bisect: avoid copying ancestor list for non-merge commits
During a bisection, hg needs to compute a list of all ancestors for every
candidate commit. This is accomplished via a bottom-up traversal of the set of
candidates, during which each revision's ancestor list is populated using the
ancestor list of its parent(s). Previously, this involved copying the entire
list, which could be very long in if the bisection range was large.
To help improve this, we can observe that each candidate commit is visited
exactly once, at which point its ancestor list is copied into its children's
lists and then dropped. In the case of non-merge commits, a commit's ancestor
list consists exactly of its parent's list plus itself. This means that we can
trivially reuse the parent's existing list for one of its non-merge children,
which avoids copying entirely if that commit is the parent's only child. This
makes bisections over linear ranges of commits much faster.
During some informal testing in the large publicly-available `mozilla-central`
repository, this noticeably sped up bisections over large ranges of history:
Setup:
$ cd mozilla-central
$ hg bisect --reset
$ hg bisect --good 0
$ hg log -r tip -T '{rev}\n'
628417
Test:
$ time hg bisect --bad tip --noupdate
Before:
real 3m35.927s
user 3m35.553s
sys 0m0.319s
After:
real 1m41.142s
user 1m40.810s
sys 0m0.285s
/**
* Copyright (c) 2016-present, Gregory Szorc
* All rights reserved.
*
* This software may be modified and distributed under the terms
* of the BSD license. See the LICENSE file for details.
*/
#include "python-zstandard.h"
extern PyObject* ZstdError;
PyDoc_STRVAR(ZstdCompressionObj__doc__,
"Perform compression using a standard library compatible API.\n"
);
static void ZstdCompressionObj_dealloc(ZstdCompressionObj* self) {
PyMem_Free(self->output.dst);
self->output.dst = NULL;
Py_XDECREF(self->compressor);
PyObject_Del(self);
}
static PyObject* ZstdCompressionObj_compress(ZstdCompressionObj* self, PyObject* args, PyObject* kwargs) {
static char* kwlist[] = {
"data",
NULL
};
Py_buffer source;
ZSTD_inBuffer input;
size_t zresult;
PyObject* result = NULL;
Py_ssize_t resultSize = 0;
if (self->finished) {
PyErr_SetString(ZstdError, "cannot call compress() after compressor finished");
return NULL;
}
#if PY_MAJOR_VERSION >= 3
if (!PyArg_ParseTupleAndKeywords(args, kwargs, "y*:compress",
#else
if (!PyArg_ParseTupleAndKeywords(args, kwargs, "s*:compress",
#endif
kwlist, &source)) {
return NULL;
}
if (!PyBuffer_IsContiguous(&source, 'C') || source.ndim > 1) {
PyErr_SetString(PyExc_ValueError,
"data buffer should be contiguous and have at most one dimension");
goto finally;
}
input.src = source.buf;
input.size = source.len;
input.pos = 0;
while (input.pos < (size_t)source.len) {
Py_BEGIN_ALLOW_THREADS
zresult = ZSTD_compressStream2(self->compressor->cctx, &self->output,
&input, ZSTD_e_continue);
Py_END_ALLOW_THREADS
if (ZSTD_isError(zresult)) {
PyErr_Format(ZstdError, "zstd compress error: %s", ZSTD_getErrorName(zresult));
Py_CLEAR(result);
goto finally;
}
if (self->output.pos) {
if (result) {
resultSize = PyBytes_GET_SIZE(result);
if (safe_pybytes_resize(&result, resultSize + self->output.pos)) {
Py_CLEAR(result);
goto finally;
}
memcpy(PyBytes_AS_STRING(result) + resultSize,
self->output.dst, self->output.pos);
}
else {
result = PyBytes_FromStringAndSize(self->output.dst, self->output.pos);
if (!result) {
goto finally;
