view mercurial/mpatch.c @ 29304:5e32852fa4bd

revset: make filteredset.__nonzero__ respect the order of the filteredset

This fix allows __nonzero__ to respect the direction of iteration of the
whole filteredset. Here's the case when it matters. Imagine that we have a
very large repository and we want to execute a command like:

    $ hg log --rev '(tip:0) and user(ikostia)' --limit 1

(we want to get the latest commit by me).

Mercurial will evaluate a filteredset lazy data structure, an
instance of the filteredset class, which will know that it has to iterate
in a descending order (isdescending() will return True if called). This
means that when some code iterates over the instance of this filteredset,
the 'and user(ikostia)' condition will be first checked on the latest
revision, then on the second latest and so on, allowing Mercurial to
print matches as it founds them. However, cmdutil.getgraphlogrevs
contains the following code:

    revs = _logrevs(repo, opts)
    if not revs:
        return revset.baseset(), None, None

The "not revs" expression is evaluated by calling filteredset.__nonzero__,
which in its current implementation will try to iterate the filteredset
in ascending order until it finds a revision that matches the 'and user(..'
condition. If the condition is only true on late revisions, a lot of
useless iterations will be done. These iterations could be avoided if
__nonzero__ followed the order of the filteredset, which in my opinion
is a sensible thing to do here.

The problem gets even worse when instead of 'user(ikostia)' some more
expensive check is performed, like grepping the commit diff.


I tested this fix on a very large repo where tip is my commit and my very
first commit comes fairly late in the revision history. Results of timing
of the above command on that very large repo.

-with my fix:
real    0m1.795s
user    0m1.657s
sys     0m0.135s

-without my fix:
real    1m29.245s
user    1m28.223s
sys     0m0.929s

I understand that this is a very specific kind of problem that presents
itself very rarely, only on very big repositories and with expensive
checks and so on. But I don't see any disadvantages to this kind of fix
either.

/*
 mpatch.c - efficient binary patching for Mercurial

 This implements a patch algorithm that's O(m + nlog n) where m is the
 size of the output and n is the number of patches.

 Given a list of binary patches, it unpacks each into a hunk list,
 then combines the hunk lists with a treewise recursion to form a
 single hunk list. This hunk list is then applied to the original
 text.

 The text (or binary) fragments are copied directly from their source
 Python objects into a preallocated output string to avoid the
 allocation of intermediate Python objects. Working memory is about 2x
 the total number of hunks.

 Copyright 2005, 2006 Matt Mackall <[e-mail]>

 This software may be used and distributed according to the terms
 of the GNU General Public License, incorporated herein by reference.
*/

#define PY_SSIZE_T_CLEAN
#include <Python.h>
#include <stdlib.h>
#include <string.h>

#include "util.h"

static char mpatch_doc[] = "Efficient binary patching.";
static PyObject *mpatch_Error;

struct frag {
	int start, end, len;
	const char *data;
};

struct flist {
	struct frag *base, *head, *tail;
};

static struct flist *lalloc(Py_ssize_t size)
{
	struct flist *a = NULL;

	if (size < 1)
		size = 1;

	a = (struct flist *)malloc(sizeof(struct flist));
	if (a) {
		a->base = (struct frag *)malloc(sizeof(struct frag) * size);
		if (a->base) {
			a->head = a->tail = a->base;
			return a;
		}
		free(a);
		a = NULL;
	}
	if (!PyErr_Occurred())
		PyErr_NoMemory();
	return NULL;
}

static void lfree(struct flist *a)
{
	if (a) {
		free(a->base);
		free(a);
	}
}

static Py_ssize_t lsize(struct flist *a)
{
	return a->tail - a->head;
}

/* move hunks in source that are less cut to dest, compensating
   for changes in offset. the last hunk may be split if necessary.
*/
static int gather(struct flist *dest, struct flist *src, int cut, int offset)
{
	struct frag *d = dest->tail, *s = src->head;
	int postend, c, l;

	while (s != src->tail) {
		if (s->start + offset >= cut)
			break; /* we've gone far enough */

