schmohlio

A state machine is defined as follows:

• Input - a set of inputs
• Output - a set of outputs
• State - a set of states
• S0 ∈ S - an initial state
• T : Input * State -> Output * State - a transition function

If you model your services (aggregates, projections, process managers, sagas, whatever) as state machines, one issue to address is management of State. There must be a mechanism to provide State to the state machine, and to persist resulting State for subsequent retrieval. One way to address this is by storing State is a key-value store. Another way is to use a SQL database. Yet another way is event sourcing. The benefit of even sourcing is that you never need to store State itself. Instead, you rely on the Output of a service to reconstitute state. In order to do that, the state machine transition function needs to be factored into two functions as follows:

schmohlio

// v2 of the great example of SSE in go by @ismasan.
// includes fixes:
//    * infinite loop ending in panic
//    * closing a client twice
//    * potentially blocked listen() from closing a connection during multiplex step.
package main

import (
	"fmt"
	"log"

schmohlio

public class BlockingQueue implements Queue {
 
    private java.util.Queue queue = new java.util.LinkedList();
 
    /**
     * Make a blocking Dequeue call so that we'll only return when the queue has
     * something on it, otherwise we'll wait until something is put on it.
     * 
     * @returns  This will return null if the thread wait() call is interrupted.
     */

schmohlio

#!/bin/bash
yum install -y aws-cli
cd /home/ec2-user/
aws s3 cp 's3://aws-codedeploy-us-east-1/latest/codedeploy-agent.noarch.rpm' . --region us-east-1
yum -y install codedeploy-agent.noarch.rpm