Added AICondition.

AICondition is like AIThreadSafeSimpleDC (it is derived from it),
and wraps some variable, protecting it with a builtin mutex.

While in a statemachine, one can call wait(condition) to make
the state machine go idle, and call condition.signal() to
wake it (or another) up again.

While normally a condition variable is used as follows:

condition.lock();
while (!whatwerewaitingfor)
{
  condition.wait();
}
// Here the condition is guaranteed to be true and we're
// still in the critical area of the mutex.
condition.unlock();

where the thread blocks in wait(), the statemachine actually
returns CPU to the thread (the AIEngine), so there is no
while loop involved, and our wait() doesn't even unlock
the mutex: that happens because the state machine returns:

condition_wat condition_w(condition);		// Lock condition.
if (!condition_w->whatwerewaitingfor())		// The variable(s) involved can only be accessed when condition is locked.
{
  wait(condition);				// Causes the state machine to go idle. This does not block.
  break;					// Leave scope (unlock condition) and return to the mainloop - but as idle state machine.
}
// Here the condition is guaranteed to be true and we're
// still in the critical area of the condition variable.

In this case, when condition.signal() is called, the thread
doesn't return from wait() with a locked mutex - but the
statemachine executes the same state again, and enters from
the top: locking the condition and doing the test again,
just like it would be when this was a while loop.

indra/aistatemachine/aistatemachine.cpp

@@ -33,6 +33,7 @@
 
 #include "linden_common.h"
 #include "aistatemachine.h"
+#include "aicondition.h"
 #include "lltimer.h"
 
 //==================================================================
@@ -960,6 +961,8 @@ 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;
   }
@@ -983,6 +986,8 @@ 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.
@@ -1023,6 +1028,13 @@ 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
@@ -1075,6 +1087,40 @@ 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(mSMDebug), "AIStateMachine::cont() [" << (void*)this << "]");
@@ -1082,6 +1128,13 @@ void AIStateMachine::cont(void)
 	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
@@ -1095,6 +1148,40 @@ 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(mSMDebug), "AIStateMachine::abort() [" << (void*)this << "]");
@@ -1104,6 +1191,13 @@ void AIStateMachine::abort(void)
 	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.