diff mercurial/dirs.c @ 21809:e250b8300e6e

parsers: inline fields of dirstate values in C version

Previously, while unpacking the dirstate we'd create 3-4 new CPython objects
for most dirstate values:

- the state is a single character string, which is pooled by CPython
- the mode is a new object if it isn't 0 due to being in the lookup set
- the size is a new object if it is greater than 255
- the mtime is a new object if it isn't -1 due to being in the lookup set
- the tuple to contain them all

In some cases such as regular hg status, we actually look at all the objects.
In other cases like hg add, hg status for a subdirectory, or hg status with the
third-party hgwatchman enabled, we look at almost none of the objects.

This patch eliminates most object creation in these cases by defining a custom
C struct that is exposed to Python with an interface similar to a tuple. Only
when tuple elements are actually requested are the respective objects created.

The gains, where they're expected, are significant. The following tests are run
against a working copy with over 270,000 files.

parse_dirstate becomes significantly faster:

$ hg perfdirstate
before: wall 0.186437 comb 0.180000 user 0.160000 sys 0.020000 (best of 35)
after:  wall 0.093158 comb 0.100000 user 0.090000 sys 0.010000 (best of 95)

and as a result, several commands benefit:

$ time hg status  # with hgwatchman enabled
before: 0.42s user 0.14s system 99% cpu 0.563 total
after:  0.34s user 0.12s system 99% cpu 0.471 total

$ time hg add new-file
before: 0.85s user 0.18s system 99% cpu 1.033 total
after:  0.76s user 0.17s system 99% cpu 0.931 total

There is a slight regression in regular status performance, but this is fixed
in an upcoming patch.

--- a/mercurial/dirs.c	Tue May 27 17:10:28 2014 -0700
+++ b/mercurial/dirs.c	Tue May 27 14:27:41 2014 -0700
@@ -138,25 +138,12 @@
 			return -1;
 		}
 		if (skipchar) {
-			PyObject *st;
-
-			if (!PyTuple_Check(value) ||
-			    PyTuple_GET_SIZE(value) == 0) {
+			if (!dirstate_tuple_check(value)) {
 				PyErr_SetString(PyExc_TypeError,
-						"expected non-empty tuple");
+						"expected a dirstate tuple");
 				return -1;
 			}
-
-			st = PyTuple_GET_ITEM(value, 0);
-
-			if (!PyString_Check(st) || PyString_GET_SIZE(st) == 0) {
-				PyErr_SetString(PyExc_TypeError,
-						"expected non-empty string "
-						"at tuple index 0");
-				return -1;
-			}
-
-			if (PyString_AS_STRING(st)[0] == skipchar)
+			if (((dirstateTupleObject *)value)->state == skipchar)
 				continue;
 		}