Flushing seek hangs

[Davide Tuccilli]

I have a simple pipeline running on a RPi2, using a decodebin connected 
to a tee, that branches into a glimagesink and a fakesink (I use the 
latter to get the last sample I need to save frame snapshots, doesn't 
seem like I can convert glimagesink samples in a format accepted by 
jpegenc/pngenc directly), each branch with its own queue.

Whether in playing or paused state, this seek call hangs and never returns:

gst_element_seek_simple(m_pipeline, GST_FORMAT_TIME, 
GST_SEEK_FLAG_FLUSH, nanoseconds);

On the other hand, if I do the same call on a playing pipeline without 
the flush flag (just using GST_SEEK_FLAG_NONE), the call terminates 
successfully.

I'm quite new to gstreamer, but everything I read states that flushing 
seeks should be the standard way of seeking, should be thread-safe 
(unlike non flushing) and might help with performances aswell.

The log didn't really help me, no error messages, only LOG/DEBUG level 
messages and I couldn't find anything helpful.