Remove unused epochguard.h

src/util/epochguard.h

@@ -1,102 +0,0 @@
-// Copyright (c) 2009-2010 Satoshi Nakamoto
-// Copyright (c) 2009-present The Bitcoin Core developers
-// Distributed under the MIT software license, see the accompanying
-// file COPYING or http://www.opensource.org/licenses/mit-license.php.
-
-#ifndef BITCOIN_UTIL_EPOCHGUARD_H
-#define BITCOIN_UTIL_EPOCHGUARD_H
-
-#include <threadsafety.h>
-#include <util/macros.h>
-
-#include <cassert>
-
-/** Epoch: RAII-style guard for using epoch-based graph traversal algorithms.
- *     When walking ancestors or descendants, we generally want to avoid
- * visiting the same transactions twice. Some traversal algorithms use
- * std::set (or setEntries) to deduplicate the transaction we visit.
- * However, use of std::set is algorithmically undesirable because it both
- * adds an asymptotic factor of O(log n) to traversals cost and triggers O(n)
- * more dynamic memory allocations.
- *     In many algorithms we can replace std::set with an internal mempool
- * counter to track the time (or, "epoch") that we began a traversal, and
- * check + update a per-transaction epoch for each transaction we look at to
- * determine if that transaction has not yet been visited during the current
- * traversal's epoch.
- *     Algorithms using std::set can be replaced on a one by one basis.
- * Both techniques are not fundamentally incompatible across the codebase.
- * Generally speaking, however, the remaining use of std::set for mempool
- * traversal should be viewed as a TODO for replacement with an epoch based
- * traversal, rather than a preference for std::set over epochs in that
- * algorithm.
- */
-
-class LOCKABLE Epoch
-{
-private:
-    uint64_t m_raw_epoch = 0;
-    bool m_guarded = false;
-
-public:
-    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; }
-
-    class Marker
-    {
-    private:
-        uint64_t m_marker = 0;
-
-        // only allow modification via Epoch member functions
-        friend class Epoch;
-        Marker& operator=(const Marker&) = delete;
-
-    public:
-        Marker() = default;
-        Marker(const Marker&) = default;
-        Marker(Marker&&) = default;
-        Marker& operator=(Marker&&) = default;
-        ~Marker() = default;
-    };
-
-    class SCOPED_LOCKABLE Guard
-    {
-    private:
-        Epoch& m_epoch;
-
-    public:
-        explicit Guard(Epoch& epoch) EXCLUSIVE_LOCK_FUNCTION(epoch) : m_epoch(epoch)
-        {
-            assert(!m_epoch.m_guarded);
-            ++m_epoch.m_raw_epoch;
-            m_epoch.m_guarded = true;
-        }
-        ~Guard() UNLOCK_FUNCTION()
-        {
-            assert(m_epoch.m_guarded);
-            ++m_epoch.m_raw_epoch; // ensure clear separation between epochs
-            m_epoch.m_guarded = false;
-        }
-    };
-
-    bool visited(Marker& marker) const EXCLUSIVE_LOCKS_REQUIRED(*this)
-    {
-        assert(m_guarded);
-        if (marker.m_marker < m_raw_epoch) {
-            // marker is from a previous epoch, so this is its first visit
-            marker.m_marker = m_raw_epoch;
-            return false;
-        } else {
-            return true;
-        }
-    }
-};
-
-#define WITH_FRESH_EPOCH(epoch) const Epoch::Guard UNIQUE_NAME(epoch_guard_)(epoch)
-
-#endif // BITCOIN_UTIL_EPOCHGUARD_H