DEV-43463: Keep LLEventPump's LLStandardSignal alive during post()

Replace LLEventPump's boost::scoped_ptr<LLStandardSignal> with
boost::shared_ptr. Take a local stack copy of that shared_ptr in post()
methods, and invoke the signal through that copy. This guards against scenario
in which LLEventPump gets destroyed during signal invocation. (See Jira for
details.) Re-enable Mani's test case that used to crash.
Introduce ll_template_cast<> to allow a template function to recognize a
parameter of a particular type.
Introduce LLListenerWrapper mechanism to support wrapper objects for
LLEventPump listeners. You instantiate an LLListenerWrapper subclass object
inline in the listen() call (typically with llwrap<>), passing it the real
listener, trusting it to forward the eventual call.
Introduce prototypical LLCoutListener and LLLogListener subclasses for
illustrative and diagnostic purposes. Test that LLLogListener doesn't block
recognizing LLEventTrackable base class bound into wrapped listener.

1 files changed, 82 insertions, 11 deletions

diff --git a/indra/llcommon/llevents.h b/indra/llcommon/llevents.h
index f52cf33fd8..5646407f6a 100644
--- a/indra/llcommon/llevents.h
+++ b/indra/llcommon/llevents.h
@@ -44,6 +44,7 @@
 #include "llsd.h"
 #include "llsingleton.h"
 #include "lldependencies.h"
+#include "ll_template_cast.h"
 
 /*==========================================================================*|
 // override this to allow binding free functions with more parameters
@@ -266,6 +267,14 @@ namespace LLEventDetail
      */
     template <typename LISTENER>
     LLBoundListener visit_and_connect(const LISTENER& listener,
+                                      const ConnectFunc& connect_func)
+    {
+        return visit_and_connect("", listener, connect_func);
+    }
+    /// overload of visit_and_connect() when we have a string identifier available
+    template <typename LISTENER>
+    LLBoundListener visit_and_connect(const std::string& name,
+                                      const LISTENER& listener,
                                       const ConnectFunc& connect_func);
 } // namespace LLEventDetail
 
@@ -468,7 +477,8 @@ public:
         // This is why listen() is a template. Conversion from boost::bind()
         // to LLEventListener performs type erasure, so it's important to look
         // at the boost::bind object itself before that happens.
-        return LLEventDetail::visit_and_connect(listener,
+        return LLEventDetail::visit_and_connect(name,
+                                                listener,
                                                 boost::bind(&LLEventPump::listen_impl,
                                                             this,
                                                             name,
@@ -522,7 +532,7 @@ private:
 
 protected:
     /// implement the dispatching
-    boost::scoped_ptr<LLStandardSignal> mSignal;
+    boost::shared_ptr<LLStandardSignal> mSignal;
 
     /// valve open?
     bool mEnabled;
@@ -664,6 +674,60 @@ private:
     LLSD mReqid;
 };
 
+/**
+ * Base class for LLListenerWrapper. See visit_and_connect() and llwrap(). We
+ * provide virtual @c accept_xxx() methods, customization points allowing a
+ * subclass access to certain data visible at LLEventPump::listen() time.
+ * Example subclass usage:
+ *
+ * @code
+ * myEventPump.listen("somename",
+ *                    llwrap<MyListenerWrapper>(boost::bind(&MyClass::method, instance, _1)));
+ * @endcode
+ *
+ * Because of the anticipated usage (note the anonymous temporary
+ * MyListenerWrapper instance in the example above), the @c accept_xxx()
+ * methods must be @c const.
+ */
+class LL_COMMON_API LLListenerWrapperBase
+{
+public:
+    /// New instance. The accept_xxx() machinery makes it important to use
+    /// shared_ptrs for our data. Many copies of this object are made before
+    /// the instance that actually ends up in the signal, yet accept_xxx()
+    /// will later be called on the @em original instance. All copies of the
+    /// same original instance must share the same data.
+    LLListenerWrapperBase():
+        mName(new std::string),
+        mConnection(new LLBoundListener)
+    {
+    }
+    /// Copy constructor. Copy shared_ptrs to original instance data.
+    LLListenerWrapperBase(const LLListenerWrapperBase& that):
+        mName(that.mName),
+        mConnection(that.mConnection)
+    {
+    }
+
+    /// Ask LLEventPump::listen() for the listener name
+    virtual void accept_name(const std::string& name) const
+    {
+        *mName = name;
+    }
+
+    /// Ask LLEventPump::listen() for the new connection
+    virtual void accept_connection(const LLBoundListener& connection) const
+    {
+        *mConnection = connection;
+    }
+
+protected:
+    /// Listener name.
+    boost::shared_ptr<std::string> mName;
+    /// Connection.
+    boost::shared_ptr<LLBoundListener> mConnection;
+};
+
 /*****************************************************************************
 *   Underpinnings
 *****************************************************************************/
@@ -898,7 +962,8 @@ namespace LLEventDetail
      * LLStandardSignal, returning LLBoundListener.
      */
     template <typename LISTENER>
-    LLBoundListener visit_and_connect(const LISTENER& raw_listener,
+    LLBoundListener visit_and_connect(const std::string& name,
+                                      const LISTENER& raw_listener,
                                       const ConnectFunc& connect_func)
     {
         // Capture the listener
@@ -913,14 +978,20 @@ namespace LLEventDetail
         // which type details have been erased. unwrap() comes from
         // Boost.Signals, in case we were passed a boost::ref().
         visit_each(visitor, LLEventDetail::unwrap(raw_listener));
-        // Make the connection using passed function. At present, wrapping
-        // this functionality into this function is a bit silly: we don't
-        // really need a visit_and_connect() function any more, just a visit()
-        // function. The definition of this function dates from when, after
-        // visit_each(), after establishing the connection, we had to
-        // postprocess the new connection with the visitor object. That's no
-        // longer necessary.
-        return connect_func(listener);
+        // Make the connection using passed function.
+        LLBoundListener connection(connect_func(listener));
+        // If the LISTENER is an LLListenerWrapperBase subclass, pass it the
+        // desired information. It's important that we pass the raw_listener
+        // so the compiler can make decisions based on its original type.
+        const LLListenerWrapperBase* lwb =
+            ll_template_cast<const LLListenerWrapperBase*>(&raw_listener);
+        if (lwb)
+        {
+            lwb->accept_name(name);
+            lwb->accept_connection(connection);
+        }
+        // In any case, show new connection to caller.
+        return connection;
     }
 } // namespace LLEventDetail