what is a group leader

Question

I am trying to configure out, what is a group leader and how it is related with I/O module, but could not find anything useful in internet. Can please someone explain me?

I have following scenario from elixir 1.2 book(Dave Thomas):

On the second window, why does he pass :erlang_group_leader? For what it is good for?

Answer 1

From documentation:

group_leader() -> pid()

Returns the process identifier of the group leader for the process evaluating the function.

Every process is a member of some process group and all groups have a group leader. All I/O from the group is channeled to the group leader. When a new process is spawned, it gets the same group leader as the spawning process. Initially, at system start-up, init is both its own group leader and the group leader of all processes.

And:

group_leader(GroupLeader, Pid) -> true

Types:

GroupLeader = Pid = pid()

Sets the group leader of Pid to GroupLeader. Typically, this is used when a process started from a certain shell is to have another group leader than init.

See also group_leader/0.

There is also some Elixir-specific documentation:

By modelling IO devices with processes, the Erlang VM allows different nodes in the same network to exchange file processes in order to read/write files in between nodes. Of all IO devices, there is one that is special to each process: the group leader.

The group leader can be configured per process and is used in different situations. For example, when executing code in a remote terminal, it guarantees messages in a remote node are redirected and printed in the terminal that triggered the request.