On 09/19/2018 02:55 AM, Vladimir Panteleev wrote:
On Wednesday, 19 September 2018 at 06:34:33 UTC, Nick Sabalausky
(Abscissa) wrote:
- Does it actually, necessarily perform those additional OS calls?
We need to expand relative paths to absolute ones, for which we need to
fetch the current directory.
So in other words, NO, it does NOT necessarily perform additional OS
calls. It ONLY performs an additional call if the given path is relative
*AND* if we've decided to not simply reject too-long relative paths
outright (which I'd be fine with as a compromise. At least it would be
well-defined and enforced with a meaningful message.)
- Is it really?
Is what really what? If you mean the memory allocation, we do need a
buffer to store the current directory. We also need to canonicalize away
things like \..\, though we may be able to get away with it without
allocating.
So, in many cases, it's NOT really "a good deal of extra logic that
performs additional OS calls and generates additional GC garbage".
- If it actually does, are those additional, necessarily OS calls
prohibitively expensive?
They are certainly going to be less expensive that actual filesystem
operations that hit the physical disk,
Sounds like QED to me. Especially if the alternative is silently
incorrect behaviour on an entirely realistic subset of cases. (Realistic
enough that both the thread's OP and the bug report's OP each ran into
purely by accident.)
but it will still be an unwanted
overhead in 99.9% of cases.
That's an extremely exaggerated figure, and we've already established
that the overhead is minor and often able to be elided. Weighted against
the cost of incorrect behaviour on a subset of non-rejected inputs, I'd
say that's a very clear "Yes, please!"
The extreme minority of currently-hypothetical cases which require
minimal overhead for individual file I/O operations are free to
low-level optimize themselves as-needed. Correct behaviour should never
be sacrificed for minor performance tweaks when the minor performance
tweak can still be obtained through other means if absolutely necessary.
In any case, the overhead is only one issue.
What's the other issue(s)?
