[DiapDealer]

I'm testing a few things that @Tex2002ans described, and I can verify the long periods when Sigil is unresponsive after merging a bunch of files together in the test epub he mentioned above. Many of them I would expect, but the UI interface freezing in general (after the merge is done) seem odd to me (as well as unique unique to Windows, in my experience).

All of my experiments/observations were done with the Preview window closed, with Sigil and it's various files/folders exempt from Windows Antimalware, and with no Power Management restrictions to contend with.

The merge of the 60(ish) chapters itself took well over a minute (i3 8Gb RAM). During that time, processor/ram/disk/gpu usage was not particularly high (both cumulatively--for all processes--and for Sigil specifically). One notable thing is that the Windows 10 task manager indicates that power consumption is "very high" during the merge process. The progress indicator for the merge job immediately jumps to 98% and then Sigil becomes unresponsive for over a minute until the merge is complete.

After the merge is complete, the UI is unresponsive for a shorter period of time, but lengthy nonetheless. To make matters worse, any Window that covers the Sigil window even briefly (including the task manager which frustrates testing) starts the unresponsiveness of Sigil's UI all over again. From thins point on, I can't really say what might trigger another round of ui unresponsiveness (with the exception of Sigil's window being occluded by another app) when trying to open menus or preferences, but when it happens, the length of time is the same.

During the unresponsive periods, Sigil's processor and memory usage spike a bit (but nothing drastic, and not nearly enough to interfere with the running of other applications) and the power consumption indicator immediately spikes to "very high". The gpu % never moves from 0% for Sigil during any of my testing.

With Preview closed and no editing being done, I guess I'm not certain why these lengthy periods of UI/menu unresponsiveness are still happening? I get the merge itself being intensive, but once done, why does Sigil not become more responsive when no editing, or rendering is being done?

Granted... this is all with the monolithic html tab open that I rarely deal with (by choice) myself, but it would seem that Sigil's Windows performance in general might be improved if we could eliminate some (seemingly) unnecessary reparsing,

EDIT: Just to clarify, this is in no way new to Sigil 1.5.1.