[binutils-gdb] Re-acquire GIL earlier in gdbpy_parse_and_eval

[Tom Tromey]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=0c8a0b88d18d9c8d6cd52bd1a56d6ab88570f287

commit 0c8a0b88d18d9c8d6cd52bd1a56d6ab88570f287
Author: Tom Tromey <tromey@adacore.com>
Date:   Thu Jul 27 07:54:18 2023 -0600

    Re-acquire GIL earlier in gdbpy_parse_and_eval
    
    Tom de Vries filed a bug about an intermittent gdb DAP failure -- and
    coincidentally, at the same time, Alexandra Hájková sent email about a
    somewhat similar failure.
    
    After looking into this for a while (with no results) using ASan and
    valgrind, I found that setting PYTHONMALLOC=malloc_debug found the bug
    instantly.
    
    The problem is that gdbpy_parse_and_eval releases the GIL while
    calling parse_and_eval, but fails to re-acquire it before calling
    value_to_value_object.  This is easily fixed by introducing a new
    scope.
    
    I wonder whether the test suite should unconditionally set
    PYTHONMALLOC=malloc_debug.
    
    Tested-by: Tom de Vries <tdevries@suse.de>
    Reviewed-By: Tom de Vries <tdevries@suse.de>
    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30686

Diff:
---
 gdb/python/python.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/gdb/python/python.c b/gdb/python/python.c
index 505fc4412d1..6a978d632e9 100644
--- a/gdb/python/python.c
+++ b/gdb/python/python.c
@@ -994,9 +994,17 @@ gdbpy_parse_and_eval (PyObject *self, PyObject *args, PyObject *kw)
   PyObject *result = nullptr;
   try
     {
-      gdbpy_allow_threads allow_threads;
       scoped_value_mark free_values;
-      struct value *val = parse_and_eval (expr_str, flags);
+      struct value *val;
+      {
+	/* Allow other Python threads to run while we're evaluating
+	   the expression.  This is important because the expression
+	   could involve inferior calls or otherwise be a lengthy
+	   calculation.  We take care here to re-acquire the GIL here
+	   before continuing with Python work.  */
+	gdbpy_allow_threads allow_threads;
+	val = parse_and_eval (expr_str, flags);
+      }
       result = value_to_value_object (val);
     }
   catch (const gdb_exception &except)