view mercurial/pathencode.c @ 30451:94ca0e13d1fc

perf: add command for measuring revlog chunk operations

Upcoming commits will teach revlogs to leverage the new compression
engine API so that new compression formats can more easily be
leveraged in revlogs. We want to be sure this refactoring doesn't
regress performance. So this commit introduces "perfrevchunks" to
explicitly test performance of reading, decompressing, and
recompressing revlog chunks.

Here is output when run on the mozilla-unified repo:

$ hg perfrevlogchunks -c
! read
! wall 0.346603 comb 0.350000 user 0.340000 sys 0.010000 (best of 28)
! read w/ reused fd
! wall 0.337707 comb 0.340000 user 0.320000 sys 0.020000 (best of 30)
! read batch
! wall 0.013206 comb 0.020000 user 0.000000 sys 0.020000 (best of 221)
! read batch w/ reused fd
! wall 0.013259 comb 0.030000 user 0.010000 sys 0.020000 (best of 222)
! chunk
! wall 1.909939 comb 1.910000 user 1.900000 sys 0.010000 (best of 6)
! chunk batch
! wall 1.750677 comb 1.760000 user 1.740000 sys 0.020000 (best of 6)
! compress
! wall 5.668004 comb 5.670000 user 5.670000 sys 0.000000 (best of 3)

$ hg perfrevlogchunks -m
! read
! wall 0.365834 comb 0.370000 user 0.350000 sys 0.020000 (best of 26)
! read w/ reused fd
! wall 0.350160 comb 0.350000 user 0.320000 sys 0.030000 (best of 28)
! read batch
! wall 0.024777 comb 0.020000 user 0.000000 sys 0.020000 (best of 119)
! read batch w/ reused fd
! wall 0.024895 comb 0.030000 user 0.000000 sys 0.030000 (best of 118)
! chunk
! wall 2.514061 comb 2.520000 user 2.480000 sys 0.040000 (best of 4)
! chunk batch
! wall 2.380788 comb 2.380000 user 2.360000 sys 0.020000 (best of 5)
! compress
! wall 9.815297 comb 9.820000 user 9.820000 sys 0.000000 (best of 3)

We already see some interesting data, such as how much slower
non-batched chunk reading is and that zlib compression appears to be
>2x slower than decompression.

I didn't have the data when I wrote this commit message, but I ran this
on Mozilla's NFS-based Mercurial server and the time for reading with a
reused file descriptor was faster. So I think it is worth testing both
with and without file descriptor reuse so we can make informed
decisions about recycling file descriptors.

/*
 pathencode.c - efficient path name encoding

 Copyright 2012 Facebook

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

/*
 * An implementation of the name encoding scheme used by the fncache
 * store.  The common case is of a path < 120 bytes long, which is
 * handled either in a single pass with no allocations or two passes
 * with a single allocation.  For longer paths, multiple passes are
 * required.
 */

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

#include "util.h"

/* state machine for the fast path */
enum path_state {
	START,   /* first byte of a path component */
	A,       /* "AUX" */
	AU,
	THIRD,   /* third of a 3-byte sequence, e.g. "AUX", "NUL" */
	C,       /* "CON" or "COMn" */
	CO,
	COMLPT,  /* "COM" or "LPT" */
	COMLPTn,
	L,
	LP,
	N,
	NU,
	P,       /* "PRN" */
	PR,
	LDOT,    /* leading '.' */
	DOT,     /* '.' in a non-leading position */
	H,       /* ".h" */
	HGDI,    /* ".hg", ".d", or ".i" */
	SPACE,
	DEFAULT  /* byte of a path component after the first */
};

