Merge lp:~tkluck/simple-scan/autosaves into lp:~simple-scan-team/simple-scan/trunk

[Timo Kluck]

[Robert Ancell (robert-ancell)]

Hi,

Thanks for working on this!

The patch seems generally good, but I'm not able to confirm it working. I can confirm the database gets written, but if I do a "killall -9 simple-scan" and then restart it the existing book is not recovered. What steps should I take to confirm the patch works?

> // FIXME: this only works on linux
> string current_pids;
> Process.spawn_command_line_sync ("pidof simple-scan | sed \"s/ /,/g\"", out current_pids);
This is a bit gross, but don't know if we can get around it.

> public void on_page_changed (Page page)
> {
> /* we don't update the database as it is to slow to do so each time
> * a scan line is received.
> */
> //update_page (page);
> }
Please remove this if it doesn't do anything.

> if (number_of_instances > 0)
> {
> assert_not_reached ();
> }
We don't use curly braces if there's just one line in a branch.

> /* FIXME: we would like to connect to a scan_fished signal on a page,
> * but it does not exist. Updating the database every time a scanline
> * has changed is much to slow. We choose to update the database every
> * now and then, instead.
Let's add that signal then.

review: Needs Information

[Timo Kluck (tkluck)]

Hi Robert,

Thanks for your detailed feedback.

> The patch seems generally good, but I'm not able to confirm it working. I can confirm the database gets written, but if I do a "killall -9 simple-scan" and then restart it the existing book is not recovered. What steps should I take to confirm the patch works?

I don't have access to a scanner atm, so I cannot make a document like you're doing. However, it did work for me as far as I remember. What does work for me right now, is to add an autosave page manually, by

sqlite3 ~/.cache/simple-scan/autosaves/autosaves.db
INSERT INTO "pages" VALUES(1,1,1,1,1,1,150,150,150,8,3,450,'',0,0,10,10,0,randomblob(150*150*3));

and then starting simple-scan. The window will open with a very colourful page. Can you confirm that this works for you?

I will put your other remarks into work soon.

[Robert Ancell (robert-ancell)]

Hi Timo,

If you ever want to test simple-scan you can pass the name of the scanner as an argument to simple-scan. Conveniently SANE has a test driver so the following:

$ simple-scan test

Works without any scanner attached!

[Timo Kluck (tkluck)]

If you ever want to test simple-scan you can pass the name of the scanner as an argument to simple-scan. Conveniently SANE has a test driver so the following:

$ simple-scan test

Works without any scanner attached!
Thanks, that's very helpful! I now see that the first scanned page is not correctly stored in the database. The next one is, and it is also being correctly recovered on my machine. A clue is that I'm getting some of those warn_if_fails failing. Are you seeing the same behaviour?

I will have to look into it later.

[Timo Kluck (tkluck)]

I've pushed some changes that seem to deal with the issues I could reproduce. Can you test the new version?

[lp:~tkluck/simple-scan/autosaves]

563. By Timo Kluck on 2012-05-30

Correctly deal with the pages that exist already when the autosave manager is started

564. By Timo Kluck on 2012-05-30

use a scan_finished signal to know when to autosave

565. By Timo Kluck on 2012-05-30

do not use curly braces for single line branches

[Robert Ancell (robert-ancell)]

I tried the following:

1. Run simple-scan with test driver:
bob@alchemy:~/bzr/simple-scan$ ./src/simple-scan test
2. Scan a single page with text mode
3. Kill simple-scan with 'killall simple-scan':
Terminated
4. Run simple-scan again
bob@alchemy:~/bzr/simple-scan$ ./src/simple-scan

** (simple-scan:8023): CRITICAL **: autosave_manager_recover_book: assertion `SQLITE_OK == _tmp8_' failed

Doesn't recover the book and gives the above error.

review: Needs Fixing

[Timo Kluck (tkluck)]

> I tried the following:
>
> 1. Run simple-scan with test driver:
> bob@alchemy:~/bzr/simple-scan$ ./src/simple-scan test
> 2. Scan a single page with text mode
> 3. Kill simple-scan with 'killall simple-scan':
> Terminated
> 4. Run simple-scan again
> bob@alchemy:~/bzr/simple-scan$ ./src/simple-scan
>
> ** (simple-scan:8023): CRITICAL **: autosave_manager_recover_book: assertion
> `SQLITE_OK == _tmp8_' failed
>
> Doesn't recover the book and gives the above error.

I'm doing the exact same thing (either first removing ~/.cache/simple-scan/autosaves/autosaves.db or not) and it works for me. I'm also puzzled by the error you're getting. It seems to be the prepare_v2 call that's failing. I cannot see how that can work on one machine and fail on the other. Are you on Precise with sqlite3 version 3.7.9-2ubuntu1 ?

