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https://issues.apache.org/jira/browse/QPID-3199?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13018581#comment-13018581
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Andrew Stitcher commented on QPID-3199:
---------------------------------------
Using this test program I established that gcc 4.5 does in fact perform as per
the spec and so this is an actual bug in our code (maybe not triggered).
#include <iostream>
#include <string>
using std::cout;
using std::string;
class Scoped {
string s;
public:
Scoped(const string& s0) :
s(s0)
{
cout << "Scoped const" << s << "\n";
}
~Scoped () {
cout << "Scoped destr" << s << "\n";
}
};
int main() {
Scoped("A"); cout << "after A\n";
Scoped s("B"); cout << "after B\n";
}
with results:
$ make CXXFLAGS=-O3 destructor-sequence
g++ -O3 destructor-sequence.cpp -o destructor-sequence
$ ./destructor-sequence
Scoped constA
Scoped destrA
after A
Scoped constB
after B
Scoped destrB
$
> Severe but difficult to diagnose lock error in qpid::sys::StateMonitor
> ----------------------------------------------------------------------
>
> Key: QPID-3199
> URL: https://issues.apache.org/jira/browse/QPID-3199
> Project: Qpid
> Issue Type: Bug
> Components: C++ Broker, C++ Client
> Affects Versions: 0.8, 0.9
> Reporter: Andrew Stitcher
> Assignee: Andrew Stitcher
> Labels: clang
> Fix For: 0.10
>
>
> The qpid::sys::StateMonitor class has 4 member functions liker this:
> void waitFor(Enum s) { ScopedWait(*this); while (s != state) wait(); }
> However the ScopeWait(*this); is in error, because it creates a temporary
> ScopedWait and then immediately destroys it. Instead of locking this and then
> unlocking it at the end of the function execution.
> What was meant was:
> void waitFor(Enum s) { ScopedWait w(*this); while (s != state) wait(); }
> which creates a local variable w which is destroyed at the end of the
> function execution unlocking this.
> It is possible that the compiler/options we use do not actually exhibit this
> bug. As the correct behaviour may not actually be implemented by all
> compilers.
> If this bug exhibits it might show as StateMonitor::waitFor() never detecting
> the desired state for instance. It is remarkable that this code has been in
> the codebase for 3.5 years and we've not noticed any bug caused by it.
> This bug was detected by the work on QPID-3004: The clang++ compiler detected
> that the value being returned by the constructor was not being used at all.
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