fixed theoretical issue when deferredGet onSize() methods destructs t…

…he underlying channel object

include/channelimpl.h

@@ -598,7 +598,7 @@ class ChannelImpl : public Watchable, public std::enable_shared_from_this<Channe
  Monitor monitor(this);
 
  // copy the callback (so that it will not be destructed during
- // the "reportSuccess" call
+ // the "reportSuccess" call, if the channel is destructed during the call)
  auto cb = _oldestCallback;
 
  // call the callback

src/deferredget.cpp

@@ -27,10 +27,10 @@ const std::shared_ptr<Deferred> &DeferredGet::reportSuccess(uint32_t messageCoun
  // we grab a self pointer to ensure that the deferred object stays alive
  auto self = shared_from_this();
 
- // report the size (technically, the channel object could be destructed now, but we ignore that case)
- if (_sizeCallback) _sizeCallback(messageCount);
-
- // we now know the name, so we can install the message callback on the channel
+ // we now know the name, so we can install the message callback on the channel, the self
+ // pointer is also captured, which ensures that 'this' is not destructed, all members stay
+ // accessible, and that the onFinalize() function will only be called after the message
+ // is reported (onFinalize() is called from the destructor of this DeferredGet object)
  _channel->install("", [self, this](const Message &message, uint64_t deliveryTag, bool redelivered) {
 
  // install a monitor to deal with the case that the channel is removed
@@ -42,6 +42,10 @@ const std::shared_ptr<Deferred> &DeferredGet::reportSuccess(uint32_t messageCoun
  // we can remove the callback now from the channel
  if (monitor.valid()) _channel->uninstall("");
  });
+
+ // report the size (note that this is the size _minus_ the message that is retrieved
+ // (and for which the callback will be called later), so it could be zero)
+ if (_sizeCallback) _sizeCallback(messageCount);
 
  // return next object
  return _next;