Command Timeout

Overview

A command timeout is the deadline you attach to a single RPC call so a caller never blocks forever waiting on a handler that isn't there or isn't responding. Commands are synchronous by design — the sender is parked until a reply arrives — so without a bound, a missing subscriber or a crashed handler turns one request into an indefinite hang that ties up the calling process and cascades into upstream timeouts.

The timeout is set per call with timeout on KubeMQ.Command.new, and it's enforced by the broker itself, not by client-side polling: the broker tracks the deadline server-side and fails the request the moment it expires, regardless of what the calling process is doing. When the window elapses with no response, KubeMQ.Client.send_command/2 returns {:error, err} with err.code set to :timeout — your signal to retry or fall back.

Gotchas: a command timeout is a broker-enforced deadline, not a local GenServer.call timeout, so don't assume a local call timing out means the broker also gave up; a slow-but-alive handler and a completely absent one produce the same :timeout code, so you can't tell them apart from the error alone; and check err.retryable? before retrying — not every timeout is safe to resend blindly.

Prerequisites

• KubeMQ server running on localhost:50000
• Elixir SDK installed ({:kubemq, "~> 1.0"} in mix.exs)

Code

channel = "elixir-rpc.command-timeout"
{:ok, client} = KubeMQ.Client.start_link(address: "localhost:50000", client_id: "elixir-cmd-timeout")

IO.puts("Sending command with 3-second timeout (no handler)...")

cmd = KubeMQ.Command.new(
  channel: channel,
  body: "this will timeout",
  timeout: 3_000
)

case KubeMQ.Client.send_command(client, cmd) do
  {:ok, response} ->
    if response.error do
      IO.puts("Command returned with error: #{response.error}")
    else
      IO.puts("Command executed: #{response.executed}")
    end

  {:error, err} ->
    IO.puts("Command timed out or failed: #{err.message}")
    IO.puts("Error code: #{err.code}")
end

IO.puts("Timeout handling complete.")
KubeMQ.Client.close(client)

How It Works

• When no handler is subscribed, send_command/2 blocks for the timeout duration
• After the timeout, an error is returned with code :timeout
• The retryable? field on the error indicates whether the operation can be retried

Related

• Send Command
• Reconnection