Merge pull request #352 from psychon/gears_cache

Add gears.cache: a generic cache which may loose values at any time

lib/gears/cache.lua

@@ -0,0 +1,52 @@
+---------------------------------------------------------------------------
+-- @author Uli Schlachter
+-- @copyright 2015 Uli Schlachter
+-- @release @AWESOME_VERSION@
+-- @classmod gears.cache
+---------------------------------------------------------------------------
+
+local select = select
+local setmetatable = setmetatable
+local unpack = unpack or table.unpack
+
+local cache = {}
+
+--- Get an entry from the cache, creating it if it's missing.
+-- @param ... Arguments for the creation callback. These are checked against the
+--            cache contents for equality.
+-- @return The entry from the cache
+function cache:get(...)
+    local result = self._cache
+    for i = 1, select("#", ...) do
+        local arg = select(i, ...)
+        local next = result[arg]
+        if not next then
+            next = {}
+            result[arg] = next
+        end
+        result = next
+    end
+    local ret = result._entry
+    if not ret then
+        ret = { self._creation_cb(...) }
+        result._entry = ret
+    end
+    return unpack(ret)
+end
+
+--- Create a new cache object. A cache keeps some data that can be
+-- garbage-collected at any time, but might be useful to keep.
+-- @param creation_cb Callback that is used for creating missing cache entries.
+-- @return A new cache object.
+function cache.new(creation_cb)
+    return setmetatable({
+        _cache = setmetatable({}, { __mode = "v" }),
+        _creation_cb = creation_cb
+    }, {
+        __index = cache
+    })
+end
+
+return setmetatable(cache, { __call = function(_, ...) return cache.new(...) end })
+
+-- vim: filetype=lua:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:textwidth=80

lib/gears/color.lua

@@ -17,7 +17,7 @@ local cairo = require("lgi").cairo
 local surface = require("gears.surface")
 
 local color = { mt = {} }
-local pattern_cache = setmetatable({}, { __mode = 'v' })
+local pattern_cache
 
 --- Parse a HTML-color.
 -- This function can parse colors like `#rrggbb` and `#rrggbbaa`.
@@ -231,13 +231,7 @@ function color.create_pattern(col)
     if cairo.Pattern:is_type_of(col) then
         return col
     end
-    local col = col or "#000000"
-    local result = pattern_cache[col]
-    if not result then
-        result = color.create_pattern_uncached(col)
-        pattern_cache[col] = result
-    end
-    return result
+    return pattern_cache:get(col or "#000000")
 end
 
 --- Check if a pattern is opaque.
@@ -296,6 +290,8 @@ function color.mt:__call(...)
     return color.create_pattern(...)
 end
 
+pattern_cache = require("gears.cache").new(color.create_pattern_uncached)
+
 return setmetatable(color, color.mt)
 
 -- vim: filetype=lua:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:textwidth=80

lib/gears/init.lua

@@ -15,6 +15,7 @@ return
     surface = require("gears.surface");
     wallpaper = require("gears.wallpaper");
     timer = require("gears.timer");
+    cache = require("gears.cache");
 }
 
 -- vim: filetype=lua:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:textwidth=80

lib/wibox/layout/base.lua

@@ -38,21 +38,7 @@ function base.fit_widget(widget, width, height)
     local width = math.max(0, width)
     local height = math.max(0, height)
 
-    -- Since the geometry cache is a weak table, we have to be careful when
-    -- doing lookups. We can't do "if cache[width] ~= nil then"!
-    local cache = widget._fit_geometry_cache
-    local result = cache[width]
-    if not result then
-        result = {}
-        cache[width] = result
-    end
-    cache, result = result, result[height]
-    if not result then
-        local w, h = widget:fit(width, height)
-        result = { width = w, height = h }
-        cache[height] = result
-    end
-    return result.width, result.height
+    return widget._fit_geometry_cache:get(width, height)
 end
 
 --- Draw a widget via a cairo context

lib/wibox/widget/base.lua

@@ -7,6 +7,7 @@
 
 local debug = require("gears.debug")
 local object = require("gears.object")
+local cache = require("gears.cache")
 local setmetatable = setmetatable
 local pairs = pairs
 local type = type
@@ -98,9 +99,12 @@ function base.make_widget(proxy, widget_name)
     end
 
     -- Add a geometry for base.fit_widget() that is cleared when necessary
-    ret._fit_geometry_cache = setmetatable({}, { __mode = 'v' })
+    local function cb(...)
+        return ret:fit(...)
+    end
+    ret._fit_geometry_cache = cache.new(cb)
     ret:connect_signal("widget::updated", function()
-        ret._fit_geometry_cache = setmetatable({}, { __mode = 'v' })
+        ret._fit_geometry_cache = cache.new(cb)
     end)
 
     -- Add __tostring method to metatable.

spec/gears/cache_spec.lua

@@ -0,0 +1,61 @@
+---------------------------------------------------------------------------
+-- @author Uli Schlachter
+-- @copyright 2015 Uli Schlachter
+---------------------------------------------------------------------------
+
+local cache = require("gears.cache")
+
+describe("gears.cache", function()
+    -- Make sure no cache is cleared during the tests
+    before_each(function()
+        collectgarbage("stop")
+    end)
+    after_each(function()
+        collectgarbage("restart")
+    end)
+
+    describe("Zero arguments", function()
+        it("Creation cb is called", function()
+            local called = false
+            local c = cache(function()
+                called = true
+            end)
+            local res = c:get()
+            assert.is_nil(res)
+            assert.is_true(called)
+        end)
+    end)
+
+    describe("Two arguments", function()
+        it("Cache works", function()
+            local num_calls = 0
+            local c = cache(function(a, b)
+                num_calls = num_calls + 1
+                return a + b
+            end)
+            local res1 = c:get(1, 2)
+            local res2 = c:get(1, 3)
+            local res3 = c:get(1, 2)
+            assert.is.equal(res1, 3)
+            assert.is.equal(res2, 4)
+            assert.is.equal(res3, 3)
+            assert.is.equal(num_calls, 2)
+        end)
+
+        it("Cache invalidation works", function()
+            local num_calls = 0
+            local c = cache(function(a, b)
+                num_calls = num_calls + 1
+                return a + b
+            end)
+            local res1 = c:get(1, 2)
+            collectgarbage("collect")
+            local res2 = c:get(1, 2)
+            assert.is.equal(res1, 3)
+            assert.is.equal(res2, 3)
+            assert.is.equal(num_calls, 2)
+        end)
+    end)
+end)
+
+-- vim: filetype=lua:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:textwidth=80

spec/wibox/test_utils.lua

@@ -4,6 +4,7 @@
 ---------------------------------------------------------------------------
 
 local object = require("gears.object")
+local cache = require("gears.cache")
 local wbase = require("wibox.widget.base")
 local lbase = require("wibox.layout.base")
 local say = require("say")
@@ -64,7 +65,7 @@ return {
             return width or 10, height or 10
         end
         w.draw = function() end
-        w._fit_geometry_cache = {}
+        w._fit_geometry_cache = cache.new(w.fit)
 
         spy.on(w, "fit")
         stub(w, "draw")