stdinout_pool: stuff goes in, stuff goes out. there's never any miscommunication.
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README.md

stdinout_pool: send to stdin and read stdout on external processes

What is it?

stdinout_pool maintains a pool of idle processes waiting for input.

You send input to a pool with stdinout:send(Pool, Data) and get back whatever the process returns on stdout or stderr.

You can also send input to a TCP port and get back the stdout output from a process in your pool.

Why is this special?

Erlang ports are unable to send EOF or close stdin on ports. To get around that limitation, stdinout_pool includes a C port to intercept stdin and forward it to a spawned process. When the C port sees a null byte (automatically appended to your input when you call stdinout:send/2), it closes stdin and sends stdout from the spawned process to normal stdout.

Note: your input must not contain null bytes or else your input will terminate on them.

API

All you need for stdinout_pool is a command to run and sit idle waiting for stdin to close or get an eof.

stdinout:start_link(Name, CommandWithArgs, [IP, Port, [NumberOfProcesses]]) IP is a string IP (e.g. "127.0.0.1") or a tuple IP (e.g. {127, 0, 0, 1}). Port is an integer.

stdinout:send(ServerNameOrPid, Data) returns an iolist of stdout from the pool

The number of default idle processes is the number of cores the erlang VM sees.

Note: there is no upper limit on the number of spawned processes. The process count is how many already-spun-up-and-waiting processes to keep lingering. If you have 4 waiting processes but suddenly get 30 requests, extra processes will be spawned to accomidate your workload (and your throughput will take a dive because you will be limited by process spawn time). When everything settles down again, you will be back to 4 idle processes.

You can optionally pass in an IP and Port combination to create a network server to respond to requests. If IP and Port are each set to the atom none, then no network server is created.

Usage

Erlang API Basic STDIN/STDOUT Usage

    61> stdinout:start_link(uglify, "/home/matt/bin/cl-uglify-js").
    {ok,<0.10143.0>}
    62> stdinout:send(uglify, "(function() { function YoLetsReturnThree(){ return 3 ; } function LOLCallingThree() { return YoLetsReturnThree() ; }; LOLCallingThree();})();").
    [<<"(function(){function b(){return a()}function a(){return 3}b()})();">>]

    63> stdinout:start_link(closure, "/usr/java/latest/bin/java -jar /home/matt/bin/closure/compiler.jar").
    {ok,<0.10149.0>}
    64> stdinout:send(closure, "(function() { function YoLetsReturnThree(){ return 3 ; } function LOLCallingThree() { return YoLetsReturnThree() ; }; LOLCallingThree();})();").
    [<<"(function(){function a(){return 3}function b(){return a()}b()})();\n">>]

    65> stdinout:start_link(yui_js, "/usr/java/latest/bin/java -jar /home/matt/bin/utils/yuicompressor/yuicompressor-2.4.2.jar --type js").
    {ok,<0.10153.0>}
    66> stdinout:send(yui_js, "(function() { function YoLetsReturnThree(){ return 3 ; } function LOLCallingThree() { return YoLetsReturnThree() ; }; LOLCallingThree();})();").
    [<<"(function(){function b(){return 3}function a(){return b()}a()})();">>]

Note: cl-uglify-js returned the result in an average of 20ms. closure.jar returned the result in an average of 800ms. yuicompressor.jar returned the result in an average of 107ms.

Erlang API STDIN->STDOUT->STDIN->...->STDOUT Pipes

Network API Usage

Start a stdinout server with an explicit IP/Port to bind: 93> stdinout:start_link(bob_network, "/home/matt/bin/cl-uglify-js", "127.0.0.1", 6641). {ok,<0.10209.0>}

Now from a shell, send some data: matt@vorash:~% echo "(function() { function YoLetsReturnThree(){ return 3 ; } function LOLCallingThree() { return YoLetsReturnThree() ; }; LOLCallingThree();})();" | nc localhost 6641 STDINOUT_POOL_ERROR: Length line too long: [(function(] (first ten bytes).

Uh oh, what went wrong? We have to tell the server how big our input is going to be first. The protocol for the network server is simple: the first line must contain the number of bytes of content you send. The line is terminated by a unix newline (i.e. "\n").

Trying again, we store the JS in a variable, use wc to get the length, then send the length on the first line and the content after it: matt@vorash:% SEND_JS="(function() { function YoLetsReturnThree(){ return 3 ; } function LOLCallingThree() { return YoLetsReturnThree() ; }; LOLCallingThree();})();" matt@vorash:% echo $SEND_JS |wc -c 142 matt@vorash:~% echo $SEND_JS |(wc -c && echo $SEND_JS) | nc localhost 6641 (function(){function b(){return a()}function a(){return 3}b()})();

Success! Here is the same example with wc/cat/nc goodness, but from a file:

    matt@vorash:~% cat send_example.js
    (function() { function YoLetsReturnThree(){ return 3 ; } function LOLCallingThree() { return YoLetsReturnThree() ; }; LOLCallingThree();})();
    matt@vorash:~% wc -c send_example.js | (awk '{print $1}' && cat send_example.js )| nc localhost 6641
    (function(){function b(){return a()}function a(){return 3}b()})();

Now you have a fully functioning stdin/stdout server accessible from erlang or from the network.

Building

Dependencies: rebar get-deps

Build: rebar compile

Testing

Automated: rebar eunit skip_deps=true

Automated with timing details: rebar eunit skip_deps=true -v

In the test/ directory there is a short script to verify error conditions. You can load test error conditions with: time seq 0 300 |xargs -n 1 -P 16 ./errors.sh TARGET-IP TARGET-PORT

P is the number of time to run the script in parallel. Increase or decrease as necessary.

You can load test sending other data to stdinout over the network too, but those tests can be target-specific depending on what you are spawning, your memory usage of spawned processes, and overall workload expectations.

Tests work properly under Linux, but two tests fail under OS X due to spacing differences in output. You can visually spot check those to make sure they are essentially the same.

History

I wanted to get on-the-fly javascript minification done as fast as possible. For small to medium-size JS snippets, starting up a Lisp or Java VM was the dominating factor for throughput (too many os:cmd/1 calls).

The obvious next step was to start up some processes, let them sit idle, send stdin when needed, swallow output, then re-spawn dead processes. It seemed so simple, except erlang is unable to close stdin or send an EOF to stdin on spawned processes. Dammit. The time came to dig out pipe/dup2 man pages and make a stdin/stdout child process forwarder. Thus, a stdin/stdout proxy named stdin_forcer.c was born.

Tying everything back together, there is now a way to close stdin on spawned programs. But, what good is tying a general concept like "data in, data out" to an erlang-only API? Not very good. Why not glue on a network server so anybody can send stdin and get stdout? There is no good reason it should not exist, so now the erlang stdin/stdout forwarder has a network API. Potential usage: cluster of machines to on-the-fly minify JS (use cl-uglify-js), CSS (yuicompressor.jar --type css), or transform anything else you can shove data into and get something useful back out.