perl5

perl5 copied to clipboard

A few places within toke.c try to return unused string buffer space by doing something like:

if (SvCUR(sv) + 5 < SvLEN(sv)) {
    SvPV_shrink_to_cur(sv);
}

The rationale for the 5 is not commented upon. Maybe it's a random thumb in the air, maybe it was 1 byte for the trailing null plus a 4 byte pointer to account for allocation alignment?

Either way, on a platform with 8 byte pointers, that code could try to shrink buffers when there's no realistic chance of doing so. (The space between chunk sizes will be at least 1x PTRSIZE, often 2x PTRSIZE at smaller sizes and then progressively more.)

For a reallocation that is at least has the potential to be meaningful, the difference between CUR and LEN should be at least:

• 1 byte for a trailing null byte +
• 1 byte to enable the SV to be COWed +
• 1x PTRSIZE

This commit changes makes that so.

---

• This set of changes does not require a perldelta entry.