Hi Bert and Julian,
Bert Huijben writes:
> > -----Original Message-----
> > From: Julian Foad [mailto:julian.f...@wandisco.com]
> > On Mon, 2010-10-11, Julian Foad wrote:
> > > <http://stackoverflow.com/questions/54188/are-c-reads-and-writes-of-
> > an-int-atomic>.
> > > "On an IA32 a correctly aligned address will be an atomic operation.
> > > [... otherwise... can't assume it is]."
> >
> > Sorry, I pressed "Send" too early. That's not the most important bit of
> > information. (That paragraph talks mostly about <= 32-bit CPUs, where
> > of course there will be problems.) Bert explained to me on IRC that
> > atomicity is not guaranteed even on >= 32 bit architectures, and the
> > highest-ranked answer on that web page agrees. I'm no expert in this so
> > I'll go away now.
>
> Let me add that calling apr_atomic_set32() instead of the 'x = <value>' part
> of the pattern will fix this issue in the way that was documented by the
> comment in the code: all threads do the same thing and one of the results is
> left in the static variable.
>
> Another option is to use an atomic initialization function to initialize the
> value just once.
I see; I don't think I know enough to comment.
Bert: So does this solve the issue or did I misunderstand something?
Index: subversion/libsvn_subr/io.c
===================================================================
--- subversion/libsvn_subr/io.c (revision 1005706)
+++ subversion/libsvn_subr/io.c (working copy)
@@ -1269,7 +1269,8 @@ static svn_error_t *
get_default_file_perms(apr_fileperms_t *perms, apr_pool_t *scratch_pool)
{
/* the default permissions as read from the temp folder */
- static apr_fileperms_t default_perms = 0;
+ static apr_fileperms_t default_perms;
+ apr_atomic_set32(&default_perms, 0);
/* Technically, this "racy": Multiple threads may use enter here and
try to figure out the default permisission concurrently. That's fine
@@ -1303,7 +1304,7 @@ get_default_file_perms(apr_fileperms_t *perms, apr
SVN_ERR(svn_io_file_close(fd, scratch_pool));
*perms = finfo.protection;
- default_perms = finfo.protection;
+ apr_atomic_set32(&default_perms, finfo.protection);
}
else
*perms = default_perms;
