txgraph: initialize Ref in AddTransaction (preparation)

Instead of returning a TxGraph::Ref from TxGraph::AddTransaction(),
pass in a TxGraph::Ref& which is updated to refer to the new transaction
in that graph.

This cleans up the usage somewhat, avoiding the need for dummy Refs in
CTxMemPoolEntry constructor calls, but the motivation is that a future
commit will allow a callback to passed to MakeTxGraph to define a
fallback order on the transaction objects. This does not work when a
Ref is created separately from the CTxMemPoolEntry it ends up living in,
as passing the newly-created Ref to the callback would be UB before it's
emplaced in its final CTxMemPoolEntry.

src/bench/blockencodings.cpp

@@ -22,7 +22,7 @@
 static void AddTx(const CTransactionRef& tx, const CAmount& fee, CTxMemPool& pool) EXCLUSIVE_LOCKS_REQUIRED(cs_main, pool.cs)
 {
     LockPoints lp;
-    TryAddToMempool(pool, CTxMemPoolEntry(TxGraph::Ref(), tx, fee, /*time=*/0, /*entry_height=*/1, /*entry_sequence=*/0, /*spends_coinbase=*/false, /*sigops_cost=*/4, lp));
+    TryAddToMempool(pool, CTxMemPoolEntry(tx, fee, /*time=*/0, /*entry_height=*/1, /*entry_sequence=*/0, /*spends_coinbase=*/false, /*sigops_cost=*/4, lp));
 }
 
 namespace {

src/bench/mempool_ephemeral_spends.cpp

@@ -29,7 +29,7 @@ static void AddTx(const CTransactionRef& tx, CTxMemPool& pool) EXCLUSIVE_LOCKS_R
     unsigned int sigOpCost{4};
     uint64_t fee{0};
     LockPoints lp;
-    TryAddToMempool(pool, CTxMemPoolEntry(TxGraph::Ref(),
+    TryAddToMempool(pool, CTxMemPoolEntry(
         tx, fee, nTime, nHeight, sequence,
         spendsCoinbase, sigOpCost, lp));
 }

src/bench/mempool_eviction.cpp

@@ -27,7 +27,7 @@ static void AddTx(const CTransactionRef& tx, const CAmount& nFee, CTxMemPool& po
     bool spendsCoinbase = false;
     unsigned int sigOpCost = 4;
     LockPoints lp;
-    TryAddToMempool(pool, CTxMemPoolEntry(TxGraph::Ref(),
+    TryAddToMempool(pool, CTxMemPoolEntry(
         tx, nFee, nTime, nHeight, sequence,
         spendsCoinbase, sigOpCost, lp));
 }

src/bench/mempool_stress.cpp

@@ -29,7 +29,7 @@ static void AddTx(const CTransactionRef& tx, CTxMemPool& pool, FastRandomContext
     bool spendsCoinbase = false;
     unsigned int sigOpCost = 4;
     LockPoints lp;
-    TryAddToMempool(pool, CTxMemPoolEntry(TxGraph::Ref(), tx, det_rand.randrange(10000)+1000, nTime, nHeight, sequence, spendsCoinbase, sigOpCost, lp));
+    TryAddToMempool(pool, CTxMemPoolEntry(tx, det_rand.randrange(10000)+1000, nTime, nHeight, sequence, spendsCoinbase, sigOpCost, lp));
 }
 
 struct Available {

src/bench/rpc_mempool.cpp

@@ -22,7 +22,7 @@
 static void AddTx(const CTransactionRef& tx, const CAmount& fee, CTxMemPool& pool) EXCLUSIVE_LOCKS_REQUIRED(cs_main, pool.cs)
 {
     LockPoints lp;
-    TryAddToMempool(pool, CTxMemPoolEntry(TxGraph::Ref(), tx, fee, /*time=*/0, /*entry_height=*/1, /*entry_sequence=*/0, /*spends_coinbase=*/false, /*sigops_cost=*/4, lp));
+    TryAddToMempool(pool, CTxMemPoolEntry(tx, fee, /*time=*/0, /*entry_height=*/1, /*entry_sequence=*/0, /*spends_coinbase=*/false, /*sigops_cost=*/4, lp));
 }
 
 static void RpcMempool(benchmark::Bench& bench)

