Issue #20766: Fix references leaked by pdb in the handling of SIGINT handlers.

2 files changed, 30 insertions, 3 deletions

diff --git a/Lib/pdb.py b/Lib/pdb.py
index b11ac0a..4797265 100755
--- a/Lib/pdb.py
+++ b/Lib/pdb.py
@@ -134,6 +134,8 @@ line_prefix = '\n-> '   # Probably a better default
 
 class Pdb(bdb.Bdb, cmd.Cmd):
 
+    _previous_sigint_handler = None
+
     def __init__(self, completekey='tab', stdin=None, stdout=None, skip=None,
                  nosigint=False):
         bdb.Bdb.__init__(self, skip=skip)
@@ -187,8 +189,6 @@ class Pdb(bdb.Bdb, cmd.Cmd):
         self.message("\nProgram interrupted. (Use 'cont' to resume).")
         self.set_step()
         self.set_trace(frame)
-        # restore previous signal handler
-        signal.signal(signal.SIGINT, self._previous_sigint_handler)
 
     def reset(self):
         bdb.Bdb.reset(self)
@@ -337,6 +337,10 @@ class Pdb(bdb.Bdb, cmd.Cmd):
                                  (expr, newvalue, oldvalue))
 
     def interaction(self, frame, traceback):
+        # Restore the previous signal handler at the Pdb prompt.
+        if Pdb._previous_sigint_handler:
+            signal.signal(signal.SIGINT, Pdb._previous_sigint_handler)
+            Pdb._previous_sigint_handler = None
         if self.setup(frame, traceback):
             # no interaction desired at this time (happens if .pdbrc contains
             # a command like "continue")
@@ -1037,7 +1041,7 @@ class Pdb(bdb.Bdb, cmd.Cmd):
         """
         if not self.nosigint:
             try:
-                self._previous_sigint_handler = \
+                Pdb._previous_sigint_handler = \
                     signal.signal(signal.SIGINT, self.sigint_handler)
             except ValueError:
                 # ValueError happens when do_continue() is invoked from
diff --git a/Lib/test/test_pdb.py b/Lib/test/test_pdb.py
index 45ba5a9..66a7b55 100644
--- a/Lib/test/test_pdb.py
+++ b/Lib/test/test_pdb.py
@@ -911,6 +911,29 @@ def test_pdb_next_command_subiterator():
     (Pdb) continue
     """
 
+def test_pdb_issue_20766():
+    """Test for reference leaks when the SIGINT handler is set.
+
+    >>> def test_function():
+    ...     i = 1
+    ...     while i <= 2:
+    ...         sess = pdb.Pdb()
+    ...         sess.set_trace(sys._getframe())
+    ...         print('pdb %d: %s' % (i, sess._previous_sigint_handler))
+    ...         i += 1
+
+    >>> with PdbTestInput(['continue',
+    ...                    'continue']):
+    ...     test_function()
+    > <doctest test.test_pdb.test_pdb_issue_20766[0]>(6)test_function()
+    -> print('pdb %d: %s' % (i, sess._previous_sigint_handler))
+    (Pdb) continue
+    pdb 1: <built-in function default_int_handler>
+    > <doctest test.test_pdb.test_pdb_issue_20766[0]>(5)test_function()
+    -> sess.set_trace(sys._getframe())
+    (Pdb) continue
+    pdb 2: <built-in function default_int_handler>
+    """
 
 class PdbTestCase(unittest.TestCase):