[Boost-users] shared_ptr conundrum

From: Timothy Ritchey (tritchey_at_[hidden])
Date: 2005-08-09 22:57:40

We have been using shared_ptrs pretty successfully throughout our 
application, but I have run across something that has just completely 
stumped me. BTW - this is a Windows .NET 2003 + Intel 8.1 compiler 
compiling in Debug mode on a multi-processor machine (dual Xeon Dell 
workstation).

The code in question is:

void Router::routeEnvelope(shared_ptr<Envelope> envelope) {

     if(!running || !envelope)
         return;

     GUID target = envelope->getTo();
     if(target == guid) {
        // PATH 1

         // check to see if it is a failure envelope
        shared_ptr<EnvelopeFailure> envelopeFailure = 
shared_dynamic_cast<EnvelopeFailure>(envelope);
         if(envelopeFailure) {
             // there was a problem sending the original envelope
             failedEnvelope(envelopeFailure->getFrom());
         }
         // pass it on up the stack
         envelopeController.injectEnvelope(envelope);

     } else {
         // PATH 2
         mutex::scoped_lock lock(envelopeQueueMonitor);
         envelopeQueue.push(envelope);
         envelopeReady.notify_all();
     }
}

The first envelope that comes in has a guid that matches target, so it 
takes code path 1. If I comment out both code path 1 and code path 2, 
the envelope is released properly, and I can see its destructor get 
called. Here is where it gets strange--if I uncomment anything in code 
path 2, and only code path 2, I no longer see the envelope get released, 
even though that code path is not executed at all. I've been doing this 
testing on an SMP machine. On a UP machine, the program runs fine 
without any issues. I am at a complete loss. The original envelope 
object is created in the function that calls this function, and as far 
as I can tell , is not touched by any other thread in the application.

Thanks for any advice.

Cheers,
tim