hg: obtain lock when creating share from pooled repo (issue5104)
There are race conditions between clients performing a shared clone
to pooled storage:
1) Clients race to create the new shared repo in the pool directory
2) 1 client is seeding the repo in the pool directory and another goes
to share it before it is fully cloned
We prevent these race conditions by obtaining a lock in the pool
directory that is derived from the name of the repo we will be
accessing.
To test this, a simple generic "lockdelay" extension has been added.
The extension inserts an optional, configurable delay before or after
lock acquisition. In the test, we delay 2 seconds after lock acquisition
in the first process and 1 second before lock acquisition in the 2nd
process. This means the first process has 1s to obtain the lock. There
is a race condition here. If we encounter it in the wild, we could
change the dummy extension to wait on the lock file to appear instead
of relying on timing. But that's more complicated. Let's see what
happens first.
/*
* diffhelpers.c - helper routines for mpatch
*
* Copyright 2007 Chris Mason <chris.mason@oracle.com>
*
* This software may be used and distributed according to the terms
* of the GNU General Public License v2, incorporated herein by reference.
*/
#include <Python.h>
#include <stdlib.h>
#include <string.h>
#include "util.h"
static char diffhelpers_doc[] = "Efficient diff parsing";
static PyObject *diffhelpers_Error;
/* fixup the last lines of a and b when the patch has no newline at eof */
static void _fix_newline(PyObject *hunk, PyObject *a, PyObject *b)
{
Py_ssize_t hunksz = PyList_Size(hunk);
PyObject *s = PyList_GET_ITEM(hunk, hunksz-1);
char *l = PyBytes_AsString(s);
Py_ssize_t alen = PyList_Size(a);
Py_ssize_t blen = PyList_Size(b);
char c = l[0];
PyObject *hline;
Py_ssize_t sz = PyBytes_GET_SIZE(s);
if (sz > 1 && l[sz-2] == '\r')
/* tolerate CRLF in last line */
sz -= 1;
hline = PyBytes_FromStringAndSize(l, sz-1);
if (!hline) {
return;
}
if (c == ' ' || c == '+') {
PyObject *rline = PyBytes_FromStringAndSize(l + 1, sz - 2);
PyList_SetItem(b, blen-1, rline);
}
if (c == ' ' || c == '-') {
Py_INCREF(hline);
PyList_SetItem(a, alen-1, hline);
}
PyList_SetItem(hunk, hunksz-1, hline);
}
/* python callable form of _fix_newline */
static PyObject *
fix_newline(PyObject *self, PyObject *args)
{
PyObject *hunk, *a, *b;
if (!PyArg_ParseTuple(args, "OOO", &hunk, &a, &b))
return NULL;
_fix_newline(hunk, a, b);
return Py_BuildValue("l", 0);
}
#if (PY_VERSION_HEX < 0x02050000)
static const char *addlines_format = "OOiiOO";
#else
static const char *addlines_format = "OOnnOO";
#endif
/*
* read lines from fp into the hunk. The hunk is parsed into two arrays
* a and b. a gets the old state of the text, b gets the new state
* The control char from the hunk is saved when inserting into a, but not b
* (for performance while deleting files)
*/
static PyObject *
addlines(PyObject *self, PyObject *args)
{
PyObject *fp, *hunk, *a, *b, *x;
Py_ssize_t i;
Py_ssize_t lena, lenb;
Py_ssize_t num;
Py_ssize_t todoa, todob;
char *s, c;
PyObject *l;
if (!PyArg_ParseTuple(args, addlines_format,
&fp, &hunk, &lena, &lenb, &a, &b))
return NULL;
while (1) {
todoa = lena - PyList_Size(a);
todob = lenb - PyList_Size(b);
num = todoa > todob ? todoa : todob;
if (num == 0)
break;
for (i = 0; i < num; i++) {
x = PyFile_GetLine(fp, 0);
s = PyBytes_AsString(x);
c = *s;
if (strcmp(s, "\\ No newline at end of file\n") == 0) {
_fix_newline(hunk, a, b);
continue;
}
if (c == '\n') {
/* Some patches may be missing the control char
* on empty lines. Supply a leading space. */
Py_DECREF(x);
x = PyBytes_FromString(" \n");
}
PyList_Append(hunk, x);
if (c == '+') {
l = PyBytes_FromString(s + 1);
PyList_Append(b, l);
Py_DECREF(l);
} else if (c == '-') {
PyList_Append(a, x);
} else {
l = PyBytes_FromString(s + 1);
PyList_Append(b, l);
Py_DECREF(l);
PyList_Append(a, x);
}
Py_DECREF(x);
}
}
return Py_BuildValue("l", 0);
}
/*
* compare the lines in a with the lines in b. a is assumed to have
* a control char at the start of each line, this char is ignored in the
* compare
*/
static PyObject *
testhunk(PyObject *self, PyObject *args)
{
PyObject *a, *b;
long bstart;
Py_ssize_t alen, blen;
Py_ssize_t i;
char *sa, *sb;
if (!PyArg_ParseTuple(args, "OOl", &a, &b, &bstart))
return NULL;
alen = PyList_Size(a);
blen = PyList_Size(b);
if (alen > blen - bstart || bstart < 0) {
return Py_BuildValue("l", -1);
}
for (i = 0; i < alen; i++) {
sa = PyBytes_AsString(PyList_GET_ITEM(a, i));
sb = PyBytes_AsString(PyList_GET_ITEM(b, i + bstart));
if (strcmp(sa + 1, sb) != 0)
return Py_BuildValue("l", -1);
}
return Py_BuildValue("l", 0);
}
static PyMethodDef methods[] = {
{"addlines", addlines, METH_VARARGS, "add lines to a hunk\n"},
{"fix_newline", fix_newline, METH_VARARGS, "fixup newline counters\n"},
{"testhunk", testhunk, METH_VARARGS, "test lines in a hunk\n"},
{NULL, NULL}
};
#ifdef IS_PY3K
static struct PyModuleDef diffhelpers_module = {
PyModuleDef_HEAD_INIT,
"diffhelpers",
diffhelpers_doc,
-1,
methods
};
PyMODINIT_FUNC PyInit_diffhelpers(void)
{
PyObject *m;
m = PyModule_Create(&diffhelpers_module);
if (m == NULL)
return NULL;
diffhelpers_Error = PyErr_NewException("diffhelpers.diffhelpersError",
NULL, NULL);
Py_INCREF(diffhelpers_Error);
PyModule_AddObject(m, "diffhelpersError", diffhelpers_Error);
return m;
}
#else
PyMODINIT_FUNC
initdiffhelpers(void)
{
Py_InitModule3("diffhelpers", methods, diffhelpers_doc);
diffhelpers_Error = PyErr_NewException("diffhelpers.diffhelpersError",
NULL, NULL);
}
#endif