Cache hash for multiple block->hash () calls (#2536)

nano/core_test/block.cpp

@@ -366,25 +366,36 @@ TEST (state_block, hashing)
 	nano::keypair key;
 	nano::state_block block (key.pub, 0, key.pub, 0, 0, key.prv, key.pub, 0);
 	auto hash (block.hash ());
+	ASSERT_EQ (hash, block.hash ()); // check cache works
 	block.hashables.account.bytes[0] ^= 0x1;
+	block.refresh ();
 	ASSERT_NE (hash, block.hash ());
 	block.hashables.account.bytes[0] ^= 0x1;
+	block.refresh ();
 	ASSERT_EQ (hash, block.hash ());
 	block.hashables.previous.bytes[0] ^= 0x1;
+	block.refresh ();
 	ASSERT_NE (hash, block.hash ());
 	block.hashables.previous.bytes[0] ^= 0x1;
+	block.refresh ();
 	ASSERT_EQ (hash, block.hash ());
 	block.hashables.representative.bytes[0] ^= 0x1;
+	block.refresh ();
 	ASSERT_NE (hash, block.hash ());
 	block.hashables.representative.bytes[0] ^= 0x1;
+	block.refresh ();
 	ASSERT_EQ (hash, block.hash ());
 	block.hashables.balance.bytes[0] ^= 0x1;
+	block.refresh ();
 	ASSERT_NE (hash, block.hash ());
 	block.hashables.balance.bytes[0] ^= 0x1;
+	block.refresh ();
 	ASSERT_EQ (hash, block.hash ());
 	block.hashables.link.bytes[0] ^= 0x1;
+	block.refresh ();
 	ASSERT_NE (hash, block.hash ());
 	block.hashables.link.bytes[0] ^= 0x1;
+	block.refresh ();
 	ASSERT_EQ (hash, block.hash ());
 }
 

nano/core_test/bootstrap.cpp

@@ -58,6 +58,7 @@ TEST (bulk_pull, end_not_owned)
 	open.hashables.account = key2.pub;
 	open.hashables.representative = key2.pub;
 	open.hashables.source = latest;
+	open.refresh ();
 	open.signature = nano::sign_message (key2.prv, key2.pub, open.hash ());
 	system.nodes[0]->work_generate_blocking (open);
 	ASSERT_EQ (nano::process_result::progress, system.nodes[0]->process (open).code);

nano/lib/blocks.cpp

@@ -76,7 +76,7 @@ size_t nano::block::size (nano::block_type type_a)
 	return result;
 }
 
-nano::block_hash nano::block::hash () const
+nano::block_hash nano::block::generate_hash () const
 {
 	nano::block_hash result;
 	blake2b_state hash_l;
@@ -88,6 +88,30 @@ nano::block_hash nano::block::hash () const
 	return result;
 }
 
+void nano::block::refresh ()
+{
+	if (!cached_hash.is_zero ())
+	{
+		cached_hash = generate_hash ();
+	}
+}
+
+nano::block_hash const & nano::block::hash () const
+{
+	if (!cached_hash.is_zero ())
+	{
+		// Once a block is created, it should not be modified (unless using refresh ())
+		// This would invalidate the cache; check it hasn't changed.
+		assert (cached_hash == generate_hash ());
+	}
+	else
+	{
+		cached_hash = generate_hash ();
+	}
+
+	return cached_hash;
+}
+
 nano::block_hash nano::block::full_hash () const
 {
 	nano::block_hash result;

nano/lib/blocks.hpp

@@ -57,7 +57,7 @@ class block
 {
 public:
 	// Return a digest of the hashables in this block.
-	nano::block_hash hash () const;
+	nano::block_hash const & hash () const;
 	// Return a digest of hashables and non-hashables in this block.
 	nano::block_hash full_hash () const;
 	std::string to_json () const;
@@ -88,6 +88,14 @@ class block
 	virtual ~block () = default;
 	virtual bool valid_predecessor (nano::block const &) const = 0;
 	static size_t size (nano::block_type);
+	// If there are any changes to the hashables, call this to update the cached hash
+	void refresh ();
+
+protected:
+	mutable nano::block_hash cached_hash{ 0 };
+
+private:
+	nano::block_hash generate_hash () const;
 };
 class send_hashables
 {

nano/node/active_transactions.cpp

@@ -99,7 +99,7 @@ void nano::active_transactions::search_frontiers (nano::transaction const & tran
 							// Calculate votes for local representatives
 							if (representative)
 							{
-								this->node.block_processor.generator.add (block->hash ());
+								this->node.block_processor.generator.add (info.head);
 							}
 						}
 					}