src/bench/txgraph.cpp

@@ -67,7 +67,7 @@ void BenchTxGraphTrim(benchmark::Bench& bench)
         for (int chaintx = 0; chaintx < NUM_TX_PER_TOP_CHAIN; ++chaintx) {
             int64_t fee = rng.randbits<27>() + 100;
             FeePerWeight feerate{fee, 1};
-            top_refs.push_back(graph->AddTransaction(feerate));
+            graph->AddTransaction(top_refs.emplace_back(), feerate);
             // Add internal dependencies linking the chain transactions together.
             if (chaintx > 0) {
                  graph->AddDependency(*(top_refs.rbegin()), *(top_refs.rbegin() + 1));
@@ -85,7 +85,8 @@ void BenchTxGraphTrim(benchmark::Bench& bench)
         // Construct the transaction.
         int64_t fee = rng.randbits<27>() + 100;
         FeePerWeight feerate{fee, 1};
-        auto bottom_tx = graph->AddTransaction(feerate);
+        TxGraph::Ref bottom_tx;
+        graph->AddTransaction(bottom_tx, feerate);
         // Determine the number of dependencies this transaction will have.
         int deps = std::min<int>(NUM_DEPS_PER_BOTTOM_TX, top_components.size());
         for (int dep = 0; dep < deps; ++dep) {

src/kernel/mempool_entry.h

@@ -84,12 +84,11 @@ private:
 
 public:
     virtual ~CTxMemPoolEntry() = default;
-    CTxMemPoolEntry(TxGraph::Ref&& ref, const CTransactionRef& tx, CAmount fee,
+    CTxMemPoolEntry(const CTransactionRef& tx, CAmount fee,
                     int64_t time, unsigned int entry_height, uint64_t entry_sequence,
                     bool spends_coinbase,
                     int64_t sigops_cost, LockPoints lp)
-        : TxGraph::Ref(std::move(ref)),
+        : tx{tx},
-          tx{tx},
           nFee{fee},
           nTxWeight{GetTransactionWeight(*tx)},
           nUsageSize{RecursiveDynamicUsage(tx)},

src/test/fuzz/txgraph.cpp

@@ -137,15 +137,16 @@ struct SimTxGraph
         return simmap[pos].get();
     }
 
-    /** Add a new transaction to the simulation. */
+    /** Add a new transaction to the simulation and the specified real graph. */
-    void AddTransaction(TxGraph::Ref&& ref, const FeePerWeight& feerate)
+    void AddTransaction(TxGraph& txgraph, const FeePerWeight& feerate)
     {
         assert(graph.TxCount() < MAX_TRANSACTIONS);
         auto simpos = graph.AddTransaction(feerate);
         real_is_optimal = false;
         MakeModified(simpos);
         assert(graph.Positions()[simpos]);
-        simmap[simpos] = std::make_shared<TxGraph::Ref>(std::move(ref));
+        simmap[simpos] = std::make_shared<TxGraph::Ref>();
+        txgraph.AddTransaction(*simmap[simpos], feerate);
         auto ptr = simmap[simpos].get();
         simrevmap[ptr] = simpos;
         // This may invalidate our cached oversized value.
@@ -455,10 +456,8 @@ FUZZ_TARGET(txgraph)
                     size = provider.ConsumeIntegralInRange<uint32_t>(1, 0xff);
                 }
                 FeePerWeight feerate{fee, size};
-                // Create a real TxGraph::Ref.
+                // Create the transaction in the simulation and the real graph.
-                auto ref = real->AddTransaction(feerate);
+                top_sim.AddTransaction(*real, feerate);
-                // Create a shared_ptr place in the simulation to put the Ref in.
-                top_sim.AddTransaction(std::move(ref), feerate);
                 break;
             } else if ((block_builders.empty() || sims.size() > 1) && top_sim.GetTransactionCount() + top_sim.removed.size() > 1 && command-- == 0) {
                 // AddDependency.

