fpath+="${(u)fpath[@]}" can hog system

fpath+="${(u)fpath[@]}" can hog system

[Sebastian Gniazdowski]

Hello
Few times it was reproducing also without the loop:

repeat 20; do fpath+="${(u)fpath[@]}"; done

It's easier to reproduce this on 5.0.8 than on 5.1 and 5.2 that might
require repeated call of the loop (one repetition was sufficient on my
system). OS X 10.11.2.

Best regards
Sebastian Gniazdowski

Re: fpath+="${(u)fpath[@]}" can hog system

[Bart Schaefer]

On Jan 27, 10:36am, Sebastian Gniazdowski wrote:
}
} repeat 20; do fpath+="${(u)fpath[@]}"; done

Why would you do that?  What's the intended result?

Appending a string to an array creates a single new array element; it
doesn't matter that you've used [@] inside the double quotes, you are
still appending a new single element to the array every time.  Since
the new element consists of all the previous elements joined, it is
always unique and (u) will never filter out anything.

And then all of that will be duplicated as a single colon-separated
string in $FPATH.

Yeah, if you increase the size (in bytes) of $fpath by 20! (factorial),
and then make a copy of that, you are going to consume a buttload of
resources.

If what you mean is to append new elements to the array, you want array
assignment syntax:

fpath+=("${(u)fpath[@]}")

But even that probably doesn't do what you meant. because unless you have
already done "typeset -U fpath" all the existing elements are still going
to be repeated twice ... and IF you HAVE done "typeset -U" then (u) is a
no-op.

Re: fpath+="${(u)fpath[@]}" can hog system

[Sebastian Gniazdowski]

On 27 January 2016 at 23:50, Bart Schaefer <schaefer@brasslantern.com> wrote:
> Why would you do that?  What's the intended result?

I wrote this by accident and saw my system going high load

> Yeah, if you increase the size (in bytes) of $fpath by 20! (factorial),
> and then make a copy of that, you are going to consume a buttload of
> resources.

It's a typical situation that I cannot submit a bug because it
reproduces in my long scripts but not in short examples. Sadly this
will probably another one for the collection. And in that collection
some might not be actually bugs. fpath+="${(u)fpath[@]}" hogged my
system after single execution (not in loop) in a freshly opened shell,
few times. That's all I can say. Tried this now and it doesn't
reproduce. That said your point about 20! is important, my script
loaded say 18 plugins  each time calling fpath+="${(u)fpath[@]}", so
this is how all the topic happened, and possibly it wasn't a bug...
Probably the only way to use such reports is taking a glance at
related source code and luckily noticing something

Best regards,
Sebastian Gniazdowski