bugGNU Octave - Bugs: bug #54571, gethostname must not be called...


bug #54571: gethostname must not be called from within DllMain on Win32 systems

Submitted by:  None
Submitted on:  Sat 25 Aug 2018 02:05:06 PM UTC  
Category:  Libraries Severity:  3 - Normal
Priority:  3 - Low Item Group:  Other
Status:  Patch Reviewed Assigned to:  None
Originator Name:  Octave user Originator Email:  -email is unavailable-
Open/Closed:  Open Release:  4.4.1
Operating System:  Microsoft Windows

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Thu 30 Aug 2018 07:28:34 AM UTC, comment #2:

No, the delay occurs just because the dll is not initialized properly.

If I'm running the test in the attached file, it executes within 0.09 seconds:

(file #44899)

Wed 29 Aug 2018 07:07:54 PM UTC, comment #1:

I have followed the links and I think I understand the point that this bug report is about. Basically on Windows, static initializers must not call functions that may be in shared libraries that haven't been fully loaded yet.

We could make some changes to defer calls to 'gethostname' until it is actually needed. But I don't think this patch is the right way to do that. If this is needed, we should properly rework those global string variables that depend on the host name to be API functions.

This patch is not ready to be applied.

How did you get a 20 second startup time from gethostname, is your system somehow configured that it doesn't even know its own name and has to reach another server, or timed out somehow querying the host name?

Mike Miller <mtmiller>
Project Administrator
Sat 25 Aug 2018 02:05:06 PM UTC, original submission:

According to DllMain there several restrictions which functions may be called from within DllMain. Especially LoadLibrary must not be called directly nor indirectly Dynamic-Link Library Best Practices.

Although octave is not providing an implementation of DllMain, it will be generated by the compiler. Any initialized global or static variable of a Dll outside of a function will be initialized in DllMain.
For example the following definition in oct-hist.cc will actually call gethostname from within DllMain:
The behaviour of such a call could be undefined because it depends on other Dll's which might not be initialized properly if their DllMain has not been called before. So it might work or might not work depending on the load order of Dll's.

The patch in the attached file fixes this issue at least in case of gethostname. It simply delays the call to gethostname until main is called.

As a side effect this patch can reduce start-up time of octave depending on OS version and system configuration.

Without patch:

With patch:



(Note: upload size limit is set to 16384 kB, after insertion of the required escape characters.)

Attach Files:

Attached Files
file #44899:  gethostname.tar.bz2 added by None (1KiB - application/octet-stream)
file #44860:  octave-gethostname.patch added by None (2KiB - application/octet-stream)


Depends on the following items: None found

Items that depend on this one: None found


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    Follow 6 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2018-08-30 None Attached File- => Added gethostname.tar.bz2, #44899
    2018-08-29 mtmiller Priority5 - Normal => 3 - Low
        StatusPatch Submitted => Patch Reviewed
    2018-08-26 mtmiller Carbon-CopyRemoved 80942 => -
    2018-08-26 mtmiller StatusNone => Patch Submitted
    2018-08-25 None Attached File- => Added octave-gethostname.patch, #44860

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