Merge bitcoin/bitcoin#32151: Follow-ups for txgraph #31363

a52b53926b clusterlin: add GetConnectedComponent (Pieter Wuille)
c7d5dcaa61 clusterlin: fix typos (Pieter Wuille)
777179bc27 txgraph: rename group_data in ApplyDependencies (Pieter Wuille)

Pull request description:

  This addresses a few review comments in #31363 after merge:
  * https://github.com/bitcoin/bitcoin/pull/31363#discussion_r2012730654 (rename `group_data` to `group_entry`)
  * https://github.com/bitcoin/bitcoin/pull/31363#discussion_r2015001561 (introduce `GetConnectedComponent` and use it in the txgraph fuzz test).
  * https://github.com/bitcoin/bitcoin/pull/31363#discussion_r2015003889 (typo in `FixLinearization`)
  * https://github.com/bitcoin/bitcoin/pull/32151#discussion_r2015764185 (more typos)

ACKs for top commit:
  instagibbs:
    ACK a52b53926b
  glozow:
    ACK a52b53926b

Tree-SHA512: e8a98101ecb9c09b860306c7fbd22cf20bd12990768879753680dfbf7db31283506d9f30bb7ee726daebd90c34a1c565d07b3e1147b2a87426247acb19058ed3

src/cluster_linearize.h

@@ -250,10 +250,8 @@ public:
         return ret;
     }
 
-    /** Find some connected component within the subset "todo" of this graph.
-     *
-     * Specifically, this finds the connected component which contains the first transaction of
-     * todo (if any).
+    /** Get the connected component within the subset "todo" that contains tx (which must be in
+     *  todo).
      *
      * Two transactions are considered connected if they are both in `todo`, and one is an ancestor
      * of the other in the entire graph (so not just within `todo`), or transitively there is a
@@ -262,10 +260,11 @@ public:
      *
      * Complexity: O(ret.Count()).
      */
-    SetType FindConnectedComponent(const SetType& todo) const noexcept
+    SetType GetConnectedComponent(const SetType& todo, DepGraphIndex tx) const noexcept
     {
-        if (todo.None()) return todo;
-        auto to_add = SetType::Singleton(todo.First());
+        Assume(todo[tx]);
+        Assume(todo.IsSubsetOf(m_used));
+        auto to_add = SetType::Singleton(tx);
         SetType ret;
         do {
             SetType old = ret;
@@ -279,6 +278,19 @@ public:
         return ret;
     }
 
+    /** Find some connected component within the subset "todo" of this graph.
+     *
+     * Specifically, this finds the connected component which contains the first transaction of
+     * todo (if any).
+     *
+     * Complexity: O(ret.Count()).
+     */
+    SetType FindConnectedComponent(const SetType& todo) const noexcept
+    {
+        if (todo.None()) return todo;
+        return GetConnectedComponent(todo, todo.First());
+    }
+
     /** Determine if a subset is connected.
      *
      * Complexity: O(subset.Count()).
@@ -1367,7 +1379,7 @@ void FixLinearization(const DepGraph<SetType>& depgraph, std::span<DepGraphIndex
         // in between forward.
         while (place_before.Any()) {
             // j cannot be 0 here; if it was, then there was necessarily nothing earlier which
-            // elem needs to be place before anymore, and place_before would be empty.
+            // elem needs to be placed before anymore, and place_before would be empty.
             Assume(j > 0);
             auto to_swap = linearization[len - 1 - (j - 1)];
             place_before.Reset(to_swap);

src/test/fuzz/cluster_linearize.cpp

@@ -446,19 +446,36 @@ FUZZ_TARGET(clusterlin_components)
     // Construct a depgraph.
     SpanReader reader(buffer);
     DepGraph<TestBitSet> depgraph;
+    std::vector<DepGraphIndex> linearization;
     try {
         reader >> Using<DepGraphFormatter>(depgraph);
     } catch (const std::ios_base::failure&) {}
 
     TestBitSet todo = depgraph.Positions();
     while (todo.Any()) {
-        // Find a connected component inside todo.
-        auto component = depgraph.FindConnectedComponent(todo);
+        // Pick a transaction in todo, or nothing.
+        std::optional<DepGraphIndex> picked;
+        {
+            uint64_t picked_num{0};
+            try {
+                reader >> VARINT(picked_num);
+            } catch (const std::ios_base::failure&) {}
+            if (picked_num < todo.Size() && todo[picked_num]) {
+                picked = picked_num;
+            }
+        }
+
+        // Find a connected component inside todo, including picked if any.
+        auto component = picked ? depgraph.GetConnectedComponent(todo, *picked)
+                                : depgraph.FindConnectedComponent(todo);
 
         // The component must be a subset of todo and non-empty.
         assert(component.IsSubsetOf(todo));
         assert(component.Any());
 