/* state machine for dir-encoding */
enum dir_state {
	DDOT,
	DH,
	DHGDI,
	DDEFAULT
};

static inline int inset(const uint32_t bitset[], char c)
{
	return bitset[((uint8_t)c) >> 5] & (1 << (((uint8_t)c) & 31));
}

static inline void charcopy(char *dest, Py_ssize_t *destlen, size_t destsize,
                            char c)
{
	if (dest) {
		assert(*destlen < destsize);
		dest[*destlen] = c;
	}
	(*destlen)++;
}

static inline void memcopy(char *dest, Py_ssize_t *destlen, size_t destsize,
                           const void *src, Py_ssize_t len)
{
	if (dest) {
		assert(*destlen + len < destsize);
		memcpy((void *)&dest[*destlen], src, len);
	}
	*destlen += len;
}

static inline void hexencode(char *dest, Py_ssize_t *destlen, size_t destsize,
			     uint8_t c)
{
	static const char hexdigit[] = "0123456789abcdef";

	charcopy(dest, destlen, destsize, hexdigit[c >> 4]);
	charcopy(dest, destlen, destsize, hexdigit[c & 15]);
}

/* 3-byte escape: tilde followed by two hex digits */
static inline void escape3(char *dest, Py_ssize_t *destlen, size_t destsize,
			   char c)
{
	charcopy(dest, destlen, destsize, '~');
	hexencode(dest, destlen, destsize, c);
}

static Py_ssize_t _encodedir(char *dest, size_t destsize,
                             const char *src, Py_ssize_t len)
{
	enum dir_state state = DDEFAULT;
	Py_ssize_t i = 0, destlen = 0;

	while (i < len) {
		switch (state) {
		case DDOT:
			switch (src[i]) {
			case 'd':
			case 'i':
				state = DHGDI;
				charcopy(dest, &destlen, destsize, src[i++]);
				break;
			case 'h':
				state = DH;
				charcopy(dest, &destlen, destsize, src[i++]);
				break;
			default:
				state = DDEFAULT;
				break;
			}
			break;
		case DH:
			if (src[i] == 'g') {
				state = DHGDI;
				charcopy(dest, &destlen, destsize, src[i++]);
			}
			else state = DDEFAULT;
			break;
		case DHGDI:
			if (src[i] == '/') {
				memcopy(dest, &destlen, destsize, ".hg", 3);
				charcopy(dest, &destlen, destsize, src[i++]);
			}
			state = DDEFAULT;
			break;
		case DDEFAULT:
			if (src[i] == '.')
				state = DDOT;
			charcopy(dest, &destlen, destsize, src[i++]);
			break;
		}
	}

	return destlen;
}

PyObject *encodedir(PyObject *self, PyObject *args)
{
	Py_ssize_t len, newlen;
	PyObject *pathobj, *newobj;
	char *path;

	if (!PyArg_ParseTuple(args, "O:encodedir", &pathobj))
		return NULL;

	if (PyBytes_AsStringAndSize(pathobj, &path, &len) == -1) {
		PyErr_SetString(PyExc_TypeError, "expected a string");
		return NULL;
	}

	newlen = len ? _encodedir(NULL, 0, path, len + 1) : 1;

	if (newlen == len + 1) {
		Py_INCREF(pathobj);
		return pathobj;
	}

	newobj = PyBytes_FromStringAndSize(NULL, newlen);

	if (newobj) {
		assert(PyBytes_Check(newobj));
		Py_SIZE(newobj)--;
		_encodedir(PyBytes_AS_STRING(newobj), newlen, path,
			   len + 1);
	}

	return newobj;
}

static Py_ssize_t _encode(const uint32_t twobytes[8], const uint32_t onebyte[8],
			  char *dest, Py_ssize_t destlen, size_t destsize,
			  const char *src, Py_ssize_t len,
			  int encodedir)
{
	enum path_state state = START;
	Py_ssize_t i = 0;

