Queue too-fast revision changes and replay them in order to avoid crashes while fast editing

src/libtomahawk/playlist.cpp

@@ -296,7 +296,12 @@ Playlist::createNewRevision( const QString& newrev, const QString& oldrev, const
 {
     qDebug() << Q_FUNC_INFO << newrev << oldrev << entries.count();
 
-    Q_ASSERT( !busy() );
+    if ( busy() )
+    {
+        m_revisionQueue.enqueue( RevisionQueueItem( newrev, oldrev, entries, oldrev == currentrevision() ) );
+        return;
+    }
+
     if ( newrev != oldrev )
         setBusy( true );
 
@@ -370,6 +375,8 @@ Playlist::setRevision( const QString& rev,
     }
     else
         emit revisionLoaded( pr );
+
+    checkRevisionQueue();
 }
 
 
@@ -569,3 +576,17 @@ Playlist::setBusy( bool b )
     m_busy = b;
     emit changed();
 }
+
+void
+Playlist::checkRevisionQueue()
+{
+    if ( !m_revisionQueue.isEmpty() )
+    {
+        RevisionQueueItem item = m_revisionQueue.dequeue();
+        if ( item.oldRev != currentrevision() && item.applyToTip ) // this was applied to the then-latest, but the already-running operation changed it so it's out of date now. fix it
+        {
+            item.oldRev = currentrevision();
+        }
+        createNewRevision( item.newRev, item.oldRev, item.entries );
+    }
+}

src/libtomahawk/playlist.h

@@ -30,6 +30,7 @@
 #include "playlistinterface.h"
 
 #include "dllmacro.h"
+#include <QQueue>
 
 class DatabaseCommand_LoadAllPlaylists;
 class DatabaseCommand_SetPlaylistRevision;
@@ -98,6 +99,17 @@ struct PlaylistRevision
     bool applied; // false if conflict
 };
 
+struct RevisionQueueItem
+{
+    QString newRev;
+    QString oldRev;
+    QList< plentry_ptr > entries;
+    bool applyToTip;
+
+    RevisionQueueItem( const QString& nRev, const QString& oRev, QList< plentry_ptr > e, bool latest ) :
+        newRev( nRev ), oldRev( oRev), entries( e ), applyToTip( latest ) {}
+};
+
 
 class DLLEXPORT Playlist : public QObject, public PlaylistInterface
 {
@@ -264,6 +276,7 @@ private:
     void init();
 
     void setBusy( bool b );
+    void checkRevisionQueue();
 
     source_ptr m_source;
     QString m_currentrevision;
@@ -277,6 +290,8 @@ private:
     QList< plentry_ptr > m_initEntries;
     QList< plentry_ptr > m_entries;
 
+    QQueue<RevisionQueueItem> m_revisionQueue;
+
     bool m_locallyChanged;
     bool m_busy;
 };