From 2f42a8714c4fc8a03bebb0192ddad7ecc8376da9 Mon Sep 17 00:00:00 2001
From: James Turner <zakalawe@mac.com>
Date: Mon, 28 Oct 2013 14:51:36 +0000
Subject: [PATCH] Terrasync: don't busy wait when no requests are running.

---
 simgear/scene/tsync/terrasync.cxx | 6 ++++++
 simgear/threads/SGQueue.hxx       | 5 +++++
 2 files changed, 11 insertions(+)

diff --git a/simgear/scene/tsync/terrasync.cxx b/simgear/scene/tsync/terrasync.cxx
index afe89639..48c0c64f 100644
--- a/simgear/scene/tsync/terrasync.cxx
+++ b/simgear/scene/tsync/terrasync.cxx
@@ -643,6 +643,12 @@ void SGTerraSync::SvnThread::runInternal()
         }
 
         _busy = anySlotBusy;
+        if (!anySlotBusy) {
+            // wait on the blocking deque here, otherwise we spin
+            // the loop very fast, since _http::update with no connections
+            // active returns immediately.
+            waitingTiles.waitOnNotEmpty();
+        }
     } // of thread running loop
 }
 
diff --git a/simgear/threads/SGQueue.hxx b/simgear/threads/SGQueue.hxx
index c4fab564..7f49b5d9 100644
--- a/simgear/threads/SGQueue.hxx
+++ b/simgear/threads/SGQueue.hxx
@@ -386,6 +386,11 @@ public:
         return this->queue.size();
     }
 
+    void waitOnNotEmpty() {
+    	SGGuard<SGMutex> g(mutex);
+    	while (this->queue.empty())
+    	    not_empty.wait(mutex);
+    }
 private:
 
     /**
-- 
2.39.5