	/*
	 * Python strings end with a zero byte, which we use as a
	 * terminal token as they are not valid inside path names.
	 */

	while (i < len) {
		switch (state) {
		case START:
			switch (src[i]) {
			case '/':
				charcopy(dest, &destlen, destsize, src[i++]);
				break;
			case '.':
				state = LDOT;
				escape3(dest, &destlen, destsize, src[i++]);
				break;
			case ' ':
				state = DEFAULT;
				escape3(dest, &destlen, destsize, src[i++]);
				break;
			case 'a':
				state = A;
				charcopy(dest, &destlen, destsize, src[i++]);
				break;
			case 'c':
				state = C;
				charcopy(dest, &destlen, destsize, src[i++]);
				break;
			case 'l':
				state = L;
				charcopy(dest, &destlen, destsize, src[i++]);
				break;
			case 'n':
				state = N;
				charcopy(dest, &destlen, destsize, src[i++]);
				break;
			case 'p':
				state = P;
				charcopy(dest, &destlen, destsize, src[i++]);
				break;
			default:
				state = DEFAULT;
				break;
			}
			break;
		case A:
			if (src[i] == 'u') {
				state = AU;
				charcopy(dest, &destlen, destsize, src[i++]);
			}
			else state = DEFAULT;
			break;
		case AU:
			if (src[i] == 'x') {
				state = THIRD;
				i++;
			}
			else state = DEFAULT;
			break;
		case THIRD:
			state = DEFAULT;
			switch (src[i]) {
			case '.':
			case '/':
			case '\0':
				escape3(dest, &destlen, destsize, src[i - 1]);
				break;
			default:
				i--;
				break;
			}
			break;
		case C:
			if (src[i] == 'o') {
				state = CO;
				charcopy(dest, &destlen, destsize, src[i++]);
			}
			else state = DEFAULT;
			break;
		case CO:
			if (src[i] == 'm') {
				state = COMLPT;
				i++;
			}
			else if (src[i] == 'n') {
				state = THIRD;
				i++;
			}
			else state = DEFAULT;
			break;
		case COMLPT:
			switch (src[i]) {
			case '1': case '2': case '3': case '4': case '5':
			case '6': case '7': case '8': case '9':
				state = COMLPTn;
				i++;
				break;
			default:
				state = DEFAULT;
				charcopy(dest, &destlen, destsize, src[i - 1]);
				break;
			}
			break;
		case COMLPTn:
			state = DEFAULT;
			switch (src[i]) {
			case '.':
			case '/':
			case '\0':
				escape3(dest, &destlen, destsize, src[i - 2]);
				charcopy(dest, &destlen, destsize, src[i - 1]);
				break;
			default:
				memcopy(dest, &destlen, destsize,
					&src[i - 2], 2);
				break;
			}
			break;
		case L:
			if (src[i] == 'p') {
				state = LP;
				charcopy(dest, &destlen, destsize, src[i++]);
			}
			else state = DEFAULT;
			break;
		case LP:
			if (src[i] == 't') {
				state = COMLPT;
				i++;
			}
			else state = DEFAULT;
			break;
		case N:
			if (src[i] == 'u') {
				state = NU;
				charcopy(dest, &destlen, destsize, src[i++]);
			}
			else state = DEFAULT;
			break;
		case NU:
			if (src[i] == 'l') {
				state = THIRD;
				i++;
			}
			else state = DEFAULT;
			break;
		case P:
			if (src[i] == 'r') {
				state = PR;
				charcopy(dest, &destlen, destsize, src[i++]);
			}
			else state = DEFAULT;
			break;
		case PR:
			if (src[i] == 'n') {
				state = THIRD;
				i++;
			}
			else state = DEFAULT;
			break;
		case LDOT:
			switch (src[i]) {
			case 'd':
			case 'i':
				state = HGDI;
				charcopy(dest, &destlen, destsize, src[i++]);
				break;
			case 'h':
				state = H;
				charcopy(dest, &destlen, destsize, src[i++]);
				break;
			default:
				state = DEFAULT;
				break;
			}
			break;
		case DOT:
			switch (src[i]) {
			case '/':
			case '\0':
				state = START;
				memcopy(dest, &destlen, destsize, "~2e", 3);
				charcopy(dest, &destlen, destsize, src[i++]);
				break;
			case 'd':
			case 'i':
				state = HGDI;
				charcopy(dest, &destlen, destsize, '.');
				charcopy(dest, &destlen, destsize, src[i++]);
				break;
			case 'h':
				state = H;
				memcopy(dest, &destlen, destsize, ".h", 2);
				i++;
				break;
			default:
				state = DEFAULT;
				charcopy(dest, &destlen, destsize, '.');
				break;
			}
			break;
		case H:
			if (src[i] == 'g') {
				state = HGDI;
				charcopy(dest, &destlen, destsize, src[i++]);
			}
			else state = DEFAULT;
			break;
		case HGDI:
			if (src[i] == '/') {
				state = START;
				if (encodedir)
					memcopy(dest, &destlen, destsize, ".hg",
						3);
				charcopy(dest, &destlen, destsize, src[i++]);
			}
			else state = DEFAULT;
			break;
		case SPACE:
			switch (src[i]) {
			case '/':
			case '\0':
				state = START;
				memcopy(dest, &destlen, destsize, "~20", 3);
				charcopy(dest, &destlen, destsize, src[i++]);
				break;
			default:
				state = DEFAULT;
				charcopy(dest, &destlen, destsize, ' ');
				break;
			}
			break;
		case DEFAULT:
			while (inset(onebyte, src[i])) {
				charcopy(dest, &destlen, destsize, src[i++]);
				if (i == len)
					goto done;
			}
			switch (src[i]) {
			case '.':
				state = DOT;
				i++;
				break;
			case ' ':
				state = SPACE;
				i++;
				break;
			case '/':
				state = START;
				charcopy(dest, &destlen, destsize, '/');
				i++;
				break;
			default:
				if (inset(onebyte, src[i])) {
					do {
						charcopy(dest, &destlen,
							 destsize, src[i++]);
					} while (i < len &&
						 inset(onebyte, src[i]));
				}
				else if (inset(twobytes, src[i])) {
					char c = src[i++];
					charcopy(dest, &destlen, destsize, '_');
					charcopy(dest, &destlen, destsize,
						 c == '_' ? '_' : c + 32);
				}
				else
					escape3(dest, &destlen, destsize,
						src[i++]);
				break;
			}
			break;
		}
	}
done:
	return destlen;
}

