Application module `start` function not called?

Questions / Help
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1

Hi

I have fairly complicated Phoenix app (but it doubt that this is Phoenix related issue?). In it I have the MyApp.Application module with start(_type, _args) function. I noticed today (after long time without working on it), that the start() function isn’t called at all. In the mix.exs file, the mod: is set correctly to that module - I haven’t changed anything there.

How one can try to debug this? What is happening before call to start() - maybe something there hangs?

I’ve tried rebuild from scratch, re-get deps, etc. And nothing, the function will not be called.
When I created new project, all seems OK in it.

I’m using Erlang/OTP 28.1 and Elixir 1.18.4

Update:
If I use MIX_ENV=prod, then I can see print at the beginning of the start() function. But I want to use the dev env :slight_smile:

2

That start callback is what starts the Endpoint, so if it isn’t being called you have no server/app at all. Is that what you’re experiencing?

3

Well I think it is not about Endpoint (I have more children, not just the Phoenix ones). I have IO.inspect(“here”) as 1st instruction in start() function (before the children definition). And it is not printed.

And I have mix.exs with application/server definitions that are OK (I haven’t changed them for like years now).

4

I asked a specific question because I am trying to narrow down what is going on. If start/2 is not being called then your app must not be starting.

Is your application starting? Is the web server running? Does it work?

5

I believe @garrison is trying to get at is if any of the children in your application are running, if so then your application is running, and your endpoint is an easy one to test if it’s running.

How are you running your application? mix phx.server from the terminal, or some other way? Is it possible something is swallowing that IO you are using to debug? Instead of IO.inspect("here") you can try raise "here"

1 Like
6

@garrison none of the children are started. The function is not called/entered.

@jswanner even with raise “here” it will not stop it. I’m using iex -S mix phx.server with some env variables.

Note that with MIX_ENV=prod it works, every time. With MIX_ENV=dev it does not. Only this MIX_ENV is different in invocation.

1 Like
7

That is odd. I don’t know off the top of my head anything that would cause that behavior, though perhaps someone else will think of something.

Given that the behavior is different between environments you may want to comb through the configs for anything that could be different, though again I’m not sure what that might be.

As for your question about what happens when the application starts, it’s described quite thoroughly in the Application docs.

8

Then the culprit should be config/prod.exs or config/runtime.exs or any code that branches on the environment variables.

9 
diff _build/{dev,prod}/lib/<app_name>/ebin/<app_name>.app
1 Like
10

It seems that the issue is with:

# Watch static and templates for browser reloading.
config :myapp, MyAppWeb.Endpoint,
  live_reload: [
    patterns: [
      ~r"priv/static/.*(js|css|png|jpeg|jpg|gif|svg)$",
      ~r"priv/gettext/.*(po)$",
      ...
    ]
  ]

Without this feature configured, the dev comes up. I wonder what might be the issue here. I will double check my paths here.

11

I take it that you redacted the app name and module namespace in the snippet above and they’re not the same in the real code? Just making sure.

Also does this code look the same in a freshly generated project?

12

Yes, I’ve redacted the true app name and redacted the paths with the app name. However, there is not one line in patters list that would cause the issue (I’ve checked). I have to remove this whole config section to see the apps starting. So I think it is not about the dir/files the inotify observes.

And yes, with new/clean project, the live_reload isn’t blocking the startup. In new project and in my project I’m using the same versions of the packages (e.g. file_system). I’ve also checked the code generated in new project - it looks the same (only some patters are different).

Update: empty patters also helps! So I do not have to remove the whole section from config file.

13

Let us know when you dig the problem out. Should be something trivial that the tooling does not yell at you for but must be this or that, I presume.

1 Like
14

Hmmm

In fail case:

iex(2)> Application.started_applications()
[
{:myapp, [], []},
{:hex, ~c"hex", ~c"2.2.2"},
{:inets, ~c"INETS  CXC 138 49", ~c"9.4.2"},
{:ssl, ~c"Erlang/OTP SSL application", ~c"11.4"},
{:public_key, ~c"Public key infrastructure", ~c"1.18.3"},
{:asn1, ~c"The Erlang ASN1 compiler version 5.4.2", ~c"5.4.2"},
{:crypto, ~c"CRYPTO", ~c"5.7"},
{:mix, ~c"mix", ~c"1.18.4"},
{:iex, ~c"iex", ~c"1.18.4"},
{:elixir, ~c"elixir", ~c"1.18.4"},
{:compiler, ~c"ERTS  CXC 138 10", ~c"9.0.2"},
{:stdlib, ~c"ERTS  CXC 138 10", ~c"7.1"},
{:kernel, ~c"ERTS  CXC 138 10", ~c"10.4"}
]

iex(4)> Application.ensure_started(:phoenix_live_reload)
{:error, {:not_started, :logger}}
iex(5)> Application.ensure_started(:logger)
:ok
iex(6)> Application.ensure_started(:phoenix_live_reload)
{:error, {:not_started, :phoenix}}
iex(7)> Application.ensure_started(:phoenix)
{:error, {:not_started, :eex}}
iex(8)> Application.ensure_started(:eex)
:ok
iex(9)> Application.ensure_started(:phoenix)
{:error, {:not_started, :plug}}
iex(10)> Application.ensure_started(:plug)
{:error, {:not_started, :mime}}
iex(11)> Application.ensure_started(:mime)
:ok
iex(12)> Application.ensure_started(:plug)
{:error, {:not_started, :plug_crypto}}
iex(13)> Application.ensure_started(:plug_crypto)
:ok
iex(14)> Application.ensure_started(:plug)
{:error, {:not_started, :telemetry}}
iex(15)> Application.ensure_started(:telemetry)
:ok
iex(16)> Application.ensure_started(:plug)
:ok
iex(17)> Application.ensure_started(:phoenix)
{:error, {:not_started, :phoenix_pubsub}}
iex(18)> Application.ensure_started(:phoenix_pubsub)
:ok
iex(19)> Application.ensure_started(:phoenix)
{:error, {:not_started, :phoenix_template}}
iex(20)> Application.ensure_started(:phoenix_templete)
{:error, {~c"no such file or directory", ~c"phoenix_templete.app"}}

Update: in the end I was able to start them all and made sure that the file is there. So I do not know if this is related (or if I’m doing it correctly anyway).