Some locale operations need to be done in proper thread

This is a step in solving #20155

The POSIX 2008 locale API introduces per-thread locales.  But the
previous global locale system is retained, probably for backward
compatibility.

The POSIX 2008 interface causes memory to be malloc'd that needs to be
freed.  In order to do this, the caller must first stop using that
memory, by switching to another locale.  perl accomplishes this during
termination by switching to the global locale, which is always available
and doesn't need to be freed.

Perl has long assumed that all that was needed to switch threads was to
change out tTHX.  That's because that structure was intended to hold all
the information for a given thread.  But it turns out that this doesn't
work when some library independently holds information about the
thread's state.  And there are now some libraries that do that.

What was happening in this case was that perl thought that it was
sufficient to switch tTHX to change to a different thread in order to do
the freeing of memory, and then used the POSIX 2008 function to change
to the global locale so that the memory could be safely freed.  But the
POSIX 2008 function doesn't care about tTHX, and actually was typically
operating on a different thread, and so changed that thread to the global
locale instead of the intended thread.  Often that was the top-level
thread, thread 0.  That caused whatever thread it was to no longer be in
the expected locale, and to no longer be thread-safe with regards to
localess,

This commit causes locale_term(), which has always been called from the
actual terminating thread that POSIX 2008 knows about, to change to the
global thread and free the memory.

It also creates a new per-interpreter variable that effectively maps the
tTHX thread to the associated POSIX 2008 memory.  During
perl_destruct(), it frees the memory this variable points to, instead of
blindly assuming the memory to free is the current tTHX thread's.

This fixes the symptoms associtated with #20155, but doesn't solve the
whole problem.  In general, a library that has independent thread status
needs to be updated to the new thread when Perl changes threads using
tTHX.  Future commits will do this.

1 files changed, 1 insertions, 0 deletions

diff --git a/sv.c b/sv.c
index bc5f95143b..99b71c65ab 100644
--- a/sv.c
+++ b/sv.c
@@ -15939,6 +15939,7 @@ perl_clone_using(PerlInterpreter *proto_perl, UV flags,
 #endif /* !USE_LOCALE_NUMERIC */
 #if defined(USE_POSIX_2008_LOCALE)
     PL_scratch_locale_obj = NULL;
+    PL_cur_locale_obj = PL_C_locale_obj;
 #endif
 
 #ifdef HAS_MBRLEN