Tidy up comments in thread.cpp

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/search.cpp

@@ -409,7 +409,8 @@ bool think(Position& pos, const SearchLimits& limits, Move searchMoves[]) {
   read_evaluation_uci_options(pos.side_to_move());
   Threads.read_uci_options();
 
-  // If needed allocate pawn and material hash tables and adjust TT size
+  // Allocate pawn and material hash tables if number of active threads
+  // increased and set a new TT size if changed.
   Threads.init_hash_tables();
   TT.set_size(Options["Hash"].value<int>());
 
@@ -2142,7 +2143,7 @@ void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
 
   while (true)
   {
-      // Slave threads can exit as soon as AllThreadsShouldExit raises,
+      // Slave threads can exit as soon as allThreadsShouldExit flag raises,
       // master should exit as last one.
       if (allThreadsShouldExit)
       {
@@ -2151,7 +2152,7 @@ void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
           return;
       }
 
-      // If we are not thinking, wait for a condition to be signaled
+      // If we are not searching, wait for a condition to be signaled
       // instead of wasting CPU time polling for work.
       while (   threadID >= activeThreads
              || threads[threadID].state == Thread::INITIALIZING
@@ -2166,7 +2167,7 @@ void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
           // Grab the lock to avoid races with Thread::wake_up()
           lock_grab(&threads[threadID].sleepLock);
 
-          // If we are master and all slaves have finished do not go to sleep
+          // If we are master and all slaves have finished don't go to sleep
           for (i = 0; sp && i < activeThreads && !sp->is_slave[i]; i++) {}
           allFinished = (i == activeThreads);
 
@@ -2176,7 +2177,10 @@ void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
               break;
           }
 
-          // Do sleep here after retesting sleep conditions
+          // Do sleep after retesting sleep conditions under lock protection, in
+          // particular we need to avoid a deadlock in case a master thread has,
+          // in the meanwhile, allocated us and sent the wake_up() call before we
+          // had the chance to grab the lock.
           if (threadID >= activeThreads || threads[threadID].state == Thread::AVAILABLE)
               cond_wait(&threads[threadID].sleepCond, &threads[threadID].sleepLock);
 
@@ -2191,7 +2195,6 @@ void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
           threads[threadID].state = Thread::SEARCHING;
 
           // Copy split point position and search stack and call search()
-          // with SplitPoint template parameter set to true.
           SearchStack ss[PLY_MAX_PLUS_2];
           SplitPoint* tsp = threads[threadID].splitPoint;
           Position pos(*tsp->pos, threadID);
@@ -2227,14 +2230,10 @@ void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
 
       if (allFinished)
       {
-          // Because sp->slaves[] is reset under lock protection,
+          // Because sp->is_slave[] is reset under lock protection,
           // be sure sp->lock has been released before to return.
           lock_grab(&(sp->lock));
           lock_release(&(sp->lock));
-
-          // In helpful master concept a master can help only a sub-tree, and
-          // because here is all finished is not possible master is booked.
-          assert(threads[threadID].state == Thread::AVAILABLE);
           return;
       }
   }

src/thread.cpp

@@ -132,9 +132,10 @@ void ThreadsManager::init() {
   // Allocate pawn and material hash tables for main thread
   init_hash_tables();
 
+  // Initialize threads lock, used when allocating slaves during splitting
   lock_init(&threadsLock);
 
-  // Initialize thread and split point locks
+  // Initialize sleep and split point locks
   for (int i = 0; i < MAX_THREADS; i++)
   {
       lock_init(&threads[i].sleepLock);
@@ -169,7 +170,7 @@ void ThreadsManager::init() {
 }
 
 
-// exit() is called to cleanly exit the threads when the program finishes
+// exit() is called to cleanly terminate the threads when the program finishes
 
 void ThreadsManager::exit() {
 
@@ -178,14 +179,14 @@ void ThreadsManager::exit() {
 
   for (int i = 0; i < MAX_THREADS; i++)
   {
-      // Wake up all the threads and waits for termination
+      // Wake up all the threads and wait for termination
       if (i != 0)
       {
           threads[i].wake_up();
           while (threads[i].state != Thread::TERMINATED) {}
       }
 
