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https://github.com/gonzalo-bulnes/inter_process_communication_demo

Playing with named pipes in Ruby.
https://github.com/gonzalo-bulnes/inter_process_communication_demo

demo inter-process-communication ruby

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Playing with named pipes in Ruby.

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Demo: Inter-process Communication

=================================



An example Ruby program to be used as a proof of concept for inter-process commnication between a _main_ program which needs to delegate hooks processing and a _worker_ program which performs those hooks.



Idea

----



The first example uses [named pipes][np] to allow the _main_ program to delegate one hook to the _worker_.



The second example was an attempt to use [signals][sig] to allow the _worker_ to peform multiple hooks depending on the _main_ program needs. The attempt failed.



The third example succeeds at performing an arbitrary number of hooks by [forking][fork] the _worker_, thus allowing it to read from a _named pipe_ as long as the _main_ program is running.



  [np]: https://en.wikipedia.org/wiki/Named_pipe

  [sig]: https://en.wikipedia.org/wiki/Unix_signal

  [fork]: https://en.wikipedia.org/wiki/Fork_%28system_call%29



Usage

-----



_Note: for now, there are no signals involved._



Install dependencies, using [RVM][rvm] is optional but strongly recommended:



```bash

# trigger the RVM hooks so the gems get installed in an dedicated gemset

cd inter_process_communication_demo



# install dependencies

bundle install

```



  [rvm]: https://rvm.io



### Basic named pipes



Create the _named pipes_ that will be used by `main.rb` and `worker.rb` to communicate:



```bash

cd lib/01_basic_named_pipes



# create a named pipe for the main program to notify

# the worker about a hook to be performed

mkfifo main_to_worker



# create another named pipe for the worker to reply

# to the main program

mkfifo worker_to_main



# once you're done using them, remove both pipes:

#rm main_to_worker worker_to_main

```



In the fist scenario, the worker is waiting for hook requests:



```bash

# Scenario 1



# start the worker

ruby worker.rb # will wait until there is a hook to perform



# in a distinct terminal, start the main program

ruby main.rb # since the worker is available, the hook is performed immediately

```



In the second scenario, the main program is waiting for workers to be available:



```bash

# Scenario 2



# start the main program

ruby main.rb # will wait until a wroker preforms the hook



# in a distinct terminal, start the worker

ruby worker.rb # since a hook request was performed, performs the hook immediately

```



### Signals



**Note**: Signals don't seem to be the way to go, see these [signals limitations][signals].



The idea was having a `worker_on_demand`, which would start the `main` program (provinding its own PID to it).

The main program would sent a signal each time a hook would need to be performed.



```bash

cd lib/02_signals



# start

ruby worker_on_demand.rb # multiple hook requests are handled by the worker

```



### Named pipes and fork



The first example has two limitations:

- only one hook request can be handled by the worker

- the main program and the worker must agree on two named pipes to communicate



To be able to handle any number of hook requests, the worker must be able to loop while the main program is running. Of course, it should exit once the main program has exited.



In order to do so, let's introduce the `worker_provider` program. It will start a looping worker, then start the main program, and make sure the worker exits when the main program does. It will also provide both named pipes to both the worker and the main program.



```bash

cd lib/03_named_pipes_and_fork



# start the worker provider program

ruby worker_provider.rb # will start a worker and a main program with several hooks to perform

```



References

----------



- [Using Named Pipes in Ruby for Inter-process Communication][dix]

- [Ruby 2.2.0 documentation: Process][doc]

- [Forking and IPC in Ruby, Part II][fk]



  [dix]: http://www.pauldix.net/2009/07/using-named-pipes-in-ruby-for-interprocess-communication.html

  [fk]: http://www.sitepoint.com/forking-ipc-ruby-part-ii

  [signals]: https://github.com/gonzalo-bulnes/inter_process_communication_demo/blob/add-signal-handling-to-handle-multiple-hooks/lib/02_signals/on_demand_worker.rb#L48-L56

  [doc]: http://ruby-doc.org/core-2.2.0/Process.html