diff --git a/indra/aistatemachine/CMakeLists.txt b/indra/aistatemachine/CMakeLists.txt
index 6db29a007..806261201 100644
--- a/indra/aistatemachine/CMakeLists.txt
+++ b/indra/aistatemachine/CMakeLists.txt
@@ -21,6 +21,7 @@ set(aistatemachine_SOURCE_FILES
     aistatemachine.cpp
     aistatemachinethread.cpp
     aitimer.cpp
+    aicondition.cpp
     )
 
 set(aistatemachine_HEADER_FILES
@@ -29,6 +30,7 @@ set(aistatemachine_HEADER_FILES
     aistatemachine.h
     aistatemachinethread.h
     aitimer.h
+    aicondition.h
     )
 
 set_source_files_properties(${aistatemachine_HEADER_FILES}
diff --git a/indra/aistatemachine/aicondition.cpp b/indra/aistatemachine/aicondition.cpp
new file mode 100644
index 000000000..fa35104a8
--- /dev/null
+++ b/indra/aistatemachine/aicondition.cpp
@@ -0,0 +1,88 @@
+/**
+ * @file aicondition.cpp
+ * @brief Implementation of AICondition
+ *
+ * Copyright (c) 2013, Aleric Inglewood.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * There are special exceptions to the terms and conditions of the GPL as
+ * it is applied to this Source Code. View the full text of the exception
+ * in the file doc/FLOSS-exception.txt in this software distribution.
+ *
+ * CHANGELOG
+ *   and additional copyright holders.
+ *
+ *   14/10/2013
+ *   Initial version, written by Aleric Inglewood @ SL
+ */
+
+#include "aicondition.h"
+#include "aistatemachine.h"
+
+void AIConditionBase::wait(AIStateMachine* state_machine)
+{
+  // The condition must be locked before calling AIStateMachine::wait().
+  llassert(mutex().isSelfLocked());
+  // Add the new state machine at the end.
+  mWaitingStateMachines.push_back(state_machine);
+}
+
+void AIConditionBase::remove(AIStateMachine* state_machine)
+{
+  mutex().lock();
+  // Remove all occurances of state_machine from the queue.
+  queue_t::iterator const end = mWaitingStateMachines.end();
+  queue_t::iterator last = end;
+  for (queue_t::iterator iter = mWaitingStateMachines.begin(); iter != last; ++iter)
+  {
+	if (iter->get() == state_machine)
+	{
+	  if (--last == iter)
+	  {
+		break;
+	  }
+	  queue_t::value_type::swap(*iter, *last);
+	}
+  }
+  // This invalidates all iterators involved, including end, but not any iterators to the remaining elements.
+  mWaitingStateMachines.erase(last, end);
+  mutex().unlock();
+}
+
+void AIConditionBase::signal(int n)
+{
+  // The condition must be locked before calling AICondition::signal or AICondition::broadcast.
+  llassert(mutex().isSelfLocked());
+  // Signal n state machines.
+  while (n > 0 && !mWaitingStateMachines.empty())
+  {
+	LLPointer<AIStateMachine> state_machine = mWaitingStateMachines.front();
+	bool success = state_machine->signalled();
+	// Only state machines that are actually still blocked should be in the queue:
+	// they are removed from the queue by calling AICondition::remove whenever
+	// they are unblocked for whatever reason...
+	llassert(success);
+	if (success)
+	{
+	  ++n;
+	}
+	else
+	{
+	  // We never get here...
+	  remove(state_machine.get());
+	}
+  }
+}
+
diff --git a/indra/aistatemachine/aicondition.h b/indra/aistatemachine/aicondition.h
new file mode 100644
index 000000000..05dd9ea42
--- /dev/null
+++ b/indra/aistatemachine/aicondition.h
@@ -0,0 +1,110 @@
+/**
+ * @file aicondition.h
+ * @brief Condition variable for statemachines.
+ *
+ * Copyright (c) 2013, Aleric Inglewood.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * There are special exceptions to the terms and conditions of the GPL as
+ * it is applied to this Source Code. View the full text of the exception
+ * in the file doc/FLOSS-exception.txt in this software distribution.
+ *
+ * CHANGELOG
+ *   and additional copyright holders.
+ *
+ *   14/10/2013
+ *   Initial version, written by Aleric Inglewood @ SL
+ */
+
+#ifndef AICONDITION_H
+#define AICONDITION_H
+
+#include <deque>
+#include <llpointer.h>
+#include "aithreadsafe.h"
+
+class AIStateMachine;
+class LLMutex;
+
+// class AICondition
+//
+// Call AIStateMachine::wait(AICondition&) in the multiplex_impl of a state machine to
+// make the state machine go idle until some thread calls AICondition::signal().
+//
+// If the state machine is no longer running or wasn't waiting anymore because
+// something else woke it up, then AICondition::signal() will wake up another
+// state machine (if any).
+//
+// Usage:
+//
+// struct Foo { bool met(); };	// Returns true when the condition is met.
+// AICondition<Foo> Condition_t;
+// AIAccess<Foo> Condition_wat;
+//
+// // Some thread-safe condition variable.
+// Condition_t condition;
+//
+// // Inside the state machine:
+// {
+//   ...
+//   state WAIT_FOR_CONDITION:
+//   {
+//     // Lock condition and check it. Wait if condition is not met yet.
+//     {
+//       Condition_wat condition_w(condition);
+//       if (!condition_w->met())
+//       {
+//         wait(condition);
+//         break;
+//       }
+//     }
+//     set_state(CONDITION_MET);
+//     break;
+//   }
+//   CONDITION_MET:
+//   {
+//
+
+class AIConditionBase
+{
+  public:
+	virtual ~AIConditionBase() { }
+
+	void signal(int n = 1);											// Call this when the condition was met to release n state machines.
+	void broadcast(void) { signal(mWaitingStateMachines.size()); }	// Release all blocked state machines.
+
+  private:
+	// These functions are called by AIStateMachine.
+	friend class AIStateMachine;
+	void wait(AIStateMachine* state_machine);
+	void remove(AIStateMachine* state_machine);
+
+  protected:
+	virtual LLMutex& mutex(void)  = 0;
+
+  protected:
+	typedef std::deque<LLPointer<AIStateMachine> > queue_t;
+	queue_t mWaitingStateMachines;
+};
+
+template<typename T>
+class AICondition : public AIThreadSafeSimpleDC<T>, public AIConditionBase
+{
+  protected:
+	/*virtual*/ LLMutex& mutex(void) { return this->mMutex; }
+};
+
+#endif
+
diff --git a/indra/aistatemachine/aistatemachine.cpp b/indra/aistatemachine/aistatemachine.cpp
index bf867fffd..fcdb2d9c8 100644
--- a/indra/aistatemachine/aistatemachine.cpp
+++ b/indra/aistatemachine/aistatemachine.cpp
@@ -33,6 +33,7 @@
 
