Use const iterator accessors for read-only traversal.

include/bitcoin/node/impl/chasers/chaser_organize.ipp

@@ -142,7 +142,7 @@ void CLASS::do_organize(typename Block::cptr block, bool prioritized,
     }
 
     const auto it = tree_.find(hash);
-    if (it != tree_.end())
+    if (it != tree_.cend())
     {
         handler(error_duplicate(), it->second->get_state()->height());
         return;
@@ -354,7 +354,7 @@ void CLASS::do_prioritize(const system::hash_digest& hash,
         return;
 
     // Only the top of a cached branch can tie the candidate top.
-    if (std::any_of(tree_.begin(), tree_.end(), [&](const auto& item) NOEXCEPT
+    if (std::any_of(tree_.cbegin(), tree_.cend(), [&](const auto& item) NOEXCEPT
         {
             return get_header(*item.second).previous_block_hash() == hash;
         }))
@@ -661,7 +661,7 @@ void CLASS::shrink_tree(bool current) NOEXCEPT
         return;
 
     shrunk_ = true;
-    tree_ = { tree_.begin(), tree_.end() };
+    tree_ = { tree_.cbegin(), tree_.cend() };
     LOGV("Tree buckets reduced to (" << tree_.bucket_count() << ").");
 }
 

src/chasers/chaser_check.cpp

@@ -221,7 +221,7 @@ void chaser_check::do_starved(object_t self) NOEXCEPT
     BC_ASSERT(stranded());
 
     // Remove the starved channel to prevent self-selection.
-    if (speeds_.find(self) != speeds_.end())
+    if (speeds_.find(self) != speeds_.cend())
         speeds_.erase(self);
 
     // Find the slowest reporting channel.
@@ -232,7 +232,7 @@ void chaser_check::do_starved(object_t self) NOEXCEPT
         });
 
     // Direct the slowest channel to split work and stop.
-    if (slowest != speeds_.end())
+    if (slowest != speeds_.cend())
     {
         // Erase entry so less likely to be claimed again before stopping.
         const auto slow = slowest->first;

src/protocols/protocol_block_in_31800.cpp

@@ -276,7 +276,7 @@ bool protocol_block_in_31800::handle_receive_block(const code& ec,
     const auto& block = message->block;
     const auto hash = block.hash();
     const auto it = map_->find(hash);
-    if (it == map_->end())
+    if (it == map_->cend())
     {
         // Allow unrequested block, not counted toward performance.
         LOGR("Unrequested block [" << encode_hash(hash) << "] from ["