# HG changeset patch
# User Bryan O'Sullivan <bryano@fb.com>
# Date 1337484108 25200
# Node ID bda96ce993f930a10d8d0a24f407e2a1eb01590a
# Parent  2631cd5dd244492e6b8c0c10c6ed84b990456723
parsers: cache the result of index_headrevs

Although index_headrevs is much faster than its Python counterpart,
it's still somewhat expensive when history is large. Since headrevs
is called several times when the tag cache is stale or missing (e.g.
after a strip or rebase), there's a win to be gained from caching
the result, which we do here.

diff -r 2631cd5dd244 -r bda96ce993f9 mercurial/parsers.c
--- a/mercurial/parsers.c	Sat May 19 19:44:58 2012 -0700
+++ b/mercurial/parsers.c	Sat May 19 20:21:48 2012 -0700
@@ -246,6 +246,7 @@
 	Py_ssize_t raw_length; /* original number of elements */
 	Py_ssize_t length;     /* current number of elements */
 	PyObject *added;       /* populated on demand */
+	PyObject *headrevs;    /* cache, invalidated on changes */
 	nodetree *nt;          /* base-16 trie */
 	int ntlength;          /* # nodes in use */
 	int ntcapacity;        /* # nodes allocated */
@@ -463,6 +464,7 @@
 	if (self->nt)
 		nt_insert(self, node, (int)offset);
 
+	Py_CLEAR(self->headrevs);
 	Py_RETURN_NONE;
 }
 
@@ -484,6 +486,7 @@
 		free(self->nt);
 		self->nt = NULL;
 	}
+	Py_CLEAR(self->headrevs);
 }
 
 static PyObject *index_clearcaches(indexObject *self)
@@ -534,12 +537,37 @@
 	return NULL;
 }
 
+/*
+ * When we cache a list, we want to be sure the caller can't mutate
+ * the cached copy.
+ */
+static PyObject *list_copy(PyObject *list)
+{
+	Py_ssize_t len = PyList_GET_SIZE(list);
+	PyObject *newlist = PyList_New(len);
+	Py_ssize_t i;
+
+	if (newlist == NULL)
+		return NULL;
+
+	for (i = 0; i < len; i++) {
+		PyObject *obj = PyList_GET_ITEM(list, i);
+		Py_INCREF(obj);
+		PyList_SET_ITEM(newlist, i, obj);
+	}
+
+	return newlist;
+}
+
 static PyObject *index_headrevs(indexObject *self)
 {
 	Py_ssize_t i, len, addlen;
 	char *nothead = NULL;
 	PyObject *heads;
 
+	if (self->headrevs)
+		return list_copy(self->headrevs);
+
 	len = index_length(self) - 1;
 	heads = PyList_New(0);
 	if (heads == NULL)
@@ -601,8 +629,9 @@
 	}
 
 done:
+	self->headrevs = heads;
 	free(nothead);
-	return heads;
+	return list_copy(self->headrevs);
 bail:
 	Py_XDECREF(heads);
 	free(nothead);
@@ -1065,6 +1094,7 @@
 		ret = PyList_SetSlice(self->added, start - self->length + 1,
 				      PyList_GET_SIZE(self->added), NULL);
 done:
+	Py_CLEAR(self->headrevs);
 	return ret;
 }
 
@@ -1155,6 +1185,7 @@
 	self->cache = NULL;
 
 	self->added = NULL;
+	self->headrevs = NULL;
 	self->offsets = NULL;
 	self->nt = NULL;
 	self->ntlength = self->ntcapacity = 0;