}
}
self->output.pos = 0;
}
}
if (NULL == result) {
result = PyBytes_FromString("");
}
finally:
PyBuffer_Release(&source);
return result;
}
static PyObject* ZstdCompressionObj_flush(ZstdCompressionObj* self, PyObject* args, PyObject* kwargs) {
static char* kwlist[] = {
"flush_mode",
NULL
};
int flushMode = compressorobj_flush_finish;
size_t zresult;
PyObject* result = NULL;
Py_ssize_t resultSize = 0;
ZSTD_inBuffer input;
ZSTD_EndDirective zFlushMode;
if (!PyArg_ParseTupleAndKeywords(args, kwargs, "|i:flush", kwlist, &flushMode)) {
return NULL;
}
if (flushMode != compressorobj_flush_finish && flushMode != compressorobj_flush_block) {
PyErr_SetString(PyExc_ValueError, "flush mode not recognized");
return NULL;
}
if (self->finished) {
PyErr_SetString(ZstdError, "compressor object already finished");
return NULL;
}
switch (flushMode) {
case compressorobj_flush_block:
zFlushMode = ZSTD_e_flush;
break;
case compressorobj_flush_finish:
zFlushMode = ZSTD_e_end;
self->finished = 1;
break;
default:
PyErr_SetString(ZstdError, "unhandled flush mode");
return NULL;
}
assert(self->output.pos == 0);
input.src = NULL;
input.size = 0;
input.pos = 0;
while (1) {
Py_BEGIN_ALLOW_THREADS
zresult = ZSTD_compressStream2(self->compressor->cctx, &self->output,
&input, zFlushMode);
Py_END_ALLOW_THREADS
if (ZSTD_isError(zresult)) {
PyErr_Format(ZstdError, "error ending compression stream: %s",
ZSTD_getErrorName(zresult));
return NULL;
}
if (self->output.pos) {
if (result) {
resultSize = PyBytes_GET_SIZE(result);
if (safe_pybytes_resize(&result, resultSize + self->output.pos)) {
Py_XDECREF(result);
return NULL;
}
memcpy(PyBytes_AS_STRING(result) + resultSize,
self->output.dst, self->output.pos);
}
else {
result = PyBytes_FromStringAndSize(self->output.dst, self->output.pos);
if (!result) {
return NULL;
}
}
self->output.pos = 0;
}
if (!zresult) {
break;
}
}
if (result) {
return result;
}
else {
return PyBytes_FromString("");
}
}
static PyMethodDef ZstdCompressionObj_methods[] = {
{ "compress", (PyCFunction)ZstdCompressionObj_compress, METH_VARARGS | METH_KEYWORDS,
PyDoc_STR("compress data") },
{ "flush", (PyCFunction)ZstdCompressionObj_flush, METH_VARARGS | METH_KEYWORDS,
PyDoc_STR("finish compression operation") },
{ NULL, NULL }
};
PyTypeObject ZstdCompressionObjType = {
PyVarObject_HEAD_INIT(NULL, 0)
"zstd.ZstdCompressionObj", /* tp_name */
sizeof(ZstdCompressionObj), /* tp_basicsize */
0, /* tp_itemsize */
(destructor)ZstdCompressionObj_dealloc, /* tp_dealloc */
0, /* tp_print */
0, /* tp_getattr */
0, /* tp_setattr */
0, /* tp_compare */
0, /* tp_repr */
0, /* tp_as_number */
0, /* tp_as_sequence */
0, /* tp_as_mapping */
0, /* tp_hash */
0, /* tp_call */
0, /* tp_str */
0, /* tp_getattro */
0, /* tp_setattro */
0, /* tp_as_buffer */
Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE, /* tp_flags */
ZstdCompressionObj__doc__, /* tp_doc */
0, /* tp_traverse */
0, /* tp_clear */
0, /* tp_richcompare */
0, /* tp_weaklistoffset */
0, /* tp_iter */
0, /* tp_iternext */
ZstdCompressionObj_methods, /* tp_methods */
0, /* tp_members */
0, /* tp_getset */
0, /* tp_base */
0, /* tp_dict */
0, /* tp_descr_get */
0, /* tp_descr_set */
0, /* tp_dictoffset */
0, /* tp_init */
0, /* tp_alloc */
PyType_GenericNew, /* tp_new */
};
void compressobj_module_init(PyObject* module) {
Py_SET_TYPE(&ZstdCompressionObjType, &PyType_Type);
if (PyType_Ready(&ZstdCompressionObjType) < 0) {
return;
}
}