[Playlist],SelectTrackKnob causes temporary GUI hang

[Sean M. Pappalardo]

When using [Playlist],SelectTrackKnob (from script) to scroll through the library for the first time after enabling a controller, the GUI hangs for about 20 seconds (on my system.) Audio continues fine and the controller still otherwise operates.

During the hang, Mixxx pins one of my CPU cores at 100% and there's no noticeable memory usage increase.

This happens as of r5642 in the 2.0 branch.

(We fixed something similar to this in like 1.8! What happened?!)

[Sean M. Pappalardo (pegasus-renegadetech)]

Stopping at another point shows:

Thread 1 (Thread 0x7ffff7fa07c0 (LWP 6947)):
#0 0x00007ffff4a1a3cf in QPersistentModelIndex::operator QModelIndex const&() const ()
   from /usr/lib/x86_64-linux-gnu/libQtCore.so.4
#1 0x00007ffff5989664 in QItemSelectionModel::currentIndex() const () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4
#2 0x00007ffff5930dc9 in QAbstractItemView::currentIndex() const () from /usr/lib/x86_64-linux-gnu/libQtGui.so.4

[Sean M. Pappalardo (pegasus-renegadetech)]

Single-stepping shows what appears to be a continuous loop through:
93 while(delta != 0) {
95 QModelIndex current = currentIndex();
96 if(delta > 0) {
106 if (row - 1 >= 0)
109 delta++;
93 while(delta != 0) {
95 QModelIndex current = currentIndex();
96 if(delta > 0) {
106 if (row - 1 >= 0)
109 delta++;
93 while(delta != 0) {

[Sean M. Pappalardo (pegasus-renegadetech)]

Found the problem, my script was setting the value to NaN. The ControllerEngine isnan check does not work with -ffast-math. See bug #1524561 for that problem.

[Swiftb0y (swiftb0y)]

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/8340