lang: add wasm_engine service

WASM engine stores the wasm runtime engine for user-defined functions.

configure.py

@@ -1007,6 +1007,7 @@ def find_headers(repodir, excluded_dirs):
                 'mutation_writer/partition_based_splitting_writer.cc',
                 'mutation_writer/feed_writers.cc',
                 'lang/lua.cc',
+                'lang/wasm_engine.cc',
                 'service/raft/schema_raft_state_machine.cc',
                 'service/raft/raft_sys_table_storage.cc',
                 'serializer.cc',

lang/wasm_engine.cc

@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) 2021-present ScyllaDB
+ */
+
+/*
+ * This file is part of Scylla.
+ *
+ * Scylla is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Scylla is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Scylla.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "wasm_engine.hh"
+
+namespace wasm {
+
+#ifdef SCYLLA_ENABLE_WASMTIME
+
+seastar::future<> init_sharded_engine(seastar::sharded<engine>& e) {
+    // Fuel defines more or less how many bytecode instructions
+    // can be performed at once. Empirically, 20k units
+    // allow for considerably less than 0.5ms of preemption-free execution time.
+    // TODO: investigate other configuration variables.
+    // We're particularly interested in limiting resource usage
+    // and yielding in the middle of execution - which is possible
+    // in the original wasmtime implementation for Rust and tightly
+    // bound with its native async support, but not yet possible
+    // in wasmtime.hh binding at the time of this writing.
+    // It's highly probable that a more generic support for yielding
+    // can be contributed to wasmtime.  
+    const uint64_t initial_fuel_amount = 20*1024;
+    e.start(initial_fuel_amount).get();
+}
+
+#else
+
+seastar::future<> init_sharded_engine(seastar::sharded<engine>& e) {
+    return seastar::make_ready_future<>();
+}
+
+
+#endif
+
+} // namespace wasm

lang/wasm_engine.hh

@@ -0,0 +1,63 @@
+/*
+ * Copyright (C) 2021-present ScyllaDB
+ */
+
+/*
+ * This file is part of Scylla.
+ *
+ * Scylla is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Scylla is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Scylla.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <seastar/core/future.hh>
+#include <seastar/core/sharded.hh>
+
+#ifdef SCYLLA_ENABLE_WASMTIME
+
+#include "wasmtime.hh"
+
+namespace wasm {
+
+class engine {
+    wasmtime::Engine _engine;
+    uint64_t _initial_fuel_amount;
+public:
+    engine(uint64_t initial_fuel_amount)
+            : _engine(make_config())
+            , _initial_fuel_amount(initial_fuel_amount)
+        {}
+    wasmtime::Engine& get() { return _engine; }
+    uint64_t initial_fuel_amount() { return _initial_fuel_amount; };
+private:
+    wasmtime::Config make_config() {
+        wasmtime::Config cfg;
+        cfg.consume_fuel(true);
+        return cfg;
+    }
+};
+
+}
+
+#else
+
+namespace wasm {
+class engine {};
+}
+
+#endif
+
+namespace wasm {
+seastar::future<> init_sharded_engine(seastar::sharded<engine>& e);
+}