 #include "linden_common.h"
 #include "aistatemachine.h"
+#include "aicondition.h"
 #include "lltimer.h"
 
 //==================================================================
@@ -283,7 +284,7 @@ char const* HelloWorld::state_str_impl(state_type run_state) const
 
 void AIEngine::add(AIStateMachine* state_machine)
 {
-  Dout(dc::statemachine, "Adding state machine [" << (void*)state_machine << "] to " << mName);
+  Dout(dc::statemachine(state_machine->mSMDebug), "Adding state machine [" << (void*)state_machine << "] to " << mName);
   engine_state_type_wat engine_state_w(mEngineState);
   engine_state_w->list.push_back(QueueElement(state_machine));
   if (engine_state_w->waiting)
@@ -330,7 +331,7 @@ void AIEngine::mainloop(void)
 	engine_state_type_wat engine_state_w(mEngineState);
 	if (!active)
 	{
-	  Dout(dc::statemachine, "Erasing state machine [" << (void*)&state_machine << "] from " << mName);
+	  Dout(dc::statemachine(state_machine.mSMDebug), "Erasing state machine [" << (void*)&state_machine << "] from " << mName);
 	  engine_state_w->list.erase(queued_element++);
 	}
 	else
@@ -392,7 +393,7 @@ void AIStateMachine::multiplex(event_type event)
   // If this fails then you are using a pointer to a state machine instead of an LLPointer.
   llassert(event == initial_run || getNumRefs() > 0);
 
-  DoutEntering(dc::statemachine, "AIStateMachine::multiplex(" << event_str(event) << ") [" << (void*)this << "]");
+  DoutEntering(dc::statemachine(mSMDebug), "AIStateMachine::multiplex(" << event_str(event) << ") [" << (void*)this << "]");
 
   base_state_type state;
   state_type run_state;
@@ -407,7 +408,7 @@ void AIStateMachine::multiplex(event_type event)
 	llassert(!mMultiplexMutex.isSelfLocked());		// We may never enter recursively!
 	if (!mMultiplexMutex.tryLock())
 	{
-	  Dout(dc::statemachine, "Leaving because it is already being run [" << (void*)this << "]");
+	  Dout(dc::statemachine(mSMDebug), "Leaving because it is already being run [" << (void*)this << "]");
 	  return;
 	}
 
@@ -421,7 +422,7 @@ void AIStateMachine::multiplex(event_type event)
 	// we should indeed run, again.
 	if (event == schedule_run && !sub_state_type_rat(mSubState)->need_run)
 	{
-	  Dout(dc::statemachine, "Leaving because it was already being run [" << (void*)this << "]");
+	  Dout(dc::statemachine(mSMDebug), "Leaving because it was already being run [" << (void*)this << "]");
 	  return;
 	}
 
@@ -440,9 +441,9 @@ void AIStateMachine::multiplex(event_type event)
 	{
 #ifdef CWDEBUG
 	  if (state == bs_multiplex)
-		Dout(dc::statemachine, "Running state bs_multiplex / " << state_str_impl(run_state) << " [" << (void*)this << "]");
+		Dout(dc::statemachine(mSMDebug), "Running state bs_multiplex / " << state_str_impl(run_state) << " [" << (void*)this << "]");
 	  else
-		Dout(dc::statemachine, "Running state " << state_str(state) << " [" << (void*)this << "]");
+		Dout(dc::statemachine(mSMDebug), "Running state " << state_str(state) << " [" << (void*)this << "]");
 #endif
 
 #ifdef SHOW_ASSERT
@@ -503,7 +504,7 @@ void AIStateMachine::multiplex(event_type event)
 		// run of bs_reset is not a problem because it happens to be a NoOp.
 		state = (state == bs_initialize) ? bs_reset : bs_abort;
 #ifdef CWDEBUG
-		Dout(dc::statemachine, "Late abort detected! Running state " << state_str(state) << " instead [" << (void*)this << "]");
+		Dout(dc::statemachine(mSMDebug), "Late abort detected! Running state " << state_str(state) << " instead [" << (void*)this << "]");
 #endif
 	  }
 #ifdef SHOW_ASSERT
@@ -665,7 +666,7 @@ void AIStateMachine::multiplex(event_type event)
 
