A command-line utility for creating a multi-input multi-output pipe
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mkmimo Build Status

Creates a multiple-input multiple-output pipe that can basically connect many parallel processes with named pipes or bash process substitution to stream lines of text without blocking.


cat emulation

cmp -b <(seq $n | cat) <(seq $n | mkmimo)

GNU split, but running in parallel

n=1000000 m=10
split -n r/$m <(seq $m) out.
seq $n | mkmimo out.*
cmp -b <(seq $n) <(sort -n out.*)

Many inputs, many outputs

numins=17 numouts=83

for i in $(seq $numins)
do inputs+=" <(seq $((($i-1) * $numlines + 1)) $(($i * $numlines)))"
for i in $(seq $numouts)
do outputs+=" >(cat >out.$i)"
rm -f out.*

eval "mkmimo $inputs \\> $outputs"

cmp <(eval "sort $inputs") <(sort out.*)

For more examples, see the .bats test files in the "/test" folder.

Runtime Parameters (Environment Variables)

Common parameters

  • MKMIMO_IMPL determines which implementation to use. Possible values are:

    • multithreaded
    • nonblocking
  • BLOCKSIZE is the initial size of each buffer in bytes. It defaults to 4096 (4KiB).

Multi-threaded implementation

This implementation keeps one thread per given input/output stream. There are two shared pools of buffers: empty and filled. Each input thread takes an empty buffer from the pool and fills it with the data read from its input stream, and the filled buffer is placed into the other pool. Each output thread takes a filled buffer from that pool and writes the data to its output stream, then returns the buffer back to the empty pool. They repeat their job until all input has been read, buffered, then written to an output.

This implementation is used when MKMIMO_IMPL=multithreaded, and the following environment variables are parsed:

  • MULTIBUFFERING that is the multiplicative factor for multiple buffering. MULTIBUFFERING=2 is double-buffering, MULTIBUFFERING=3 is triple-buffering, MULTIBUFFERING=4 is quad, and so on. It defaults to 2, double-buffering.

Non-blocking I/O implementation

This implementation keeps a single thread that uses poll(2) system call to find input/output streams that can be read/written and performs non-blocking I/O exchanging buffers between them until all data has been transferred. On OS X 10.11 (El Capitan), the way this implementation calls poll(2) is known to have a kernel panic issue.

This implementation is used when MKMIMO_IMPL=nonblocking, and the following environment variables are parsed:

  • THROTTLE_SLEEP_USEC is the number of microseconds to sleep between poll(2) system calls when no I/O streams were readable/writable. It defaults to 1, meaning it will sleep 1us upon such states. Set it to 0 to rather busy wait for maximum throughput at the expense of processor time.

  • POLL_TIMEOUT_MSEC is the number of milliseconds to wait until any I/O activity is picked up by the poll(2) system call. On Mac, it defaults to 1000 or one second, because poll(2) does not pick up close events timely. It defaults to -1 on other OSes, which means poll(2) should wait indefinitely.

Development Guide

Build/Test Dependencies

The most accurate up-to-date details are always in the Travis CI configuration.

To run tests on Mac OS X, you need to install several packages including GNU coreutils and pv. They can be easily installed with Homebrew:

brew install coreutils pv

You may need to configure your PATH environment in your .bash_profile:

PATH="$(brew --prefix coreutils)/libexec/gnubin:$PATH"


make  # or make mkmimo

Bash implementation

To try the proof-of-concept written in Bash, use:

make MKMIMO_IMPL=bash mkmimo

Running Tests

After everything is installed, you can run the tests using:

make test

To test selectively, run:

make test   ONLY+=/path/to/bats/files

To exclude certain tests:

make test EXCEPT+=/path/to/bats/files

To enumerate all tests:

make test-list


To print debug statements, build with the debug flag:

make clean DEBUG=1

Formatting Code

To format all code:

make format

To specify which clang-format to use:

make format CLANG_FORMAT=clang-format-3.7