Could you help me debug this? There's no way I can do that without seeing it happen for myself. Can you recover the exit code of the prepare_v2 call? And can you recover the sql string after it has been formatted?

Thanks!

[Robert Ancell (robert-ancell)]

Could you update it to log the error codes? That way it will be safer in the future.

[lp:~tkluck/simple-scan/autosaves]

566. By Timo Kluck on 2012-08-09

add verbose logging output for autosave manager database access

[Timo Kluck (tkluck)]

I've just pushed a version that logs all the query strings and the resulting error codes. It would be great if you could send me the resulting logfile. (don't forget to specify --debug on the command line).

[Robert Ancell (robert-ancell)]

It doesn't crash anymore but I get the following error:

[+0.00s] DEBUG: simple-scan.vala:582: Starting Simple Scan 3.6.0, PID=5391
[+0.00s] DEBUG: Connecting to session manager
[+0.03s] WARNING: g_object_set_valist: invalid object type `GtkAdjustment' for value type `GtkWidget'
[+0.03s] DEBUG: ui.vala:1463: Restoring window to 774x607 pixels
[+0.03s] DEBUG: ui.vala:1468: Restoring window to maximized
[+0.03s] DEBUG: autosave-manager.vala:214: Executing query "
            CREATE TABLE IF NOT EXISTS pages (
                id integer PRIMARY KEY,
                process_id integer,
                page_hash integer,
                book_hash integer,
                book_revision integer,
                page_number integer,
                dpi integer,
                width integer,
                height integer,
                depth integer,
                n_channels integer,
                rowstride integer,
                color_profile string,
                crop_x integer,
                crop_y integer,
                crop_width integer,
                crop_height integer,
                scan_direction integer,
                pixels binary
            )"
[+0.04s] DEBUG: autosave-manager.vala:113: preparing query "
                   SELECT process_id, book_hash, book_revision FROM pages
                   WHERE NOT process_id IN (5391)
                   LIMIT 1
                "
[+0.04s] DEBUG: autosave-manager.vala:134: Executing query "
                        UPDATE pages
                           SET process_id = 5391
                         WHERE process_id = 5359
                           AND book_hash = 11118128
                           AND book_revision = 0"
[+0.23s] DEBUG: autosave-manager.vala:396: preparing query "
            SELECT process_id,
                page_hash,
                book_hash,
                book_revision,
                page_number,
                dpi,
                width,
                height,
                depth,
                n_channels,
                rowstride,
                color_profile,
                crop_x,
                crop_y,
                crop_width,
                crop_height,
                scan_direction,
                pixels,
                id
            FROM pages
            WHERE process_id = 5391
              AND book_revision = (
                  SELECT MAX(book_revision) WHERE process_id = 5391
              )
            ORDER BY page_number
        "
[+0.23s] WARNING: autosave-manager.vala:399: error 1 while preparing statement
[+0.28s] DEBUG: scanner.vala:1419: sane_init () -> SANE_STATUS_GOOD
[+0.28s] DEBUG: scanner.vala:1425: SANE version 1.0.23
[+0.28s] DEBUG: scanner.vala:1486: Requesting redetection of scan devices
[+0.28s] DEBUG: scanner.vala:776: Processing request
[+2.69s] DEBUG: scanner.vala:338: sane_get_devices () -> SANE_STATUS_GOOD
[+3.30s] DEBUG: scanner.vala:1559: Stopping scan thread
[+3.30s] DEBUG: scanner.vala:776: Processing request
[+3.31s] DEBUG: scanner.vala:1567: sane_exit ()

review: Needs Fixing

[Robert Ancell (robert-ancell)]

It seems to be this part - removing it makes it work.
AND book_revision = ( SELECT MAX(book_revision) WHERE process_id = 5391 )

Is a particular version of SQLite required for this syntax to be supported?

[lp:~tkluck/simple-scan/autosaves]

567. By Timo Kluck on 2012-11-27

Fix subquery

[Timo Kluck (tkluck)]

I could reproduce this error now (!). I'm surprised that it worked before, because the subquery misses a FROM clause. I just pushed a fix. Can you let me know your results?

[Robert Ancell (robert-ancell)]

That fixes that error, but still not books being restored.

I am running the following:
1. $ simple-scan test -d
2. Pressing scan
3. Killing simple-scan with ctrl-C (or killall simple-scan)
4. $ simple-scan

No pages are restored.

