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https://issues.apache.org/jira/browse/QPID-3193?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13017613#comment-13017613
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Chuck Rolke commented on QPID-3193:
-----------------------------------
You are correct about the IsDisposed leaving a window open. The binding objects
really want to be multithread safe so they must then do more heavy lifting.
The stackoverflow article talks about controls that have an IsDisposed
property. As is, the classes don't have such a property and this Jira is a
proposal to add one. But by making each class more thread safe with a lock and
adding the dispose check then users won't need an IsDisposed property.
{code:title=Existing Code|borderStyle=solid}
System::String ^ Message::GetContent()
{
System::String ^ result = nullptr;
System::Exception ^ newException = nullptr;
try
{
result = gcnew String(messagep->getContent().c_str());
}
catch (const ::qpid::types::Exception & error)
{
String ^ errmsg = gcnew String(error.what());
newException = gcnew QpidException(errmsg);
}
if (newException != nullptr)
{
throw newException;
}
return result;
}
{code}
When a user generates the AccVio C# code sees the following exception.
Curiously, this exception is not caught and rethrown by the GetContent
function. It is caught directly by the C# caller program (which I had trouble
catching previously).
{noformat}
Exception System.AccessViolationException:
Attempted to read or write protected memory.
This is often an indication that other memory is corrupt.
at qpid.messaging.Message.getContentSize(Message* )
at Org.Apache.Qpid.Messaging.Message.get_ContentSize() in
d:\qpid\cpp\bindings\qpid\dotnet\src\message.h:line 350
at Org.Apache.Qpid.Messaging.Program.Main(String[] args) in
D:\qpid\cpp\...\csharp.example.helloworld.cs:line 80.
{noformat}
The code could be fixed up by adding a lock for thread safety and a check for
disposed objects that throws ObjectDisposed when seen.
{code:title=ProposedCode|borderStyle=solid}
System::String ^ Message::GetContent()
{
System::String ^ result = nullptr;
System::Exception ^ newException = nullptr;
msclr::lock lk(this);
if (NULL == messagep)
{
newException = gcnew
ObjectDisposedException("Message");
}
else
{
try
{
result = gcnew String(messagep->getContent().c_str());
}
catch (const ::qpid::types::Exception & error)
{
String ^ errmsg = gcnew String(error.what());
newException = gcnew QpidException(errmsg);
}
}
if (newException != nullptr)
{
throw newException;
}
return result;
}
{code}
This same pattern must be applied to all function and property references to
all Messaging bound classes.
> .NET Binding for Messaging classes need a test to check that binding is still
> in effect
> ---------------------------------------------------------------------------------------
>
> Key: QPID-3193
> URL: https://issues.apache.org/jira/browse/QPID-3193
> Project: Qpid
> Issue Type: Improvement
> Affects Versions: 0.11
> Reporter: Chuck Rolke
> Assignee: Chuck Rolke
>
> The .NET Binding for Messaging could be made more user-friendly with the
> addition of a property that indicates whether or not the underlying binding
> is still available. A C# coder may innocently write:
> (1) Message mA = new Message("a");
> (2) Message mB = mA;
> ...
> (N) mB.Dispose();
> After disposing of message mB then message mA is clobbered. 'Message' is a
> 'ref class' type and messages mA and mB refer to the same object on managed
> heap. When message mB is disposed then the bound C++ Messaging object is
> deleted [1]. Any reference to the bound message part of mA will result in an
> illegal memory reference (to 0) and a process exit. The .NET runtime can't
> catch this fault.
> The obvious answer is not to do that. If the second line of code was 'Message
> mB = new Message(mA)' then mA and mB would have been completely separate and
> disposing of either would have no effect on the other.
> Another answer is to have the binding check for a null binding reference on
> each and every access and then to throw if the underlying binding is gone.
> This is not very appealing from a performance standpoint.
> As a compromise I would like to add a property isBound to each class. Users
> then have a fighting chance to check that the binding is still in effect and
> that function calls on the object shouldn't blow up. This property would be
> useful in Assert statements or in debugging.
> [1] If anyone knows how to have my binding library intercept example code
> line (2) and create reference counts, please let me know.
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