Sometimes Trac install crashes on Windows at startup

[pkou at ua.fm]

Environment: Clean Trac install from source:/trunk@3787​ on Windows XP and typical CGI configuration via Apache 2.0.55.

Problem: The system crashes while accessing Trac with the following details:

Oops...

Trac detected an internal error: 'module' object has no attribute 'fcntl'

Traceback (most recent call last):
  File "C:/Program Files/Apache Group/Apache2/cgi-bin/trac.cgi", line 20, in ?
    cgi_frontend.run()
  File "C:\Python23\Lib\site-packages\trac\web\cgi_frontend.py", line 55, in run
    flags = fcntl.fcntl(fd, fcntl.F_GETFL)
AttributeError: 'module' object has no attribute 'fcntl'

Reason: The specified place is protected from not existing modules using ImportError. However, it is not protected from the cases when the specific module exists but it does not have the required symbols.

Solution is proposed in the following patch:

trac/web/cgi_frontend.py

@@ -54 +54 @@
             fd = stream.fileno()
             flags = fcntl.fcntl(fd, fcntl.F_GETFL)
             fcntl.fcntl(fd, fcntl.F_SETFL, flags & ~os.O_NONBLOCK)
-    except ImportError:
+    except (ImportError, AttributeError):
         pass
 
     try: # Use binary I/O on Windows
         import msvcrt
         msvcrt.setmode(sys.stdin.fileno(), os.O_BINARY)
         msvcrt.setmode(sys.stdout.fileno(), os.O_BINARY)
-    except ImportError:
+    except (ImportError, AttributeError):
         pass
 
     gateway = CGIGateway()

trac/web/_fcgi.py

@@ -948 +948 @@
                 # Attempt to glean the maximum number of connections
                 # from the OS.
                 maxConns = resource.getrlimit(resource.RLIMIT_NOFILE)[0]
-            except ImportError:
+            except (ImportError, AttributeError):
                 maxConns = 100 # Just some made up number.
             maxReqs = maxConns
             if multiplexed:

[cboos]

Looks good to me, except maybe the msvcrt one. It doesn't look like setmode can be missing if msvcrt can be imported...

[cboos]

Fixed in r3790.

[mgood]

The module fcntl should not be available on Windows. The docs specifically list "Availablility: Unix" for the module, not specific functions: ​http://docs.python.org/lib/module-fcntl.html

I just tested Python 2.3, 2.4, and 2.5 on Windows and this module is not available on any of these. So, I'd kind of like to know what's really going on here before we just throw on a patch.

[cboos]

Here's what I've found after some research:

• ​http://pydoc.org/get.cgi/usr/lib/python2.2/FCNTL.py
• ​http://mail.python.org/pipermail/python-dev/2004-July/046322.html

From other references, it looks like some Windows 2.3 installations still have a fcntl.pyc in their Python23\Lib...

I think that r3790 doesn't "hurt" that much, and if it helps Trac to work out-of-the-box even on those "broken" installations, I'd say we should keep it.

[mgood]

Replying to cboos:

Here's what I've found after some research:

• ​http://pydoc.org/get.cgi/usr/lib/python2.2/FCNTL.py
• ​http://mail.python.org/pipermail/python-dev/2004-July/046322.html

Ok, that seems like a good enough reason.