Can you add some debugging messages that note what the the autosave manager is doing? I would expect to see the following in the log

"Restoring book with 5 pages"
"No book to restore"
"Failed to restore book: Error Sqlite.ERROR when getting pages"
"Autosaving book to ~/.cache/simple-scan/autosaves/autosaves.db"

[lp:~tkluck/simple-scan/autosaves]

568. By Timo Kluck on 2012-12-06

even more verbose logging

[Timo Kluck (tkluck)]

I just pushed some extra verbose logging. Could you post your log for when it is failing? And, just to make sure, can you also

    rm -rf ~/.cache/simple-scan/autosaves

before testing?

[Robert Ancell (robert-ancell)]

Did the following:
0. $ ~/.cache/simple-scan/autosaves/autosaves.db
1. $ simple-scan test
2. Pressing scan
3. Ctrl+C
4. $ simple-scan

It worked some times but not always. The log from a failure is:
[+0.00s] DEBUG: simple-scan.vala:582: Starting Simple Scan 3.6.0, PID=11515
[+0.00s] DEBUG: Connecting to session manager
[+0.04s] WARNING: g_object_set_valist: invalid object type `GtkAdjustment' for value type `GtkWidget'
[+0.04s] DEBUG: ui.vala:1463: Restoring window to 774x607 pixels
[+0.04s] DEBUG: autosave-manager.vala:87: creating a new instance of the autosave manager
[+0.04s] DEBUG: autosave-manager.vala:220: Executing query "
            CREATE TABLE IF NOT EXISTS pages (
                id integer PRIMARY KEY,
                process_id integer,
                page_hash integer,
                book_hash integer,
                book_revision integer,
                page_number integer,
                dpi integer,
                width integer,
                height integer,
                depth integer,
                n_channels integer,
                rowstride integer,
                color_profile string,
                crop_x integer,
                crop_y integer,
                crop_width integer,
                crop_height integer,
                scan_direction integer,
                pixels binary
            )"
[+0.06s] DEBUG: autosave-manager.vala:117: preparing query "
                   SELECT process_id, book_hash, book_revision FROM pages
                   WHERE NOT process_id IN (11515)
                   LIMIT 1
                "
[+0.06s] DEBUG: autosave-manager.vala:123: found at least one autosave page, taking ownership
[+0.06s] DEBUG: autosave-manager.vala:139: Executing query "
                        UPDATE pages
                           SET process_id = 11515
                         WHERE process_id = 11505
                           AND book_hash = -671049168
                           AND book_revision = 0"
[+0.06s] DEBUG: autosave-manager.vala:404: preparing query "
            SELECT process_id,
                page_hash,
                book_hash,
                book_revision,
                page_number,
                dpi,
                width,
                height,
                depth,
                n_channels,
                rowstride,
                color_profile,
                crop_x,
                crop_y,
                crop_width,
                crop_height,
                scan_direction,
                pixels,
                id
            FROM pages
            WHERE process_id = 11515
              AND book_revision = (
                  SELECT MAX(book_revision) FROM pages WHERE process_id = 11515
              )
            ORDER BY page_number
        "
[+0.06s] DEBUG: autosave-manager.vala:474: no pages found to recover
[+0.06s] DEBUG: autosave-manager.vala:57: setting book to autosave
[+0.06s] DEBUG: autosave-manager.vala:72: connecting to signals of new book
[+0.10s] DEBUG: scanner.vala:1419: sane_init () -> SANE_STATUS_GOOD
[+0.10s] DEBUG: scanner.vala:1425: SANE version 1.0.23
[+0.10s] DEBUG: scanner.vala:1486: Requesting redetection of scan devices
[+0....

[Robert Ancell (robert-ancell)]

