refactor: init indexes, decouple 'Start()' from the creation step

No behavior change.

The goal here is to group indexes, so we can perform the same
initialization and verification process equally for all of them.

The checks performed inside `StartIndexes` will be expanded
in the subsequent commits.

src/init.cpp

@@ -1554,25 +1554,22 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
         }
 
         g_txindex = std::make_unique<TxIndex>(interfaces::MakeChain(node), cache_sizes.tx_index, false, fReindex);
-        if (!g_txindex->Start()) {
-            return false;
-        }
+        node.indexes.emplace_back(g_txindex.get());
     }
 
     for (const auto& filter_type : g_enabled_filter_types) {
         InitBlockFilterIndex([&]{ return interfaces::MakeChain(node); }, filter_type, cache_sizes.filter_index, false, fReindex);
-        if (!GetBlockFilterIndex(filter_type)->Start()) {
-            return false;
-        }
+        node.indexes.emplace_back(GetBlockFilterIndex(filter_type));
     }
 
     if (args.GetBoolArg("-coinstatsindex", DEFAULT_COINSTATSINDEX)) {
         g_coin_stats_index = std::make_unique<CoinStatsIndex>(interfaces::MakeChain(node), /*cache_size=*/0, false, fReindex);
-        if (!g_coin_stats_index->Start()) {
-            return false;
-        }
+        node.indexes.emplace_back(g_coin_stats_index.get());
     }
 
+    // Now that all indexes are loaded, start them
+    StartIndexes(node);
+
     // ********************************************************* Step 9: load wallet
     for (const auto& client : node.chain_clients) {
         if (!client->load()) {
@@ -1878,3 +1875,9 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
 
     return true;
 }
+
+bool StartIndexes(NodeContext& node)
+{
+    for (auto index : node.indexes) if (!index->Start()) return false;
+    return true;
+}

src/init.h

@@ -73,4 +73,7 @@ bool AppInitMain(node::NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip
  */
 void SetupServerArgs(ArgsManager& argsman);
 
+/** Validates requirements to run the indexes and spawns each index initial sync thread */
+bool StartIndexes(node::NodeContext& node);
+
 #endif // BITCOIN_INIT_H

src/node/context.h

@@ -15,8 +15,9 @@
 #include <vector>
 
 class ArgsManager;
-class BanMan;
 class AddrMan;
+class BanMan;
+class BaseIndex;
 class CBlockPolicyEstimator;
 class CConnman;
 class CScheduler;
@@ -58,6 +59,7 @@ struct NodeContext {
     std::unique_ptr<ChainstateManager> chainman;
     std::unique_ptr<BanMan> banman;
     ArgsManager* args{nullptr}; // Currently a raw pointer because the memory is not managed by this struct
+    std::vector<BaseIndex*> indexes; // raw pointers because memory is not managed by this struct
     std::unique_ptr<interfaces::Chain> chain;
     //! List of all chain clients (wallet processes or other client) connected to node.
     std::vector<std::unique_ptr<interfaces::ChainClient>> chain_clients;