[hwmontemp] Bring back sysfs path cache

Cache sysfs path resolved from given name index in local table. This avoids
spawning a `grep` process over and over again for each invocation.

Co-authored-by: Nguyễn Gia Phong <mcsinyx@disroot.org>

widgets/hwmontemp_linux.lua

@@ -1,5 +1,5 @@
 -- widget type providing name-indexed temperatures from /sys/class/hwmon
--- Copyright (C) 2019  Alexander Koch <lynix47@gmail.com>
+-- Copyright (C) 2019, 2020  Alexander Koch <lynix47@gmail.com>
 -- Copyright (C) 2019  Nguyễn Gia Phong <vn.mcsinyx@gmail.com>
 --
 -- This file is part of Vicious.
@@ -25,6 +25,14 @@ local io = { open = io.open }
 local helpers = require"vicious.helpers"
 local spawn = require"vicious.spawn"
 
+local pathcache = {}
+
+local function read_sensor(path, callback)
+    local f = io.open(path, "r")
+    callback{ tonumber(f:read"*line") / 1000 }
+    f:close()
+end
+
 -- hwmontemp: provides name-indexed temps from /sys/class/hwmon
 -- vicious.widgets.hwmontemp
 return helpers.setasyncall{
@@ -32,6 +40,7 @@ return helpers.setasyncall{
         if type(warg) ~= "table" or type(warg[1]) ~= "string" then
             return callback{}
         end
+
         local input = warg[2]
         if type(input) == "number" then
             input = ("temp%d_input"):format(input)
@@ -39,16 +48,20 @@ return helpers.setasyncall{
             input = "temp1_input"
         end
 
+        local sensor = warg[1]
+        if pathcache[sensor] then
+            read_sensor(pathcache[sensor] .. input, callback)
+        else
             spawn.easy_async_with_shell(
-            "grep " .. warg[1] .. " -wl /sys/class/hwmon/*/name",
+                "grep " .. sensor .. " -wl /sys/class/hwmon/*/name",
                 function (stdout, stderr, exitreason, exitcode)
                     if exitreason == "exit" and exitcode == 0 then
-                    local f = io.open(stdout:gsub("name%s+", input), "r")
-                    callback{ tonumber(f:read"*line") / 1000 }
-                    f:close()
+                        pathcache[sensor] = stdout:gsub("name%s+", "")
+                        read_sensor(pathcache[sensor] .. input, callback)
                     else
                         callback{}
                     end
                 end)
+        end
     end }
 -- vim: ts=4:sw=4:expandtab