Hi
Op 15-02-2023 om 14:38 schreef Tomas Kalibera:
On 2/15/23 01:24, Ben Engbers wrote:
Hi,
December 27, 2021 I started a thread asking for help troubleshooting
non-blocking sockets.
..
I have two questions.
The first is where I can find R documentation on proper use of
non-blocking sockets and on the proper use of the socketSelect function?
In addition to the demos I sent to you in that 2021 thread on
R-pkg-devel, you could also have a look at how it is used in R itself,
in the parallel package, in snowSOCK.R, to set up the snow cluster in
parallel. Some hints may be also found in the blog post
https://blog.r-project.org/2020/03/17/socket-connections-update/. But,
in principle, R API is just a thin layer on top of what the OS provides,
so general literature and tutorials on sockets should help, there should
be even textbooks used at CS universities in networking classes.
Thanks for the suggestions!
Basically select() can tell you when data is ready (on input), when the
socket interface is able to accept more data (on output) or when there
is an incoming connection. In practice, you should not need any delays
to be inserted in your program to make it work - if that is needed, it
means that is an error in it (a race condition). If the program is
polling (checking in a loop whether something has already happened, and
then sleeping for a short while), the duration of the sleep may indeed
influence latency, but should not affect correctness - if it does, there
is an error.
In RBaseX I first calculate an MD5 hash that is send to the server and
then I check the status byte that is returned by the server.
writeBin(auth, private$conn)
socketSelect(list(conn))
Accepted <- readBin(conn, what = "raw", n = 1) == 0
Without the second line, 'Accepted' is always FALSE. With this line it
is TRUE.
BaseX provides example API's in several languages. I've looked at
several but indeed none uses any form of delay.
All API's follow the same pattern, calculate a MD5, send it to the
server and check the status byte. So the server is not likely to enforce
a delay. So there is nothing left but to look for that racing condition ;-(
Ben
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