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Docs: Use lzma_cputhreads() in 04_compress_easy_mt.c.

This commit is contained in:
Lasse Collin 2014-12-21 18:58:44 +02:00
parent 8dbb57238d
commit cbafa71091
1 changed files with 26 additions and 4 deletions
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30
doc/examples/04_compress_easy_mt.c
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@ -31,10 +31,6 @@ init_encoder(lzma_stream *strm)
// No flags are needed.
.flags = 0,
// Set the number of threads to use.
// FIXME: Add how to autodetect a reasonable number.
.threads = 4,
// Let liblzma determine a sane block size.
.block_size = 0,
@ -57,6 +53,32 @@ init_encoder(lzma_stream *strm)
.check = LZMA_CHECK_CRC64,
};
// Detect how many threads the CPU supports.
mt.threads = lzma_cputhreads();
// If the number of CPU cores/threads cannot be detected,
// use one thread. Note that this isn't the same as the normal
// single-threaded mode as this will still split the data into
// blocks and use more RAM than the normal single-threaded mode.
// You may want to consider using lzma_easy_encoder() or
// lzma_stream_encoder() instead of lzma_stream_encoder_mt() if
// lzma_cputhreads() returns 0 or 1.
if (mt.threads == 0)
mt.threads = 1;
// If the number of CPU cores/threads exceeds threads_max,
// limit the number of threads to keep memory usage lower.
// The number 8 is arbitrarily chosen and may be too low or
// high depending on the compression preset and the computer
// being used.
//
// FIXME: A better way could be to check the amount of RAM
// (or available RAM) and use lzma_stream_encoder_mt_memusage()
// to determine if the number of threads should be reduced.
const uint32_t threads_max = 8;
if (mt.threads > threads_max)
mt.threads = threads_max;
// Initialize the threaded encoder.
lzma_ret ret = lzma_stream_encoder_mt(strm, &mt);