hgdemandimport: apply lazy module loading to sys.meta_path finders
Python's `sys.meta_path` finders are the primary objects whose job it
is to find a module at import time. When `import` is called, Python
iterates objects in this list and calls `o.find_spec(...)` to find
a `ModuleSpec` (or None if the module couldn't be found by that
finder). If no meta path finder can find a module, import fails.
One of the default meta path finders is `PathFinder`. Its job is to
import modules from the filesystem and is probably the most important
importer. This finder looks at `sys.path` and `sys.path_hooks` to do
its job.
The `ModuleSpec` returned by `MetaPathImporter.find_spec()` has a
`loader` attribute, which defines the concrete module loader to use.
`sys.path_hooks` is a hook point for teaching `PathFinder` to
instantiate custom loader types.
Previously, we injected a custom `sys.path_hook` that told `PathFinder`
to wrap the default loaders with a loader that creates a module object
that is lazy.
This approach worked. But its main limitation was that it only applied
to the `PathFinder` meta path importer. There are other meta path
importers that are registered. And in the case of PyOxidizer loading
modules from memory, `PathFinder` doesn't come into play since
PyOxidizer's own meta path importer was handling all imports.
This commit changes our approach to lazy module loading by proxying
all meta path importers. Specifically, we overload the `find_spec()`
method to swap in a wrapped loader on the `ModuleSpec` before it
is returned. The end result of this is all meta path importers should
be lazy.
As much as I would have loved to utilize .__class__ manipulation to
achieve this, some meta path importers are implemented in C/Rust
in such a way that they cannot be monkeypatched. This is why we
use __getattribute__ to define a proxy.
Also, this change could theoretically open us up to regressions in
meta path importers whose loader is creating module objects which
can't be monkeypatched. But I'm not aware of any of these in the
wild. So I think we'll be safe.
According to hyperfine, this change yields a decent startup time win of
5-6ms:
```
Benchmark #1: ~/.pyenv/versions/3.6.10/bin/python ./hg version
Time (mean ± σ): 86.8 ms ± 0.5 ms [User: 78.0 ms, System: 8.7 ms]
Range (min … max): 86.0 ms … 89.1 ms 50 runs
Time (mean ± σ): 81.1 ms ± 2.7 ms [User: 74.5 ms, System: 6.5 ms]
Range (min … max): 77.8 ms … 90.5 ms 50 runs
Benchmark #2: ~/.pyenv/versions/3.7.6/bin/python ./hg version
Time (mean ± σ): 78.9 ms ± 0.6 ms [User: 70.2 ms, System: 8.7 ms]
Range (min … max): 78.1 ms … 81.2 ms 50 runs
Time (mean ± σ): 73.4 ms ± 0.6 ms [User: 65.3 ms, System: 8.0 ms]
Range (min … max): 72.4 ms … 75.7 ms 50 runs
Benchmark #3: ~/.pyenv/versions/3.8.1/bin/python ./hg version
Time (mean ± σ): 78.1 ms ± 0.6 ms [User: 70.2 ms, System: 7.9 ms]
Range (min … max): 77.4 ms … 80.9 ms 50 runs
Time (mean ± σ): 72.1 ms ± 0.4 ms [User: 64.4 ms, System: 7.6 ms]
Range (min … max): 71.4 ms … 74.1 ms 50 runs
```
Differential Revision: https://phab.mercurial-scm.org/D7954
/*
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, PY23("s#:lowerencode", "y#: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 = PyImport_ImportModule("hashlib");
if (hashlib == NULL) {
PyErr_SetString(PyExc_ImportError,
"pathencode failed to find hashlib");
return -1;
}
shafunc = PyObject_GetAttrString(hashlib, "sha1");
Py_DECREF(hashlib);
if (shafunc == NULL) {
PyErr_SetString(PyExc_AttributeError,
"module 'hashlib' has no "
"attribute 'sha1' in pathencode");
return -1;
}
}
shaobj = PyObject_CallFunction(shafunc, PY23("s#", "y#"), 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;
}