[Mono-bugs] [Bug 666173] New: Writing to an asynchronous HttpWebRequest request stream causes a fatal exception when the request is cancelled

bugzilla_noreply at novell.com bugzilla_noreply at novell.com
Fri Jan 21 10:12:33 EST 2011



           Summary: Writing to an asynchronous HttpWebRequest request
                    stream causes a fatal exception when the request is
    Classification: Mono
           Product: MonoTouch
           Version: unspecified
          Platform: Other
               URL: http://stackoverflow.com/questions/4592150/monotouch-w
        OS/Version: Apple iOS 4.2
            Status: NEW
          Severity: Normal
          Priority: P5 - None
         Component: Class Libraries
        AssignedTo: mono-bugs at lists.ximian.com
        ReportedBy: novell at fcmobile.nl
         QAContact: mono-bugs at lists.ximian.com
                CC: novell at fcmobile.nl
          Found By: Third Party Developer/Partner
           Blocker: No

When I cancel an asynchronous HttpWebRequest request and the application tries
to write to the request stream, a NullReference exception is thrown.
Even if I catch this exception, the application crashes.

iOS version 4.2.1 (8C148)
Monotouch version: 3.2.4

Code fragment (full code listing see

            using (var stream = _request.EndGetRequestStream(asyncResult))
                using (var textStream = new StreamWriter(stream))
            _request.BeginGetResponse(new AsyncCallback(ProcessResponse),

If the user cancels the request, _request.Abort() is called on the main thread.
1. If this happens before the call to _request.EndGetRequestStream, a
WebException is thrown when calling _request.EndGetRequestStream (correct).
2. If this happens after the call to Save(textStream), a WebException is thrown
when calling _request.BeginGetResponse (correct).
3. If this happens after the call to _request.EndGetRequestStream but BEFORE
the call to Save(textStream), a NullReference exception is thrown when calling
and even if you catch that exception the application crashes.

Native stacktrace:

    0   MyApp                               0x006765c4
mono_handle_native_sigsegv + 404
    1   MyApp                               0x0065fc9c
mono_sigsegv_signal_handler + 348
    2   libSystem.B.dylib                   0x33bd3ddf _sigtramp + 42
    3   MyApp                               0x00686418 add_var + 232
    4   MyApp                               0x00686418 add_var + 232
    5   MyApp                               0x0068c79c frame_commands + 1492
    6   MyApp                               0x0068ded0 debugger_thread + 1232
    7   MyApp                               0x0078bc2c thread_start_routine +
    8   MyApp                               0x007bac38 GC_start_routine + 132
    9   libSystem.B.dylib                   0x33bd688d _pthread_start + 248
    10  libSystem.B.dylib                   0x33bcba90 thread_assign_default +

Got a SIGSEGV while executing native code. This usually indicates
a fatal error in the mono runtime or one of the native libraries 
used by your application.

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