Add Inspecting The Process Message Queue as an elixir til

README.md

@@ -10,7 +10,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 For a steady stream of TILs from a variety of rocketeers, checkout
 [til.hashrocket.com](https://til.hashrocket.com/).
 
-_524 TILs and counting..._
+_525 TILs and counting..._
 
 ---
 
@@ -111,6 +111,7 @@ _524 TILs and counting..._
 - [Execute Raw SQL In An Ecto Migration](elixir/execute-raw-sql-in-an-ecto-migration.md)
 - [Expose Internal Representation](elixir/expose-internal-representation.md)
 - [Include Captures With String.split](elixir/include-captures-with-string-split.md)
+- [Inspecting The Process Message Queue](elixir/inspecting-the-process-message-queue.md)
 - [List Functions For A Module](elixir/list-functions-for-a-module.md)
 - [Listing Files In IEx](elixir/listing-files-in-iex.md)
 - [Pattern Matching In Anonymous Functions](elixir/pattern-matching-in-anonymous-functions.md)

elixir/inspecting-the-process-message-queue.md

@@ -0,0 +1,33 @@
+# 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.
+
+```elixir
+> 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`](http://erlang.org/doc/man/erlang.html#process_info-2) for
+more details.