Re: [xml] [PATCH] always dllexport the singlethreaded variables

On 08/31/2018 11:57 AM, Nick Wellnhofer wrote:
On 25/05/2018 17:46, Michael Haubenwallner wrote:
When an application using libxml2 does not enable multithreaded support
for itself, we provide the singlethreaded variables, eventually tagged
with dllimport.  So even when we build the multithreaded libxml2, our
singlethreaded variables still eventually need the dllexport tag.

I don't understand the issue. Do you mean an application linked with a DLL configured without thread 
support and compiled with single-thread headers, and THEN swapping the DLL with a multi-thread version? I'm 
not sure whether this should be supported.

Actually it's the other way round:
The xml library is configured with thread support, but
the application is created without thread support - with
the application in question being gettext (as of version 0.19.7,
but it's the same even in gettext master still).

Without patching, gettext does explicitly use the --disable-auto-import
linker flag on Cygwin and MinGW, relying on symbols to be dllexport'ed, see

However, the Cygwin distro currently does modify this m4/woe32-dll.m4 to
stay with auto-import enabled, simply to get a working gettext package.

So even when thread support is enabled in xml, it still is useful in
single threaded applications - and xml should support this use case.

Right now, LIBXML_THREAD_ENABLED is defined in xmlversion.h only if the
*application* does enable threads, otherwise the single threaded xml
symbols are declared - which are not dllexport'ed when thread support
is configured for libxml, yet they are still there but auto-imported.

However, another variant might be to declare the threaded symbols when
xml is *configured* with threads enabled, not depending on whether the
application has threads enabled. Beyond that, omitting the single threaded
symbols from the dll may make sense, but that would require a SONAME bump.


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