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https://issues.apache.org/jira/browse/QPID-2926?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12928691#action_12928691
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Chuck Rolke commented on QPID-2926:
-----------------------------------
Here's my second suggestion. It is actually Possible Fix #1 from the last post:
In a brand new windows-only qpidmessaging source file
void HandleInstantiatorDoNotCall(void)
{
// This function exists to instantiate various template Handle
// bool functions. The instances are then available to
// the qpidmessaging DLL and subsequently exported.
// This function must not be exported nor called called.
// For further information refer to
// https://issues.apache.org/jira/browse/QPID-2926
Connection connection;
if (connection.isValid()) connection.close();
if (connection.isNull() ) connection.close();
if (connection ) connection.close();
if (!connection ) connection.close();
Receiver receiver;
if (receiver.isValid()) receiver.close();
if (receiver.isNull() ) receiver.close();
if (receiver ) receiver.close();
if (!receiver ) receiver.close();
Sender sender;
if (sender.isValid()) sender.close();
if (sender.isNull() ) sender.close();
if (sender ) sender.close();
if (!sender ) sender.close();
Session session;
if (session.isValid()) session.close();
if (session.isNull() ) session.close();
if (session ) session.close();
if (!session ) session.close();
}
Points:
1. The code is in a new, windows-only qpidmessaging source file.
2. The fix does not change any source module for linux and it changes no
interface definitions.
> Simple example code does not link under Windows
> -----------------------------------------------
>
> Key: QPID-2926
> URL: https://issues.apache.org/jira/browse/QPID-2926
> Project: Qpid
> Issue Type: Bug
> Components: C++ Client
> Affects Versions: 0.7
> Environment: Windows platform, native C++ client example
> Reporter: Chuck Rolke
> Assignee: Chuck Rolke
> Fix For: 0.7
>
>
> Using one of the existing examples that has a line such as
> "connection.close();"
> change to
> "if (connection) connection.close();"
> causes error:
> Error 2 error LNK2019: unresolved external symbol
> "__declspec(dllimport)public: __thiscall qpid::messaging::Handle<class
> qpid::messaging::ConnectionImpl>::operator bool(void)const
> "(__imp_??b?$han...@vconnectionimpl@messag...@qpid@@@messag...@qpid@@QBE_NXZ)
> referenced in function __catch$_main$0 client.obj messaging_clien
> The missing routine undecorates to:
> "public: __thiscall qpid::messaging::Handle<class
> qpid::messaging::ConnectionImpl>::operator bool(void)const "
> I think the problem is that the messaging Connection class has a template
> Handle class in its interface, and then this interface is exported by a DLL.
> At DLL-compile time the DLL source code never instantiates the Handle class
> template and thus has no actual instance of Handle to export in the DLL. On a
> Linux build the instances of Handle are created on the client host system and
> are not imported from a library - but this is purely a guess. See also
> http://www.codeproject.com/kb/cpp/templatesourceorg.aspx
> --------------
> Possible fixes
> 1. Add a separate compilation unit to Windows builds that creates actual
> instances of Handle<>. Then export these in the DLL to satisfy the link.
> This may work but it does not sound easy to support in the long run.
> 2. Define the function definitions in Connection proper and not let the work
> fall into class Handle. In Connection.cpp adding
> QPID_MESSAGING_EXTERN operator bool() const {
> return qpid::messaging::Handle<ConnectionImpl>::operator bool();
> }
> solves the issue. This same pattern applies to several functions in each of
> Connection, Receiver, Sender, and Session.
> This would probably work in Linux, too, but could be conditionaled to only be
> active in Windows.
> If anyone has some other ideas I'd love to hear them. Also, is having a
> template class in a Messaging library interface a good idea?
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