Reformat and simplify previous patch

No functional change.

src/search.cpp

@@ -987,7 +987,7 @@ moves_loop: // When in check and at SpNode search starts from here
           &&  Threads.size() >= 2
           &&  depth >= Threads.minimumSplitDepth
           &&  (   !thisThread->activeSplitPoint
-               || !thisThread->activeSplitPoint->allowLatejoin)
+               || !thisThread->activeSplitPoint->allSlavesSearching)
           &&  thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
       {
           assert(bestValue > -VALUE_INFINITE && bestValue < beta);
@@ -1529,9 +1529,10 @@ void Thread::idle_loop() {
 
           assert(searching);
 
+          searching = false;
           activePosition = NULL;
           sp->slavesMask.reset(idx);
-          sp->allowLatejoin = false;
+          sp->allSlavesSearching = false;
           sp->nodes += pos.nodes_searched();
 
           // Wake up the master thread so to allow it to return from the idle
@@ -1550,9 +1551,36 @@ void Thread::idle_loop() {
           // if we are exiting there is a chance that they are already freed.
           sp->mutex.unlock();
 
-          // Try to late join to another splitpoint
-          if (Threads.size() <= 2 || !attempt_to_latejoin()) // FIXME: attempt_to_latejoin() is theoretically unsafe when were are exiting the program...
-              searching = false;
+          // Try to late join to another split point if none of its slaves has
+          // already finished.
+          if (Threads.size() > 2)
+              for (size_t i = 0; i < Threads.size(); ++i)
+              {
+                  int size = Threads[i]->splitPointsSize; // Local copy
+                  sp = size ? &Threads[i]->splitPoints[size - 1] : NULL;
+
+                  if (   sp
+                      && sp->allSlavesSearching
+                      && available_to(Threads[i]))
+                  {
+                      // Recheck the conditions under lock protection
+                      Threads.mutex.lock();
+                      sp->mutex.lock();
+
+                      if (   sp->allSlavesSearching
+                          && available_to(Threads[i]))
+                      {
+                           sp->slavesMask.set(idx);
+                           activeSplitPoint = sp;
+                           searching = true;
+                      }
+
+                      sp->mutex.unlock();
+                      Threads.mutex.unlock();
+
+                      break; // Just a single attempt
+                  }
+              }
       }
 
       // If this thread is the master of a split point and all slaves have finished
@@ -1568,44 +1596,6 @@ void Thread::idle_loop() {
   }
 }
 
-bool Thread::attempt_to_latejoin()
-{
-    SplitPoint *sp;
-    size_t i;
-    bool success = false;
-
-    for (i = 0; i < Threads.size(); ++i)
-    {
-        int size = Threads[i]->splitPointsSize; // Make a local copy to prevent size from changing under our feet.
-
-        sp = size ? &Threads[i]->splitPoints[size - 1] : NULL;
-
-        if (   sp
-            && sp->allowLatejoin
-            && available_to(Threads[i], true))
-            break;
-    }
-
-    if (i == Threads.size())
-        return false; // No suitable splitpoint found!
-
-    // Recheck conditions under lock protection
-    Threads.mutex.lock();
-    sp->mutex.lock();
-
-    if (   sp->allowLatejoin
-        && available_to(Threads[i], true))
-    {
-         activeSplitPoint = sp;
-         sp->slavesMask.set(this->idx);
-         success = true;
-    }
-
-    sp->mutex.unlock();
-    Threads.mutex.unlock();
-
-    return success;
-}
 
 /// check_time() is called by the timer thread when the timer triggers. It is
 /// used to print debug info and, more importantly, to detect when we are out of

src/thread.cpp

@@ -112,9 +112,9 @@ bool Thread::cutoff_occurred() const {
 // which are busy searching the split point at the top of slave's split point
 // stack (the "helpful master concept" in YBWC terminology).
 
-bool Thread::available_to(const Thread* master, bool latejoin) const {
+bool Thread::available_to(const Thread* master) const {
 
-  if (searching && !latejoin)
+  if (searching)
       return false;
 
   // Make a local copy to be sure it doesn't become zero under our feet while
@@ -239,7 +239,7 @@ void ThreadPool::read_uci_options() {
 Thread* ThreadPool::available_slave(const Thread* master) const {
 
   for (const_iterator it = begin(); it != end(); ++it)
-      if ((*it)->available_to(master, false))
+      if ((*it)->available_to(master))
           return *it;
 
   return NULL;
@@ -292,7 +292,7 @@ void Thread::split(Position& pos, const Stack* ss, Value alpha, Value beta, Valu
   Threads.mutex.lock();
   sp.mutex.lock();
 
-  sp.allowLatejoin = true; // Only set this under lock protection
+  sp.allSlavesSearching = true; // Must be set under lock protection
   ++splitPointsSize;
   activeSplitPoint = &sp;
   activePosition = NULL;

src/thread.h

@@ -77,7 +77,7 @@ struct SplitPoint {
   // Shared data
   Mutex mutex;
   std::bitset<MAX_THREADS> slavesMask;
-  volatile bool allowLatejoin;
+  volatile bool allSlavesSearching;
   volatile uint64_t nodes;
   volatile Value alpha;
   volatile Value bestValue;
@@ -114,9 +114,8 @@ struct Thread : public ThreadBase {
 
   Thread();
   virtual void idle_loop();
-  bool attempt_to_latejoin();
   bool cutoff_occurred() const;
-  bool available_to(const Thread* master, bool latejoin) const;
+  bool available_to(const Thread* master) const;
 
   template <bool Fake>
   void split(Position& pos, const Search::Stack* ss, Value alpha, Value beta, Value* bestValue, Move* bestMove,