This hopefully does more good than bad:
+ It's faster by default.
+ Only the threaded compressor creates files that
can be decompressed in threaded mode.
- Compression ratio is worse, usually not too much though.
When it matters, -T1 must be used.
- Memory usage increases.
- Scripts that assume single-threaded mode but don't use -T1 will
possibly use too much resources, for example, if they run
multiple xz processes in parallel to compress multiple files.
- Output from single-threaded and multi-threaded compressors
differ but such changes could happen for other reasons too
(they just haven't happened since 5.0.0).
/// Maximum number of worker threads. This can be set with
/// the --threads=NUM command line option.
-static uint32_t threads_max = 1;
+static uint32_t threads_max;
/// True when the number of threads is automatically determined based
/// on the available hardware threads.
memlimit_mt_default = mem_ceiling;
#endif
+ // Enable threaded mode by default. xz 5.4.x and older
+ // used single-threaded mode by default.
+ hardware_threads_set(0);
+
return;
}
" does not affect decompressor memory requirements"));
puts(_(
-" -T, --threads=NUM use at most NUM threads; the default is 1; set to 0\n"
-" to use as many threads as there are processor cores"));
+" -T, --threads=NUM use at most NUM threads; the default is 0 which uses\n"
+" as many threads as there are processor cores"));
if (long_help) {
puts(_(
but files compressed in single-threaded mode don't even if
.BI \-\-block\-size= size
has been used.
+.IP ""
+The default value for
+.I threads
+is
+.BR 0 .
+In
+.B xz
+5.4.x and older the default is
+.BR 1 .
.
.SS "Custom compressor filter chains"
A custom filter chain allows specifying