[erlang-questions] '--' BIF to be used with caution?

Malcolm Dowse <>
Tue Jan 13 13:04:06 CET 2009


Hello,

I ran into an issue with Erlang the other day. I'm not sure if it's a bug,
but I thought I should warn others.

I was using '--' to get the difference between two large lists. As expected
it was very slow, but, to my surprise, ERTS became completely unresponsive
for a long time. (Only one CPU was maxed out, and there was still plenty of
memory available.)

To reproduce (on Ubuntu 7.x, R12B-x), open an Erlang shell and type:

spawn(fun() -> lists:seq(1,1000000) -- lists:seq(1,1000000,2) end).

The unresponsiveness seems to be caused by '--' being a BIF. Is there a good
reason for making it a BIF if it's not always an improvement?

All the best,

Malcolm
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