src/test/fuzz/util/mempool.cpp

@@ -27,5 +27,5 @@ CTxMemPoolEntry ConsumeTxMemPoolEntry(FuzzedDataProvider& fuzzed_data_provider,
     const auto entry_height{fuzzed_data_provider.ConsumeIntegralInRange<uint32_t>(0, max_height)};
     const bool spends_coinbase = fuzzed_data_provider.ConsumeBool();
     const unsigned int sig_op_cost = fuzzed_data_provider.ConsumeIntegralInRange<unsigned int>(0, MAX_BLOCK_SIGOPS_COST);
-    return CTxMemPoolEntry{TxGraph::Ref(), MakeTransactionRef(tx), fee, time, entry_height, entry_sequence, spends_coinbase, sig_op_cost, {}};
+    return CTxMemPoolEntry{MakeTransactionRef(tx), fee, time, entry_height, entry_sequence, spends_coinbase, sig_op_cost, {}};
 }

src/test/txgraph_tests.cpp

@@ -46,11 +46,11 @@ BOOST_AUTO_TEST_CASE(txgraph_trim_zigzag)
     refs.reserve(NUM_TOTAL_TX);
     // First all bottom transactions: the i'th bottom transaction is at position i.
     for (unsigned int i = 0; i < NUM_BOTTOM_TX; ++i) {
-        refs.push_back(graph->AddTransaction(FeePerWeight{200 - i, 100}));
+        graph->AddTransaction(refs.emplace_back(), FeePerWeight{200 - i, 100});
     }
     // Then all top transactions: the i'th top transaction is at position NUM_BOTTOM_TX + i.
     for (unsigned int i = 0; i < NUM_TOP_TX; ++i) {
-        refs.push_back(graph->AddTransaction(FeePerWeight{100 - i, 100}));
+        graph->AddTransaction(refs.emplace_back(), FeePerWeight{100 - i, 100});
     }
 
     // Create the zigzag dependency structure.
@@ -109,9 +109,9 @@ BOOST_AUTO_TEST_CASE(txgraph_trim_flower)
     refs.reserve(NUM_TOTAL_TX);
 
     // Add all transactions. They are in individual clusters.
-    refs.push_back(graph->AddTransaction({1, 100}));
+    graph->AddTransaction(refs.emplace_back(), {1, 100});
     for (unsigned int i = 0; i < NUM_TOP_TX; ++i) {
-        refs.push_back(graph->AddTransaction(FeePerWeight{500 + i, 100}));
+        graph->AddTransaction(refs.emplace_back(), FeePerWeight{500 + i, 100});
     }
     graph->SanityCheck();
 
@@ -196,8 +196,8 @@ BOOST_AUTO_TEST_CASE(txgraph_trim_huge)
             // Use random fees, size 1.
             int64_t fee = rng.randbits<27>() + 100;
             FeePerWeight feerate{fee, 1};
-            top_refs.push_back(graph->AddTransaction(feerate));
+            graph->AddTransaction(top_refs.emplace_back(), feerate);
-            // Add internal dependencies linked the chain transactions together.
+            // Add internal dependencies linking the chain transactions together.
             if (chaintx > 0) {
                  graph->AddDependency(*(top_refs.rbegin()), *(top_refs.rbegin() + 1));
             }
@@ -215,7 +215,8 @@ BOOST_AUTO_TEST_CASE(txgraph_trim_huge)
         // Construct the transaction.
         int64_t fee = rng.randbits<27>() + 100;
         FeePerWeight feerate{fee, 1};
-        auto bottom_tx = graph->AddTransaction(feerate);
+        TxGraph::Ref bottom_tx;
+        graph->AddTransaction(bottom_tx, feerate);
         // Determine the number of dependencies this transaction will have.
         int deps = std::min<int>(NUM_DEPS_PER_BOTTOM_TX, top_components.size());
         for (int dep = 0; dep < deps; ++dep) {
@@ -271,7 +272,7 @@ BOOST_AUTO_TEST_CASE(txgraph_trim_big_singletons)
         // The 88th transaction is oversized.
         // Every 20th transaction is oversized.
         const FeePerWeight feerate{500 + i, (i == 88 || i % 20 == 0) ? MAX_CLUSTER_SIZE + 1 : 100};
-        refs.push_back(graph->AddTransaction(feerate));
+        graph->AddTransaction(refs.emplace_back(), feerate);
     }
     graph->SanityCheck();
 
@@ -334,23 +335,23 @@ BOOST_AUTO_TEST_CASE(txgraph_chunk_chain)
 
