr/include/boost/multi_index_container.hpp:705:12: note: in instantiation of function template specialization 'boost::multi_index::multi_index_container<CTxMemPoolEntry, boost::multi_index::indexed_by<boost::multi_index::hashed_unique<mempoolentry_txid, SaltedTxidHasher>, boost::multi_index::hashed_unique<boost::multi_index::tag<index_by_wtxid>, mempoolentry_wtxid, SaltedTxidHasher>, boost::multi_index::ordered_non_unique<boost::multi_index::tag<descendant_score>, boost::multi_index::identity<CTxMemPoolEntry>, CompareTxMemPoolEntryByDescendantScore>, boost::multi_index::ordered_non_unique<boost::multi_index::tag<entry_time>, boost::multi_index::identity<CTxMemPoolEntry>, CompareTxMemPoolEntryByEntryTime>, boost::multi_index::ordered_non_unique<boost::multi_index::tag<ancestor_score>, boost::multi_index::identity<CTxMemPoolEntry>, CompareTxMemPoolEntryByAncestorFee>>>::insert_<boost::multi_index::detail::lvalue_tag>' requested here
      return insert_(v,detail::lvalue_tag());
             ^
  /usr/include/boost/multi_index/detail/index_base.hpp:213:21: note: in instantiation of member function 'boost::multi_index::multi_index_container<CTxMemPoolEntry, boost::multi_index::indexed_by<boost::multi_index::hashed_unique<mempoolentry_txid, SaltedTxidHasher>, boost::multi_index::hashed_unique<boost::multi_index::tag<index_by_wtxid>, mempoolentry_wtxid, SaltedTxidHasher>, boost::multi_index::ordered_non_unique<boost::multi_index::tag<descendant_score>, boost::multi_index::identity<CTxMemPoolEntry>, CompareTxMemPoolEntryByDescendantScore>, boost::multi_index::ordered_non_unique<boost::multi_index::tag<entry_time>, boost::multi_index::identity<CTxMemPoolEntry>, CompareTxMemPoolEntryByEntryTime>, boost::multi_index::ordered_non_unique<boost::multi_index::tag<ancestor_score>, boost::multi_index::identity<CTxMemPoolEntry>, CompareTxMemPoolEntryByAncestorFee>>>::insert_' requested here
      {return final().insert_(x);}
                      ^
  /usr/include/boost/multi_index/hashed_index.hpp:284:46: note: in instantiation of member function 'boost::multi_index::detail::index_base<CTxMemPoolEntry, boost::multi_index::indexed_by<boost::multi_index::hashed_unique<mempoolentry_txid, SaltedTxidHasher>, boost::multi_index::hashed_unique<boost::multi_index::tag<index_by_wtxid>, mempoolentry_wtxid, SaltedTxidHasher>, boost::multi_index::ordered_non_unique<boost::multi_index::tag<descendant_score>, boost::multi_index::identity<CTxMemPoolEntry>, CompareTxMemPoolEntryByDescendantScore>, boost::multi_index::ordered_non_unique<boost::multi_index::tag<entry_time>, boost::multi_index::identity<CTxMemPoolEntry>, CompareTxMemPoolEntryByEntryTime>, boost::multi_index::ordered_non_unique<boost::multi_index::tag<ancestor_score>, boost::multi_index::identity<CTxMemPoolEntry>, CompareTxMemPoolEntryByAncestorFee>>, std::allocator<CTxMemPoolEntry>>::final_insert_' requested here
      std::pair<final_node_type*,bool> p=this->final_insert_(x);
                                               ^
  txmempool.cpp:363:53: note: in instantiation of member function 'boost::multi_index::detail::hashed_index<mempoolentry_txid, SaltedTxidHasher, std::equal_to<uint256>, boost::multi_index::detail::nth_layer<1, CTxMemPoolEntry, boost::multi_index::indexed_by<boost::multi_index::hashed_unique<mempoolentry_txid, SaltedTxidHasher>, boost::multi_index::hashed_unique<boost::multi_index::tag<index_by_wtxid>, mempoolentry_wtxid, SaltedTxidHasher>, boost::multi_index::ordered_non_unique<boost::multi_index::tag<descendant_score>, boost::multi_index::identity<CTxMemPoolEntry>, CompareTxMemPoolEntryByDescendantScore>, boost::multi_index::ordered_non_unique<boost::multi_index::tag<entry_time>, boost::multi_index::identity<CTxMemPoolEntry>, CompareTxMemPoolEntryByEntryTime>, boost::multi_index::ordered_non_unique<boost::multi_index::tag<ancestor_score>, boost::multi_index::identity<CTxMemPoolEntry>, CompareTxMemPoolEntryByAncestorFee>>, std::allocator<CTxMemPoolEntry>>, boost::mpl::vector0<>, boost::multi_index::detail::hashed_unique_tag>::insert' requested here