-      // Now we can safely destroy the locks and wait conditions
+      // Now we can safely destroy locks and wait conditions
       lock_destroy(&threads[i].sleepLock);
       cond_destroy(&threads[i].sleepCond);
 
@@ -258,25 +259,25 @@ Value ThreadsManager::split(Position& pos, SearchStack* ss, Value alpha, Value b
       return bestValue;
 
   // Pick the next available split point object from the split point stack
-  SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints];
+  SplitPoint* sp = masterThread.splitPoints + masterThread.activeSplitPoints;
 
   // Initialize the split point object
-  splitPoint.parent = masterThread.splitPoint;
+  sp->parent = masterThread.splitPoint;
-  splitPoint.master = master;
+  sp->master = master;
-  splitPoint.is_betaCutoff = false;
+  sp->is_betaCutoff = false;
-  splitPoint.depth = depth;
+  sp->depth = depth;
-  splitPoint.threatMove = threatMove;
+  sp->threatMove = threatMove;
-  splitPoint.alpha = alpha;
+  sp->alpha = alpha;
-  splitPoint.beta = beta;
+  sp->beta = beta;
-  splitPoint.nodeType = nodeType;
+  sp->nodeType = nodeType;
-  splitPoint.bestValue = bestValue;
+  sp->bestValue = bestValue;
-  splitPoint.mp = mp;
+  sp->mp = mp;
-  splitPoint.moveCount = moveCount;
+  sp->moveCount = moveCount;
-  splitPoint.pos = &pos;
+  sp->pos = &pos;
-  splitPoint.nodes = 0;
+  sp->nodes = 0;
-  splitPoint.ss = ss;
+  sp->ss = ss;
   for (i = 0; i < activeThreads; i++)
-      splitPoint.is_slave[i] = false;
+      sp->is_slave[i] = false;
 
   // If we are here it means we are not available
   assert(masterThread.state == Thread::SEARCHING);
@@ -292,8 +293,8 @@ Value ThreadsManager::split(Position& pos, SearchStack* ss, Value alpha, Value b
       if (i != master && threads[i].is_available_to(master))
       {
           workersCnt++;
-          splitPoint.is_slave[i] = true;
+          sp->is_slave[i] = true;
-          threads[i].splitPoint = &splitPoint;
+          threads[i].splitPoint = sp;
 
           // This makes the slave to exit from idle_loop()
           threads[i].state = Thread::WORKISWAITING;
@@ -308,7 +309,7 @@ Value ThreadsManager::split(Position& pos, SearchStack* ss, Value alpha, Value b
   if (!Fake && workersCnt == 1)
       return bestValue;
 
-  masterThread.splitPoint = &splitPoint;
+  masterThread.splitPoint = sp;
   masterThread.activeSplitPoints++;
   masterThread.state = Thread::WORKISWAITING;
 
@@ -317,7 +318,11 @@ Value ThreadsManager::split(Position& pos, SearchStack* ss, Value alpha, Value b
   // Thread::WORKISWAITING. We send the split point as a second parameter to
   // the idle loop, which means that the main thread will return from the idle
   // loop when all threads have finished their work at this split point.
-  idle_loop(master, &splitPoint);
+  idle_loop(master, sp);
+
+  // In helpful master concept a master can help only a sub-tree, and
+  // because here is all finished is not possible master is booked.
+  assert(masterThread.state == Thread::AVAILABLE);
 
   // We have returned from the idle loop, which means that all threads are
   // finished. Note that changing state and decreasing activeSplitPoints is done
@@ -326,12 +331,13 @@ Value ThreadsManager::split(Position& pos, SearchStack* ss, Value alpha, Value b
 
   masterThread.state = Thread::SEARCHING;
   masterThread.activeSplitPoints--;
-  masterThread.splitPoint = splitPoint.parent;
 
   lock_release(&threadsLock);
 
-  pos.set_nodes_searched(pos.nodes_searched() + splitPoint.nodes);
+  masterThread.splitPoint = sp->parent;
-  return splitPoint.bestValue;
+  pos.set_nodes_searched(pos.nodes_searched() + sp->nodes);
+
+  return sp->bestValue;
 }
 
 // Explicit template instantiations