From: Marco Costalba <mcostalba@gmail.com>
Date: Sat, 21 Feb 2015 10:33:03 +0000 (+0100)
Subject: Further refine SMP code
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=5fd5453e594ee6cadf4a3c502bc53d28cfe5aa8b

Further refine SMP code

Backported from C++11 branch:

https://github.com/official-stockfish/Stockfish/commit/7ff965eebfbc17d2b
https://github.com/official-stockfish/Stockfish/commit/e74c2df907d5336d3d2b

Fully verified it is equivalent to master (see log msg
of individual commits for details).

No functional change.
---

diff --git a/src/search.cpp b/src/search.cpp
index 15b93a72..6e0552be 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1524,9 +1524,9 @@ void Thread::idle_loop() {
 
   // Pointer 'this_sp' is not null only if we are called from split(), and not
   // at the thread creation. This means we are the split point's master.
-  SplitPoint* this_sp = splitPointsSize ? activeSplitPoint : NULL;
+  SplitPoint* this_sp = activeSplitPoint;
 
-  assert(!this_sp || (this_sp->masterThread == this && searching));
+  assert(!this_sp || (this_sp->master == this && searching));
 
   while (!exit)
   {
@@ -1536,6 +1536,7 @@ void Thread::idle_loop() {
           Threads.mutex.lock();
 
           assert(activeSplitPoint);
+
           SplitPoint* sp = activeSplitPoint;
 
           Threads.mutex.unlock();
@@ -1574,11 +1575,11 @@ void Thread::idle_loop() {
 
           // Wake up the master thread so to allow it to return from the idle
           // loop in case we are the last slave of the split point.
-          if (    this != sp->masterThread
-              &&  sp->slavesMask.none())
+          if (this != sp->master && sp->slavesMask.none())
           {
-              assert(!sp->masterThread->searching);
-              sp->masterThread->notify_one();
+              assert(!sp->master->searching);
+
+              sp->master->notify_one();
           }
 
           // After releasing the lock we can't access any SplitPoint related data
@@ -1589,7 +1590,6 @@ void Thread::idle_loop() {
           // Try to late join to another split point if none of its slaves has
           // already finished.
           SplitPoint* bestSp = NULL;
-          Thread* bestThread = NULL;
           int bestScore = INT_MAX;
 
           for (size_t i = 0; i < Threads.size(); ++i)
@@ -1617,7 +1617,6 @@ void Thread::idle_loop() {
                   if (score < bestScore)
                   {
                       bestSp = sp;
-                      bestThread = Threads[i];
                       bestScore = score;
                   }
               }
@@ -1633,7 +1632,7 @@ void Thread::idle_loop() {
 
               if (   sp->allSlavesSearching
                   && sp->slavesMask.count() < MAX_SLAVES_PER_SPLITPOINT
-                  && available_to(bestThread))
+                  && available_to(sp->master))
               {
                   sp->slavesMask.set(idx);
                   activeSplitPoint = sp;
@@ -1645,7 +1644,7 @@ void Thread::idle_loop() {
           }
       }
 
-      // Grab the lock to avoid races with Thread::notify_one()
+      // Avoid races with notify_one() fired from last slave of the split point
       mutex.lock();
 
       // If we are master and all slaves have finished then exit idle_loop
diff --git a/src/thread.cpp b/src/thread.cpp
index 18870021..786258a2 100644
--- a/src/thread.cpp
+++ b/src/thread.cpp
@@ -153,7 +153,7 @@ void Thread::split(Position& pos, Stack* ss, Value alpha, Value beta, Value* bes
   // Pick and init the next available split point
   SplitPoint& sp = splitPoints[splitPointsSize];
 
-  sp.masterThread = this;
+  sp.master = this;
   sp.parentSplitPoint = activeSplitPoint;
   sp.slavesMask = 0, sp.slavesMask.set(idx);
   sp.depth = depth;
diff --git a/src/thread.h b/src/thread.h
index 04e9a370..f530913c 100644
--- a/src/thread.h
+++ b/src/thread.h
@@ -72,7 +72,7 @@ struct SplitPoint {
   // Const data after split point has been setup
   const Position* pos;
   Search::Stack* ss;
-  Thread* masterThread;
+  Thread* master;
   Depth depth;
   Value beta;
   int nodeType;