xz: Use threaded mode by defaut (as if --threads=0 was used).
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).
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@ -15,7 +15,7 @@
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/// Maximum number of worker threads. This can be set with
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/// the --threads=NUM command line option.
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static uint32_t threads_max = 1;
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static uint32_t threads_max;
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/// True when the number of threads is automatically determined based
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/// on the available hardware threads.
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@ -334,5 +334,9 @@ hardware_init(void)
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memlimit_mt_default = mem_ceiling;
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#endif
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// Enable threaded mode by default. xz 5.4.x and older
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// used single-threaded mode by default.
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hardware_threads_set(0);
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return;
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}
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@ -1022,8 +1022,8 @@ message_help(bool long_help)
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" does not affect decompressor memory requirements"));
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puts(_(
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" -T, --threads=NUM use at most NUM threads; the default is 1; set to 0\n"
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" to use as many threads as there are processor cores"));
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" -T, --threads=NUM use at most NUM threads; the default is 0 which uses\n"
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" as many threads as there are processor cores"));
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if (long_help) {
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puts(_(
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@ -1303,6 +1303,15 @@ meet this condition,
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but files compressed in single-threaded mode don't even if
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.BI \-\-block\-size= size
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has been used.
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.IP ""
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The default value for
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.I threads
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is
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.BR 0 .
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In
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.B xz
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5.4.x and older the default is
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.BR 1 .
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.
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.SS "Custom compressor filter chains"
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A custom filter chain allows specifying
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