Log when the database was created:
[+0.00s] DEBUG: simple-scan.vala:582: Starting Simple Scan 3.6.0, PID=11458
[+0.00s] DEBUG: Connecting to session manager
[+0.03s] WARNING: g_object_set_valist: invalid object type `GtkAdjustment' for value type `GtkWidget'
[+0.03s] DEBUG: ui.vala:1463: Restoring window to 774x607 pixels
[+0.03s] DEBUG: autosave-manager.vala:87: creating a new instance of the autosave manager
[+0.03s] DEBUG: autosave-manager.vala:220: Executing query "
            CREATE TABLE IF NOT EXISTS pages (
                id integer PRIMARY KEY,
                process_id integer,
                page_hash integer,
                book_hash integer,
                book_revision integer,
                page_number integer,
                dpi integer,
                width integer,
                height integer,
                depth integer,
                n_channels integer,
                rowstride integer,
                color_profile string,
                crop_x integer,
                crop_y integer,
                crop_width integer,
                crop_height integer,
                scan_direction integer,
                pixels binary
            )"
[+0.23s] DEBUG: autosave-manager.vala:117: preparing query "
                   SELECT process_id, book_hash, book_revision FROM pages
                   WHERE NOT process_id IN (11458)
                   LIMIT 1
                "
[+0.23s] DEBUG: autosave-manager.vala:57: setting book to autosave
[+0.23s] DEBUG: autosave-manager.vala:72: connecting to signals of new book
[+0.23s] DEBUG: autosave-manager.vala:300: adding an autosave for a new page
[+0.23s] DEBUG: autosave-manager.vala:313: Executing query "
            INSERT INTO pages
                (process_id,
                page_hash,
                book_hash,
                book_revision)
                VALUES
                (11458,
                20112144,
                1744869936,
                0)
        "
[+0.39s] DEBUG: autosave-manager.vala:322: updating the autosave for a page
[+0.39s] DEBUG: autosave-manager.vala:351: preparing query "
            UPDATE pages
                SET
                page_number=0,
                dpi=300,
                width=2362,
                height=2362,
                depth=0,
                n_channels=0,
                rowstride=0,
                crop_x=0,
                crop_y=0,
                crop_width=0,
                crop_height=0,
                scan_direction=0,
                color_profile=?1,
                pixels=?2
                WHERE process_id = 11458
                  AND page_hash = 20112144
                  AND book_hash = 1744869936
                  AND book_revision = 0
            "
[+0.58s] DEBUG: scanner.vala:1419: sane_init () -> SANE_STATUS_GOOD
[+0.58s] DEBUG: scanner.vala:1425: SANE version 1.0.23
[+0.58s] DEBUG: scanner.vala:1486: Requesting redetection of scan devices
[+0.58s] DEBUG: scanner.vala:776: Processing request
[+1.73s] DEBUG: simple-scan.vala:310: Requesting scan at 150 dpi from device 'test'
[+1.73s] DEBUG: scanner.vala:1532: Scanner.scan ("test", dpi=150, scan_mode=ScanMode.GRAY, depth=2, type=ScanType...

[Timo Kluck (tkluck)]

I think I've got it. The book_hash parameter may be formatted as a signed
int by vala into the query, and then it doesn't match unsigned value in the
record.

I'll do the proper thing and use bind_int for these things. I'll let you
know as soon as I've pushed an updated version.

Thanks for the extensive logs and testing!

[lp:~tkluck/simple-scan/autosaves]

569. By Timo Kluck on 2012-12-18

use bind_int64 for the direct_hash values

[Timo Kluck (tkluck)]

Could you test again? I could reproduce the problems with your database but I can't generate the same erroneous database on my machine, so I can't be 100% sure this last commit tackled the problem.

[Robert Ancell (robert-ancell)]

Pushed with some coding style changes, thanks for the patience!

=== modified file '.bzrignore'
--- .bzrignore	2011-06-12 10:13:06 +0000
+++ .bzrignore	2012-12-18 23:23:21 +0000
@@ -32,3 +32,4 @@
 src/scanner.c
 src/simple-scan.c
 src/ui.c
+src/autosave-manager.c

=== modified file 'configure.ac'
--- configure.ac	2012-10-14 20:16:55 +0000
+++ configure.ac	2012-12-18 23:23:21 +0000
@@ -27,6 +27,7 @@
     cairo
     gdk-pixbuf-2.0
     gudev-1.0
+    sqlite3
 ])
 
 PKG_CHECK_MODULES(COLORD, [

=== modified file 'src/Makefile.am'
--- src/Makefile.am	2011-07-10 06:59:21 +0000
+++ src/Makefile.am	2012-12-18 23:23:21 +0000
@@ -11,13 +11,15 @@
 	sane.vapi \
 	simple-scan.vala \
 	scanner.vala \
-	ui.vala
+	ui.vala \
+	autosave-manager.vala
 
 simple_scan_VALAFLAGS = \
 	--pkg=zlib \
 	--pkg=gudev-1.0 \
 	--pkg=gio-2.0 \
-	--pkg=gtk+-3.0
+	--pkg=gtk+-3.0 \
+	--pkg=sqlite3
 
