fix #1064 by adding timestamp of document in cache key

so that when document is modified the persistent cache will
be invalidated automatically because the cache key will not
be matched. There is no perfermance overhead here at all. We
even don't need to check the modification time of the cache item
on disk, because the name of the on disk cache is a md5sum of the
cacheitem key, now the filename of the cache files contains the
modification time information.
If the document is modified since one rendered page is cached to disk,
the cache key won't match the cache file. And the cache file will
be discarded without the need to open the cache file or to check
the modification time of the cache file itself.

frontend/document/document.lua

@@ -1,11 +1,12 @@
-local DrawContext = require("ffi/drawcontext")
-local Blitbuffer = require("ffi/blitbuffer")
-local Cache = require("cache")
-local CacheItem = require("cacheitem")
 local TileCacheItem = require("document/tilecacheitem")
-local Geom = require("ui/geometry")
+local DrawContext = require("ffi/drawcontext")
 local Configurable = require("configurable")
+local Blitbuffer = require("ffi/blitbuffer")
+local lfs = require("libs/libkoreader-lfs")
+local CacheItem = require("cacheitem")
+local Geom = require("ui/geometry")
 local Math = require("optmath")
+local Cache = require("cache")
 local DEBUG = require("dbg")
 
 --[[
@@ -114,6 +115,7 @@ function Document:getNativePageDimensions(pageno)
 end
 
 function Document:_readMetadata()
+    self.mod_time = lfs.attributes(self.file, "modification")
     self.info.number_of_pages = self._document:getPages()
     return true
 end
@@ -215,8 +217,13 @@ function Document:getCoverPageImage()
     return nil
 end
 
+function Document:getFullPageHash(pageno, zoom, rotation, gamma, render_mode)
+    return "renderpg|"..self.file.."|"..self.mod_time.."|"..pageno.."|"
+                    ..zoom.."|"..rotation.."|"..gamma.."|"..render_mode
+end
+
 function Document:renderPage(pageno, rect, zoom, rotation, gamma, render_mode)
-    local hash = "renderpg|"..self.file.."|"..pageno.."|"..zoom.."|"..rotation.."|"..gamma.."|"..render_mode
+    local hash = self:getFullPageHash(pageno, zoom, rotation, gamma, render_mode)
     local page_size = self:getPageDimensions(pageno, zoom, rotation)
     -- this will be the size we actually render
     local size = page_size
@@ -231,12 +238,13 @@ function Document:renderPage(pageno, rect, zoom, rotation, gamma, render_mode)
             return
         end
         -- only render required part
-        hash = "renderpg|"..self.file.."|"..pageno.."|"..zoom.."|"..rotation.."|"..gamma.."|"..render_mode.."|"..tostring(rect)
+        hash = self:getFullPageHash(pageno, zoom, rotation, gamma, render_mode).."|"..tostring(rect)
         size = rect
     end
 
     -- prepare cache item with contained blitbuffer
     local tile = TileCacheItem:new{
+        persistent = true,
         size = size.w * size.h + 64, -- estimation
         excerpt = size,
         pageno = pageno,
@@ -274,7 +282,7 @@ end
 -- a hint for the cache engine to paint a full page to the cache
 -- TODO: this should trigger a background operation
 function Document:hintPage(pageno, zoom, rotation, gamma, render_mode)
-    local hash_full_page = "renderpg|"..self.file.."|"..pageno.."|"..zoom.."|"..rotation.."|"..gamma.."|"..render_mode
+    local hash_full_page = self:getFullPageHash(pageno, zoom, rotation, gamma, render_mode)
     if not Cache:check(hash_full_page, TileCacheItem) then
         DEBUG("hinting page", pageno)
         self:renderPage(pageno, nil, zoom, rotation, gamma, render_mode)
@@ -290,7 +298,7 @@ Draw page content to blitbuffer.
 @rect: visible_area inside document page
 --]]
 function Document:drawPage(target, x, y, rect, pageno, zoom, rotation, gamma, render_mode)
-    local hash_full_page = "renderpg|"..self.file.."|"..pageno.."|"..zoom.."|"..rotation.."|"..gamma.."|"..render_mode
+    local hash_full_page = self:getFullPageHash(pageno, zoom, rotation, gamma, render_mode)
     local hash_excerpt = hash_full_page.."|"..tostring(rect)
     local tile = Cache:check(hash_full_page, TileCacheItem)
     if not tile then

frontend/document/koptinterface.lua

@@ -107,7 +107,8 @@ function KoptInterface:getContextHash(doc, pageno, bbox)
     local screen_size = Screen:getSize()
     local screen_size_hash = screen_size.w.."|"..screen_size.h
     local bbox_hash = bbox.x0.."|"..bbox.y0.."|"..bbox.x1.."|"..bbox.y1
-    return doc.file.."|"..pageno.."|"..doc.configurable:hash("|").."|"..bbox_hash.."|"..screen_size_hash
+    return doc.file.."|"..doc.mod_time.."|"..pageno.."|"
+            ..doc.configurable:hash("|").."|"..bbox_hash.."|"..screen_size_hash
 end
 
 function KoptInterface:getPageBBox(doc, pageno)
@@ -215,6 +216,7 @@ function KoptInterface:getCachedContext(doc, pageno)
         DEBUG("reflowed page", pageno, "fullwidth:", fullwidth, "fullheight:", fullheight)
         self.last_context_size = fullwidth * fullheight + 128 -- estimation
         Cache:insert(kctx_hash, ContextCacheItem:new{
+            persistent = true,
             size = self.last_context_size,
             kctx = kc
         })
@@ -289,7 +291,7 @@ function KoptInterface:renderReflowedPage(doc, pageno, rect, zoom, rotation, ren
         end
         -- prepare cache item with contained blitbuffer
         local tile = TileCacheItem:new{
-            size = fullwidth * fullheight / 2 + 64, -- estimation
+            size = fullwidth * fullheight + 64, -- estimation
             excerpt = Geom:new{ w = fullwidth, h = fullheight },
             pageno = pageno,
         }
@@ -311,7 +313,7 @@ function KoptInterface:renderOptimizedPage(doc, pageno, rect, zoom, rotation, re
     local context_hash = self:getContextHash(doc, pageno, bbox)
     local renderpg_hash = "renderoptpg|"..context_hash..zoom
 
-    local cached = Cache:check(renderpg_hash)
+    local cached = Cache:check(renderpg_hash, TileCacheItem)
     if not cached then
         local page_size = Document.getNativePageDimensions(doc, pageno)
         local bbox = {
@@ -329,7 +331,8 @@ function KoptInterface:renderOptimizedPage(doc, pageno, rect, zoom, rotation, re
         local fullwidth, fullheight = kc:getPageDim()
         -- prepare cache item with contained blitbuffer
         local tile = TileCacheItem:new{
-            size = fullwidth * fullheight / 2 + 64, -- estimation
+            persistent = true,
+            size = fullwidth * fullheight + 64, -- estimation
             excerpt = Geom:new{
                 x = 0, y = 0,
                 w = fullwidth,