[PATCH] bdiff.bdiff: release the GIL before doing expensive diff operations

[Augie Fackler]

# HG changeset patch
# User Augie Fackler <raf at durin42.com>
# Date 1334938094 18000
# Branch stable
# Node ID b3e8717ff95fefdf352c051e373df16dd053f7eb
# Parent  ee553e6cd8c445ff40ed15ca0ab1b9a3636a9ddc
bdiff.bdiff: release the GIL before doing expensive diff operations

This means that threaded webservers will have more of a chance of
doing something useful while the C extension is busy computing a
delta. Not doing this was causing problems for Google Code with a 25
meg text file that takes O(7 minutes) to deltify.

diff --git a/mercurial/bdiff.c b/mercurial/bdiff.c
--- a/mercurial/bdiff.c
+++ b/mercurial/bdiff.c
@@ -339,10 +339,12 @@
 	struct line *al, *bl;
 	struct hunk l, *h;
 	int an, bn, len = 0, la, lb, count;
+	PyThreadState *_save;
 
 	if (!PyArg_ParseTuple(args, "s#s#:bdiff", &sa, &la, &sb, &lb))
 		return NULL;
 
+	_save = PyEval_SaveThread();
 	an = splitlines(sa, la, &al);
 	bn = splitlines(sb, lb, &bl);
 	if (!al || !bl)
@@ -361,6 +363,8 @@
 		la = h->a2;
 		lb = h->b2;
 	}
+	PyEval_RestoreThread(_save);
+	_save = NULL;
 
 	result = PyBytes_FromStringAndSize(NULL, len);
 
@@ -385,6 +389,7 @@
 	}
 
 nomem:
+	if (_save) PyEval_RestoreThread(_save);
 	free(al);
 	free(bl);
 	freehunks(l.next);