Ditch `LLEventTrackable` aka `boost::signals2::trackable`.

Remove documented `LLEventPump` support for `LLEventTrackable`. That claimed
support was always a little bit magical/fragile. IF:

* a class included `LLEventTrackable` as a base class AND
* an instance of that class was managed by `boost::shared_ptr` AND
* you passed one of that class's methods and the `boost::shared_ptr`
  specifically to `boost::bind()` AND
* the resulting `boost::bind()` object was passed into `LLEventPump::listen()`

THEN the promise was that on destruction of that object, that listener would
automatically be disconnected -- instead of leaving a dangling pointer bound
into the `LLEventPump`, causing a crash on the next `LLEventPump::post()` call.

The only existing code in the viewer code base that exercised `LLEventTrackable`
functionality was in test programs. When the viewer calls `LLEventPump::listen()`,
it typically stores the resulting connection object in an `LLTempBoundListener`
variable, which guarantees disconnection on destruction of that variable.

The fact that `LLEventTrackable` support is specific to `boost::bind()`, that it
silently fails to keep its promise with `std::bind()` or a lambda or any other
form of C++ callable, makes it untrustworthy for new code.

Note that the code base still uses `boost::signals2::trackable` for other
`boost::signals2::signal` instances not associated with `LLEventPump`. We are
not changing those at this time.

6 files changed, 15 insertions, 112 deletions

diff --git a/indra/llcommon/llevents.h b/indra/llcommon/llevents.h
index 8ef3a5af95..abc25ba400 100644
--- a/indra/llcommon/llevents.h
+++ b/indra/llcommon/llevents.h
@@ -364,56 +364,13 @@ testable:
 };
 
 /*****************************************************************************
-*   LLEventTrackable
-*****************************************************************************/
-/**
- * LLEventTrackable wraps boost::signals2::trackable, which resembles
- * boost::trackable. Derive your listener class from LLEventTrackable instead,
- * and use something like
- * <tt>LLEventPump::listen(boost::bind(&YourTrackableSubclass::method,
- * instance, _1))</tt>. This will implicitly disconnect when the object
- * referenced by @c instance is destroyed.
- *
- * @note
- * LLEventTrackable doesn't address a couple of cases:
- * * Object destroyed during call
- *   - You enter a slot call in thread A.
- *   - Thread B destroys the object, which of course disconnects it from any
- *     future slot calls.
- *   - Thread A's call uses 'this', which now refers to a defunct object.
- *     Undefined behavior results.
- * * Call during destruction
- *   - @c MySubclass is derived from LLEventTrackable.
- *   - @c MySubclass registers one of its own methods using
- *     <tt>LLEventPump::listen()</tt>.
- *   - The @c MySubclass object begins destruction. <tt>~MySubclass()</tt>
- *     runs, destroying state specific to the subclass. (For instance, a
- *     <tt>Foo*</tt> data member is <tt>delete</tt>d but not zeroed.)
- *   - The listening method will not be disconnected until
- *     <tt>~LLEventTrackable()</tt> runs.
- *   - Before we get there, another thread posts data to the @c LLEventPump
- *     instance, calling the @c MySubclass method.
- *   - The method in question relies on valid @c MySubclass state. (For
- *     instance, it attempts to dereference the <tt>Foo*</tt> pointer that was
- *     <tt>delete</tt>d but not zeroed.)
- *   - Undefined behavior results.
- */
-typedef boost::signals2::trackable LLEventTrackable;
-
-/*****************************************************************************
 *   LLEventPump
 *****************************************************************************/
 /**
  * LLEventPump is the base class interface through which we access the
  * concrete subclasses such as LLEventStream.
- *
- * @NOTE
- * LLEventPump derives from LLEventTrackable so that when you "chain"
- * LLEventPump instances together, they will automatically disconnect on
- * destruction. Please see LLEventTrackable documentation for situations in
- * which this may be perilous across threads.
  */
-class LL_COMMON_API LLEventPump: public LLEventTrackable
+class LL_COMMON_API LLEventPump
 {
 public:
     static const std::string ANONYMOUS; // constant for anonymous listeners.
diff --git a/indra/llui/llnotifications.h b/indra/llui/llnotifications.h
index ab4f009a80..206c521592 100644
--- a/indra/llui/llnotifications.h
+++ b/indra/llui/llnotifications.h
@@ -734,7 +734,7 @@ typedef std::multimap<std::string, LLNotificationPtr> LLNotificationMap;
 // all of the built-in tests should attach to the "Visible" channel
 //
 class LLNotificationChannelBase :
-    public LLEventTrackable,
+    public boost::signals2::trackable,
     public LLRefCount
 {
     LOG_CLASS(LLNotificationChannelBase);
diff --git a/indra/llui/llnotificationslistener.cpp b/indra/llui/llnotificationslistener.cpp
index ace9e37e25..2ad1689a45 100644
--- a/indra/llui/llnotificationslistener.cpp
+++ b/indra/llui/llnotificationslistener.cpp
@@ -204,7 +204,7 @@ void LLNotificationsListener::ignore(const LLSD& params) const
     }
 }
 
