Spectator

Spectator is a BEAM observer tool written in Gleam, that plays well with gleam_otp processes.

Features

This is a work in progress, so far it has the following features:

• Show processes in a sortable table
• Tag individual processes for easy identification
• Show process details
• Show OTP process state
• Suspend / resume OTP processes
• List ETS tables
• View content of ETS tables
• List of active ports
• Clickable links between resources
• Dashboard with basic statistics
• Inspect other BEAM nodes

Installation

gleam add spectator

Usage

🦔 Please be aware spectator is still new, and a work in progress, reliability is not guaranteed, use at your own peril!

Call spectator.start() in your application, to start the spectator service and WebUI.

In order to make it easier to identify your Gleam processes in the process list, you can tag them with a friendly name with spectator.tag, spectator.tag_subject or spectator.tag_result after starting the spectator service.

Example

import gleam/erlang/process
import spectator
import utils/pantry

pub fn main() {
  // Start the spectator service
  let assert Ok(_) = spectator.start()

  // Start an OTP actor
  let assert Ok(sub) = pantry.new()

  // Tag the actor with a name for easier identification in the spectator UI
  // Note: this only works because we called spectator.start before!
  sub
  |> spectator.tag_subject("Pantry Actor")

  // Add some state to the actor
  pantry.add_item(sub, "This actor has some state")
  pantry.add_item(sub, "Another item in the state of this actor")
  pantry.add_item(sub, "And some more state I've put into this demo actor")

  // Sleep on the main process so the program doesn't exit
  process.sleep_forever()
}

Considerations

Please be aware of the following implications of running spectator:

• Spectator may slow down your system
  All displayed processes are probed in the configured interval using Erlang's process_info/2 function which puts a temporary lock on the process being infoed. If the process is handling a lot of messages, this may have performance implications for the system
• Spectator will send system messages to selected processes
  In order to get a selected processes OTP state, spectator needs to send it system messages. If you select a process that is not handling these messages properly, spectator may fill up its message queue, as it is sending a new message every tick in the configured interval. If the processes message queue is over a certain size, spectator will stop sending new messages, however the process may never handle the already queued up messages
• Spectator will create atoms dynamically
  When you choose to connect to other Erlang nodes, spectator needs to convert the node name and cookie you provide into atoms. Therefore it is possible to exhaust the memory of the BEAM instance running spectator using its user interface, as atoms are never garbage collected.

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Further documentation can be found at https://hexdocs.pm/spectator.