Der Schlüssel war eine Kombination Process.monitor(pid) des Anrufers - dann werden Sie Anrufe handle_info erhalten - und Supervisor.start_child manuell aufrufen, die gibt Ihnen pids.
Ich hatte zuvor versucht, handle_info zu verwenden, konnte aber nie dazu gebracht werden, es zu nennen. muss von demselben Prozess aufgerufen werden, der die Benachrichtigungen erhalten soll. Sie müssen ihn also innerhalb einer handle_call-Funktion aufrufen, um den Monitor mit Ihrem Serverprozess zu verknüpfen. Es kann eine Funktion geben, Code als einen anderen Prozess auszuführen (d. H. run_from_process(job_queue_pid, fn -> Process.monitor(pid_to_monitor) end)), aber ich konnte nichts finden.
Attached ist eine sehr naive Implementierung einer Jobwarteschlange. Ich bin nur einen Tag in Elixir, also ist der Code sowohl unordentlich als auch nicht-idiomatisch, aber ich füge ihn an, weil es anscheinend an Code-Beispielen fehlt.
Betrachten Sie HeavyIndustry.JobQueue, handle_info, create_new_worker. Es gibt ein offensichtliches Problem mit diesem Code: Er kann Mitarbeiter beim Absturz neu starten, aber es ist nicht in der Lage, die Warteschlange beim nächsten Job von diesem Code aus zu starten (weil GenServer.call innerhalb handle_info erforderlich ist, was uns blockiert). Ich denke, Sie könnten dies beheben, indem Sie den Prozess, der die Jobs startet, vom Prozess trennen, der die Jobs verfolgt. Wenn Sie den Beispielcode ausführen, werden Sie feststellen, dass er schließlich keine Jobs mehr ausführt, obwohl sich noch einer in der Warteschlange befindet (:crash).
defmodule HeavyIndustry.Supervisor do
use Supervisor
def start_link do
Supervisor.start_link(__MODULE__, :ok)
end
def init(:ok) do
# default to supervising nothing, we will add
supervise([], strategy: :one_for_one)
end
def create_children(supervisor, worker_count) do
# create the job queue. defaults to no workers
Supervisor.start_child(supervisor, worker(HeavyIndustry.JobQueue, [[supervisor, worker_count]]))
end
end
defmodule HeavyIndustry.JobQueue do
use GenServer
@job_queue_name __MODULE__
def start_link(args, _) do
GenServer.start_link(__MODULE__, args, name: @job_queue_name)
end
def init([supervisor, n]) do
# set some default state
state = %{
supervisor: supervisor,
max_workers: n,
jobs: [],
workers: %{
idle: [],
busy: []
}
}
{:ok, state}
end
def setup() do
# we want to be aware of worker failures. we hook into this by calling
# Process.monitor(pid), but this links the calling process with the monitored
# process. To make sure the calls come to US and not the process that called
# setup, we create the workers by passing a message to our server process
state = GenServer.call(@job_queue_name, :setup)
# gross passing the whole state back here to monitor but the monitoring must
# be started from the server process and we can't call GenServer.call from
# inside the :setup call else we deadlock.
workers = state.workers.idle
GenServer.call(@job_queue_name, {:monitor_pids, workers})
end
def add_job(from, job) do
# add job to queue
{:ok, our_job_id} = GenServer.call(@job_queue_name, {:create_job, %{job: job, reply_to: from}})
