From 05af5d856c105c66efee0f22dfe5bc5ff45c3511 Mon Sep 17 00:00:00 2001
From: Oliver Kowalke <oliver.kowalke@gmx.de>
Date: Sun, 3 Nov 2013 13:58:40 +0100
Subject: [PATCH] some improved spinlock

---
 src/detail/spinlock.cpp | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/src/detail/spinlock.cpp b/src/detail/spinlock.cpp
index ebbc018b..38b4a8d7 100644
--- a/src/detail/spinlock.cpp
+++ b/src/detail/spinlock.cpp
@@ -22,13 +22,24 @@ spinlock::spinlock() :
 void
 spinlock::lock()
 {
-    while ( LOCKED == state_.exchange( LOCKED) )
+    for (;;)
     {
-        // busy-wait
-        if ( scheduler::instance()->active() )
-            scheduler::instance()->yield();
-        else
-            this_thread::yield();
+        // access to CPU's cache
+        // first access to state_ -> cache miss
+        // sucessive acccess to state_ > cache hit
+        while ( LOCKED == state_)
+        {
+            // busy-wait
+            if ( scheduler::instance()->active() )
+                scheduler::instance()->yield();
+            else
+                this_thread::yield();
+        }
+        // state_ was released by other
+        // cached copies are invalidated -> cache miss
+        // test-and-set over the bus 
+        if ( UNLOCKED == state_.exchange( LOCKED) )
+            return;
     }
 }