From bfde9ecae6a0e995def46f6aa2452b3c58f2d855 Mon Sep 17 00:00:00 2001
From: Oliver Kowalke <oliver.kowalke@gmx.de>
Date: Sat, 10 Jan 2015 21:21:36 +0100
Subject: [PATCH] improve spinlock code

---
 src/detail/spinlock.cpp | 20 +++++++-------------
 1 file changed, 7 insertions(+), 13 deletions(-)

diff --git a/src/detail/spinlock.cpp b/src/detail/spinlock.cpp
index d999f25f..ec95f392 100644
--- a/src/detail/spinlock.cpp
+++ b/src/detail/spinlock.cpp
@@ -22,25 +22,19 @@ spinlock::spinlock() :
 void
 spinlock::lock()
 {
-    for (;;)
-    {
+    do {
         // access to CPU's cache
         // first access to state_ -> cache miss
-        // sucessive acccess to state_ > cache hit
-        while ( LOCKED == state_)
-        {
+        // sucessive acccess to state_ -> cache hit
+        while ( LOCKED == state_.load( boost::memory_order_relaxed) ) {
             // busy-wait
-            if ( 0 != fm_active() )
-                fm_yield();
-           else
-                this_thread::yield();
+            fm_yield();
         }
-        // state_ was released by other
+        // state_ was released by other fiber
         // cached copies are invalidated -> cache miss
-        // test-and-set over the bus 
-        if ( UNLOCKED == state_.exchange( LOCKED) )
-            return;
+        // test-and-set signaled over the bus
     }
+    while ( UNLOCKED != state_.exchange( LOCKED, boost::memory_order_acquire) );
 }
 
 void