[release/5.x] Cherry pick: Prevent racey access to indexer state (#6886) (#6913)

Author: eddyashton

include/ccf/indexing/indexer_interface.h

@@ -4,6 +4,7 @@
 
 #include "ccf/indexing/strategy.h"
 #include "ccf/node_subsystem_interface.h"
+#include "ccf/pal/locking.h"
 
 #include <map>
 #include <memory>
@@ -19,6 +20,7 @@ namespace ccf::indexing
   class IndexingStrategies : public ccf::AbstractNodeSubSystem
   {
   protected:
+    ccf::pal::Mutex lock;
     std::set<StrategyPtr> strategies;
 
   public:
@@ -36,11 +38,13 @@ namespace ccf::indexing
         throw std::logic_error("Tried to install null strategy");
       }
 
+      std::lock_guard<ccf::pal::Mutex> guard(lock);
       return strategies.insert(strategy).second;
     }
 
     void uninstall_strategy(const StrategyPtr& strategy)
     {
+      std::lock_guard<ccf::pal::Mutex> guard(lock);
       if (strategy == nullptr || strategies.find(strategy) == strategies.end())
       {
         throw std::logic_error("Strategy doesn't exist");
@@ -49,8 +53,9 @@ namespace ccf::indexing
       strategies.erase(strategy);
     }
 
-    nlohmann::json describe() const
+    nlohmann::json describe()
     {
+      std::lock_guard<ccf::pal::Mutex> guard(lock);
       auto j = nlohmann::json::array();
 
       for (const auto& strategy : strategies)

include/ccf/indexing/strategy.h

@@ -3,6 +3,7 @@
 #pragma once
 
 #include "ccf/kv/read_only_store.h"
+#include "ccf/pal/locking.h"
 #include "ccf/tx_id.h"
 
 #include <optional>
@@ -68,6 +69,7 @@ namespace ccf::indexing
   class LazyStrategy : public Base
   {
   protected:
+    ccf::pal::Mutex lock;
     ccf::SeqNo max_requested_seqno = 0;
 
   public:
@@ -78,6 +80,7 @@ namespace ccf::indexing
       const auto base = Base::next_requested();
       if (base.has_value())
       {
+        std::lock_guard<ccf::pal::Mutex> guard(lock);
         if (*base <= max_requested_seqno)
         {
           return base;
@@ -89,6 +92,7 @@ namespace ccf::indexing
 
     void extend_index_to(ccf::TxID to_txid)
     {
+      std::lock_guard<ccf::pal::Mutex> guard(lock);
       if (to_txid.seqno > max_requested_seqno)
       {
         max_requested_seqno = to_txid.seqno;

src/indexing/indexer.h

@@ -68,6 +68,9 @@ namespace ccf::indexing
       update_commit(newly_committed);
 
       std::optional<ccf::SeqNo> min_requested = std::nullopt;
+
+      std::lock_guard<ccf::pal::Mutex> guard(lock);
+
       for (auto& strategy : strategies)
       {
         strategy->tick();