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c77fe55ddb
This is a soft limit in sense that it only affects the number of threads. It never makes xz fail and it never makes xz change settings that would affect the compressed output. The idea is to make -T0 have more reasonable behavior when the system has very many cores or when a memory-hungry compression options are used. This also helps with 32-bit xz, preventing it from running out of address space. The downside of this commit is that now the number of threads might become too low compared to what the user expected. I hope this to be an acceptable compromise as the old behavior has been a source of well-argued complaints for a long time.
74 lines
3.1 KiB
C
74 lines
3.1 KiB
C
///////////////////////////////////////////////////////////////////////////////
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//
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/// \file hardware.h
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/// \brief Detection of available hardware resources
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//
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// Author: Lasse Collin
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//
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// This file has been put into the public domain.
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// You can do whatever you want with this file.
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//
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///////////////////////////////////////////////////////////////////////////////
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/// Initialize some hardware-specific variables, which are needed by other
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/// hardware_* functions.
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extern void hardware_init(void);
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/// Set the maximum number of worker threads.
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extern void hardware_threads_set(uint32_t threadlimit);
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/// Get the maximum number of worker threads.
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extern uint32_t hardware_threads_get(void);
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/// Returns true if multithreaded mode should be used for .xz compression.
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/// This can be true even if the number of threads is one.
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extern bool hardware_threads_is_mt(void);
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/// Set the memory usage limit. There are separate limits for compression,
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/// decompression (also includes --list), and multithreaded decompression.
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/// Any combination of these can be set with a single call to this function.
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/// Zero indicates resetting the limit back to the defaults.
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/// The limit can also be set as a percentage of installed RAM; the
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/// percentage must be in the range [1, 100].
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extern void hardware_memlimit_set(uint64_t new_memlimit,
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bool set_compress, bool set_decompress, bool set_mtdec,
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bool is_percentage);
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/// Get the current memory usage limit for compression or decompression.
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/// This is a hard limit that will not be exceeded. This is obeyed in
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/// both single-threaded and multithreaded modes.
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extern uint64_t hardware_memlimit_get(enum operation_mode mode);
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/// This returns a system-specific default value if all of the following
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/// conditions are true:
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///
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/// - An automatic number of threads was requested (--threads=0).
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///
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/// - --memlimit-compress wasn't used or it was reset to the default
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/// value by setting it to 0.
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///
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/// Otherwise this is identical to hardware_memlimit_get(MODE_COMPRESS).
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///
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/// The idea is to keep automatic thread count reasonable so that too
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/// high memory usage is avoided and, with 32-bit xz, running out of
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/// address space is avoided.
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extern uint64_t hardware_memlimit_mtenc_get(void);
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/// Returns true if the value returned by hardware_memlimit_mtenc_get() is
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/// a system-specific default value. coder.c uses this to ignore the default
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/// memlimit in case it's too small even for a single thread in multithreaded
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/// mode. This way the default limit will never make xz fail or affect the
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/// compressed output; it will only make xz reduce the number of threads.
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extern bool hardware_memlimit_mtenc_is_default(void);
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/// Get the current memory usage limit for multithreaded decompression.
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/// This is only used to reduce the number of threads. This limit can be
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/// exceeded if the number of threads are reduce to one. Then the value
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/// from hardware_memlimit_get() will be honored like in single-threaded mode.
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extern uint64_t hardware_memlimit_mtdec_get(void);
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/// Display the amount of RAM and memory usage limits and exit.
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extern void hardware_memlimit_show(void) lzma_attribute((__noreturn__));
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