static Py_ssize_t basicencode(char *dest, size_t destsize,
			      const char *src, Py_ssize_t len)
{
	static const uint32_t twobytes[8] = { 0, 0, 0x87fffffe };

	static const uint32_t onebyte[8] = {
		1, 0x2bff3bfa, 0x68000001, 0x2fffffff,
	};

	Py_ssize_t destlen = 0;

	return _encode(twobytes, onebyte, dest, destlen, destsize,
		       src, len, 1);
}

static const Py_ssize_t maxstorepathlen = 120;

static Py_ssize_t _lowerencode(char *dest, size_t destsize,
			       const char *src, Py_ssize_t len)
{
	static const uint32_t onebyte[8] = {
		1, 0x2bfffbfb, 0xe8000001, 0x2fffffff
	};

	static const uint32_t lower[8] = { 0, 0, 0x7fffffe };

	Py_ssize_t i, destlen = 0;

	for (i = 0; i < len; i++) {
		if (inset(onebyte, src[i]))
			charcopy(dest, &destlen, destsize, src[i]);
		else if (inset(lower, src[i]))
			charcopy(dest, &destlen, destsize, src[i] + 32);
		else
			escape3(dest, &destlen, destsize, src[i]);
	}

	return destlen;
}

PyObject *lowerencode(PyObject *self, PyObject *args)
{
	char *path;
	Py_ssize_t len, newlen;
	PyObject *ret;

	if (!PyArg_ParseTuple(args, "s#:lowerencode", &path, &len))
		return NULL;

