SegFault problems with Proxies

galbe

Hi

The program I'm writing is intended to be used by a lot of people, who will merge it with their own code. Since I can't controll the behaviour of this code, I'm testing my program for robustness to check how it behaves in the case of local failure.

Unfortunatly I'm encountering problems, I don't understand:

After the Server has "crashed"(using abort(), NO Shutdown of the Ice::Communicator), sometimes the proxies on the clientside are causing segmentation faults, if

1. I call a method on the proxy
2. the Proxy is destroyed.

Is there a way for me to ensure, that a local failure does not propagate and cause failures in other Processes as well?
Ideally I would expect to get a ConnectionLostException in EVERY case I'm trying to access the proxy.
At the moment I'm a bit confused by this behaviour.

Thanx in advance

Gerald

marc

The client should not crash because the server crashes. You should get a ConnectFailedException or ConnectionLostException. You can test this with all the demos. For example, with the demo in demo/Ice/hello: Kill the server, and the client will report an exception when you try to send a request to the server.

I'm not aware of any problems in Ice that could cause a segmentation fault instead of an exception. I'm afraid without a code example, I cannot give much advice.

galbe

Hi, thanx for the answer.

I know, this shouldn't happen, that's why I'm confused

This is a SHORT Version of the Code.

void ObjectX::registerInterceptor(const InterceptorPrx& proxy, const Ice::Current&) {
IceUtil::RecMutex::Lock lock(_mutex);

//More happening here, this is just a short version

//proxy is a oneway-proxy
_interceptors.push_back(proxy);
}


void ObjectX::somethingHappens() {

//More happening here

IceUtil::RecMutex::Lock lock(_mutex);

std::list<InterceptorPrx>::iterator k;
for (k = _interceptors.begin(); k != _interceptors.end(); k++) {
try {
//SEGFAULT
(*k)->somethingHappens();
}catch(const Ice::Exception&) {
_interceptors.erase(k);
}}}

The Stacktrace looks like this:

ObjectX::somethingHappens() at *MY CODE*
IceProxy::Interceptor::somethingHappens() at *GENERATED CODE*
IceProxy::Ice::Object::__defaultContext() at Proxy.cpp:836
IceUtil::HandleBase<IceInternal::Reference>::operator->() at Handle.h:42

Thanx in Advance

Gerald

marc

I believe this is a problem with the erase() in the for-loop. Unfortuantely, I don't have my copy of "Effective STL" handy, but I believe the code should look like this:

std::list<InterceptorPrx>::iterator k = _interceptors.begin();
while(k != _interceptors.end())
{
try
{
(*k)->somethingHappens();
++k;
}
catch(const Ice::Exception&)
{
_interceptors.erase(k++);
}
}

The problem with just doing a erase(k) is that this invalidates the iterator, and thus the next k++ fails. By using erase(k++), a temporary is passed to erase, and the iterator is not invalidated.

Of course this doesn't have anything to do with Ice

kssreeram

looks like problem in app code

Originally posted by galbe

std::list<InterceptorPrx>::iterator k;
for (k = _interceptors.begin(); k != _interceptors.end(); k++) {
try {
//SEGFAULT
(*k)->somethingHappens();
}catch(const Ice::Exception&) {
_interceptors.erase(k);
}}}

Looks like its a problem in the application code. Lets assume that the remote app is down. You'd then get an exception, at which point you're doing

_interceptors.erase(k);

As soon as this is done, 'k' becomes invalid. After this again you're doing 'k++', as part of the 'for' statement. Thus, in the next iteration of the loop you'll referencing invalid memory.

That could be one of the reasons why you're getting a segfault

galbe

Thanx for your help.