Issue #11453: asyncore: emit a ResourceWarning when an unclosed file_wrapper

object is destroyed. The destructor now closes the file if needed. The close()
method can now be called twice: the second call does nothing.

Lib/asyncore.py

@@ -614,6 +614,11 @@ if os.name == 'posix':
         def __init__(self, fd):
             self.fd = os.dup(fd)
 
+        def __del__(self):
+            if self.fd >= 0:
+                warnings.warn("unclosed file %r" % self, ResourceWarning)
+            self.close()
+
         def recv(self, *args):
             return os.read(self.fd, *args)
 
@@ -632,7 +637,10 @@ if os.name == 'posix':
         write = send
 
         def close(self):
+            if self.fd < 0:
+                return
             os.close(self.fd)
+            self.fd = -1
 
         def fileno(self):
             return self.fd

Lib/test/test_asyncore.py

@@ -436,6 +436,22 @@ class FileWrapperTest(unittest.TestCase):
         asyncore.loop(timeout=0.01, use_poll=True, count=2)
         self.assertEqual(b"".join(data), self.d)
 
+    def test_resource_warning(self):
+        # Issue #11453
+        fd = os.open(support.TESTFN, os.O_RDONLY)
+        f = asyncore.file_wrapper(fd)
+        with support.check_warnings(('', ResourceWarning)):
+            f = None
+            support.gc_collect()
+
+    def test_close_twice(self):
+        fd = os.open(support.TESTFN, os.O_RDONLY)
+        f = asyncore.file_wrapper(fd)
+        f.close()
+        self.assertEqual(f.fd, -1)
+        # calling close twice should not fail
+        f.close()
+
 
 class BaseTestHandler(asyncore.dispatcher):
 

Misc/NEWS

@@ -27,6 +27,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #11453: asyncore: emit a ResourceWarning when an unclosed file_wrapper
+  object is destroyed. The destructor now closes the file if needed. The
+  close() method can now be called twice: the second call does nothing.
+
 - Issue #21858: Better handling of Python exceptions in the sqlite3 module.
 
 - Issue #21476: Make sure the email.parser.BytesParser TextIOWrapper is