		postend = offset + s->start + s->len;
		if (postend <= cut) {
			/* save this hunk */
			offset += s->start + s->len - s->end;
			*d++ = *s++;
		}
		else {
			/* break up this hunk */
			c = cut - offset;
			if (s->end < c)
				c = s->end;
			l = cut - offset - s->start;
			if (s->len < l)
				l = s->len;

			offset += s->start + l - c;

			d->start = s->start;
			d->end = c;
			d->len = l;
			d->data = s->data;
			d++;
			s->start = c;
			s->len = s->len - l;
			s->data = s->data + l;

			break;
		}
	}

	dest->tail = d;
	src->head = s;
	return offset;
}

/* like gather, but with no output list */
static int discard(struct flist *src, int cut, int offset)
{
	struct frag *s = src->head;
	int postend, c, l;

	while (s != src->tail) {
		if (s->start + offset >= cut)
			break;

		postend = offset + s->start + s->len;
		if (postend <= cut) {
			offset += s->start + s->len - s->end;
			s++;
		}
		else {
			c = cut - offset;
			if (s->end < c)
				c = s->end;
			l = cut - offset - s->start;
			if (s->len < l)
				l = s->len;

			offset += s->start + l - c;
			s->start = c;
			s->len = s->len - l;
			s->data = s->data + l;

			break;
		}
	}

	src->head = s;
	return offset;
}

/* combine hunk lists a and b, while adjusting b for offset changes in a/
   this deletes a and b and returns the resultant list. */
static struct flist *combine(struct flist *a, struct flist *b)
{
	struct flist *c = NULL;
	struct frag *bh, *ct;
	int offset = 0, post;

	if (a && b)
		c = lalloc((lsize(a) + lsize(b)) * 2);

	if (c) {

		for (bh = b->head; bh != b->tail; bh++) {
			/* save old hunks */
			offset = gather(c, a, bh->start, offset);

			/* discard replaced hunks */
			post = discard(a, bh->end, offset);

			/* insert new hunk */
			ct = c->tail;
			ct->start = bh->start - offset;
			ct->end = bh->end - post;
			ct->len = bh->len;
			ct->data = bh->data;
			c->tail++;
			offset = post;
		}

		/* hold on to tail from a */
		memcpy(c->tail, a->head, sizeof(struct frag) * lsize(a));
		c->tail += lsize(a);
	}

	lfree(a);
	lfree(b);
	return c;
}

/* decode a binary patch into a hunk list */
static struct flist *decode(const char *bin, Py_ssize_t len)
{
	struct flist *l;
	struct frag *lt;
	int pos = 0;

	/* assume worst case size, we won't have many of these lists */
	l = lalloc(len / 12 + 1);
	if (!l)
		return NULL;

	lt = l->tail;

	while (pos >= 0 && pos < len) {
		lt->start = getbe32(bin + pos);
		lt->end = getbe32(bin + pos + 4);
		lt->len = getbe32(bin + pos + 8);
		lt->data = bin + pos + 12;
		pos += 12 + lt->len;
		if (lt->start > lt->end || lt->len < 0)
			break; /* sanity check */
		lt++;
	}

	if (pos != len) {
		if (!PyErr_Occurred())
			PyErr_SetString(mpatch_Error, "patch cannot be decoded");
		lfree(l);
		return NULL;
	}

	l->tail = lt;
	return l;
}

/* calculate the size of resultant text */
static Py_ssize_t calcsize(Py_ssize_t len, struct flist *l)
{
	Py_ssize_t outlen = 0, last = 0;
	struct frag *f = l->head;

	while (f != l->tail) {
		if (f->start < last || f->end > len) {
			if (!PyErr_Occurred())
				PyErr_SetString(mpatch_Error,
				                "invalid patch");
			return -1;
		}
		outlen += f->start - last;
		last = f->end;
		outlen += f->len;
		f++;
	}

	outlen += len - last;
	return outlen;
}

static int apply(char *buf, const char *orig, Py_ssize_t len, struct flist *l)
{
	struct frag *f = l->head;
	int last = 0;
	char *p = buf;

	while (f != l->tail) {
		if (f->start < last || f->end > len) {
			if (!PyErr_Occurred())
				PyErr_SetString(mpatch_Error,
				                "invalid patch");
			return 0;
		}
		memcpy(p, orig + last, f->start - last);
		p += f->start - last;
		memcpy(p, f->data, f->len);
		last = f->end;
		p += f->len;
		f++;
	}
	memcpy(p, orig + last, len - last);
	return 1;
}