 if HAVE_COLORD
 simple_scan_VALAFLAGS += -D HAVE_COLORD

=== added file 'src/autosave-manager.vala'
--- src/autosave-manager.vala	1970-01-01 00:00:00 +0000
+++ src/autosave-manager.vala	2012-12-18 23:23:21 +0000
@@ -0,0 +1,521 @@
+/*
+ * Copyright (C) 2011 Timo Kluck
+ * Author: Timo Kluck <[e-mail]>
+ *
+ * This program is free software: you can redistribute it and/or modify it under
+ * the terms of the GNU General Public License as published by the Free Software
+ * Foundation, either version 3 of the License, or (at your option) any later
+ * version. See http://www.gnu.org/copyleft/gpl.html the full text of the
+ * license.
+ */
+
+/*
+ * We store autosaves in a database named
+ *    ~/.cache/simple-scan/autosaves/autosaves.db
+ * It contains a single table of pages, each containing the process id (pid) of
+ * the simple-scan instance that saved it, and a hash of the Book and Page
+ * objects corresponding to it. The pixels are saved as a BLOB. 
+ * Additionally, the autosaves directory contains a number of tiff files that
+ * the user can use for manual recovery.
+ *
+ * At startup, we check whether autosaves.db contains any records
+ * with a pid that does not match a current pid for simple-scan. If so, we take
+ * ownership by an UPDATE statement changing to our own pid. Then, we
+ * recover the book. We're trying our best to avoid the possible race
+ * condition if several instances of simple-scan are started simultaneously.
+ *
+ * At application exit, we delete the records corresponding to our own pid.
+ * 
+ * Important notes:
+ *  - We enforce that there is only one AutosaveManager instance in a given
+ *    process by using a create function.
+ *  - It should be possible to change the book object at runtime, although this 
+ *    is not used in the current implementation so it has not been tested.
+ */
+
+public class AutosaveManager 
+{
+    private static string AUTOSAVE_DIR = Path.build_filename (Environment.get_user_cache_dir (), "simple-scan", "autosaves");
+    private static string AUTOSAVE_NAME = "autosaves";
+    private static string AUTOSAVE_EXT = ".db";
+    private static string AUTOSAVE_FILENAME = Path.build_filename (AUTOSAVE_DIR, AUTOSAVE_NAME + AUTOSAVE_EXT);
+
+    private static string PID = ((int)(Posix.getpid ())).to_string ();
+    private static int number_of_instances = 0;
+    
+    private Sqlite.Database database_connection;
+    private Book _book = null;
+
+    public Book book
+    {
+        get
+        {
+            return _book;
+        }
+        set
+        {
+            debug("setting book to autosave");
+            if (_book != null)
+            {
+                debug("disconnecting from signals of old book");
+                for (var i = 0; i < _book.get_n_pages (); i++)
+                {
+                    var page = _book.get_page (i);
+                    on_page_removed (page);
+                }
+                _book.page_added.disconnect (on_page_added);
+                _book.page_removed.disconnect (on_page_removed);
+                _book.reordered.disconnect (on_reordered);
+                _book.cleared.disconnect (on_cleared);
+            }
+            _book = value;
+            debug("connecting to signals of new book");
+            _book.page_added.connect (on_page_added);
+            _book.page_removed.connect (on_page_removed);
+            _book.reordered.connect (on_reordered);
+            _book.cleared.connect (on_cleared);
+        }
+    }
+
+    public static AutosaveManager? create (ref Book book)
+    {
+        /* compare autosave directories with pids of current instances of simple-scan
+         * take ownership of one of the ones that are unowned by renaming to the
+         * own pid. Then open the database and fill the book with the pages it
+         * contains.
+         */
+        debug("creating a new instance of the autosave manager");
+        if (number_of_instances > 0)
+            assert_not_reached ();
+
+        var man = new AutosaveManager ();
+        number_of_instances++;
+
+        try 
+        {
+            man.database_connection = open_database_connection ();
+        }
+        catch
+        {
+            warning ("Could not connect to the autosave database; no autosaves will be kept.");
+            return null;
+        }
+
+        bool any_pages_recovered = false;
+        try
+        {
+            // FIXME: this only works on linux. We can maybe use Gtk.Application and some session bus id instead?
+            string current_pids;
+            Process.spawn_command_line_sync ("pidof simple-scan | sed \"s/ /,/g\"", out current_pids);
+            current_pids = current_pids.strip ();
+            Sqlite.Statement stmt;
+            string query = @"
+                   SELECT process_id, book_hash, book_revision FROM pages
+                   WHERE NOT process_id IN ($current_pids)
+                   LIMIT 1
+                ";
+            debug("preparing query \"%s\"", query);
+            int result = man.database_connection.prepare_v2 (query, -1, out stmt);
+            if(Sqlite.OK == result)
+            {
+                while (Sqlite.ROW == stmt.step ())
+                {
+                    debug("found at least one autosave page, taking ownership");
+                    var unowned_pid = stmt.column_int (0);
+                    var book_hash = stmt.column_int (1);
+                    var book_revision = stmt.column_int (2);
+                    /* there's a possible race condition here when several instances
+                     * try to take ownership of the same rows. What would happen is
+                     * that this operations would affect no rows if another process
+                     * has taken ownership in the mean time. In that case, recover_book
+                     * does nothing, so there should be no problem.
+                     */            
+                    query = @"
+                        UPDATE pages
+                           SET process_id = $PID
+                         WHERE process_id = ?2
+                           AND book_hash = ?3
+                           AND book_revision = ?4";
+                    debug("Preparing query \"%s\"", query);
+                    Sqlite.Statement stmt2;
+                    result = man.database_connection.prepare_v2(query, -1, out stmt2);
+                    if (Sqlite.OK != result)
+                    {
+                        warning (@"Error preparing statement: $query");
+                    }
+                    stmt2.bind_int64 (2, unowned_pid);