     // everytime adding a transaction, test the chunk status
     // [A]
-    refs.push_back(graph->AddTransaction(feerateA));
+    graph->AddTransaction(refs.emplace_back(), feerateA);
     BOOST_CHECK_EQUAL(graph->GetTransactionCount(TxGraph::Level::TOP), 1);
     block_builder_checker({{&refs[0]}});
     // [A, B]
-    refs.push_back(graph->AddTransaction(feerateB));
+    graph->AddTransaction(refs.emplace_back(), feerateB);
     graph->AddDependency(/*parent=*/refs[0], /*child=*/refs[1]);
     BOOST_CHECK_EQUAL(graph->GetTransactionCount(TxGraph::Level::TOP), 2);
     block_builder_checker({{&refs[0]}, {&refs[1]}});
 
     // [A, BC]
-    refs.push_back(graph->AddTransaction(feerateC));
+    graph->AddTransaction(refs.emplace_back(), feerateC);
     graph->AddDependency(/*parent=*/refs[1], /*child=*/refs[2]);
     BOOST_CHECK_EQUAL(graph->GetTransactionCount(TxGraph::Level::TOP), 3);
     block_builder_checker({{&refs[0]}, {&refs[1], &refs[2]}});
 
     // [ABCD]
-    refs.push_back(graph->AddTransaction(feerateD));
+    graph->AddTransaction(refs.emplace_back(), feerateD);
     graph->AddDependency(/*parent=*/refs[2], /*child=*/refs[3]);
     BOOST_CHECK_EQUAL(graph->GetTransactionCount(TxGraph::Level::TOP), 4);
     block_builder_checker({{&refs[0], &refs[1], &refs[2], &refs[3]}});
@@ -383,7 +384,7 @@ BOOST_AUTO_TEST_CASE(txgraph_staging)
 
     // everytime adding a transaction, test the chunk status
     // [A]
-    refs.push_back(graph->AddTransaction(feerateA));
+    graph->AddTransaction(refs.emplace_back(), feerateA);
     BOOST_CHECK_EQUAL(graph->HaveStaging(), false);
     BOOST_CHECK_EQUAL(graph->GetTransactionCount(TxGraph::Level::TOP), 1);
 
@@ -392,7 +393,7 @@ BOOST_AUTO_TEST_CASE(txgraph_staging)
     BOOST_CHECK_EQUAL(graph->GetTransactionCount(TxGraph::Level::TOP), 1);
 
     // [A, B]
-    refs.push_back(graph->AddTransaction(feerateB));
+    graph->AddTransaction(refs.emplace_back(), feerateB);
     BOOST_CHECK_EQUAL(graph->GetTransactionCount(TxGraph::Level::MAIN), 1);
     BOOST_CHECK_EQUAL(graph->GetTransactionCount(TxGraph::Level::TOP), 2);
     BOOST_CHECK_EQUAL(graph->Exists(refs[0], TxGraph::Level::TOP), true);

src/test/util/txmempool.cpp

@@ -38,7 +38,7 @@ CTxMemPoolEntry TestMemPoolEntryHelper::FromTx(const CMutableTransaction& tx) co
 
 CTxMemPoolEntry TestMemPoolEntryHelper::FromTx(const CTransactionRef& tx) const
 {
-    return CTxMemPoolEntry{TxGraph::Ref(), tx, nFee, TicksSinceEpoch<std::chrono::seconds>(time), nHeight, m_sequence, spendsCoinbase, sigOpCost, lp};
+    return CTxMemPoolEntry{tx, nFee, TicksSinceEpoch<std::chrono::seconds>(time), nHeight, m_sequence, spendsCoinbase, sigOpCost, lp};
 }
 
 std::optional<std::string> CheckPackageMempoolAcceptResult(const Package& txns,

src/txgraph.cpp

@@ -753,7 +753,7 @@ public:
 
     // Implementations for the public TxGraph interface.
 
-    Ref AddTransaction(const FeePerWeight& feerate) noexcept final;
+    void AddTransaction(Ref& arg, const FeePerWeight& feerate) noexcept final;
     void RemoveTransaction(const Ref& arg) noexcept final;
     void AddDependency(const Ref& parent, const Ref& child) noexcept final;
     void SetTransactionFee(const Ref&, int64_t fee) noexcept final;
@@ -2115,20 +2115,19 @@ void TxGraphImpl::MakeAllAcceptable(int level) noexcept
 
 GenericClusterImpl::GenericClusterImpl(uint64_t sequence) noexcept : Cluster{sequence} {}
 
