[PATCH 2 of 5 v5] store: implement fncache basic path encoding in C
Bryan O'Sullivan
bos at serpentine.com
Mon Sep 10 15:34:59 CDT 2012
# HG changeset patch
# User Bryan O'Sullivan <bryano at fb.com>
# Date 1347309263 25200
# Node ID 16373c8d5e1d3bba4383184993c8382362c2db47
# Parent bb0216c05e3f9d11269667edb4cc2975377d5054
store: implement fncache basic path encoding in C
(This is not yet enabled; it will be turned on in a followup patch.)
The path encoding performed by fncache is complex and (perhaps
surprisingly) slow enough to negatively affect the overall performance
of Mercurial.
For a short path (< 120 bytes), the Python code can be reduced to a fairly
tractable state machine that either determines that nothing needs to be
done in a single pass, or performs the encoding in a second pass.
For longer paths, we avoid the more complicated hashed encoding scheme
for now, and fall back to Python.
Raw performance: I measured in a repo containing 150,000 files in its tip
manifest, with a median path name length of 57 bytes, and 95th percentile
of 96 bytes.
In this repo, the Python code takes 3.1 seconds to encode all path
names, while the hybrid C-and-Python code (called from Python) takes
0.21 seconds, for a speedup of about 14.
Across several other large repositories, I've measured the speedup from
the C code at between 26x and 40x.
For path names above 120 bytes where we must fall back to Python for
hashed encoding, the speedup is about 1.7x. Thus absolute performance
will depend strongly on the characteristics of a particular repository.
diff --git a/mercurial/parsers.c b/mercurial/parsers.c
--- a/mercurial/parsers.c
+++ b/mercurial/parsers.c
@@ -1506,11 +1506,14 @@
static char parsers_doc[] = "Efficient content parsing.";
+PyObject *pathencode(PyObject *self, PyObject *args);
+
static PyMethodDef methods[] = {
{"pack_dirstate", pack_dirstate, METH_VARARGS, "pack a dirstate\n"},
{"parse_manifest", parse_manifest, METH_VARARGS, "parse a manifest\n"},
{"parse_dirstate", parse_dirstate, METH_VARARGS, "parse a dirstate\n"},
{"parse_index2", parse_index2, METH_VARARGS, "parse a revlog index\n"},
+ {"pathencode", pathencode, METH_VARARGS, "fncache-encode a path\n"},
{NULL, NULL}
};
diff --git a/mercurial/pathencode.c b/mercurial/pathencode.c
new file mode 100644
--- /dev/null
+++ b/mercurial/pathencode.c
@@ -0,0 +1,437 @@
+/*
+ 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.
+ */
+
+#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 */
+};
+
+static inline int isset(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 _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 (isset(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 (isset(onebyte, src[i])) {
+ do {
+ charcopy(dest, &destlen,
+ destsize, src[i++]);
+ } while (i < len &&
+ isset(onebyte, src[i]));
+ }
+ else if (isset(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;
+
+ if (len < 5 || memcmp(src, "data/", 5) != 0) {
+ memcopy(dest, &destlen, destsize, src, len);
+ return destlen;
+ }
+
+ memcopy(dest, &destlen, destsize, "data/", 5);
+
+ return _encode(twobytes, onebyte, dest, destlen, destsize,
+ src + 5, len - 5, 1);
+}
+
+static const Py_ssize_t maxstorepathlen = 120;
+
+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 (PyString_AsStringAndSize(pathobj, &path, &len) == -1) {
+ PyErr_SetString(PyExc_TypeError, "expected a string");
+ return NULL;
+ }
+
+ newlen = len ? basicencode(NULL, 0, path, len + 1) : 1;
+
+ if (newlen <= maxstorepathlen + 1) {
+ if (newlen == len + 1) {
+ Py_INCREF(pathobj);
+ return pathobj;
+ }
+
+ newobj = PyString_FromStringAndSize(NULL, newlen);
+
+ if (newobj) {
+ PyString_GET_SIZE(newobj)--;
+ basicencode(PyString_AS_STRING(newobj), newlen, path,
+ len + 1);
+ }
+ } else {
+ newobj = Py_None;
+ Py_INCREF(newobj);
+ }
+
+ return newobj;
+}
diff --git a/mercurial/util.h b/mercurial/util.h
--- a/mercurial/util.h
+++ b/mercurial/util.h
@@ -121,6 +121,7 @@
#ifdef _MSC_VER
/* msvc 6.0 has problems */
#define inline __inline
+typedef unsigned char uint8_t;
typedef unsigned long uint32_t;
typedef unsigned __int64 uint64_t;
#else
diff --git a/setup.py b/setup.py
--- a/setup.py
+++ b/setup.py
@@ -421,7 +421,8 @@
Extension('mercurial.bdiff', ['mercurial/bdiff.c']),
Extension('mercurial.diffhelpers', ['mercurial/diffhelpers.c']),
Extension('mercurial.mpatch', ['mercurial/mpatch.c']),
- Extension('mercurial.parsers', ['mercurial/parsers.c']),
+ Extension('mercurial.parsers', ['mercurial/parsers.c',
+ 'mercurial/pathencode.c']),
]
osutil_ldflags = []
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