Unable to use maximum compression and multithreading

[cyril-bouthors]

pxz only uses one core when using maximum compression, it takes 42 seconds and only 100% CPU (1 core):

11:57 root@squeeze:/tmp# time ./pxz/pxz -T 4 -9 > mantis.sql.pxz < mantis.sql

real    0m42.240s
user    0m41.940s
sys     0m0.652s

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
16308 root      20   0 1514912 261212    700 R 100.2 2.139   0:03.61 pxz

The same thing uses 400% CPU and only takes 15 seconds when using the default compression level :

11:58 root@squeeze:/tmp# time ./pxz/pxz -T 4 > mantis.sql.pxz < mantis.sql

real    0m15.513s
user    0m51.088s
sys     0m0.724s

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
16339 root      20   0  649556 447300    704 R 393.2 3.662   0:15.40 pxz

Would it be possible to use multi threading with maximum compression?