 #ifdef CWDEBUG
 		if (state != state_w->base_state)
-		  Dout(dc::statemachine, "Base state changed from " << state_str(state) << " to " << state_str(state_w->base_state) <<
+		  Dout(dc::statemachine(mSMDebug), "Base state changed from " << state_str(state) << " to " << state_str(state_w->base_state) <<
 			  "; need_new_run = " << (need_new_run ? "true" : "false") << " [" << (void*)this << "]");
 #endif
 	  }
@@ -699,11 +700,15 @@ void AIStateMachine::multiplex(event_type event)
 			// Mark that we're added to this engine, and at the same time, that we're not added to the previous one.
 			state_w->current_engine = engine;
 		  }
+#ifdef SHOW_ASSERT
+		  // We are leaving the loop, but we're not idle. The statemachine should re-enter the loop again.
+		  mDebugShouldRun = true;
+#endif
 		}
 		else
 		{
-		  // Remove this state machine from any engine.
-		  // Cause the engine to remove us.
+		  // Remove this state machine from any engine,
+		  // causing the engine to remove us.
 		  state_w->current_engine = NULL;
 		}
 
@@ -749,7 +754,7 @@ void AIStateMachine::multiplex(event_type event)
 
 AIStateMachine::state_type AIStateMachine::begin_loop(base_state_type base_state)
 {
-  DoutEntering(dc::statemachine, "AIStateMachine::begin_loop(" << state_str(base_state) << ") [" << (void*)this << "]");
+  DoutEntering(dc::statemachine(mSMDebug), "AIStateMachine::begin_loop(" << state_str(base_state) << ") [" << (void*)this << "]");
 
   sub_state_type_wat sub_state_w(mSubState);
   // Honor a subsequent call to idle() (only necessary in bs_multiplex, but it doesn't hurt to reset this flag in other states too).
@@ -759,7 +764,7 @@ AIStateMachine::state_type AIStateMachine::begin_loop(base_state_type base_state
   // Honor previous calls to advance_state() (once run_state is initialized).
   if (base_state == bs_multiplex && sub_state_w->advance_state > sub_state_w->run_state)
   {
-	Dout(dc::statemachine, "Copying advance_state to run_state, because it is larger [" << state_str_impl(sub_state_w->advance_state) << " > " << state_str_impl(sub_state_w->run_state) << "]");
+	Dout(dc::statemachine(mSMDebug), "Copying advance_state to run_state, because it is larger [" << state_str_impl(sub_state_w->advance_state) << " > " << state_str_impl(sub_state_w->run_state) << "]");
 	sub_state_w->run_state = sub_state_w->advance_state;
   }
 #ifdef SHOW_ASSERT
@@ -789,7 +794,7 @@ AIStateMachine::state_type AIStateMachine::begin_loop(base_state_type base_state
 
 void AIStateMachine::run(AIStateMachine* parent, state_type new_parent_state, bool abort_parent, bool on_abort_signal_parent, AIEngine* default_engine)
 {
-  DoutEntering(dc::statemachine, "AIStateMachine::run(" <<
+  DoutEntering(dc::statemachine(mSMDebug), "AIStateMachine::run(" <<
 	  (void*)parent << ", " <<
 	  (parent ? parent->state_str_impl(new_parent_state) : "NA") <<
 	  ", abort_parent = " << (abort_parent ? "true" : "false") <<
@@ -839,7 +844,7 @@ void AIStateMachine::run(AIStateMachine* parent, state_type new_parent_state, bo
 
 void AIStateMachine::run(callback_type::signal_type::slot_type const& slot, AIEngine* default_engine)
 {
-  DoutEntering(dc::statemachine, "AIStateMachine::run(<slot>, default_engine = " << default_engine->name() << ") [" << (void*)this << "]");
+  DoutEntering(dc::statemachine(mSMDebug), "AIStateMachine::run(<slot>, default_engine = " << default_engine->name() << ") [" << (void*)this << "]");
 
 #ifdef SHOW_ASSERT
   {
@@ -874,7 +879,7 @@ void AIStateMachine::run(callback_type::signal_type::slot_type const& slot, AIEn
 
 void AIStateMachine::callback(void)
 {
-  DoutEntering(dc::statemachine, "AIStateMachine::callback() [" << (void*)this << "]");
+  DoutEntering(dc::statemachine(mSMDebug), "AIStateMachine::callback() [" << (void*)this << "]");
 
   bool aborted = sub_state_type_rat(mSubState)->aborted;
   if (mParent)
@@ -920,7 +925,7 @@ void AIStateMachine::force_killed(void)
 
 void AIStateMachine::kill(void)
 {
-  DoutEntering(dc::statemachine, "AIStateMachine::kill() [" << (void*)this << "]");
+  DoutEntering(dc::statemachine(mSMDebug), "AIStateMachine::kill() [" << (void*)this << "]");
 #ifdef SHOW_ASSERT
   {
 	multiplex_state_type_rat state_r(mState);
@@ -937,7 +942,7 @@ void AIStateMachine::kill(void)
 
 void AIStateMachine::reset()
 {
-  DoutEntering(dc::statemachine, "AIStateMachine::reset() [" << (void*)this << "]");
+  DoutEntering(dc::statemachine(mSMDebug), "AIStateMachine::reset() [" << (void*)this << "]");
 #ifdef SHOW_ASSERT
   mDebugAborted = false;
   mDebugContPending = false;
@@ -960,6 +965,8 @@ void AIStateMachine::reset()
 	sub_state_w->reset = true;
 	// Start running.
 	sub_state_w->idle = false;
+	// We're not waiting for a condition.
+	sub_state_w->blocked = NULL;
 	// Keep running till we reach at least bs_multiplex.
 	sub_state_w->need_run = true;
   }
@@ -972,7 +979,7 @@ void AIStateMachine::reset()
 
 void AIStateMachine::set_state(state_type new_state)
 {
-  DoutEntering(dc::statemachine, "AIStateMachine::set_state(" << state_str_impl(new_state) << ") [" << (void*)this << "]");
+  DoutEntering(dc::statemachine(mSMDebug), "AIStateMachine::set_state(" << state_str_impl(new_state) << ") [" << (void*)this << "]");
 #ifdef SHOW_ASSERT
   {
 	multiplex_state_type_rat state_r(mState);
@@ -983,6 +990,8 @@ void AIStateMachine::set_state(state_type new_state)
   }
 #endif
   sub_state_type_wat sub_state_w(mSubState);
+  // It should never happen that set_state() is called while we're blocked.
+  llassert(!sub_state_w->blocked);
   // Force current state to the requested state.
   sub_state_w->run_state = new_state;
   // Void last call to advance_state.
@@ -999,13 +1008,13 @@ void AIStateMachine::set_state(state_type new_state)
 
