Today I Learned

A Hashrocket project

Inspecting The Process Message Queue

A core tenant of Elixir is message passing between processes. So, if a process is sent a message, where does that message go? What happens if it gets sent many messages? The Process.info/2 function allows us to inspect the message queue.

First, let's send some messages (to ourself) and then keep an eye on the length of the message queue as we go.

> send self(), {:error, "this is bad"}
{:error, "this is bad"}
> Process.info(self(), :message_queue_len)
{:message_queue_len, 1}
> send self(), {:hello, "world"}
{:hello, "world"}
> Process.info(self(), :message_queue_len)
{:message_queue_len, 2}

Now, I am curious what those specific messages are. Let's ask Process.info/2 for the messages that are in the message queue.

> Process.info(self(), :messages)
{:messages, [error: "this is bad", hello: "world"]}

There are a lot of other things that Process.info/2 can tell us about a process. See the Erlang docs for process_info for more details.

Looking for help? Elixir is quickly gaining momentum for web applications that need concurrency, performance, and the ability to connect to many different clients. The developers at Hashrocket are learning along with the rest of the development community that Elixir and Phoenix are viable Rails alternatives for the right application. Contact us if you need help with your Elixir project.