lua: Init with config and pool (#321)

* lua: Intial impl with config and pool

Signed-off-by: James Hillyerd <james@hillyerd.com>

pkg/extension/luahost/pool.go

@@ -0,0 +1,91 @@
+package luahost
+
+import (
+	"sync"
+
+	lua "github.com/yuin/gopher-lua"
+)
+
+type statePool struct {
+	sync.Mutex
+	funcProto *lua.FunctionProto         // Compiled lua.
+	states    []*lua.LState              // Pool of available LStates.
+	channels  map[string]chan lua.LValue // Global interop channels.
+}
+
+func newStatePool(funcProto *lua.FunctionProto) *statePool {
+	return &statePool{
+		funcProto: funcProto,
+		channels:  make(map[string]chan lua.LValue),
+	}
+}
+
+// newState creates a new LState and configures it. Lock must be held.
+func (lp *statePool) newState() (*lua.LState, error) {
+	ls := lua.NewState()
+
+	// Setup channels.
+	for name, ch := range lp.channels {
+		ls.SetGlobal(name, lua.LChannel(ch))
+	}
+
+	// Run compiled script.
+	ls.Push(ls.NewFunctionFromProto(lp.funcProto))
+	if err := ls.PCall(0, lua.MultRet, nil); err != nil {
+		return nil, err
+	}
+
+	return ls, nil
+}
+
+// getState returns a free LState, or creates a new one.
+func (lp *statePool) getState() (*lua.LState, error) {
+	lp.Lock()
+	defer lp.Unlock()
+
+	ln := len(lp.states)
+	if ln == 0 {
+		return lp.newState()
+	}
+
+	state := lp.states[ln-1]
+	lp.states = lp.states[0 : ln-1]
+
+	return state, nil
+}
+
+// putState returns the LState to the pool.
+func (lp *statePool) putState(state *lua.LState) {
+	if state.IsClosed() {
+		return
+	}
+
+	// Clear stack.
+	state.Pop(state.GetTop())
+
+	lp.Lock()
+	defer lp.Unlock()
+
+	lp.states = append(lp.states, state)
+}
+
+// createChannel creates a new channel, which will become a global variable in
+// newly created LStates.  We also destroy any pooled states.
+//
+// Warning: There may still be checked out LStates that will not have the value
+// set, which could be put back into the pool.
+func (lp *statePool) createChannel(name string) chan lua.LValue {
+	lp.Lock()
+	defer lp.Unlock()
+
+	ch := make(chan lua.LValue, 10)
+	lp.channels[name] = ch
+
+	// Flush state pool.
+	for _, s := range lp.states {
+		s.Close()
+	}
+	lp.states = lp.states[:0]
+
+	return ch
+}