Fix performance issue in block_uniquer cleanup. (#4326)

The entire container is now cleaned periodically instead of the previous, more complex way.

nano/core_test/block.cpp

@@ -6,6 +6,8 @@
 
 #include <boost/property_tree/json_parser.hpp>
 
+#include <thread>
+
 #include <crypto/ed25519-donna/ed25519.h>
 
 TEST (ed25519, signing)
@@ -589,17 +591,14 @@ TEST (block_uniquer, cleanup)
 				  .build_shared ();
 
 	nano::block_uniquer uniquer;
-	auto block3 (uniquer.unique (block1));
-	auto block4 (uniquer.unique (block2));
+	auto block3 = uniquer.unique (block1);
+	auto block4 = uniquer.unique (block2);
 	block2.reset ();
 	block4.reset ();
 	ASSERT_EQ (2, uniquer.size ());
-	auto iterations (0);
-	while (uniquer.size () == 2)
-	{
-		auto block5 (uniquer.unique (block1));
-		ASSERT_LT (iterations++, 200);
-	}
+	std::this_thread::sleep_for (nano::block_uniquer::cleanup_cutoff);
+	auto block5 = uniquer.unique (block1);
+	ASSERT_EQ (1, uniquer.size ());
 }
 
 TEST (block_builder, from)

nano/lib/blocks.cpp

@@ -1881,24 +1881,19 @@ std::shared_ptr<nano::block> nano::block_uniquer::unique (std::shared_ptr<nano::
 		{
 			existing = block_a;
 		}
-		release_assert (std::numeric_limits<CryptoPP::word32>::max () > blocks.size ());
-		for (auto i (0); i < cleanup_count && !blocks.empty (); ++i)
+		auto now = std::chrono::steady_clock::now ();
+		if (cleanup_cutoff < now - cleanup_last)
 		{
-			auto random_offset (nano::random_pool::generate_word32 (0, static_cast<CryptoPP::word32> (blocks.size () - 1)));
-			auto existing (std::next (blocks.begin (), random_offset));
-			if (existing == blocks.end ())
+			cleanup_last = now;
+			for (auto i = blocks.begin (), n = blocks.end (); i != n;)
 			{
-				existing = blocks.begin ();
-			}
-			if (existing != blocks.end ())
-			{
-				if (auto block_l = existing->second.lock ())
+				if (auto block_l = i->second.lock ())
 				{
-					// Still live
+					++i;
 				}
 				else
 				{
-					blocks.erase (existing);
+					i = blocks.erase (i);
 				}
 			}
 		}

nano/lib/blocks.hpp

@@ -413,7 +413,10 @@ class block_uniquer
 private:
 	nano::mutex mutex{ mutex_identifier (mutexes::block_uniquer) };
 	std::unordered_map<std::remove_const_t<value_type::first_type>, value_type::second_type> blocks;
-	static unsigned constexpr cleanup_count = 2;
+	std::chrono::steady_clock::time_point cleanup_last{ std::chrono::steady_clock::now () };
+
+public:
+	static std::chrono::milliseconds constexpr cleanup_cutoff{ 500 };
 };
 
 std::unique_ptr<container_info_component> collect_container_info (block_uniquer & block_uniquer, std::string const & name);