[gitg] Fix racy conditions in commit walking

[Jesse van den Kieboom <jessevdk src gnome org>]

commit 7136f0e0867165f25f7cd4309b8b9e7b230e666d
Author: Jesse van den Kieboom <jessevdk gnome org>
Date:   Wed Aug 5 20:50:40 2015 +0200

    Fix racy conditions in commit walking

 libgitg/gitg-commit-model.vala |   85 +++++++++++++++++++++-------------------
 plugins/diff/gitg-diff.vala    |    8 ++++
 2 files changed, 53 insertions(+), 40 deletions(-)
---
diff --git a/libgitg/gitg-commit-model.vala b/libgitg/gitg-commit-model.vala
index af1b97d..7f13527 100644
--- a/libgitg/gitg-commit-model.vala
+++ b/libgitg/gitg-commit-model.vala
@@ -101,6 +101,11 @@ namespace Gitg
                        get { return d_repository; }
                        set
                        {
+                               if (d_repository == value)
+                               {
+                                       return;
+                               }
+
                                cancel();
 
                                d_walker = null;
@@ -122,9 +127,6 @@ namespace Gitg
                construct
                {
                        d_lanes = new Lanes();
-                       d_cancellable = new Cancellable();
-                       d_cancellable.cancel();
-
                        d_sortmode = Ggit.SortMode.TIME | Ggit.SortMode.TOPOLOGICAL;
                }
 
@@ -135,47 +137,61 @@ namespace Gitg
 
                private void cancel()
                {
-                       if (!d_cancellable.is_cancelled())
+                       if (d_cancellable != null)
                        {
-                               d_cancellable.cancel();
+                               var cancellable = d_cancellable;
+                               d_cancellable = null;
+
+                               cancellable.cancel();
 
                                d_thread.join();
                                d_thread = null;
-                       }
 
-                       if (d_idleid != 0)
-                       {
-                               Source.remove(d_idleid);
-                               d_idleid = 0;
+                               if (d_idleid != 0)
+                               {
+                                       Source.remove(d_idleid);
+                                       d_idleid = 0;
+                               }
+
+                               finished();
                        }
 
+                       clear();
+
                        d_ids = new Commit[0];
                        d_hidden_ids = new Commit[0];
                        d_advertized_size = 0;
 
                        d_id_hash = new Gee.HashMap<Ggit.OId, int>();
-
-                       emit_started();
-                       finished();
                }
 
                public void reload()
                {
                        cancel();
 
-                       if (d_include.length == 0)
+                       if (d_repository == null || d_include.length == 0)
                        {
                                return;
                        }
 
-                       walk.begin((obj, res) => {
+                       var cancellable = new Cancellable();
+                       d_cancellable = cancellable;
+
+                       started();
+
+                       walk.begin(cancellable, (obj, res) => {
                                walk.end(res);
 
-                               d_cancellable.cancel();
-                               if (d_thread != null)
+                               if (cancellable == d_cancellable)
                                {
-                                       d_thread.join();
-                                       d_thread = null;
+                                       finished();
+                                       d_cancellable = null;
+
+                                       if (d_thread != null)
+                                       {
+                                               d_thread.join();
+                                               d_thread = null;
+                                       }
                                }
                        });
                }
@@ -212,7 +228,7 @@ namespace Gitg
                        d_exclude = ids;
                }
 
-               private void notify_batch(bool isend)
+               private void notify_batch(owned SourceFunc? finishedcb)
                {
                        lock(d_idleid)
                        {
@@ -240,9 +256,9 @@ namespace Gitg
 
                                        emit_update(added);
 
-                                       if (isend)
+                                       if (finishedcb != null)
                                        {
-                                               finished();
+                                               finishedcb();
                                        }
                                }
 
@@ -273,7 +289,7 @@ namespace Gitg
                        }
                }
 
-               private async void walk()
+               private async void walk(Cancellable cancellable)
                {
                        Ggit.OId[] included = d_include;
                        Ggit.OId[] excluded = d_exclude;
@@ -291,7 +307,7 @@ namespace Gitg
                                        }
                                        catch
                                        {
-                                               notify_batch(true);
+                                               notify_batch((owned)cb);
                                                return null;
                                        }
                                }
@@ -363,7 +379,7 @@ namespace Gitg
                                        Ggit.OId? id;
                                        Commit? commit;
 
-                                       if (d_cancellable.is_cancelled())
+                                       if (cancellable.is_cancelled())
                                        {
                                                break;
                                        }
@@ -403,7 +419,7 @@ namespace Gitg
 
                                        if (timer.elapsed() >= 200)
                                        {
-                                               notify_batch(false);
+                                               notify_batch(null);
                                                timer.start();
                                        }
 
@@ -413,32 +429,21 @@ namespace Gitg
                                        }
                                }
 
-                               notify_batch(true);
-
-                               Idle.add((owned)cb);
+                               notify_batch((owned)cb);
                                return null;
                        };
 
                        try
                        {
-                               d_cancellable.reset();
-                               emit_started();
                                d_thread = new Thread<void*>.try("gitg-history-walk", (owned)run);
-                               yield;
                        }
                        catch
                        {
-                               finished();
-
-                               d_cancellable.cancel();
                                d_thread = null;
+                               return;
                        }
-               }
 
-               private void emit_started()
-               {
-                       clear();
-                       started();
+                       yield;
                }
 
                private void clear()
diff --git a/plugins/diff/gitg-diff.vala b/plugins/diff/gitg-diff.vala
index 43907bb..e5ee789 100644
--- a/plugins/diff/gitg-diff.vala
+++ b/plugins/diff/gitg-diff.vala
@@ -126,6 +126,8 @@ namespace GitgDiff
 
                private void on_selection_changed(GitgExt.History history)
                {
+                       var hasset = false;
+
                        history.foreach_selected((commit) => {
                                var c = commit as Gitg.Commit;
 
@@ -133,6 +135,7 @@ namespace GitgDiff
                                {
                                        d_whenMapped.update(() => {
                                                d_diff.commit = c;
+                                               hasset = true;
                                        }, this);
 
                                        return false;
@@ -140,6 +143,11 @@ namespace GitgDiff
 
                                return true;
                        });
+
+                       if (!hasset)
+                       {
+                               d_diff.commit = null;
+                       }
                }
 
                public Gtk.Widget? widget