+        // If picked was provided, the component must include it.
+        if (picked) assert(component[*picked]);
+
         // If todo is the entire graph, and the entire graph is connected, then the component must
         // be the entire graph.
         if (todo == depgraph.Positions()) {

src/test/fuzz/txgraph.cpp

@@ -561,36 +561,23 @@ FUZZ_TARGET(txgraph)
                 std::shuffle(refs.begin(), refs.end(), rng);
                 // Invoke the real function.
                 auto result = real->CountDistinctClusters(refs, use_main);
-                // Build a vector with representatives of the clusters the Refs occur in in the
+                // Build a set with representatives of the clusters the Refs occur in in the
                 // simulated graph. For each, remember the lowest-index transaction SimPos in the
                 // cluster.
-                std::vector<DepGraphIndex> sim_reps;
+                SimTxGraph::SetType sim_reps;
                 for (auto ref : refs) {
                     // Skip Refs that do not occur in the simulated graph.
                     auto simpos = sel_sim.Find(ref);
                     if (simpos == SimTxGraph::MISSING) continue;
-                    // Start with component equal to just the Ref's SimPos.
-                    auto component = SimTxGraph::SetType::Singleton(simpos);
-                    // Keep adding ancestors/descendants of all elements in component until it no
-                    // longer changes.
-                    while (true) {
-                        auto old_component = component;
-                        for (auto i : component) {
-                            component |= sel_sim.graph.Ancestors(i);
-                            component |= sel_sim.graph.Descendants(i);
-                        }
-                        if (component == old_component) break;
-                    }
+                    // Find the component that includes ref.
+                    auto component = sel_sim.graph.GetConnectedComponent(sel_sim.graph.Positions(), simpos);
                     // Remember the lowest-index SimPos in component, as a representative for it.
                     assert(component.Any());
-                    sim_reps.push_back(component.First());
+                    sim_reps.Set(component.First());
                 }
-                // Remove duplicates from sim_reps.
-                std::sort(sim_reps.begin(), sim_reps.end());
-                sim_reps.erase(std::unique(sim_reps.begin(), sim_reps.end()), sim_reps.end());
                 // Compare the number of deduplicated representatives with the value returned by
                 // the real function.
-                assert(result == sim_reps.size());
+                assert(result == sim_reps.Count());
                 break;
             } else if (command-- == 0) {
                 // DoWork.

src/txgraph.cpp

@@ -335,7 +335,7 @@ public:
 
     // Simple helper functions.
 
-    /** Swap the Entrys referred to by a and b. */
+    /** Swap the Entry referred to by a and the one referred to by b. */
     void SwapIndexes(GraphIndex a, GraphIndex b) noexcept;
     /** If idx exists in the specified level ClusterSet (explicitly, or in the level below and not
     *   removed), return the Cluster it is in. Otherwise, return nullptr. */
@@ -408,8 +408,8 @@ public:
 
     // Functions related to various normalization/application steps.
     /** Get rid of unlinked Entry objects in m_entries, if possible (this changes the GraphIndex
-     *  values for remaining Entrys, so this only does something when no to-be-applied operations
-     *  or staged removals referring to GraphIndexes remain). */
+     *  values for remaining Entry objects, so this only does something when no to-be-applied
+     *  operations or staged removals referring to GraphIndexes remain). */
     void Compact() noexcept;
     /** If cluster is not in staging, copy it there, and return a pointer to it. This has no
     *   effect if only a main graph exists, but if staging exists this modifies the locators of its
@@ -505,7 +505,7 @@ void TxGraphImpl::ClearLocator(int level, GraphIndex idx) noexcept
 
 void Cluster::Updated(TxGraphImpl& graph) noexcept
 {
-    // Update all the Locators for this Cluster's Entrys.
+    // Update all the Locators for this Cluster's Entry objects.
     for (DepGraphIndex idx : m_linearization) {
         auto& entry = graph.m_entries[m_mapping[idx]];
         entry.m_locator[m_level].SetPresent(this, idx);
@@ -1321,9 +1321,9 @@ void TxGraphImpl::ApplyDependencies(int level) noexcept
     if (clusterset.m_group_data->m_group_oversized) return;
 
     // For each group of to-be-merged Clusters.
-    for (const auto& group_data : clusterset.m_group_data->m_groups) {
+    for (const auto& group_entry : clusterset.m_group_data->m_groups) {
         auto cluster_span = std::span{clusterset.m_group_data->m_group_clusters}
-                                .subspan(group_data.m_cluster_offset, group_data.m_cluster_count);
+                                .subspan(group_entry.m_cluster_offset, group_entry.m_cluster_count);
         // Pull in all the Clusters that contain dependencies.
         if (level == 1) {
             for (Cluster*& cluster : cluster_span) {
@@ -1335,7 +1335,7 @@ void TxGraphImpl::ApplyDependencies(int level) noexcept
         // Actually apply all to-be-added dependencies (all parents and children from this grouping
         // belong to the same Cluster at this point because of the merging above).
         auto deps_span = std::span{clusterset.m_deps_to_add}
-                             .subspan(group_data.m_deps_offset, group_data.m_deps_count);
+                             .subspan(group_entry.m_deps_offset, group_entry.m_deps_count);
         Assume(!deps_span.empty());
         const auto& loc = m_entries[deps_span[0].second].m_locator[level];
         Assume(loc.IsPresent());
@@ -1937,7 +1937,7 @@ void Cluster::SanityCheck(const TxGraphImpl& graph, int level) const
             assert(m_depgraph.IsConnected(linchunking.GetChunk(0).transactions));
         }
     }
-    // Verify that each element of m_depgraph occured in m_linearization.
+    // Verify that each element of m_depgraph occurred in m_linearization.
     assert(m_done == m_depgraph.Positions());
 }
 

src/txgraph.h

@@ -99,7 +99,7 @@ public:
     /** Create a staging graph (which cannot exist already). This acts as if a full copy of
      *  the transaction graph is made, upon which further modifications are made. This copy can
      *  be inspected, and then either discarded, or the main graph can be replaced by it by
-     *  commiting it. */
+     *  committing it. */
     virtual void StartStaging() noexcept = 0;
     /** Discard the existing active staging graph (which must exist). */
     virtual void AbortStaging() noexcept = 0;