	newlen = _lowerencode(NULL, 0, path, len);
	ret = PyBytes_FromStringAndSize(NULL, newlen);
	if (ret)
		_lowerencode(PyBytes_AS_STRING(ret), newlen, path, len);

	return ret;
}

/* See store.py:_auxencode for a description. */
static Py_ssize_t auxencode(char *dest, size_t destsize,
			    const char *src, Py_ssize_t len)
{
	static const uint32_t twobytes[8];

	static const uint32_t onebyte[8] = {
		~0U, 0xffff3ffe, ~0U, ~0U, ~0U, ~0U, ~0U, ~0U,
	};

	return _encode(twobytes, onebyte, dest, 0, destsize, src, len, 0);
}

static PyObject *hashmangle(const char *src, Py_ssize_t len, const char sha[20])
{
	static const Py_ssize_t dirprefixlen = 8;
	static const Py_ssize_t maxshortdirslen = 68;
	char *dest;
	PyObject *ret;

	Py_ssize_t i, d, p, lastslash = len - 1, lastdot = -1;
	Py_ssize_t destsize, destlen = 0, slop, used;

	while (lastslash >= 0 && src[lastslash] != '/') {
		if (src[lastslash] == '.' && lastdot == -1)
			lastdot = lastslash;
		lastslash--;
	}

#if 0
	/* All paths should end in a suffix of ".i" or ".d".
           Unfortunately, the file names in test-hybridencode.py
           violate this rule.  */
	if (lastdot != len - 3) {
		PyErr_SetString(PyExc_ValueError,
				"suffix missing or wrong length");
		return NULL;
	}
#endif

	/* If src contains a suffix, we will append it to the end of
	   the new string, so make room. */
	destsize = 120;
	if (lastdot >= 0)
		destsize += len - lastdot - 1;

	ret = PyBytes_FromStringAndSize(NULL, destsize);
	if (ret == NULL)
		return NULL;

	dest = PyBytes_AS_STRING(ret);
	memcopy(dest, &destlen, destsize, "dh/", 3);

	/* Copy up to dirprefixlen bytes of each path component, up to
	   a limit of maxshortdirslen bytes. */
	for (i = d = p = 0; i < lastslash; i++, p++) {
		if (src[i] == '/') {
			char d = dest[destlen - 1];
			/* After truncation, a directory name may end
			   in a space or dot, which are unportable. */
			if (d == '.' || d == ' ')
				dest[destlen - 1] = '_';
			/* The + 3 is to account for "dh/" in the beginning */
			if (destlen > maxshortdirslen + 3)
				break;
			charcopy(dest, &destlen, destsize, src[i]);
			p = -1;
		}
		else if (p < dirprefixlen)
			charcopy(dest, &destlen, destsize, src[i]);
	}

	/* Rewind to just before the last slash copied. */
	if (destlen > maxshortdirslen + 3)
		do {
			destlen--;
		} while (destlen > 0 && dest[destlen] != '/');

	if (destlen > 3) {
		if (lastslash > 0) {
			char d = dest[destlen - 1];
			/* The last directory component may be
			   truncated, so make it safe. */
			if (d == '.' || d == ' ')
				dest[destlen - 1] = '_';
		}

		charcopy(dest, &destlen, destsize, '/');
	}

	/* Add a prefix of the original file's name. Its length
	   depends on the number of bytes left after accounting for
	   hash and suffix. */
	used = destlen + 40;
	if (lastdot >= 0)
		used += len - lastdot - 1;
	slop = maxstorepathlen - used;
	if (slop > 0) {
		Py_ssize_t basenamelen =
			lastslash >= 0 ? len - lastslash - 2 : len - 1;

		if (basenamelen > slop)
			basenamelen = slop;
		if (basenamelen > 0)
			memcopy(dest, &destlen, destsize, &src[lastslash + 1],
				basenamelen);
	}

