bpo-31009: Move fd_count() to test.support (#7308)

* Move fd_count() from test.libregrtest.refleak to test.support
* Fix support.fd_count() on Windows: Call CrtSetReportMode() to not
  kill the process on invalid file descriptor if Python is compiled
  in debug mode.

Lib/test/libregrtest/refleak.py

@@ -13,30 +13,6 @@
     MAXFD = 256
 
 
-def fd_count():
-    """Count the number of open file descriptors"""
-    if sys.platform.startswith(('linux', 'freebsd')):
-        try:
-            names = os.listdir("/proc/self/fd")
-            return len(names)
-        except FileNotFoundError:
-            pass
-
-    count = 0
-    for fd in range(MAXFD):
-        try:
-            # Prefer dup() over fstat(). fstat() can require input/output
-            # whereas dup() doesn't.
-            fd2 = os.dup(fd)
-        except OSError as e:
-            if e.errno != errno.EBADF:
-                raise
-        else:
-            os.close(fd2)
-            count += 1
-    return count
-
-
 def dash_R(the_module, test, indirect_test, huntrleaks):
     """Run a test multiple times, looking for reference leaks.
 
@@ -182,7 +158,7 @@ def dash_R_cleanup(fs, ps, pic, zdc, abcs):
     func1 = sys.getallocatedblocks
     func2 = sys.gettotalrefcount
     gc.collect()
-    return func1(), func2(), fd_count()
+    return func1(), func2(), support.fd_count()
 
 
 def clear_caches():

Lib/test/support/__init__.py

@@ -107,7 +107,7 @@
     "check_warnings", "check_no_resource_warning", "EnvironmentVarGuard",
     "run_with_locale", "swap_item",
     "swap_attr", "Matcher", "set_memlimit", "SuppressCrashReport", "sortdict",
-    "run_with_tz", "PGO", "missing_compiler_executable",
+    "run_with_tz", "PGO", "missing_compiler_executable", "fd_count",
     ]
 
 class Error(Exception):
@@ -2691,6 +2691,63 @@ def disable_faulthandler():
             faulthandler.enable(file=fd, all_threads=True)
 
 
+def fd_count():
+    """Count the number of open file descriptors.
+    """
+    if sys.platform.startswith(('linux', 'freebsd')):
+        try:
+            names = os.listdir("/proc/self/fd")
+            return len(names)
+        except FileNotFoundError:
+            pass
+
+    old_modes = None
+    if sys.platform == 'win32':
+        # bpo-25306, bpo-31009: Call CrtSetReportMode() to not kill the process
+        # on invalid file descriptor if Python is compiled in debug mode
+        try:
+            import msvcrt
+            msvcrt.CrtSetReportMode
+        except (AttributeError, ImportError):
+            # no msvcrt or a release build
+            pass
+        else:
+            old_modes = {}
+            for report_type in (msvcrt.CRT_WARN,
+                                msvcrt.CRT_ERROR,
+                                msvcrt.CRT_ASSERT):
+                old_modes[report_type] = msvcrt.CrtSetReportMode(report_type, 0)
+
+    MAXFD = 256
+    if hasattr(os, 'sysconf'):
+        try:
+            MAXFD = os.sysconf("SC_OPEN_MAX")
+        except OSError:
+            pass
+
+    try:
+        count = 0
+        for fd in range(MAXFD):
+            try:
+                # Prefer dup() over fstat(). fstat() can require input/output
+                # whereas dup() doesn't.
+                fd2 = os.dup(fd)
+            except OSError as e:
+                if e.errno != errno.EBADF:
+                    raise
+            else:
+                os.close(fd2)
+                count += 1
+    finally:
+        if old_modes is not None:
+            for report_type in (msvcrt.CRT_WARN,
+                                msvcrt.CRT_ERROR,
+                                msvcrt.CRT_ASSERT):
+                msvcrt.CrtSetReportMode(report_type, old_modes[report_type])
+
+    return count
+
+
 class SaveSignals:
     """
     Save an restore signal handlers.

Lib/test/test_regrtest.py

@@ -835,22 +835,10 @@ def test_huntrleaks_fd_leak(self):
             import os
             import unittest
 
-            # Issue #25306: Disable popups and logs to stderr on assertion
-            # failures in MSCRT
-            try:
-                import msvcrt
-                msvcrt.CrtSetReportMode
-            except (ImportError, AttributeError):
-                # no Windows, o release build
-                pass
-            else:
-                for m in [msvcrt.CRT_WARN, msvcrt.CRT_ERROR, msvcrt.CRT_ASSERT]:
-                    msvcrt.CrtSetReportMode(m, 0)
-
             class FDLeakTest(unittest.TestCase):
                 def test_leak(self):
                     fd = os.open(__file__, os.O_RDONLY)
-                    # bug: never cloes the file descriptor
+                    # bug: never close the file descriptor
         """)
         self.check_leak(code, 'file descriptors')