/* recursively generate a patch of all bins between start and end */
static struct flist *fold(PyObject *bins, Py_ssize_t start, Py_ssize_t end)
{
	Py_ssize_t len, blen;
	const char *buffer;

	if (start + 1 == end) {
		/* trivial case, output a decoded list */
		PyObject *tmp = PyList_GetItem(bins, start);
		if (!tmp)
			return NULL;
		if (PyObject_AsCharBuffer(tmp, &buffer, &blen))
			return NULL;
		return decode(buffer, blen);
	}

	/* divide and conquer, memory management is elsewhere */
	len = (end - start) / 2;
	return combine(fold(bins, start, start + len),
		       fold(bins, start + len, end));
}

static PyObject *
patches(PyObject *self, PyObject *args)
{
	PyObject *text, *bins, *result;
	struct flist *patch;
	const char *in;
	char *out;
	Py_ssize_t len, outlen, inlen;

	if (!PyArg_ParseTuple(args, "OO:mpatch", &text, &bins))
		return NULL;

	len = PyList_Size(bins);
	if (!len) {
		/* nothing to do */
		Py_INCREF(text);
		return text;
	}

	if (PyObject_AsCharBuffer(text, &in, &inlen))
		return NULL;

	patch = fold(bins, 0, len);
	if (!patch)
		return NULL;

	outlen = calcsize(inlen, patch);
	if (outlen < 0) {
		result = NULL;
		goto cleanup;
	}
	result = PyBytes_FromStringAndSize(NULL, outlen);
	if (!result) {
		result = NULL;
		goto cleanup;
	}
	out = PyBytes_AsString(result);
	if (!apply(out, in, inlen, patch)) {
		Py_DECREF(result);
		result = NULL;
	}
cleanup:
	lfree(patch);
	return result;
}

/* calculate size of a patched file directly */
static PyObject *
patchedsize(PyObject *self, PyObject *args)
{
	long orig, start, end, len, outlen = 0, last = 0, pos = 0;
	Py_ssize_t patchlen;
	char *bin;

	if (!PyArg_ParseTuple(args, "ls#", &orig, &bin, &patchlen))
		return NULL;

	while (pos >= 0 && pos < patchlen) {
		start = getbe32(bin + pos);
		end = getbe32(bin + pos + 4);
		len = getbe32(bin + pos + 8);
		if (start > end)
			break; /* sanity check */
		pos += 12 + len;
		outlen += start - last;
		last = end;
		outlen += len;
	}

	if (pos != patchlen) {
		if (!PyErr_Occurred())
			PyErr_SetString(mpatch_Error, "patch cannot be decoded");
		return NULL;
	}

	outlen += orig - last;
	return Py_BuildValue("l", outlen);
}

static PyMethodDef methods[] = {
	{"patches", patches, METH_VARARGS, "apply a series of patches\n"},
	{"patchedsize", patchedsize, METH_VARARGS, "calculed patched size\n"},
	{NULL, NULL}
};

#ifdef IS_PY3K
static struct PyModuleDef mpatch_module = {
	PyModuleDef_HEAD_INIT,
	"mpatch",
	mpatch_doc,
	-1,
	methods
};

PyMODINIT_FUNC PyInit_mpatch(void)
{
	PyObject *m;

	m = PyModule_Create(&mpatch_module);
	if (m == NULL)
		return NULL;

	mpatch_Error = PyErr_NewException("mercurial.mpatch.mpatchError",
					  NULL, NULL);
	Py_INCREF(mpatch_Error);
	PyModule_AddObject(m, "mpatchError", mpatch_Error);

	return m;
}
#else
PyMODINIT_FUNC
initmpatch(void)
{
	Py_InitModule3("mpatch", methods, mpatch_doc);
	mpatch_Error = PyErr_NewException("mercurial.mpatch.mpatchError",
					  NULL, NULL);
}
#endif