-TxGraph::Ref TxGraphImpl::AddTransaction(const FeePerWeight& feerate) noexcept
+void TxGraphImpl::AddTransaction(Ref& arg, const FeePerWeight& feerate) noexcept
 {
     Assume(m_main_chunkindex_observers == 0 || GetTopLevel() != 0);
     Assume(feerate.size > 0);
-    // Construct a new Ref.
+    Assume(GetRefGraph(arg) == nullptr);
-    Ref ret;
     // Construct a new Entry, and link it with the Ref.
     auto idx = m_entries.size();
     m_entries.emplace_back();
     auto& entry = m_entries.back();
     entry.m_main_chunkindex_iterator = m_main_chunkindex.end();
-    entry.m_ref = &ret;
+    entry.m_ref = &arg;
-    GetRefGraph(ret) = this;
+    GetRefGraph(arg) = this;
-    GetRefIndex(ret) = idx;
+    GetRefIndex(arg) = idx;
     // Construct a new singleton Cluster (which is necessarily optimally linearized).
     bool oversized = uint64_t(feerate.size) > m_max_cluster_size;
     auto cluster = CreateEmptyCluster(1);
@@ -2146,8 +2145,6 @@ TxGraph::Ref TxGraphImpl::AddTransaction(const FeePerWeight& feerate) noexcept
         clusterset.m_oversized = true;
         clusterset.m_group_data = std::nullopt;
     }
-    // Return the Ref.
-    return ret;
 }
 
 void TxGraphImpl::RemoveTransaction(const Ref& arg) noexcept

src/txgraph.h

@@ -67,12 +67,14 @@ public:
 
     /** Virtual destructor, so inheriting is safe. */
     virtual ~TxGraph() = default;
-    /** Construct a new transaction with the specified feerate, and return a Ref to it.
+    /** Initialize arg (which must be an empty Ref) to refer to a new transaction in this graph
+     *  with the specified feerate.
+     *
      *  If a staging graph exists, the new transaction is only created there. feerate.size must be
-     *  strictly positive. In all further calls, only Refs created by AddTransaction() are allowed
+     *  strictly positive. In all further calls, only Refs passed to AddTransaction() are allowed
      *  to be passed to this TxGraph object (or empty Ref objects). Ref objects may outlive the
-     *  TxGraph they were created for. */
+     *  TxGraph they were added to. */
-    [[nodiscard]] virtual Ref AddTransaction(const FeePerWeight& feerate) noexcept = 0;
+    virtual void AddTransaction(Ref& arg, const FeePerWeight& feerate) noexcept = 0;
     /** Remove the specified transaction. If a staging graph exists, the removal only happens
      *  there. This is a no-op if the transaction was already removed.
      *
@@ -235,8 +237,7 @@ public:
         /** Index into the Graph's m_entries. Only used if m_graph != nullptr. */
         GraphIndex m_index = GraphIndex(-1);
     public:
-        /** Construct an empty Ref. Non-empty Refs can only be created using
+        /** Construct an empty Ref. It can be initialized through TxGraph::AddTransaction. */
-         *  TxGraph::AddTransaction. */
         Ref() noexcept = default;
         /** Destroy this Ref. If it is not empty, the corresponding transaction is removed (in both
          *  main and staging, if it exists). */

src/txmempool.cpp

@@ -1000,8 +1000,9 @@ CTxMemPool::ChangeSet::TxHandle CTxMemPool::ChangeSet::StageAddition(const CTran
     CAmount delta{0};
     m_pool->ApplyDelta(tx->GetHash(), delta);
 
-    TxGraph::Ref ref(m_pool->m_txgraph->AddTransaction(FeePerWeight(fee, GetSigOpsAdjustedWeight(GetTransactionWeight(*tx), sigops_cost, ::nBytesPerSigOp))));
+    FeePerWeight feerate(fee, GetSigOpsAdjustedWeight(GetTransactionWeight(*tx), sigops_cost, ::nBytesPerSigOp));
-    auto newit = m_to_add.emplace(std::move(ref), tx, fee, time, entry_height, entry_sequence, spends_coinbase, sigops_cost, lp).first;
+    auto newit = m_to_add.emplace(tx, fee, time, entry_height, entry_sequence, spends_coinbase, sigops_cost, lp).first;
+    m_pool->m_txgraph->AddTransaction(const_cast<CTxMemPoolEntry&>(*newit), feerate);
     if (delta) {
         newit->UpdateModifiedFee(delta);
         m_pool->m_txgraph->SetTransactionFee(*newit, newit->GetModifiedFee());