There is a large buffering effect when using zstdmt in MT mode.
Consequently, data is read first, pushed to workers,
and only later will the compressed result come out.
That means there is no longer immediate correlation
between amount of data read, and amount of data written.
This patch disables the displaying of % compression
when multi-threading is enabled.
It adds the displaying of total size when it can be determined
(it usually can be determined for files, but not for stdin)
so the user has a sense of "how far from the end" the compression compressed is.
There is no modification to decompression side,
since decompression is only single-threaded for now.
fileio.c was continually pushing more content without giving a chance to flush compressed one.
It would block the job queue when input data was accumulated too fast (requiring to define many threads).
Fixed : fileio flushes whatever it can after each input attempt.
By default, section sizes are 4x window size.
This new setting allow manual selection of section sizes.
The larger they are, the (slightly) better the compression ratio,
but also the higher the memory allocation cost,
and eventually the lesser the nb of possible threads,
since each section is compressed by a single thread.
It also introduces a prototype to set generic parameters,
ZSTDMT_setMTCtxParameter()
The idea is that it's possible to add enums
to extend the list of parameters that can be set this way.
This is more long-term oriented than a fixed-size struct.
Consider it as a test.
Also : fixed corner case, where nb of jobs completed becomes > jobQueueSize
which is possible when many flushes are issued
while there is not enough dst buffer to flush completed ones.
The new strategy involves cutting frame at block level.
The result is a single frame, preserving ZSTD_getDecompressedSize()
As a consequence, bench can now make a full round-trip,
since the result is compatible with ZSTD_decompress().
This strategy will not make it possible to decode the frame with multiple threads
since the exact cut between independent blocks is not known.
MT decoding needs further discussions.
Yann Collet
Nick Terrell
Yann Collet
Przemyslaw Skibinski
cyan4973
Andrew Janke