 void AIStateMachine::advance_state(state_type new_state)
 {
-  DoutEntering(dc::statemachine, "AIStateMachine::advance_state(" << state_str_impl(new_state) << ") [" << (void*)this << "]");
+  DoutEntering(dc::statemachine(mSMDebug), "AIStateMachine::advance_state(" << state_str_impl(new_state) << ") [" << (void*)this << "]");
   {
 	sub_state_type_wat sub_state_w(mSubState);
 	// Ignore call to advance_state when the currently queued state is already greater or equal to the requested state.
 	if (sub_state_w->advance_state >= new_state)
 	{
-	  Dout(dc::statemachine, "Ignored, because " << state_str_impl(sub_state_w->advance_state) << " >= " << state_str_impl(new_state) << ".");
+	  Dout(dc::statemachine(mSMDebug), "Ignored, because " << state_str_impl(sub_state_w->advance_state) << " >= " << state_str_impl(new_state) << ".");
 	  return;
 	}
 	// Ignore call to advance_state when the current state is greater than the requested state: the new state would be
@@ -1014,7 +1023,7 @@ void AIStateMachine::advance_state(state_type new_state)
 	// the state change is and should be being ignored: the statemachine would start running it's current state (again).
 	if (sub_state_w->run_state > new_state)
 	{
-	  Dout(dc::statemachine, "Ignored, because " << state_str_impl(sub_state_w->run_state) << " > " << state_str_impl(new_state) << " (current state).");
+	  Dout(dc::statemachine(mSMDebug), "Ignored, because " << state_str_impl(sub_state_w->run_state) << " > " << state_str_impl(new_state) << " (current state).");
 	  return;
 	}
 	// Increment state.
@@ -1023,6 +1032,13 @@ void AIStateMachine::advance_state(state_type new_state)
 	sub_state_w->idle = false;
 	// Ignore a call to idle if it occurs before we leave multiplex_impl().
 	sub_state_w->skip_idle = true;
+	// No longer say we woke up when signalled() is called.
+	if (sub_state_w->blocked)
+	{
+	  Dout(dc::statemachine(mSMDebug), "Removing statemachine from condition " << (void*)sub_state_w->blocked);
+	  sub_state_w->blocked->remove(this);
+	  sub_state_w->blocked = NULL;
+	}
 	// Mark that a re-entry of multiplex() is necessary.
 	sub_state_w->need_run = true;
 #ifdef SHOW_ASSERT
@@ -1048,7 +1064,7 @@ void AIStateMachine::advance_state(state_type new_state)
 
 void AIStateMachine::idle(void)
 {
-  DoutEntering(dc::statemachine, "AIStateMachine::idle() [" << (void*)this << "]");
+  DoutEntering(dc::statemachine(mSMDebug), "AIStateMachine::idle() [" << (void*)this << "]");
 #ifdef SHOW_ASSERT
   {
 	multiplex_state_type_rat state_r(mState);
@@ -1066,7 +1082,7 @@ void AIStateMachine::idle(void)
   // Ignore call to idle() when advance_state() was called since last call to set_state().
   if (sub_state_w->skip_idle)
   {
-	Dout(dc::statemachine, "Ignored, because skip_idle is true (advance_state() was called last).");
+	Dout(dc::statemachine(mSMDebug), "Ignored, because skip_idle is true (advance_state() was called last).");
 	return;
   }
   // Mark that we are idle.
@@ -1075,13 +1091,54 @@ void AIStateMachine::idle(void)
   mSleep = 0;
 }
 
+// This function is very much like idle().
+void AIStateMachine::wait(AIConditionBase& condition)
+{
+  DoutEntering(dc::statemachine(mSMDebug), "AIStateMachine::wait(" << (void*)&condition << ") [" << (void*)this << "]");
+#ifdef SHOW_ASSERT
+  {
+	multiplex_state_type_rat state_r(mState);
+	// wait() may only be called multiplex_impl().
+	llassert(state_r->base_state == bs_multiplex);
+	// May only be called by the thread that is holding mMultiplexMutex.
+	llassert(mThreadId.equals_current_thread());
+  }
+  // wait() following set_state() cancels the reason to run because of the call to set_state.
+  mDebugSetStatePending = false;
+#endif
+  sub_state_type_wat sub_state_w(mSubState);
+  // As wait() may only be called from within the state machine, it should never happen that the state machine is already idle.
+  llassert(!sub_state_w->idle);
+  // Ignore call to wait() when advance_state() was called since last call to set_state().
+  if (sub_state_w->skip_idle)
+  {
+	Dout(dc::statemachine(mSMDebug), "Ignored, because skip_idle is true (advance_state() was called last).");
+	return;
+  }
+  // Register ourselves with the condition object.
+  condition.wait(this);
+  // Mark that we are idle.
+  sub_state_w->idle = true;
+  // Mark that we are waiting for a condition.
+  sub_state_w->blocked = &condition;
+  // Not sleeping (anymore).
+  mSleep = 0;
+}
+
 void AIStateMachine::cont(void)
 {
-  DoutEntering(dc::statemachine, "AIStateMachine::cont() [" << (void*)this << "]");
+  DoutEntering(dc::statemachine(mSMDebug), "AIStateMachine::cont() [" << (void*)this << "]");
   {
 	sub_state_type_wat sub_state_w(mSubState);
 	// Void last call to idle(), if any.
 	sub_state_w->idle = false;
+	// No longer say we woke up when signalled() is called.
+	if (sub_state_w->blocked)
+	{
+	  Dout(dc::statemachine(mSMDebug), "Removing statemachine from condition " << (void*)sub_state_w->blocked);
+	  sub_state_w->blocked->remove(this);
+	  sub_state_w->blocked = NULL;
+	}
 	// Mark that a re-entry of multiplex() is necessary.
 	sub_state_w->need_run = true;
 #ifdef SHOW_ASSERT
@@ -1095,15 +1152,56 @@ void AIStateMachine::cont(void)
   }
 }
 
