Debugging snippets for Elixir/Erlang applications
Table of Contents
Working with processes
Find the pid of regiestered process
:erlang.whereis(MyApp.Supervisor)
Get the proess info for pid
iex(1)> Process.info(pid) [ registered_name: MyApp.Supervisor, current_function: {:gen_server, :loop, 7}, initial_call: {:proc_lib, :init_p, 5}, status: :waiting, message_queue_len: 0, links: [#PID<0.707.0>, #PID<0.708.0>, #PID<0.561.0>], dictionary: [ "$initial_call": {:supervisor, Phoenix.Endpoint.Supervisor, 1}, "$ancestors": [MyApp.Parent.Supervisor, #PID<0.559.0>] ], trap_exit: true, error_handler: :error_handler, priority: :normal, group_leader: #PID<0.558.0>, total_heap_size: 3196, heap_size: 1598, stack_size: 11, reductions: 4213, garbage_collection: [ max_heap_size: %{error_logger: true, kill: true, size: 0}, min_bin_vheap_size: 46422, min_heap_size: 233, fullsweep_after: 65535, minor_gcs: 7 ], suspending: [] ]
`links`: specify to which process is the current process linked i.e. parent and children `$ancestors`: represent the parent process tree of this process
Convert to a pid and get its info
'<0.8718.0>' |> :erlang.list_to_pid() |> Process.info()
Get the message list of a process
Process.info(pid, :messages)
Get the state of process
:sys.get_state(pid)
Terminate a process
# method 1 :erlang.exit(pid, :kill) # method 1 Process.exit(pid, :kill) #method 2 :sys.terminate(pid, :kill)
Display system information for all processes
:c.i()
List all registered proceses
:c.regs()
Get node memory consumption
:c.memory()
Tracing
Enable VM traceing
Enable the trace
:erlang.trace(:new_processes, true, [:all])
Stop the trace
:erlang.trace(:all, false, [:all])
Export trace to file
The trace is captured as messages in the shell proesses message box and can be expored as follows,
{:messages, messages} = Process.info(self(), :messages)
{:ok, fd} = File.open("/tmp/trace-#{NaiveDateTime.utc_now() |> NaiveDateTime.to_iso8601()}", [:write])
messages |> Enum.map(fn m -> IO.puts(fd, inspect(m)) end)
File.close(fd)
Disassamble beam file
:file.write_file("/tmp/producer_disasm", :io_lib.fwrite("~p.\n", [:beam_disasm.file('/path/to/file/Elixir.Something.beam')]))