	/* Add hash and suffix. */
	for (i = 0; i < 20; i++)
		hexencode(dest, &destlen, destsize, sha[i]);

	if (lastdot >= 0)
		memcopy(dest, &destlen, destsize, &src[lastdot],
			len - lastdot - 1);

	assert(PyBytes_Check(ret));
	Py_SIZE(ret) = destlen;

	return ret;
}

/*
 * Avoiding a trip through Python would improve performance by 50%,
 * but we don't encounter enough long names to be worth the code.
 */
static int sha1hash(char hash[20], const char *str, Py_ssize_t len)
{
	static PyObject *shafunc;
	PyObject *shaobj, *hashobj;

	if (shafunc == NULL) {
		PyObject *hashlib, *name = PyBytes_FromString("hashlib");

		if (name == NULL)
			return -1;

		hashlib = PyImport_Import(name);
		Py_DECREF(name);

		if (hashlib == NULL) {
			PyErr_SetString(PyExc_ImportError, "hashlib");
			return -1;
		}
		shafunc = PyObject_GetAttrString(hashlib, "sha1");
		Py_DECREF(hashlib);

		if (shafunc == NULL) {
			PyErr_SetString(PyExc_AttributeError,
					"module 'hashlib' has no "
					"attribute 'sha1'");
			return -1;
		}
	}

	shaobj = PyObject_CallFunction(shafunc, "s#", str, len);

	if (shaobj == NULL)
		return -1;

	hashobj = PyObject_CallMethod(shaobj, "digest", "");
	Py_DECREF(shaobj);
	if (hashobj == NULL)
		return -1;

	if (!PyBytes_Check(hashobj) || PyBytes_GET_SIZE(hashobj) != 20) {
		PyErr_SetString(PyExc_TypeError,
				"result of digest is not a 20-byte hash");
		Py_DECREF(hashobj);
		return -1;
	}

	memcpy(hash, PyBytes_AS_STRING(hashobj), 20);
	Py_DECREF(hashobj);
	return 0;
}

#define MAXENCODE 4096 * 4

static PyObject *hashencode(const char *src, Py_ssize_t len)
{
	char dired[MAXENCODE];
	char lowered[MAXENCODE];
	char auxed[MAXENCODE];
	Py_ssize_t dirlen, lowerlen, auxlen, baselen;
	char sha[20];

	baselen = (len - 5) * 3;
	if (baselen >= MAXENCODE) {
		PyErr_SetString(PyExc_ValueError, "string too long");
		return NULL;
	}

	dirlen = _encodedir(dired, baselen, src, len);
	if (sha1hash(sha, dired, dirlen - 1) == -1)
		return NULL;
	lowerlen = _lowerencode(lowered, baselen, dired + 5, dirlen - 5);
	auxlen = auxencode(auxed, baselen, lowered, lowerlen);
	return hashmangle(auxed, auxlen, sha);
}

PyObject *pathencode(PyObject *self, PyObject *args)
{
	Py_ssize_t len, newlen;
	PyObject *pathobj, *newobj;
	char *path;

	if (!PyArg_ParseTuple(args, "O:pathencode", &pathobj))
		return NULL;

	if (PyBytes_AsStringAndSize(pathobj, &path, &len) == -1) {
		PyErr_SetString(PyExc_TypeError, "expected a string");
		return NULL;
	}

	if (len > maxstorepathlen)
		newlen = maxstorepathlen + 2;
	else
		newlen = len ? basicencode(NULL, 0, path, len + 1) : 1;

	if (newlen <= maxstorepathlen + 1) {
		if (newlen == len + 1) {
			Py_INCREF(pathobj);
			return pathobj;
		}

		newobj = PyBytes_FromStringAndSize(NULL, newlen);

		if (newobj) {
			assert(PyBytes_Check(newobj));
			Py_SIZE(newobj)--;
			basicencode(PyBytes_AS_STRING(newobj), newlen, path,
				    len + 1);
		}
	}
	else
		newobj = hashencode(path, len + 1);

	return newobj;
}