# try to run the next job
case GenServer.call(@job_queue_name, :start_next_job) do
# started our job
{:ok, started_job_id = ^our_job_id} -> {:ok, :started}
# started *a* job
{:ok, _} -> {:ok, :pending}
# couldnt start any job but its ok...
{:error, :no_idle_workers} -> {:ok, :pending}
# something fell over...
{:error, e} -> {:error, e}
# yeah I know this is bad.
_ -> {:ok}
end
end
def start_next_job do
GenServer.call(@job_queue_name, :start_next_job)
end
##
# Internal API
##
def handle_call(:setup, _, state) do
workers = Enum.map(0..(state.max_workers-1), fn (n) ->
{:ok, pid} = start_new_worker(state.supervisor)
pid
end)
state = %{state | workers: %{state.workers | idle: workers}}
{:reply, state, state}
end
defp start_new_worker(supervisor) do
spec = Supervisor.Spec.worker(HeavyIndustry.Worker, [], id: :"Worker.#{:os.system_time}", restart: :temporary)
# start worker
Supervisor.start_child(supervisor, spec)
end
def handle_call({:monitor_pids, list}, _, state) do
Enum.each(list, &Process.monitor(&1))
{:reply, :ok, state}
end
def handle_call({:create_job, job}, from, state) do
job = %{
job: job.job,
reply_to: job.reply_to,
id: :os.system_time, # id for task
status: :pending, # start pending, go active, then remove
pid: nil
}
# add new job to jobs list
state = %{state | jobs: state.jobs ++ [job]}
{:reply, {:ok, job.id}, state}
end
def handle_call(:start_next_job, _, state) do
IO.puts "==> Start Next Job"
IO.inspect state
IO.puts "=================="
reply = case {find_idle_worker(state.workers), find_next_job(state.jobs)} do
{{:error, :no_idle_workers}, _} ->
# no workers for job, doesnt matter if we have a job
{:error, :no_idle_workers}
{_, nil} ->
# no job, doesnt matter if we have a worker
{:error, :no_more_jobs}
{{:ok, worker}, job} ->
# have worker, have job, do work
# update state to set job active and worker busy
jobs = state.jobs -- [job]
job = %{job | status: :active, pid: worker}
jobs = jobs ++ [job]
idle = state.workers.idle -- [worker]
busy = state.workers.busy ++ [worker]
state = %{state | jobs: jobs, workers: %{idle: idle, busy: busy}}
{:ok, task_id} = Task.start(fn ->
result = GenServer.call(worker, job.job)
remove_job(job)
free_worker(worker)
send job.reply_to, %{answer: result, job: job.job}
start_next_job
end)
{:ok, job.id}
end
{:reply, reply, state}
end
defp find_idle_worker(workers) do
case workers do
%{idle: [], busy: _} -> {:error, :no_idle_workers}
%{idle: [worker | idle], busy: busy} -> {:ok, worker}
end
end
defp find_next_job(jobs) do
jobs |> Enum.find(&(&1.status == :pending))
end
defp free_worker(worker) do
GenServer.call(@job_queue_name, {:free_worker, worker})
end
defp remove_job(job) do
GenServer.call(@job_queue_name, {:remove_job, job})
end
def handle_call({:free_worker, worker}, from, state) do
idle = state.workers.idle ++ [worker]
busy = state.workers.busy -- [worker]
{:reply, :ok, %{state | workers: %{idle: idle, busy: busy}}}
end
def handle_call({:remove_job, job}, from, state) do
jobs = state.jobs -- [job]
{:reply, :ok, %{state | jobs: jobs}}
end
def handle_info(msg = {reason, ref, :process, pid, _reason}, state) do
IO.puts "Worker collapsed: #{reason} #{inspect pid}, clear and restart job"
# find job for collapsed worker
# set job to pending again
job = Enum.find(state.jobs, &(&1.pid == pid))
fixed_job = %{job | status: :pending, pid: nil}
jobs = (state.jobs -- [job]) ++ [fixed_job]
# remote worker from lists
idle = state.workers.idle -- [pid]
busy = state.workers.busy -- [pid]
# start new worker
{:ok, pid} = start_new_worker(state.supervisor)
# add worker from lists
idle = state.workers.idle ++ [pid]
# cant call GenServer.call from here to monitor pid,
# so duplicate the code a bit...
Process.monitor(pid)
# update state
state = %{state | jobs: jobs, workers: %{idle: idle, busy: busy}}
{:noreply, state}
end
end
defmodule HeavyIndustry.Worker do
use GenServer
def start_link do
GenServer.start_link(__MODULE__, :ok)
end
def init(:ok) do
# workers have no persistent state
IO.puts "==> Worker up! #{inspect self}"
{:ok, nil}
end
def handle_call({:sum, list}, from, _) do
sum = Enum.reduce(list, fn (n, acc) -> acc + n end)
{:reply, sum, nil}
end
def handle_call({:fib, n}, from, _) do
sum = fib_calc(n)
{:reply, sum, nil}
end
def handle_call({:stop}, from, state) do
{:stop, "my-stop-reason", "my-stop-reply", state}
end
def handle_call({:crash}, from, _) do
{:reply, "this will crash" ++ 1234, nil}
end
def handle_call({:timeout}, from, _) do
:timer.sleep 10000
{:reply, "this will timeout", nil}
end
# Slow fib
defp fib_calc(0), do: 0
defp fib_calc(1), do: 1
defp fib_calc(n), do: fib_calc(n-1) + fib_calc(n-2)
end
defmodule Looper do
def start do
{:ok, pid} = HeavyIndustry.Supervisor.start_link
{:ok, job_queue} = HeavyIndustry.Supervisor.create_children(pid, 2)
HeavyIndustry.JobQueue.setup()
add_jobs
loop
end
def add_jobs do
jobs = [
{:sum, [100, 200, 300]},
{:crash},
{:fib, 35},
{:fib, 35},
{:sum, [88, 88, 99]},
{:fib, 35},
{:fib, 35},
{:fib, 35},
{:sum, 0..100},
# {:stop}, # stop not really a failure
{:sum, [88, 88, 99]},
# {:timeout},
{:sum, [-1]}
]
Enum.each(jobs, fn (job) ->
IO.puts "~~~~> Add job: #{inspect job}"
case HeavyIndustry.JobQueue.add_job(self, job) do
{:ok, :started} -> IO.puts "~~~~> Started job immediately"
{:ok, :pending} -> IO.puts "~~~~> Job in queue"
val -> IO.puts "~~~~> ... val: #{inspect val}"
end
end)
end
def loop do
receive do
value ->
IO.puts "~~~~> Received: #{inspect value}"
loop
end
end
end
Looper.start