+// This function is very much like cont(), except that it has no effect when we are not in a blocked state.
+// Returns true if the state machine was unblocked, false if it was already unblocked.
+bool AIStateMachine::signalled(void)
+{
+  DoutEntering(dc::statemachine(mSMDebug), "AIStateMachine::signalled() [" << (void*)this << "]");
+  {
+	sub_state_type_wat sub_state_w(mSubState);
+	// Test if we are blocked or not.
+	if (sub_state_w->blocked)
+	{
+	  Dout(dc::statemachine(mSMDebug), "Removing statemachine from condition " << (void*)sub_state_w->blocked);
+	  sub_state_w->blocked->remove(this);
+	  sub_state_w->blocked = NULL;
+	}
+	else
+	{
+	  return false;
+	}
+	// Void last call to wait().
+	sub_state_w->idle = false;
+	// Mark that a re-entry of multiplex() is necessary.
+	sub_state_w->need_run = true;
+#ifdef SHOW_ASSERT
+	// From this moment.
+	mDebugContPending = true;
+#endif
+  }
+  if (!mMultiplexMutex.isSelfLocked())
+  {
+	multiplex(schedule_run);
+  }
+  return true;
+}
+
 void AIStateMachine::abort(void)
 {
-  DoutEntering(dc::statemachine, "AIStateMachine::abort() [" << (void*)this << "]");
+  DoutEntering(dc::statemachine(mSMDebug), "AIStateMachine::abort() [" << (void*)this << "]");
   bool is_waiting = false;
   {
 	multiplex_state_type_rat state_r(mState);
 	sub_state_type_wat sub_state_w(mSubState);
 	// Mark that we are aborted, iff we didn't already finish.
 	sub_state_w->aborted = !sub_state_w->finished;
+	// No longer say we woke up when signalled() is called.
+	if (sub_state_w->blocked)
+	{
+	  Dout(dc::statemachine(mSMDebug), "Removing statemachine from condition " << (void*)sub_state_w->blocked);
+	  sub_state_w->blocked->remove(this);
+	  sub_state_w->blocked = NULL;
+	}
 	// Mark that a re-entry of multiplex() is necessary.
 	sub_state_w->need_run = true;
 	// Schedule a new run when this state machine is waiting.
@@ -1128,7 +1226,7 @@ void AIStateMachine::abort(void)
 
 void AIStateMachine::finish(void)
 {
-  DoutEntering(dc::statemachine, "AIStateMachine::finish() [" << (void*)this << "]");
+  DoutEntering(dc::statemachine(mSMDebug), "AIStateMachine::finish() [" << (void*)this << "]");
 #ifdef SHOW_ASSERT
   {
 	multiplex_state_type_rat state_r(mState);
@@ -1147,7 +1245,7 @@ void AIStateMachine::finish(void)
 
 void AIStateMachine::yield(void)
 {
-  DoutEntering(dc::statemachine, "AIStateMachine::yield() [" << (void*)this << "]");
+  DoutEntering(dc::statemachine(mSMDebug), "AIStateMachine::yield() [" << (void*)this << "]");
   multiplex_state_type_rat state_r(mState);
   // yield() may only be called from multiplex_impl().
   llassert(state_r->base_state == bs_multiplex);
@@ -1160,7 +1258,7 @@ void AIStateMachine::yield(void)
 void AIStateMachine::yield(AIEngine* engine)
 {
   llassert(engine);
-  DoutEntering(dc::statemachine, "AIStateMachine::yield(" << engine->name() << ") [" << (void*)this << "]");
+  DoutEntering(dc::statemachine(mSMDebug), "AIStateMachine::yield(" << engine->name() << ") [" << (void*)this << "]");
 #ifdef SHOW_ASSERT
   {
 	multiplex_state_type_rat state_r(mState);
@@ -1173,9 +1271,19 @@ void AIStateMachine::yield(AIEngine* engine)
   mYieldEngine = engine;
 }
 
+bool AIStateMachine::yield_if_not(AIEngine* engine)
+{
+  if (engine && multiplex_state_type_rat(mState)->current_engine != engine)
+  {
+	yield(engine);
+	return true;
+  }
+  return false;
+}
+
 void AIStateMachine::yield_frame(unsigned int frames)
 {
-  DoutEntering(dc::statemachine, "AIStateMachine::yield_frame(" << frames << ") [" << (void*)this << "]");
+  DoutEntering(dc::statemachine(mSMDebug), "AIStateMachine::yield_frame(" << frames << ") [" << (void*)this << "]");
   mSleep = -(S64)frames;
   // Sleeping is always done from the main thread.
   yield(&gMainThreadEngine);
@@ -1183,7 +1291,7 @@ void AIStateMachine::yield_frame(unsigned int frames)
 
