Port selection without using listenany

[vchuravy]

UCX.jl/src/UCX.jl

Lines 276 to 281 in 6a369d8

	# Choose free port
	if port === nothing || port == 0
	port_hint = 9000 + (getpid() % 1000)
	port, sock = listenany(UInt16(port_hint))
	close(sock) # FIXME: https://github.com/rapidsai/ucx-py/blob/72552d1dd1d193d1c8ce749171cdd34d64523d53/ucp/core.py#L288-L304
	end

[fatteneder]

Hi,

I thought I give this issue a try. I should say that I don't know much about networking, but perhaps I can learn something from here :)

So I started with some research:

Firstly, I looked into ucx-py under the link mentioned above.
There they use the psutils to gather all used ports into a list and then randomly select one that is not on there.
I could not find any Julia implementation of what psutils.net_connections() does.
But I looked into how psutils.net_connections() works and I (think) what it does is to parse all socket 'files' found under /procs/ to extract the port numbers, cf. https://github.com/giampaolo/psutil/blob/dd57b9a109d6db9a87247d5f47303b87672dfa78/psutil/_pslinux.py#L975-L1004

I then looked into what listenany does: It generates new sockets with incremented port numbers (starting from port_hint) till it finds an used one.

I also found that in the meantime ucx-py changed the implemention, cf. https://github.com/rapidsai/ucx-py/blob/933b373a73d45f7d0a0b91043a6386b396eaebb8/ucp/core.py#L226-L275
I think what they now do is to forward the port selection to the ucx library and the ucp_listener_create method.
I did not check how ucp_listener_create finds an open port ...

Q: Which of the these approaches is the preferred one?
Q: (Naive question) For what reasons should listenany be replaced? Is it expected to be slower than the psutils.net_connections() approach?

Cheers