+                    stmt2.bind_int64 (3, book_hash);
+                    stmt2.bind_int64 (4, book_revision);
+                    result = stmt2.step();
+                    if (Sqlite.DONE == result)
+                    {
+                        any_pages_recovered = true;
+                        man.recover_book (ref book);
+                    }
+                    else
+                    {
+                        warning ("error %d while executing query", result);
+                    }
+                }
+            }
+            else
+                warning("error %d while preparing statement", result);
+        }
+        catch (SpawnError e)
+        {
+            warning ("Could not obtain current process ids; not restoring any autosaves");
+        }
+
+        man.book = book;
+        if (!any_pages_recovered) {
+            for (var i = 0; i < book.get_n_pages (); i++)
+            {
+                var page = book.get_page (i);
+                man.on_page_added (page);
+            }
+        }
+
+        return man;
+    }
+
+    private AutosaveManager ()
+    {
+    }
+
+    public void cleanup () {
+        // delete autosave records
+        debug("clean exit; deleting autosave records");
+        warn_if_fail (Sqlite.OK == database_connection.exec (@"
+            DELETE FROM pages
+                WHERE process_id = $PID
+        "));
+    }
+
+    
+    static Sqlite.Database open_database_connection () throws Error
+    {
+        var autosaves_dir = File.new_for_path (AUTOSAVE_DIR);
+        try
+        {
+            autosaves_dir.make_directory_with_parents ();
+        }
+        catch
+        { // the directory already exists
+            // pass
+        }
+        Sqlite.Database connection;
+        if (Sqlite.OK != Sqlite.Database.open (AUTOSAVE_FILENAME, out connection))
+            throw new IOError.FAILED ("Could not connect to autosave database");
+        string query = @"
+            CREATE TABLE IF NOT EXISTS pages (
+                id integer PRIMARY KEY,
+                process_id integer,
+                page_hash integer,
+                book_hash integer,
+                book_revision integer,
+                page_number integer,
+                dpi integer,
+                width integer,
+                height integer,
+                depth integer,
+                n_channels integer,
+                rowstride integer,
+                color_profile string,
+                crop_x integer,
+                crop_y integer,
+                crop_width integer,
+                crop_height integer,
+                scan_direction integer,
+                pixels binary
+            )";
+        debug("Executing query \"%s\"", query);
+        int result = connection.exec(query);
+        if (Sqlite.OK != result)
+            warning("error %d while executing query", result);
+        return connection;
+    }
+
+    void on_page_added (Page page)
+    {
+        insert_page (page);
+        // TODO: save a tiff file
+        page.size_changed.connect (on_page_changed);
+        page.scan_direction_changed.connect (on_page_changed);
+        page.crop_changed.connect (on_page_changed);
+        page.scan_finished.connect (on_page_changed);
+    }
+    
+    public void on_page_removed (Page page)
+    {
+        page.pixels_changed.disconnect (on_page_changed);
+        page.size_changed.disconnect (on_page_changed);
+        page.scan_direction_changed.disconnect (on_page_changed);
+        page.crop_changed.disconnect (on_page_changed);
+        page.scan_finished.connect (on_page_changed);
+
+        string query = @"
+        DELETE FROM pages
+            WHERE process_id = $PID
+              AND page_hash = ?2
+              AND book_hash = ?3
+              AND book_revision = ?4
+        ";
+        debug("Executing query \"%s\"", query);
+        Sqlite.Statement stmt;
+        int result = database_connection.prepare_v2 (query, -1, out stmt);
+        if (Sqlite.OK != result)
+            warning(@"error $result while preparing query");
+        stmt.bind_int64 (2, direct_hash (page));
+        stmt.bind_int64 (3, direct_hash (book));
+        stmt.bind_int64 (4, cur_book_revision);
+
+        result = stmt.step();
+        if (Sqlite.DONE != result)
+            warning("error %d while executing query", result);
+    }
+    
+    public void on_reordered ()
+    {
+        for (var i=0; i < book.get_n_pages (); i++)
+        {
+            var page = book.get_page (i);
+            string query = @"
+            UPDATE pages SET page_number = ?5
+            WHERE process_id = $PID
+              AND page_hash = ?2
+              AND book_hash = ?3
+              AND book_revision = ?4
+            ";
+            debug("Executing query \"%s\"", query);
+            Sqlite.Statement stmt;
+            int result = database_connection.prepare_v2 (query, -1, out stmt);
+            if (Sqlite.OK != result)
+                warning(@"error $result while preparing query");
+            stmt.bind_int64 (5, i);
+            stmt.bind_int64 (2, direct_hash (page));
+            stmt.bind_int64 (3, direct_hash (book));
+            stmt.bind_int64 (4, cur_book_revision);
+
+            result = stmt.step();
+            if (Sqlite.DONE != result)
+                warning("error %d while executing query", result);
+        }
+    }
+
+    public void on_page_changed (Page page)
+    {
+        update_page (page);
+    }
+
+    public void on_needs_saving_changed (Book book)
+    {
+        for (int n = 0; n < book.get_n_pages (); n++)
+        {
+            var page = book.get_page (n);
+            update_page (page);
+        }
+    }
+
+    private int cur_book_revision = 0;
+
+    public void on_cleared ()
+    {
+        cur_book_revision++;
+    }
+
+    private void insert_page (Page page)
+    {
+        debug("adding an autosave for a new page");
+        string query = @"
+            INSERT INTO pages
+                (process_id,
+                page_hash,
+                book_hash,
+                book_revision)
+                VALUES
+                ($PID,
+                ?2,
+                ?3,
+                ?4)
+        ";
+        debug("Executing query \"%s\"", query);
+          Sqlite.Statement stmt;
+          int result = database_connection.prepare_v2 (query, -1, out stmt);
+          if (Sqlite.OK != result)
+              warning(@"error $result while preparing query");
+          stmt.bind_int64 (2, direct_hash (page));
