GenServer.call

You're seeing just the function call, go back to GenServer module for more information.
Link to this function

call(server, request, timeout \\ 5000)

View Source

Specs

call(server(), term(), timeout()) :: term()

Makes a synchronous call to the server and waits for its reply.

The client sends the given request to the server and waits until a reply arrives or a timeout occurs. handle_call/3 will be called on the server to handle the request.

server can be any of the values described in the "Name registration" section of the documentation for this module.

Timeouts

timeout is an integer greater than zero which specifies how many milliseconds to wait for a reply, or the atom :infinity to wait indefinitely. The default value is 5000. If no reply is received within the specified time, the function call fails and the caller exits. If the caller catches the failure and continues running, and the server is just late with the reply, it may arrive at any time later into the caller's message queue. The caller must in this case be prepared for this and discard any such garbage messages that are two-element tuples with a reference as the first element.