 void AIStateMachine::yield_ms(unsigned int ms)
 {
-  DoutEntering(dc::statemachine, "AIStateMachine::yield_ms(" << ms << ") [" << (void*)this << "]");
+  DoutEntering(dc::statemachine(mSMDebug), "AIStateMachine::yield_ms(" << ms << ") [" << (void*)this << "]");
   mSleep = get_clock_count() + calc_clock_frequency() * ms / 1000;
   // Sleeping is always done from the main thread.
   yield(&gMainThreadEngine);
@@ -1233,7 +1341,7 @@ void AIEngine::threadloop(void)
 	engine_state_type_wat engine_state_w(mEngineState);
 	if (!active)
 	{
-	  Dout(dc::statemachine, "Erasing state machine [" << (void*)&state_machine << "] from " << mName);
+	  Dout(dc::statemachine(state_machine.mSMDebug), "Erasing state machine [" << (void*)&state_machine << "] from " << mName);
 	  engine_state_w->list.erase(queued_element++);
 	}
 	else
diff --git a/indra/aistatemachine/aistatemachine.h b/indra/aistatemachine/aistatemachine.h
index 2b019c91f..047fe0515 100644
--- a/indra/aistatemachine/aistatemachine.h
+++ b/indra/aistatemachine/aistatemachine.h
@@ -39,6 +39,7 @@
 #include <list>
 #include <boost/signals2.hpp>
 
+class AIConditionBase;
 class AIStateMachine;
 
 class AIEngine
@@ -132,6 +133,7 @@ class AIStateMachine : public LLThreadSafeRefCount
 	struct sub_state_type {
 	  state_type		run_state;
 	  state_type		advance_state;
+	  AIConditionBase*	blocked;
 	  bool				reset;
 	  bool				need_run;
 	  bool				idle;
@@ -195,20 +197,36 @@ class AIStateMachine : public LLThreadSafeRefCount
 	bool mDebugAdvanceStatePending;				// True while advance_state() was called by not handled yet.
 	bool mDebugRefCalled;						// True when ref() is called (or will be called within the critial area of mMultiplexMutex).
 #endif
+#ifdef CWDEBUG
+  protected:
+	bool mSMDebug;								// Print debug output only when true.
+#endif
+  private:
 	U64 mRuntime;								// Total time spent running in the main thread (in clocks).
 
   public:
-	AIStateMachine(void) : mCallback(NULL), mDefaultEngine(NULL), mYieldEngine(NULL),
+	AIStateMachine(CWD_ONLY(bool debug)) : mCallback(NULL), mDefaultEngine(NULL), mYieldEngine(NULL),
 #ifdef SHOW_ASSERT
 		mThreadId(AIThreadID::none), mDebugLastState(bs_killed), mDebugShouldRun(false), mDebugAborted(false), mDebugContPending(false),
 		mDebugSetStatePending(false), mDebugAdvanceStatePending(false), mDebugRefCalled(false),
+#endif
+#ifdef CWDEBUG
+		mSMDebug(debug),
 #endif
 		mRuntime(0)
 	{ }
 
   protected:
-	// The user should call finish() (or abort(), or kill() from the call back when finish_impl() calls run()), not delete a class derived from AIStateMachine directly.
-	virtual ~AIStateMachine() { llassert(multiplex_state_type_rat(mState)->base_state == bs_killed); }
+	// The user should call finish() (or abort(), or kill() from the call back when finish_impl() calls run()),
+	// not delete a class derived from AIStateMachine directly. Deleting it directly before calling run() is
+	// ok however.
+	virtual ~AIStateMachine()
+	{
+#ifdef SHOW_ASSERT
+	  base_state_type state = multiplex_state_type_rat(mState)->base_state;
+	  llassert(state == bs_killed || state == bs_reset);
+#endif
+	}
  
   public:
 	// These functions may be called directly after creation, or from within finish_impl(), or from the call back function.
@@ -224,11 +242,13 @@ class AIStateMachine : public LLThreadSafeRefCount
 	void set_state(state_type new_state);									// Run this state the NEXT loop.
 	// These functions can only be called from within multiplex_impl().
 	void idle(void);														// Go idle unless cont() or advance_state() were called since the start of the current loop, or until they are called.
+	void wait(AIConditionBase& condition);									// The same as idle(), but wake up when AICondition<T>::signal() is called.
 	void finish(void);														// Mark that the state machine finished and schedule the call back.
 	void yield(void);														// Yield to give CPU to other state machines, but do not go idle.
 	void yield(AIEngine* engine);											// Yield to give CPU to other state machines, but do not go idle. Continue running from engine 'engine'.
 	void yield_frame(unsigned int frames);									// Run from the main-thread engine after at least 'frames' frames have passed.
 	void yield_ms(unsigned int ms);											// Run from the main-thread engine after roughly 'ms' miliseconds have passed.
+	bool yield_if_not(AIEngine* engine);									// Do not really yield, unless the current engine is not 'engine'. Returns true if it switched engine.
 
   public:
 	// This function can be called from multiplex_imp(), but also by a child state machine and
@@ -236,11 +256,12 @@ class AIStateMachine : public LLThreadSafeRefCount
 	// to access this state machine.
 	void abort(void);														// Abort the state machine (unsuccessful finish).
 
-	// These are the only two functions that can be called by any thread at any moment.
+	// These are the only three functions that can be called by any thread at any moment.
 	// Those threads should use an LLPointer<AIStateMachine> to access this state machine.
 	void cont(void);														// Guarantee at least one full run of multiplex() after this function is called. Cancels the last call to idle().
 	void advance_state(state_type new_state);								// Guarantee at least one full run of multiplex() after this function is called
 																			// iff new_state is larger than the last state that was processed.
+	bool signalled(void);													// Call cont() iff this state machine is still blocked after a call to wait(). Returns false if it already unblocked.
 
