The COW patch has been revised for minimal impact to the outside world. The only files changed are: resources.h, resources.c, string.h, string.c There is one API change: Parrot_reallocate_string has an additional parameter. However, nobody outside string.c really has any business calling that anyway; and currently nobody else does.
The STRING structure has one change: a new field, void *buffer, points to the start of the physical buffer allocation. I tested a version that eliminated this requirement, by placing the allocated buffer length in the string tail; but this made the code in compact_string_pool very cumbersome, and the performance was several percent slower than my current implementation. Once the latest memory management patch is in, I will resync and submit the COW code as a separate patch, and we'll see what everybody thinks about it. I have just done a benchmark using Melvin's reverse.cola program. Reversing string.c went from 3.42 user seconds down to 3.12 with the COW patch; while reversing core_ops.c went from 94.39 to 92.26. Since this program does a large amount of stack manipulation, I suspect that the much smaller percentage improvement achieved on the larger file is due to stack overhead - I haven't had a change to profile it yet, but I will do as soon as I can. Unrelated subject: I see that Steve has modified string.c to get around the problem with the temporary transcoded strings - I believe we need to finalise a standard way of handling these situations soon. If anybody is interested, I will resync my previous 'neonate' patch - it needs a bit of work to fit with the latest changes to resources.c -- Peter Gibbs EmKel Systems
