slideshow do not work from icon with mouse
press F9 slideshow work

Confirmed. Slideshow works using F9 or the View -> Slideshow menu. When using the slideshow toolbar icon/popup menu, Digikam hangs.

I tried to reproduce the problem on my test machine (Debian 6.0 - Squeeze, TDE R14.0.1 preliminary) and the slideshow works for me all four of the above methods.

> digikam-trinity slideshow (F9) do not work in TDE R14 debian 7 or 8

> Confirmed. Slideshow works using F9 or the View -> Slideshow menu.
> When using the slideshow toolbar icon/popup menu, Digikam hangs.

> I tried to reproduce the problem on my test machine (Debian 6.0 - Squeeze)

Could it be a problem with Debian 7 and 8 only? Perhaps caused by a newer version of some library?
Steffen reported problems on Debian 7 and 8 and I also confirmed it in Debian 8.
Slavek, could you test on Wheezy or Jessie and see if you also see the problem?

(In reply to Michele Calgaro from comment #4)
> > digikam-trinity slideshow (F9) do not work in TDE R14 debian 7 or 8
> 
> > Confirmed. Slideshow works using F9 or the View -> Slideshow menu.
> > When using the slideshow toolbar icon/popup menu, Digikam hangs.
> 
> > I tried to reproduce the problem on my test machine (Debian 6.0 - Squeeze)
> 
> Could it be a problem with Debian 7 and 8 only? Perhaps caused by a newer
> version of some library?
> Steffen reported problems on Debian 7 and 8 and I also confirmed it in
> Debian 8.
> Slavek, could you test on Wheezy or Jessie and see if you also see the
> problem?

I performed a second test - my test notebook with Debian 7.8 - Wheezy. Again, everything works fine.

> > Confirmed. Slideshow works using F9 or the View -> Slideshow menu.
> > When using the slideshow toolbar icon/popup menu, Digikam hangs.
> 
> > I tried to reproduce the problem on my test machine (Debian 6.0 - Squeeze)
> I performed a second test - my test notebook with Debian 7.8 - Wheezy. Again, > everything works fine.

(In reply to Slávek Banko from comment #5)
Tried again today after a fresh digikam rebuild on Debian Stretch, problem still there. Digikam goes nut with CPU utilization near 100%.
I will try to investigate it once I complete a full TDE rebuild, so sometimes next week.

First analysis: digikam does not hang completely, but becomes very slow when executing the for loop in digicamview.cpp:1525-1546. If I wait enough, the slideshow actually starts.
Most likely this is caused by a race condition triggered when the toolbar slideshow button popup menu is displayed, which cause processEvent() to consume a lot of time.

Fixed (well, patched) in commit 2fb9f1c (master) and 0783a62 (r14.0.x).

This was a weird one. At digicamview.cpp:1546, kapp->processEvents() was used. Installing an event filter did not show any significant difference when F9 was used or when the toolbar slideshow button was used. Somehow though, when called from the toolbar button, kapp->processEvents() did not return immediately if there were no events but instead waited until the default 3 second timer expired.
The patch calls the event loop processEvents() directly, specifying not to wait for new events. Pending events (if any) can get processed but the default wait of 3 seconds is no longer there. 

As a note in case we have time to spend on this, probably the real cause should be researched in TQEventLoop::processEvents() at tqt3/src/kernel/qeventloop_x11.cpp:135. Part of the code relates to the GUI thread and the only difference in calling "slideshow" using F9 or the toolbar button is an additional popup menu being displayed.