   public:
 	// Accessors.
diff --git a/indra/aistatemachine/aistatemachinethread.h b/indra/aistatemachine/aistatemachinethread.h
index 780060bb6..2891cbb77 100644
--- a/indra/aistatemachine/aistatemachinethread.h
+++ b/indra/aistatemachine/aistatemachinethread.h
@@ -181,7 +181,11 @@ class AIStateMachineThreadBase : public AIStateMachine {
 	static state_type const max_state = wait_stopped + 1;
 
   protected:
-	AIStateMachineThreadBase(void) { }
+	AIStateMachineThreadBase(CWD_ONLY(bool debug))
+#ifdef CWDEBUG
+	  : AIStateMachine(debug)
+#endif
+	{ }
 
   private:
 	// Handle initializing the object.
@@ -217,7 +221,10 @@ class AIStateMachineThread : public AIStateMachineThreadBase {
 
   public:
 	// Constructor.
-	AIStateMachineThread(void)
+	AIStateMachineThread(CWD_ONLY(bool debug))
+#ifdef CWDEBUG
+		: AIStateMachineThreadBase(debug)
+#endif
 	{
 	  *AIThreadImpl::StateMachineThread_wat(mThreadImpl.mStateMachineThread) = this;
 	}
diff --git a/indra/aistatemachine/aitimer.h b/indra/aistatemachine/aitimer.h
index 5b028c6e0..3ee510007 100644
--- a/indra/aistatemachine/aitimer.h
+++ b/indra/aistatemachine/aitimer.h
@@ -76,7 +76,11 @@ class AITimer : public AIStateMachine {
 	F64 mInterval;					//!< Input variable: interval after which the event will be generated, in seconds.
 
   public:
-	AITimer(void) : mInterval(0) { DoutEntering(dc::statemachine, "AITimer(void) [" << (void*)this << "]"); }
+	AITimer(CWD_ONLY(bool debug = false)) :
+#ifdef CWDEBUG
+		AIStateMachine(debug),
+#endif
+		mInterval(0) { DoutEntering(dc::statemachine(mSMDebug), "AITimer(void) [" << (void*)this << "]"); }
 
 	/**
 	 * @brief Set the interval after which the timer should expire.
@@ -96,7 +100,7 @@ class AITimer : public AIStateMachine {
 
   protected:
 	// Call finish() (or abort()), not delete.
-	/*virtual*/ ~AITimer() { DoutEntering(dc::statemachine, "~AITimer() [" << (void*)this << "]"); mFrameTimer.cancel(); }
+	/*virtual*/ ~AITimer() { DoutEntering(dc::statemachine(mSMDebug), "~AITimer() [" << (void*)this << "]"); mFrameTimer.cancel(); }
 
 	// Handle initializing the object.
 	/*virtual*/ void initialize_impl(void);
diff --git a/indra/cwdebug/debug.h b/indra/cwdebug/debug.h
index 4167813ea..d3c4e686b 100644
--- a/indra/cwdebug/debug.h
+++ b/indra/cwdebug/debug.h
@@ -144,6 +144,7 @@ extern LL_COMMON_API fake_channel const snapshot;
 #define CWDEBUG_MARKER 0
 
 #define BACKTRACE do { } while(0)
+#define CWD_ONLY(...)
 
 #endif // !DOXYGEN
 
@@ -180,6 +181,7 @@ extern LL_COMMON_API fake_channel const snapshot;
 #include <set>
 
 #define CWD_API __attribute__ ((visibility("default")))
+#define CWD_ONLY(...) __VA_ARGS__
 
 //! Debug specific code.
 namespace debug {
diff --git a/indra/llmessage/aicurleasyrequeststatemachine.cpp b/indra/llmessage/aicurleasyrequeststatemachine.cpp
index 0437055f5..294f41586 100644
--- a/indra/llmessage/aicurleasyrequeststatemachine.cpp
+++ b/indra/llmessage/aicurleasyrequeststatemachine.cpp
@@ -250,10 +250,13 @@ void AICurlEasyRequestStateMachine::finish_impl(void)
   }
 }
 
-AICurlEasyRequestStateMachine::AICurlEasyRequestStateMachine(void) :
+AICurlEasyRequestStateMachine::AICurlEasyRequestStateMachine(CWD_ONLY(bool debug)) :
+#ifdef CWDEBUG
+	AIStateMachine(debug),
+#endif
     mTotalDelayTimeout(AIHTTPTimeoutPolicy::getDebugSettingsCurlTimeout().getTotalDelay())
 {
-  Dout(dc::statemachine, "Calling AICurlEasyRequestStateMachine(void) [" << (void*)this << "] [" << (void*)mCurlEasyRequest.get() << "]");
+  Dout(dc::statemachine(mSMDebug), "Calling AICurlEasyRequestStateMachine(void) [" << (void*)this << "] [" << (void*)mCurlEasyRequest.get() << "]");
   AICurlInterface::Stats::AICurlEasyRequestStateMachine_count++;
 }
 
@@ -264,7 +267,7 @@ void AICurlEasyRequestStateMachine::setTotalDelayTimeout(F32 totalDelayTimeout)
 
 AICurlEasyRequestStateMachine::~AICurlEasyRequestStateMachine()
 {
-  Dout(dc::statemachine, "Calling ~AICurlEasyRequestStateMachine() [" << (void*)this << "] [" << (void*)mCurlEasyRequest.get() << "]");
+  Dout(dc::statemachine(mSMDebug), "Calling ~AICurlEasyRequestStateMachine() [" << (void*)this << "] [" << (void*)mCurlEasyRequest.get() << "]");
   --AICurlInterface::Stats::AICurlEasyRequestStateMachine_count;
 }
 
diff --git a/indra/llmessage/aicurleasyrequeststatemachine.h b/indra/llmessage/aicurleasyrequeststatemachine.h
index 662efbe20..9bab7166b 100644
--- a/indra/llmessage/aicurleasyrequeststatemachine.h
+++ b/indra/llmessage/aicurleasyrequeststatemachine.h
@@ -52,7 +52,7 @@
 // Construction of a AICurlEasyRequestStateMachine might throw AICurlNoEasyHandle.
 class AICurlEasyRequestStateMachine : public AIStateMachine, public AICurlEasyHandleEvents {
   public:
-	AICurlEasyRequestStateMachine(void);
+	AICurlEasyRequestStateMachine(CWD_ONLY(bool debug = false));
 
