/eiger_cache

Primary LanguageElixir

Periodic Self-Rehydrating Cache

This Elixir application implements an in-memory cache based on these requirements.

Find the documentation in the doc folder. Once you clone the repo, you can open doc/index.html in your browser.

Try it

The application API is defined in the Cache module.

$ mix deps.get
Resolving Hex dependencies...
Dependency resolution completed:
...

$ iex -S mix
iex(1)> Cache.register_function(fn -> {:ok, length(Process.list)} end, :proc_count, 120_000, 60_000)
:ok
iex(2)> Cache.get(:proc_count)
{:ok, 108}
iex(3)> Cache.get(:foo) # no registered key
{:error, :not_registered}
iex(4)> Cache.register_function(fn -> {:ok, :timer.sleep(30_000)} end, :slow_fn, 120_000, 60_000)
:ok
iex(5)> Cache.get(:slow_fn, 1000) # timeout for slow executions
{:error, :timeout}

Run credo, tests and coverage

$ mix credo --strict
Checking 10 source files ...

Please report incorrect results: https://github.com/rrrene/credo/issues

Analysis took 0.1 seconds (0.04s to load, 0.1s running 64 checks on 10 files)
26 mods/funs, found no issues.
$ mix coveralls
===> Compiling parse_trans
...
==> eiger_cache
Compiling 5 files (.ex)
Generated eiger_cache app
....................

Finished in 4.9 seconds
20 tests, 0 failures

Randomized with seed 603260
----------------
COV    FILE                                        LINES RELEVANT   MISSED
100.0% lib/cache.ex                                   70        3        0
100.0% lib/cache/application.ex                       13        1        0
100.0% lib/cache/store.ex                             58        6        0
100.0% lib/cache/supervisor.ex                        48        5        0
100.0% lib/cache/worker.ex                           129       17        0
[TOTAL] 100.0%
----------------

Implementation Details

  • The application uses an ETS to store the data. Check Cache.Store documentation for details
  • Every time a new function is registered (by calling Cache.register_function/4), Cache.Supervisor spawns a new Cache.Worker process
  • The Cache.Worker processes are gen_servers. They are registered globally with the given key, mainly because the :global module allows to use any type of term as name (the requirements specify that key can be of any type, key :: any)
  • Each Cache.Worker process sends a message to itself every refresh_interval milliseconds to execute the function and (if the function returns {:ok, any()}) update the store