-class LLNotificationsListener::Forwarder: public LLEventTrackable
+class LLNotificationsListener::Forwarder: public boost::signals2::trackable
 {
     LOG_CLASS(LLNotificationsListener::Forwarder);
 public:
@@ -213,8 +213,10 @@ public:
         mRespond(false)
     {
         // Connect to the specified channel on construction. Because
-        // LLEventTrackable is a base, we should automatically disconnect when
-        // destroyed.
+        // boost::signals2::trackable is a base, because we use boost::bind()
+        // below, and because connectPassedFilter() directly calls
+        // boost::signals2::signal::connect(), we should automatically
+        // disconnect when destroyed.
         LLNotificationChannelPtr channelptr(llnotifications.getChannel(channel));
         if (channelptr)
         {
@@ -252,10 +254,10 @@ void LLNotificationsListener::forward(const LLSD& params)
     if (! forward)
     {
         // This is a request to stop forwarding notifications on the specified
-        // channel. The rest of the params don't matter.
-        // Because mForwarders contains scoped_ptrs, erasing the map entry
-        // DOES delete the heap Forwarder object. Because Forwarder derives
-        // from LLEventTrackable, destroying it disconnects it from the
+        // channel. The rest of the params don't matter. Because mForwarders
+        // contains scoped_ptrs, erasing the map entry DOES delete the heap
+        // Forwarder object. Because Forwarder derives from
+        // boost::signals2::trackable, destroying it disconnects it from the
         // channel.
         mForwarders.erase(channel);
         return;
diff --git a/indra/newview/llspeakers.h b/indra/newview/llspeakers.h
index 234de42953..d3304dba59 100644
--- a/indra/newview/llspeakers.h
+++ b/indra/newview/llspeakers.h
@@ -37,7 +37,7 @@ class LLSpeakerMgr;
 class LLAvatarName;
 
 // data for a given participant in a voice channel
-class LLSpeaker : public LLRefCount, public LLOldEvents::LLObservable, public LLHandleProvider<LLSpeaker>, public boost::signals2::trackable
+class LLSpeaker : public LLRefCount, public LLOldEvents::LLObservable, public LLHandleProvider<LLSpeaker>
 {
 public:
     typedef enum e_speaker_type
diff --git a/indra/test/llevents_tut.cpp b/indra/test/llevents_tut.cpp
index 875ca9ad89..f9cc99203b 100644
--- a/indra/test/llevents_tut.cpp
+++ b/indra/test/llevents_tut.cpp
@@ -429,7 +429,7 @@ void events_object::test<9>()
 {
     set_test_name("listen(boost::bind(...TempListener...))");
     // listen() can't do anything about a plain TempListener instance:
-    // it's not managed with shared_ptr, nor is it an LLEventTrackable subclass
+    // it's not managed with shared_ptr
     bool live = false;
     LLEventPump& heaptest(pumps.obtain("heaptest"));
     LLBoundListener connection;
@@ -453,60 +453,4 @@ void events_object::test<9>()
     heaptest.stopListening("temp");
 }
 
-class TempTrackableListener: public TempListener, public LLEventTrackable
-{
-public:
-    TempTrackableListener(const std::string& name, bool& liveFlag):
-        TempListener(name, liveFlag)
-    {}
-};
-
-template<> template<>
-void events_object::test<10>()
-{
-    set_test_name("listen(boost::bind(...TempTrackableListener ref...))");
-    bool live = false;
-    LLEventPump& heaptest(pumps.obtain("heaptest"));
-    LLBoundListener connection;
-    {
-        TempTrackableListener tempListener("temp", live);
-        ensure("TempTrackableListener constructed", live);
-        connection = heaptest.listen(tempListener.getName(),
-                                     boost::bind(&TempTrackableListener::call,
-                                                 boost::ref(tempListener), _1));
-        heaptest.post(1);
-        check_listener("received", tempListener, 1);
-    } // presumably this will make tempListener go away?
-    // verify that
-    ensure("TempTrackableListener destroyed", ! live);
-    ensure("implicit disconnect", ! connection.connected());
-    // now just make sure we don't blow up trying to access a freed object!
-    heaptest.post(2);
-}
-
-template<> template<>
-void events_object::test<11>()
-{
-    set_test_name("listen(boost::bind(...TempTrackableListener pointer...))");
-    bool live = false;
-    LLEventPump& heaptest(pumps.obtain("heaptest"));
-    LLBoundListener connection;
-    {
-        TempTrackableListener* newListener(new TempTrackableListener("temp", live));
-        ensure("TempTrackableListener constructed", live);
-        connection = heaptest.listen(newListener->getName(),
-                                     boost::bind(&TempTrackableListener::call,
-                                                 newListener, _1));
-        heaptest.post(1);
-        check_listener("received", *newListener, 1);
-        // explicitly destroy newListener
-        delete newListener;
-    }
-    // verify that
-    ensure("TempTrackableListener destroyed", ! live);
-    ensure("implicit disconnect", ! connection.connected());
-    // now just make sure we don't blow up trying to access a freed object!
-    heaptest.post(2);
-}
-
 } // namespace tut
diff --git a/indra/viewer_components/login/tests/lllogin_test.cpp b/indra/viewer_components/login/tests/lllogin_test.cpp
index 8aea3b37aa..f051f8c67f 100644
--- a/indra/viewer_components/login/tests/lllogin_test.cpp
+++ b/indra/viewer_components/login/tests/lllogin_test.cpp
@@ -66,7 +66,7 @@
 *   Helper classes
 *****************************************************************************/
 // This is a listener to receive results from lllogin.
-class LoginListener: public LLEventTrackable
+class LoginListener
 {
     std::string mName;
     LLSD mLastEvent;
@@ -137,7 +137,7 @@ public:
     }
 };
 
-class LLXMLRPCListener: public LLEventTrackable
+class LLXMLRPCListener
 {
     std::string mName;
     LLSD mEvent;