 	// Transparent access.
 	AICurlEasyRequest mCurlEasyRequest;
diff --git a/indra/newview/llmeshrepository.cpp b/indra/newview/llmeshrepository.cpp
index 55afaecee..80e68f608 100644
--- a/indra/newview/llmeshrepository.cpp
+++ b/indra/newview/llmeshrepository.cpp
@@ -1414,7 +1414,10 @@ void LLMeshUploadThread::preStart()
 
 AIMeshUpload::AIMeshUpload(LLMeshUploadThread::instance_list& data, LLVector3& scale, bool upload_textures, bool upload_skin, bool upload_joints, std::string const& upload_url, bool do_upload,
 	LLHandle<LLWholeModelFeeObserver> const& fee_observer, LLHandle<LLWholeModelUploadObserver> const& upload_observer) :
-		mMeshUpload(new AIStateMachineThread<LLMeshUploadThread>), mWholeModelUploadURL(upload_url)
+#ifdef CWDEBUG
+		AIStateMachine(false),
+#endif
+		mMeshUpload(new AIStateMachineThread<LLMeshUploadThread>(CWD_ONLY(false))), mWholeModelUploadURL(upload_url)
 {
 	mMeshUpload->thread_impl().init(data, scale, upload_textures, upload_skin, upload_joints, do_upload, fee_observer, upload_observer);
 }
diff --git a/indra/newview/statemachine/aifetchinventoryfolder.cpp b/indra/newview/statemachine/aifetchinventoryfolder.cpp
index d8e952c0d..840a0249e 100644
--- a/indra/newview/statemachine/aifetchinventoryfolder.cpp
+++ b/indra/newview/statemachine/aifetchinventoryfolder.cpp
@@ -155,7 +155,7 @@ void AIFetchInventoryFolder::multiplex_impl(state_type run_state)
 		  // Create the folder.
 		  mFolderUUID = gInventory.createNewCategory(mParentFolder, LLFolderType::FT_NONE, mFolderName);
 		  llassert_always(!mFolderUUID.isNull());
-		  Dout(dc::statemachine, "Created folder \"" << mFolderName << "\".");
+		  Dout(dc::statemachine(mSMDebug), "Created folder \"" << mFolderName << "\".");
 		  mNeedNotifyObservers = true;
 		}
 		mCreated = true;
diff --git a/indra/newview/statemachine/aifetchinventoryfolder.h b/indra/newview/statemachine/aifetchinventoryfolder.h
index 2b10c0351..59419fc86 100644
--- a/indra/newview/statemachine/aifetchinventoryfolder.h
+++ b/indra/newview/statemachine/aifetchinventoryfolder.h
@@ -58,8 +58,12 @@ class AIFetchInventoryFolder : public AIStateMachine {
 	bool mNeedNotifyObservers;
 
   public:
-	AIFetchInventoryFolder(void) : mCreate(false), mFetchContents(false), mExists(false), mCreated(false)
-        { Dout(dc::statemachine, "Calling AIFetchInventoryFolder constructor [" << (void*)this << "]"); }
+	AIFetchInventoryFolder(CWD_ONLY(bool debug = false)) :
+#ifdef CWDEBUG
+		AIStateMachine(debug),
+#endif
+		mCreate(false), mFetchContents(false), mExists(false), mCreated(false)
+        { Dout(dc::statemachine(mSMDebug), "Calling AIFetchInventoryFolder constructor [" << (void*)this << "]"); }
 
 	/**
 	 * @brief Fetch an inventory folder by name, optionally creating it.
@@ -132,7 +136,7 @@ class AIFetchInventoryFolder : public AIStateMachine {
 
   protected:
 	// Call finish() (or abort()), not delete.
-	/*virtual*/ ~AIFetchInventoryFolder() { Dout(dc::statemachine, "Calling ~AIFetchInventoryFolder() [" << (void*)this << "]"); }
+	/*virtual*/ ~AIFetchInventoryFolder() { Dout(dc::statemachine(mSMDebug), "Calling ~AIFetchInventoryFolder() [" << (void*)this << "]"); }
 
 	// Handle initializing the object.
 	/*virtual*/ void initialize_impl(void);
diff --git a/indra/newview/statemachine/aifilepicker.cpp b/indra/newview/statemachine/aifilepicker.cpp
index 636fc2343..6754142e4 100644
--- a/indra/newview/statemachine/aifilepicker.cpp
+++ b/indra/newview/statemachine/aifilepicker.cpp
@@ -60,7 +60,11 @@ char const* AIFilePicker::state_str_impl(state_type run_state) const
 	return "UNKNOWN STATE";
 }
 
-AIFilePicker::AIFilePicker(void) : mPluginManager(NULL), mCanceled(false)
+AIFilePicker::AIFilePicker(CWD_ONLY(bool debug)) :
+#ifdef CWDEBUG
+	AIStateMachine(debug),
+#endif
+	mPluginManager(NULL), mCanceled(false)
 {
 }
 
diff --git a/indra/newview/statemachine/aifilepicker.h b/indra/newview/statemachine/aifilepicker.h
index cd1c7fe86..9ef02017b 100644
--- a/indra/newview/statemachine/aifilepicker.h
+++ b/indra/newview/statemachine/aifilepicker.h
@@ -168,7 +168,7 @@ public:
 
 public:
 	// The derived class must have a default constructor.
-	AIFilePicker(void);
+	AIFilePicker(CWD_ONLY(bool debug = false));
 
 	// Create a dynamically created AIFilePicker object.
 	static AIFilePicker* create(void) { AIFilePicker* filepicker = new AIFilePicker; return filepicker; }