+          stmt.bind_int64 (3, direct_hash (book));
+          stmt.bind_int64 (4, cur_book_revision);
+          result = stmt.step();
+          if (Sqlite.DONE != result)
+              warning("error %d while executing query", result);
+        update_page (page);     
+    }
+
+    private void update_page (Page page)
+    {
+        debug("updating the autosave for a page");
+        int crop_x;
+        int crop_y;
+        int crop_width;
+        int crop_height;
+        page.get_crop (out crop_x, out crop_y, out crop_width, out crop_height);
+        Sqlite.Statement stmt;
+        string query = @"
+            UPDATE pages
+                SET
+                page_number=$(book.get_page_index (page)),
+                dpi=$(page.get_dpi ()),
+                width=$(page.get_width ()),
+                height=$(page.get_height ()),
+                depth=$(page.get_depth ()),
+                n_channels=$(page.get_n_channels ()),
+                rowstride=$(page.get_rowstride ()),
+                crop_x=$crop_x,
+                crop_y=$crop_y,
+                crop_width=$crop_width,
+                crop_height=$crop_height,
+                scan_direction=$((int)page.get_scan_direction ()),
+                color_profile=?1,
+                pixels=?2
+                WHERE process_id = $PID
+                  AND page_hash = ?4
+                  AND book_hash = ?5
+                  AND book_revision = ?6
+            ";
+        debug("preparing query \"%s\"", query);
+        int result = database_connection.prepare_v2 (query, -1, out stmt);
+        if(Sqlite.OK != result) {
+            warning("error %d while preparing statement", result);
+            return_if_reached();
+        }
+        stmt.bind_int64 (4, direct_hash (page));
+        stmt.bind_int64 (5, direct_hash (book));
+        stmt.bind_int64 (6, cur_book_revision);
+        result = stmt.bind_text (1, page.get_color_profile () ?? "");
+        if(Sqlite.OK != result) {
+            warning("error %d while binding text", result);
+        }
+        if (page.get_pixels () != null) {
+            // (-1) is the special value SQLITE_TRANSIENT
+            result = stmt.bind_blob (2, page.get_pixels (), page.get_pixels ().length, (DestroyNotify)(-1));
+            if(Sqlite.OK != result) {
+                warning("error %d while binding blob", result);
+            }
+        } else
+            warn_if_fail (Sqlite.OK == stmt.bind_null (2));
+
+        warn_if_fail (Sqlite.DONE == stmt.step ());
+    }
+
+    private void recover_book (ref Book book)
+    {
+        Sqlite.Statement stmt;
+        string query = @"
+            SELECT process_id,
+                page_hash,
+                book_hash,
+                book_revision,
+                page_number,
+                dpi,
+                width,
+                height,
+                depth,
+                n_channels,
+                rowstride,
+                color_profile,
+                crop_x,
+                crop_y,
+                crop_width,
+                crop_height,
+                scan_direction,
+                pixels,
+                id
+            FROM pages
+            WHERE process_id = $PID
+              AND book_revision = (
+                  SELECT MAX(book_revision) FROM pages WHERE process_id = $PID
+              )
+            ORDER BY page_number
+        ";
+        debug("preparing query \"%s\"", query);
+        int result = database_connection.prepare_v2 (query, -1, out stmt);
+        if (Sqlite.OK != result) {
+            warning("error %d while preparing statement", result);
+        }
+        bool first = true;
+        while (Sqlite.ROW == stmt.step ())
+        {
+            debug("found a page that needs to be recovered");
+            if (first) 
+            {
+                book.clear ();
+                first = false;
+            }
+            var dpi = stmt.column_int (5);
+            var width = stmt.column_int (6);
+            var height = stmt.column_int (7);
+            var depth = stmt.column_int (8);
+            var n_channels = stmt.column_int (9);
+            var scan_direction = (ScanDirection)stmt.column_int (16);
+
+            if (width <= 0 || height <= 0) 
+                continue;
+            
+            debug(@"restoring a page of size $(width) x $(height)");
+            var new_page = book.append_page (width, height, dpi, scan_direction);
+
+            if (depth > 0 && n_channels > 0) 
+            {
+                var info = new ScanPageInfo ();
+                info.width = width;
+                info.height = height;
+                info.depth = depth;
+                info.n_channels = n_channels;
+                info.dpi = dpi;
+                info.device = "";
+                new_page.set_page_info (info);
+            }
+
+            new_page.set_color_profile (stmt.column_text (11));
+            var crop_x = stmt.column_int (12);
+            var crop_y = stmt.column_int (13);
+            var crop_width = stmt.column_int (14);
+            var crop_height = stmt.column_int (15);
+            if (crop_width > 0 && crop_height > 0) 
+            {
+                new_page.set_custom_crop (crop_width, crop_height);
+                new_page.move_crop (crop_x, crop_y);
+            }
+
+            uchar[] new_pixels = new uchar[stmt.column_bytes (17)];
+            Memory.copy (new_pixels, stmt.column_blob (17), stmt.column_bytes (17));
+            new_page.set_pixels (new_pixels);
+
+            var id = stmt.column_int (18);
+            debug("updating autosave to point to our new copy of the page");
+            query = @"
+                UPDATE pages
+                   SET page_hash=?1,
+                       book_hash=?2,
+                       book_revision=?3
+                WHERE id = $id
+            ";
+            debug("executing query \"%s\"", query);
+            Sqlite.Statement stmt2;
+            int result2 = database_connection.prepare_v2 (query, -1, out stmt2);
+            if (Sqlite.OK != result2)
+                warning(@"error $result2 while preparing query");
+            stmt2.bind_int64 (1, direct_hash (new_page));
+            stmt2.bind_int64 (2, direct_hash (book));
+            stmt2.bind_int64 (3, cur_book_revision);
+
+            result2 = stmt2.step();
+            if (Sqlite.DONE != result2)
+                warning("error %d while executing query", result);
+        }
+        if (first) {
+            debug("no pages found to recover");
+        }
+    }
+}

