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Table of Contents

System Requirements

  • Linux is the operating system.

  • Python is the programming language.

  • Invocation is from the command line.

  • All communication among AGENTS and the MESSAGE_BUS is over TCP/IP.

  • The TCP/IP ports used start at 30000 and may range up to 31000.

Message Structure

  • An AGENT can pass a MESSAGE to the MESSAGE_BUS.

  • The format of the MESSAGE is JSON.

  • The MESSAGE contains the following fields:

    • AGENT_NAME - A string that uniquely identifies an AGENT.

    • AGENT_TYPE - A string that provides the type of AGENT.

    • OPERATION - A string that describes an ACTION performed by an AGENT.

    • OPERAND-1 - A number that participates in an OPERATION.

    • OPERAND-2 - A number that participates in an OPERATION.

    • ANSWER - A number that is produced from an OPERATION.

  • The AGENT_TYPE must have exactly one of the values "producer" or "consumer".

  • Any AGENT_TYPE that is not one of the allowed values must cause the process to terminate with a graceful message.

  • The OPERATIONS must have exactly one of the values "buy", "retrieve", or "sell".

Message Bus

  • The MESSAGE_BUS uses the design pattern of message passing using a bus architecture as commonly found in industry literature.

  • The purpose of the MESSAGE_BUS is to facilitate the passing of MESSAGES among AGENTS.

  • The invocation of the MESSAGE_BUS from the command line is done with "python bus.py"

  • The MESSAGE_BUS maintains a FIFO queue of messages.

    • Additions to the FIFO queue occur at the end of the queue only.

    • Removals from the FIFO queue occur at the front of the queue by default.

    • If a search is performed on the FIFO queue, a removal from the queue may occur for the message that was found in the search.

    • There is exactly one FIFO queue in the MESSAGE_BUS.

  • When inside the MESSAGE_BUS, a MESSAGE can take on the role of incoming MESSAGE, existing MESSAGE, or outgoing MESSAGE:

    • A MESSAGE is an incoming MESSAGE when it comes from an AGENT and is sent to the MESSAGE_BUS.

    • A MESSAGE is an existing MESSAGE when it is stored in the FIFO queue.

    • A MESSAGE becomes an outgoing MESSAGE when it has been removed from the FIFO queue and is being provided to an AGENT by the MESSAGE_BUS.

  • The MESSAGE_BUS listens on TCP/IP for AGENTS to provide incoming MESSAGES.

  • When an incoming MESSAGE has an AGENT_TYPE of "consumer" and an OPERATION of "buy", the MESSAGE_BUS takes the following actions:

    • Search from the front of the FIFO queue for the first existing message that matches the AGENT_NAME and OPERATION of the MESSAGE.

    • If the search finds an existing MESSAGE already on the FIFO queue, return it to the AGENT immediately and take no further action.

    • If the search does not find an existing MESSAGE already on the FIFO queue, place the incoming MESSAGE at the end of the FIFO queue.

  • When an incoming MESSAGE has an AGENT_TYPE of "producer" and an OPERATION of "retrieve", the MESSAGE_BUS takes the following actions:

    • If the FIFO queue is empty, return the MESSAGE back to the AGENT that made the request with no changes and skip the remaining steps.

    • Search from the front of the FIFO queue for the first existing MESSAGE that contains an OPERATION of "buy".

    • Remove the existing MESSAGE from the FIFO queue and provide it to the AGENT.

  • The MESSAGE_BUS runs indefinitely until a USER sends Control-C.

Producer

  • The invocation of the PRODUCER from the command line is done with "python producer.py"

  • The PRODUCER listens to the TCP/IP port.

  • The PRODUCER consumes a MESSAGE from the TCP/IP port.

  • The PRODUCER finds the OPERATION in the MESSAGE.

  • If the OPERATION is "multiply", the PRODUCER determines the product of OPERAND-1 and OPERAND-2 as the ANSWER

  • If the OPERATION is "add", the PRODUCER determines the sum of OPERAND-1 and OPERAND-2 as the ANSWER.

  • The PRODUCER builds a message to return in the manner prescribed next.

  • The PRODUCER puts all the original parts of the message it received so that the inputs are traceable.

  • The PRODUCER puts the ANSWER into the MESSAGE.

  • The PRODUCER shows the message on the command line so the USER can see the content.

  • The PRODUCER sends the MESSAGE over the TCP/IP port so the CONSUMER can receive it.

  • The PRODUCER waits for another message.

  • The PRODUCER runs indefinitely until a USER sends Control-C.

Consumer

  • The invocation of the CONSUMER from the command line is done with "python consumer.py"

  • The command line takes the following positional parameters:

    • AGENT_NAME

    • OPERATION

    • OPERAND-1

    • OPERAND-2

  • If any parameters are not present, the user is given a help message on how to properly pass parameters.

  • The CONSUMER puts AGENT_NAME, OPERATION, OPERAND-1, OPERAND-2 into the MESSAGE format that is common to both the PRODUCER and CONSUMER.

  • The CONSUMER leaves the ANSWER blank.

  • The CONSUMER connects to TCP/IP port 30101 and sends the MESSAGE it has built.

  • The CONSUMER waits for a MESSAGE from the PRODUCER to come over the TCP/IP port.

  • When a return MESSAGE is received from the PRODUCER, the CONSUMER displays it on the screen for the USER.

User

  • The USER is a human at the Linux command line.

  • The USER will invoke the PRODUCER for it to run indefinitely.

  • The USER will invoke the CONSUMER each time it needs an ANSWER by running "python consumer.py" with parameters.

  • The USER may provide different parameters to the CONSUMER each time the CONSUMER is run.

1. Notes

Ignore everything in this section and the remainder of the page. These are notes not requirements.

for i in {1..1000}; do python consumer.py add $(RANDOM % 10) + 1 $(RANDOM % 10) + 1 ; done

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