[Bug 32374] New: List box with LBS_NODATA set, has very low performance, depending on items count.

http://bugs.winehq.org/show_bug.cgi?id=32374

Bug #: 32374
           Summary: List box with LBS_NODATA set, has very low
                    performance, depending on items count.
           Product: Wine
           Version: unspecified
          Platform: x86
        OS/Version: Linux
            Status: UNCONFIRMED
          Severity: major
          Priority: P2
         Component: user32
        AssignedTo: [e-mail]
        ReportedBy: [e-mail]
    Classification: Unclassified

Created attachment 42719
  --> http://bugs.winehq.org/attachment.cgi?id=42719
Test application that illustrates the bug. Source code included.

List box control, when has LBS_NODATA style set, needs very big time to process
LB_SETCOUNT message (this message works only for list box with LBS_NODATA set).

On Windows this message is handled for less than 1ms regardless of the count
sent by LB_SETCOUNT (because the list box has nothing to allocate/reallocate
when LBS_NODATA is set. It only need to set the scroll bar parameters).

In WINE (every version but in v1.4 and v1.5 it is really slow) processing this
message needs some amount of time, proportional to the item count set by
LB_SETCOUNT.

As long as this list box style is provided because of its speed, such a
behavior can block the execution of the application for very long time.

Small test application is attached which measures the time needed for
LB_SETCOUNT to be executed on list box with LBS_NODATA set. Source code
included.