#8 RTU session for boiler, added transaction controller

supervisor/session/rtu/txnctrl.lua

@@ -0,0 +1,95 @@
+--
+-- MODBUS Transaction Controller
+--
+
+local util = require("scada-common.util")
+
+local txnctrl = {}
+
+local TIMEOUT = 3000 -- 3000ms max wait
+
+-- create a new transaction controller
+txnctrl.new = function ()
+    local self = {
+        list = {},
+        next_id = 0
+    }
+
+    ---@class transaction_controller
+    local public = {}
+
+    local insert = table.insert
+
+    -- get the length of the transaction list
+    public.length = function ()
+        return #self.list
+    end
+
+    -- check if there are no active transactions
+    public.empty = function ()
+        return #self.list == 0
+    end
+
+    -- create a new transaction of the given type
+    ---@param txn_type integer
+    ---@return integer txn_id
+    public.create = function (txn_type)
+        local txn_id = self.next_id
+
+        insert(self.list, {
+            txn_id = txn_id,
+            txn_type = txn_type,
+            expiry = util.time() + TIMEOUT
+        })
+
+        self.next_id = self.next_id + 1
+
+        return txn_id
+    end
+
+    -- mark a transaction as resolved to get its transaction type
+    ---@param txn_id integer
+    ---@return integer txn_type
+    public.resolve = function (txn_id)
+        local txn_type = nil
+
+        for i = 1, public.length() do
+            if self.list[i].txn_id == txn_id then
+                txn_type = self.list[i].txn_type
+                self.list[i] = nil
+            end
+        end
+
+        return txn_type
+    end
+
+    -- close timed-out transactions
+    public.cleanup = function ()
+        local now = util.time()
+
+        local move_to = 1
+        for i = 1, public.length() do
+            local txn = self.list[i]
+            if txn ~= nil then
+                if txn.expiry <= now then
+                    self.list[i] = nil
+                else
+                    if self.list[move_to] == nil then
+                        self.list[move_to] = txn
+                        self.list[i] = nil
+                    end
+                    move_to = move_to + 1
+                end
+            end
+        end
+    end
+
+    -- clear the transaction list
+    public.clear = function ()
+        self.list = {}
+    end
+
+    return public
+end
+
+return txnctrl