=== modified file 'src/page.vala'
--- src/page.vala	2012-08-16 02:09:28 +0000
+++ src/page.vala	2012-12-18 23:23:21 +0000
@@ -63,6 +63,7 @@
     public signal void scan_line_changed ();
     public signal void scan_direction_changed ();
     public signal void crop_changed ();
+    public signal void scan_finished ();
 
     public Page (int width, int height, int dpi, ScanDirection scan_direction)
     {
@@ -199,6 +200,7 @@
         if (size_has_changed)
             size_changed ();
         scan_line_changed ();
+        scan_finished ();
     }
 
     public ScanDirection get_scan_direction ()
@@ -541,6 +543,13 @@
         return pixels;
     }
 
+    public void set_pixels (uchar[] new_pixels)
+    {
+        pixels = new_pixels;
+        has_data_ = new_pixels != null;
+        pixels_changed ();
+    }
+
     // FIXME: Copied from page-view, should be shared code
     private uchar get_sample (uchar[] pixels, int offset, int x, int depth, int n_channels, int channel)
     {

=== modified file 'src/ui.vala'
--- src/ui.vala	2012-11-01 07:45:01 +0000
+++ src/ui.vala	2012-12-18 23:23:21 +0000
@@ -74,6 +74,8 @@
     private Book book;
     private string? book_uri = null;
 
+    private AutosaveManager? autosave_manager;
+
     private BookView book_view;
     private bool updating_page_menu;
     private int default_page_width;
@@ -103,6 +105,8 @@
         settings = new Settings ("org.gnome.SimpleScan");
 
         load ();
+
+        autosave_manager = AutosaveManager.create (ref book);
     }
 
     ~UserInterface ()
@@ -1139,6 +1143,11 @@
 
         window.destroy ();
 
+        if (autosave_manager != null)
+        {
+            autosave_manager.cleanup ();
+        }
+
         return true;
     }