exq v0.13.0 Exq.Middleware.Server

Middleware Server is responsible for storing middleware chain that is evaluated when performing particular job. Middleware chain defaults to Stats, Job and Manager middlewares.

To push new middleware you must create module with common interface. Interface is similar to Plug implementation. It has three functions, every function receives Exq.Middlewares.Pipeline structure and every function must return the same structure, modified or not.

Basically, before_work/1 function may update worker state, while after_processed_work/1 and after_failed_work/1 are for cleanup and notification stuff.

For example, here is a valid middleware module:

  defmodule MyMiddleware do
    @behaiour Exq.Middleware.Behaviour

    def before_work(pipeline) do
      # some functionality goes here...
      pipeline
    end

    def after_processed_work(pipeline) do
      # some functionality goes here...
      pipeline
    end

    def after_failed_work(pipeline) do
      # some functionality goes here...
      pipeline
    end
  end

To add this module to middleware chain:

  Exq.Middleware.Server.push(middleware_server_pid, MyMiddleware)

Link to this section Summary

Functions

all(pid)

Retrieves list of middleware modules

child_spec(arg)

Returns a specification to start this module under a supervisor

init(args)

Invoked when the server is started. start_link/3 or start/3 will block until it returns

push(pid, middleware)

Adds specified middleware module into the end of middleware list. middleware should have Exq.Middleware.Behaviour behaviour

server_name(name)

Returns middleware server name

start_link(opts \\ [])

Starts middleware server

Link to this section Functions

all(pid)

Retrieves list of middleware modules

child_spec(arg)

Returns a specification to start this module under a supervisor.

See Supervisor.

init(args)

Invoked when the server is started. start_link/3 or start/3 will block until it returns.

args is the argument term (second argument) passed to start_link/3.

Returning {:ok, state} will cause start_link/3 to return {:ok, pid} and the process to enter its loop.

Returning {:ok, state, timeout} is similar to {:ok, state} except handle_info(:timeout, state) will be called after timeout milliseconds if no messages are received within the timeout.

Returning {:ok, state, :hibernate} is similar to {:ok, state} except the process is hibernated before entering the loop. See c:handle_call/3 for more information on hibernation.

Returning {:ok, state, {:continue, continue}} is similar to {:ok, state} except that immediately after entering the loop the c:handle_continue/2 callback will be invoked with the value continue as first argument.

Returning :ignore will cause start_link/3 to return :ignore and the process will exit normally without entering the loop or calling c:terminate/2. If used when part of a supervision tree the parent supervisor will not fail to start nor immediately try to restart the GenServer. The remainder of the supervision tree will be started and so the GenServer should not be required by other processes. It can be started later with Supervisor.restart_child/2 as the child specification is saved in the parent supervisor. The main use cases for this are:

The GenServer is disabled by configuration but might be enabled later.
An error occurred and it will be handled by a different mechanism than the Supervisor. Likely this approach involves calling Supervisor.restart_child/2 after a delay to attempt a restart.