      indexed_transaction_set::iterator newit = mapTx.insert(entry).first;
  ```

  ```bash
  In file included from test/fuzz/policy_estimator.cpp:9:
  In file included from ./test/fuzz/util.h:27:
  In file included from ./txmempool.h:24:
  ./util/epochguard.h:53:17: warning: definition of implicit copy constructor for 'Marker' is deprecated because it has a user-declared copy assignment operator [-Wdeprecated-copy]
          Marker& operator=(const Marker&) = delete;
                  ^
  ./txmempool.h:81:7: note: in implicit copy constructor for 'Epoch::Marker' first required here
  class CTxMemPoolEntry
        ^
  /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/ext/new_allocator.h:150:23: note: in implicit move constructor for 'CTxMemPoolEntry' first required here
          { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
                               ^
  /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/bits/alloc_traits.h:512:8: note: in instantiation of function template specialization '__gnu_cxx::new_allocator<CTxMemPoolEntry>::construct<CTxMemPoolEntry, CTxMemPoolEntry>' requested here
            __a.construct(__p, std::forward<_Args>(__args)...);
                ^
  /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/bits/vector.tcc:115:21: note: in instantiation of function template specialization 'std::allocator_traits<std::allocator<CTxMemPoolEntry>>::construct<CTxMemPoolEntry, CTxMemPoolEntry>' requested here
              _Alloc_traits::construct(this->_M_impl, this->_M_impl._M_finish,
                             ^
  /usr/bin/../lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/bits/stl_vector.h:1204:9: note: in instantiation of function template specialization 'std::vector<CTxMemPoolEntry>::emplace_back<CTxMemPoolEntry>' requested here
        { emplace_back(std::move(__x)); }
          ^
  test/fuzz/policy_estimator.cpp:49:37: note: in instantiation of member function 'std::vector<CTxMemPoolEntry>::push_back' requested here
                      mempool_entries.push_back(ConsumeTxMemPoolEntry(fuzzed_data_provider, tx));
  ```
  </p></details>

ACKs for top commit:
  laanwj:
    Code review ACK 7b3a20b
  vasild:
    ACK 7b3a20b

Tree-SHA512: 0406dfcec180152d4f9ed07cbc2f406ad739b41f9c9cb38f8c75159c15d9d8a9a5c7526765966e40d695d265c178f6a80152e7edf82da344a65e55938dddb63d

Author: laanwj

src/util/epochguard.h

@@ -40,6 +40,9 @@ class LOCKABLE Epoch
     Epoch() = default;
     Epoch(const Epoch&) = delete;
     Epoch& operator=(const Epoch&) = delete;
+    Epoch(Epoch&&) = delete;
+    Epoch& operator=(Epoch&&) = delete;
+    ~Epoch() = default;
 
     bool guarded() const { return m_guarded; }
 
@@ -51,6 +54,13 @@ class LOCKABLE Epoch
         // only allow modification via Epoch member functions
         friend class Epoch;
         Marker& operator=(const Marker&) = delete;
+
+    public:
+        Marker() = default;
+        Marker(const Marker&) = default;
+        Marker(Marker&&) = delete;
+        Marker& operator=(Marker&&) = delete;
+        ~Marker() = default;
     };
 
     class SCOPED_LOCKABLE Guard