[PATCH stable] fileset, revset: do not use global parser object for thread safety

[Yuya Nishihara]

Hi,

This problem was originally reported as a bug of TortoiseHg, but hgweb would
have the same issue.

https://bitbucket.org/tortoisehg/thg/issue/3533/

script to reproduce the exception:

import threading
from mercurial import revset

spec = '()'
for i in xrange(10):
    spec = '(%s or %d)' % (spec, i)
print spec

for _i in xrange(50):
    th = threading.Thread(target=lambda: revset.parse(spec))
    th.start()

# HG changeset patch
# User Yuya Nishihara <yuya at tcha.org>
# Date 1387597459 -32400
#      Sat Dec 21 12:44:19 2013 +0900
# Branch stable
# Node ID 61a47fd64f308ecf18696f06f84918bef9564d7c
# Parent  d4be314b20711b6ecfa7a6f8b46970231134004a
fileset, revset: do not use global parser object for thread safety

parse() cannot be called at the same time because a parser object keeps its
states.  This is no problem for command-line hg client, but it would cause
strange errors in multi-threaded hgweb.

Creating parser object is not too expensive.

original:
% python -m timeit -s 'from mercurial import revset' 'revset.parse("0::tip")'
100000 loops, best of 3: 11.3 usec per loop

thread-safe:
% python -m timeit -s 'from mercurial import revset' 'revset.parse("0::tip")'
100000 loops, best of 3: 13.1 usec per loop

diff --git a/mercurial/fileset.py b/mercurial/fileset.py
--- a/mercurial/fileset.py
+++ b/mercurial/fileset.py
@@ -78,7 +78,9 @@ def tokenize(program):
         pos += 1
     yield ('end', None, pos)
 
-parse = parser.parser(tokenize, elements).parse
+def parse(expr):
+    p = parser.parser(tokenize, elements)
+    return p.parse(expr)
 
 def getstring(x, err):
     if x and (x[0] == 'string' or x[0] == 'symbol'):
diff --git a/mercurial/revset.py b/mercurial/revset.py
--- a/mercurial/revset.py
+++ b/mercurial/revset.py
@@ -1880,7 +1880,9 @@ def findaliases(ui, tree):
         aliases[alias.name] = alias
     return _expandaliases(aliases, tree, [], {})
 
-parse = parser.parser(tokenize, elements).parse
+def parse(spec):
+    p = parser.parser(tokenize, elements)
+    return p.parse(spec)
 
 def match(ui, spec):
     if not spec: