[Lzip-bug] On Windows unpacking does not use all cores

[Romano]

Greetings Antonio, I have an issue with utilizing all 4 cores of my CPU 
during unpacking, it seems to only use around 25-43% of my 4 core cpu in 
any case, even if using stdio.

Yesterday I compiled latest lzlib 1.9 and plzip 1.7 under cygwin(also 
latest, just installed yesterday) on Windows 7 and as a 64bit both. It 
compiled without any errors or warning and tool also work fine. During 
packing it is able to utilize all CPU cores to 100% so multithreading 
works. Same with testing using -t flag. Howerver, when I actually try to 
unpack with -d it never even peak above 50%. This despite -n option, 
even if I double the number to -n 8. On parallel, until now I always 
used FreeArc's internal 4x4:lzma which always fully utilized my cpu and 
it shows as during unpacking without io limitation it could reach ~200Mib/s.

I am aware of blocks concept as well, tool also did not utilized all CPU 
with smaller -B block and big enough file, and I know for sure its not 
my HDD limiting it because first it is quicker than output and FreeArc 
can still utilize its max, but also because it does not utilize full CPU 
even if using stdin/stdout.

I tried it alone as well as in conjuction with FreeArc as I am 
considering its own 32bit lzma to replace with plzip, if I can fix this 
problem. I never liked xz and 7zip and their lzma2 preciselly because it 
doesnt support unpacking on more threads. I see this tool as finally 
something with better vision. For reference, if you are familiar with 
FreeArc here is my setup:

[External compressor:plzip]
default = -s 64Mi -m 273 -B 128Mi
packcmd   = plzip.exe -c -n 4 {options} - - <stdin> <stdout>
unpackcmd = plzip.exe -c -n 8 -d        - - <stdin> <stdout>

^Decompress seem to ignore -n option, here as well as on its own command 
line. Thesting 8+Gib archive with this option(using "test archive" under 
FreeArc gui) would result on using only 25-40% cpu again, while FA 
internal 4x4:lzma would peak CPU fully. I also include compiled binaries 
if it help. But they were compiled with -march=native -O2 on Haswell, so 
need avx2 cpu. I can compile another one for you if you cannot run this. 
I hope this help you and thanks for a great tool you did.

Best regards, Romano

(PS: Also, I dont know if this is a bug in plzip, but if I compress 
under Freearc and click "cancel", first 3 threads eventually cancel as 
they should but last one remain with CPU at 25% forever - thus plzip 
never quit.)

plzip_compiled.zip
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