See all messages in process's mailbox with pid XY

[tomaz....@gmail.com]

Is it possible to see all messages that are in mailbox of a process with a given pid? I know it is possible to use flush in console process. But flush removes all messages and I just want to see them and not just for console mailbox, but for any mailbox I know.

[Saša Jurić]

You can use :erlang.process_info

E.g.:

iex(1)> shell_process = self

iex(2)> spawn(fn ->

...(2)>   send(shell_process, :foobar)

...(2)>   :erlang.process_info(shell_process, :messages) |> IO.inspect

...(2)> end)

{:messages, [:foobar]}

You can have a GUI interface via observer application. Just start it from the shell with :observer.start, head to Processes tab, find the target process, double click it, and in messages you should see a snapshot of the message queue.

It is also possible to use Erlang's tracing via :sys, :dbg module, and :erlang.trace/3 function to dynamically start traces for various events. Among other things, you can trace messages sent to or from particular process(es).

[Tomaž Žlender]

Awesome! Thank you :)

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[Robert Virding]

You should be aware that getting all the messages in another process's mailbox can be a very costly operation. All the messages are copied from the other process to your process. Processes don't share data. To be safe it might be better to first check the length of the message queue using Process.info(pid, :message_queue_len).

Robert