Mercurial > hg
changeset 24624:6f0e6fa9fdd7
dirs._addpath: don't mutate Python strings after exposing them (issue4589)
One of the rules of Python strings is that they're immutable. dirs._addpath
breaks this assumption for performance, which is fine as long as it is done
safely -- once a string is no longer internal-only it shouldn't be mutated.
Unfortunately, we weren't being safe here -- we were mutating 'key' even after
adding it to a dictionary.
This only really affects other C code that reads strings, so it's somewhat hard
to write a test for this without poking into the internal representation of the
string via ctypes or similar. There is currently no C code that reads the
output of the string, but there will likely be some soon as the bug indicates.
There's no significant difference in performance.
author | Siddharth Agarwal <sid0@fb.com> |
---|---|
date | Mon, 06 Apr 2015 10:46:44 -0700 |
parents | 2262d7bc469e |
children | 2cebf17c0fcc |
files | mercurial/dirs.c |
diffstat | 1 files changed, 5 insertions(+), 5 deletions(-) [+] |
line wrap: on
line diff
--- a/mercurial/dirs.c Mon Apr 06 08:23:27 2015 -0700 +++ b/mercurial/dirs.c Mon Apr 06 10:46:44 2015 -0700 @@ -93,11 +93,11 @@ if (ret == -1) goto bail; - if (pos != 0) - PyString_AS_STRING(key)[pos] = '/'; - else - key = NULL; - Py_CLEAR(key); + /* Clear the key out since we've already exposed it to Python + and can't mutate it further. key's refcount is currently 2 so + we can't just use Py_CLEAR. */ + Py_DECREF(key); + key = NULL; } ret = 0;