ircd::db: Leverage the RocksDB WriteBatch with an initializer_list.

include/ircd/db.h

@@ -119,6 +119,27 @@ struct opts
 	template<class... list> opts(list&&... l): optlist<opt>{std::forward<list>(l)...} {}
 };
 
+enum op
+{
+	PUT,
+	MERGE,
+	DELETE,
+	SINGLE_DELETE,
+	DELETE_RANGE,
+};
+
+struct delta
+:std::tuple<op, string_view, string_view>
+{
+	delta(const enum op &op, const string_view &key, const string_view &val = {})
+	:std::tuple<enum op, string_view, string_view>{op, key, val}
+	{}
+
+	delta(const string_view &key, const string_view &val, const enum op &op = op::PUT)
+	:std::tuple<enum op, string_view, string_view>{op, key, val}
+	{}
+};
+
 struct handle
 {
 	struct const_iterator;
@@ -146,6 +167,10 @@ struct handle
 	void operator()(const string_view &key, const closure &func, const gopts & = {});
 	void operator()(const string_view &key, const gopts &, const closure &func);
 
+	// Perform operations in a sequence as a single transaction.
+	void operator()(const delta &, const sopts & = {});
+	void operator()(const std::initializer_list<delta> &, const sopts & = {});
+
 	// Get data into your buffer. The signed char buffer is null terminated; the unsigned is not.
 	size_t get(const string_view &key, char *const &buf, const size_t &max, const gopts & = {});
 	size_t get(const string_view &key, uint8_t *const &buf, const size_t &max, const gopts & = {});

ircd/db.cc

@@ -263,6 +263,59 @@ db::handle::get(const string_view &key,
 	return ret;
 }
 
+namespace ircd {
+namespace db   {
+
+static
+void append(rocksdb::WriteBatch &batch,
+            const delta &delta)
+{
+	const rocksdb::Slice k
+	{
+		std::get<1>(delta).data(), std::get<1>(delta).size()
+	};
+
+	const rocksdb::Slice v
+	{
+		std::get<2>(delta).data(), std::get<2>(delta).size()
+	};
+
+	switch(std::get<0>(delta))
+	{
+		case op::PUT:            batch.Put(k, v);           break;
+		case op::MERGE:          batch.Merge(k, v);         break;
+		case op::DELETE:         batch.Delete(k);           break;
+		case op::SINGLE_DELETE:  batch.SingleDelete(k);     break;
+		case op::DELETE_RANGE:   batch.DeleteRange(k, v);   break;
+	}
+}
+
+} // namespace db
+} // namespace ircd
+
+void
+db::handle::operator()(const std::initializer_list<delta> &deltas,
+                       const sopts &sopts)
+{
+	rocksdb::WriteBatch batch;
+	for(const auto &delta : deltas)
+		append(batch, delta);
+
+	auto opts(make_opts(sopts));
+	throw_on_error(d->Write(opts, &batch));
+}
+
+void
+db::handle::operator()(const delta &delta,
+                       const sopts &sopts)
+{
+	rocksdb::WriteBatch batch;
+	append(batch, delta);
+
+	auto opts(make_opts(sopts));
+	throw_on_error(d->Write(opts, &batch));
+}
+
 void
 db::handle::operator()(const string_view &key,
                        const gopts &gopts,