1 files changed, 70 insertions, 0 deletions
diff --git a/acf2/transaction/backend.lua b/acf2/transaction/backend.lua
new file mode 100644
index 0000000..79ea83a
--- /dev/null
+++ b/acf2/transaction/backend.lua
@@ -0,0 +1,70 @@
+--[[
+Copyright (c) 2012-2013 Kaarle Ritvanen
+See LICENSE file for license details
+--]]
+
+local M = {}
+
+local err = require('acf2.error')
+
+-- TODO each transaction backend (i.e. persistence manager or
+-- transaction proper) should be implemented as a thread or have its
+-- internal state stored in shared storage (with appropriate locking)
+
+
+local generation = 0
+function M.gen_number()
+   generation = generation + 1
+   return generation
+end
+
+
+M.TransactionBackend = require('acf2.object').class()
+
+function M.TransactionBackend:init() self.mod_time = {} end
+
+function M.TransactionBackend:get_if_older(path, timestamp)
+   local value, ts = self:get(path)
+   if ts > timestamp then err.raise('conflict', path) end
+   return value, ts
+end
+
+function M.TransactionBackend:set(path, value)
+   self:set_multiple{{path, value}}
+end
+
+function M.TransactionBackend:set_multiple(mods)
+   -- TODO delegate to PM backends?
+   local timestamp = M.gen_number()
+   local effective = {}
+
+   local function tostr(s) return s ~= nil and tostring(s) or nil end
+
+   for _, mod in ipairs(mods) do
+      local path, value = unpack(mod)
+
+      if type(value) == 'table' or type(
+	 self:get(path)
+      ) == 'table' or self:get(path) ~= value then
+
+	 table.insert(effective, mod)
+	 self.mod_time[path] = timestamp
+      end
+   end
+
+   self:_set_multiple(effective)
+end
+
+-- TODO should be atomic, mutex with set_multiple
+function M.TransactionBackend:comp_and_setm(accessed, mods)
+   local errors = err.ErrorDict()
+   for path, timestamp in pairs(accessed) do
+      errors:collect(self.get_if_older, self, path, timestamp)
+   end
+   errors:raise()
+
+   self:set_multiple(mods)
+end
+
+
+return M