Digikam hangs constantly for no apparent reason.  Occurs when maint. tools are used (thumbnails), but also occurs at other times.
====================
Compiled sources
Build date: Mar 9 2015 (target: debugfull)
Rev.: 52dc2861efca3d8deda9fe20fefc46e85029e484
=======================
digiKam version 4.9.0
CPU cores: 4
Demosaic GPL2 pack support: Unknown
Demosaic GPL3 pack support: Unknown
Exiv2 can write to Jp2: Yes
Exiv2 can write to Jpeg: Yes
Exiv2 can write to Pgf: Yes
Exiv2 can write to Png: Yes
Exiv2 can write to Tiff: Yes
Exiv2 supports XMP metadata: Yes
LibCImg: 130
LibEigen: 3.2.4
LibExiv2: 0.24
LibJPEG: 62
LibJasper: 1.900.1
LibKDE: 4.14.4
LibKExiv2: 2.4.0
LibKGeoMap: 3.1.0
LibKdcraw: 2.4.2
LibLCMS: 2060
LibLensFun: 0.2.8-0
LibLqr support: yes
LibPGF: 6.13.45
LibPNG: 1.6.10
LibQt: 4.8.6
LibRaw: 0.16.0
LibTIFF: LIBTIFF, Version 4.0.3 Copyright (c) 1988-1996 Sam Leffler Copyright (c) 1991-1996 Silicon Graphics, Inc.
Marble Widget: 0.19.95 (0.20 Beta 3)
Parallelized demosaicing: Unknown
RawSpeed codec support: Unknown
Baloo support: no
Database backend: QSQLITE
Kdepimlibs support: Yes
Kipi-Plugins: 4.9.0
LibGphoto2: 2.5.7
LibKface: 3.5.0
LibKipi: 2.2.0
LibOpenCV: 2.4.9
Sqlite2 support: Yes
=======================

Trace when break out with Cont-C
=========================
Program received signal SIGINT, Interrupt.
0x00007ffff5508607 in Digikam::ManagedLoadSaveThread::findExistingTask (
    this=0x145f4f0, loadingDescription=...)
    at /home/shipman/Downloads/dk/core/libs/threadimageio/managedloadsavethread.cpp:141
141	        if (task->type() == LoadSaveTask::TaskTypeLoading)
(gdb) n
143	            loadingTask = static_cast<LoadingTask*>(task);
(gdb) 
145	            if (loadingTask->loadingDescription() == loadingDescription)
(gdb) 
137	    for (int i = 0; i < m_todo.size(); ++i)
(gdb) 
139	        LoadSaveTask* const task = m_todo[i];
(gdb) print i, m_todo.size()
$13 = 105567
(gdb) print i
$14 = 41168
(gdb) n
141	        if (task->type() == LoadSaveTask::TaskTypeLoading)
(gdb) 
143	            loadingTask = static_cast<LoadingTask*>(task);
(gdb) 
145	            if (loadingTask->loadingDescription() == loadingDescription)
(gdb) 
137	    for (int i = 0; i < m_todo.size(); ++i)
(gdb) 
139	        LoadSaveTask* const task = m_todo[i];
(gdb) 
141	        if (task->type() == LoadSaveTask::TaskTypeLoading)
(gdb) 
143	            loadingTask = static_cast<LoadingTask*>(task);
(gdb) 
145	            if (loadingTask->loadingDescription() == loadingDescription)
(gdb) 
=========================
round and round it goes.
Jim Shipman