/conservation

Primary LanguageElixir

Conservation

A very simple example demonstrating how to achieve GenServer state conservation by using a pair of processes as discussed in the Conserving genserver state between crashes with a companion process post in the Tech Dominator blog.

genservers diagram

The Server GenServer allows to increment integers while keeping track of the numbers of increments performed.

The StateContainer GenServer allows Server to store and recover its state in the event of a crash.

The ProcSupervisor supervises the execution of the two previous GenServers.

Running the example

By opening an iex session by issuing an iex -S mix and running the Conservation.run function you can see the following explanatory output:

iex(1)> Incrementing 1
  result was => 2

Incrementing 4
  result was => 5

Incrementing 6
  result was => 7

Incrementing 7
  result was => 8

Server's current state:
=======================
{4, :container}

Now let's cause a crash!

Server's current state:
=======================
{4, :container}

Same as before crash :-)
:ok
iex(2)> 
09:45:22.546 [error] GenServer :server terminating
** (ArithmeticError) bad argument in arithmetic expression (omitted output...)

N.B

  • Use the Conservation.Server.increment/2 function to increment an integer

  • Use the Conservation.Server.die/1 function to cause the GenServer to crash

  • Try inspecting Server's state via :sys.get_state for example to see how the state is conserved between crashes

The application launches named GenServers having the following names:

  • Conservation.Server => :server
  • Conservation.StateContainer => :container