Move idle_loop() under Thread

This greatly removes clutter from the difficult idle_loop() function

No functional change.

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

src/search.cpp

@@ -2130,50 +2130,56 @@ split_point_start: // At split points actual search starts from here
 } // namespace
 
 
-// ThreadsManager::idle_loop() is where the threads are parked when they have no work
+// Little helper used by idle_loop() to check that all the slaves of a
-// to do. The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
+// master thread have finished searching.
-// object for which the current thread is the master.
 
-void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
+static bool all_slaves_finished(SplitPoint* sp) {
 
-  assert(threadID >= 0 && threadID < MAX_THREADS);
+  assert(sp);
 
-  int i;
+  for (int i = 0; i < Threads.size(); i++)
-  bool allFinished;
+      if (sp->is_slave[i])
+          return false;
+
+  return true;
+}
+
+
+// Thread::idle_loop() is where the thread is parked when it has no work to do.
+// The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint object
+// for which the thread is the master.
+
+void Thread::idle_loop(SplitPoint* sp) {
 
   while (true)
   {
-      // Slave threads can exit as soon as allThreadsShouldExit flag raises,
+      // If we are not searching, wait for a condition to be signaled
-      // master should exit as last one.
+      // instead of wasting CPU time polling for work.
-      if (allThreadsShouldExit)
+      while (   do_sleep
+             || do_terminate
+             || (Threads.use_sleeping_threads() && state == Thread::AVAILABLE))
+      {
+          assert(!sp || Threads.use_sleeping_threads());
+          assert(threadID != 0 || Threads.use_sleeping_threads());
+
+          // Slave thread should exit as soon as do_terminate flag raises
+          if (do_terminate)
           {
               assert(!sp);
-          threads[threadID].state = Thread::TERMINATED;
+              state = Thread::TERMINATED;
               return;
           }
 
-      // If we are not searching, wait for a condition to be signaled
+          if (state == Thread::INITIALIZING)
-      // instead of wasting CPU time polling for work.
+              state = Thread::AVAILABLE;
-      while (   threadID >= activeThreads
-             || threads[threadID].state == Thread::INITIALIZING
-             || (useSleepingThreads && threads[threadID].state == Thread::AVAILABLE))
-      {
-          assert(!sp || useSleepingThreads);
-          assert(threadID != 0 || useSleepingThreads);
-
-          if (threads[threadID].state == Thread::INITIALIZING)
-              threads[threadID].state = Thread::AVAILABLE;
 
           // Grab the lock to avoid races with Thread::wake_up()
-          lock_grab(&threads[threadID].sleepLock);
+          lock_grab(&sleepLock);
 
           // 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++) {}
+          if (sp && all_slaves_finished(sp))
-          allFinished = (i == activeThreads);
-
-          if (allFinished || allThreadsShouldExit)
           {
-              lock_release(&threads[threadID].sleepLock);
+              lock_release(&sleepLock);
               break;
           }
 
@@ -2181,22 +2187,22 @@ void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
           // 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)
+          if (do_sleep || state == Thread::AVAILABLE)
-              cond_wait(&threads[threadID].sleepCond, &threads[threadID].sleepLock);
+              cond_wait(&sleepCond, &sleepLock);
 
-          lock_release(&threads[threadID].sleepLock);
+          lock_release(&sleepLock);
       }
 
       // If this thread has been assigned work, launch a search
-      if (threads[threadID].state == Thread::WORKISWAITING)
+      if (state == Thread::WORKISWAITING)
       {
-          assert(!allThreadsShouldExit);
+          assert(!do_terminate);
 
-          threads[threadID].state = Thread::SEARCHING;
+          state = Thread::SEARCHING;
 
           // Copy split point position and search stack and call search()
           SearchStack ss[PLY_MAX_PLUS_2];
-          SplitPoint* tsp = threads[threadID].splitPoint;
+          SplitPoint* tsp = splitPoint;
           Position pos(*tsp->pos, threadID);
 
           memcpy(ss, tsp->ss - 1, 4 * sizeof(SearchStack));
@@ -2211,24 +2217,21 @@ void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
           else
               assert(false);
 
-          assert(threads[threadID].state == Thread::SEARCHING);
+          assert(state == Thread::SEARCHING);
 
-          threads[threadID].state = Thread::AVAILABLE;
+          state = Thread::AVAILABLE;
 
           // Wake up master thread so to allow it to return from the idle loop in
           // case we are the last slave of the split point.
-          if (   useSleepingThreads
+          if (   Threads.use_sleeping_threads()
               && threadID != tsp->master
-              && threads[tsp->master].state == Thread::AVAILABLE)
+              && Threads[tsp->master].state == Thread::AVAILABLE)
-              threads[tsp->master].wake_up();
+              Threads[tsp->master].wake_up();
       }
 
       // If this thread is the master of a split point and all slaves have
       // finished their work at this split point, return from the idle loop.
-      for (i = 0; sp && i < activeThreads && !sp->is_slave[i]; i++) {}
+      if (sp && all_slaves_finished(sp))
-      allFinished = (i == activeThreads);
-
-      if (allFinished)
       {
           // Because sp->is_slave[] is reset under lock protection,
           // be sure sp->lock has been released before to return.

src/thread.cpp

@@ -35,7 +35,7 @@ namespace { extern "C" {
 
   DWORD WINAPI start_routine(LPVOID threadID) {
 
-    Threads.idle_loop(*(int*)threadID, NULL);
+    Threads[*(int*)threadID].idle_loop(NULL);
     return 0;
   }
 
@@ -43,7 +43,7 @@ namespace { extern "C" {
 
   void* start_routine(void* threadID) {
 
-    Threads.idle_loop(*(int*)threadID, NULL);
+    Threads[*(int*)threadID].idle_loop(NULL);
     return NULL;
   }
 
@@ -111,7 +111,22 @@ void ThreadsManager::read_uci_options() {
   maxThreadsPerSplitPoint = Options["Maximum Number of Threads per Split Point"].value<int>();
   minimumSplitDepth       = Options["Minimum Split Depth"].value<int>() * ONE_PLY;
   useSleepingThreads      = Options["Use Sleeping Threads"].value<bool>();
-  activeThreads           = Options["Threads"].value<int>();
+
+  set_size(Options["Threads"].value<int>());
+}
+
+
+// set_size() changes the number of active threads and raises do_sleep flag for
+// all the unused threads that will go immediately to sleep.
+
+void ThreadsManager::set_size(int cnt) {
+
+  assert(cnt > 0 && cnt <= MAX_THREADS);
+
+  activeThreads = cnt;
+
+  for (int i = 0; i < MAX_THREADS; i++)
+      threads[i].do_sleep = !(i < activeThreads);
 }
 
 
@@ -120,14 +135,10 @@ void ThreadsManager::read_uci_options() {
 
 void ThreadsManager::init() {
 
-  int threadID[MAX_THREADS];
-
-  // This flag is needed to properly end the threads when program exits
-  allThreadsShouldExit = false;
-
   // Threads will sent to sleep as soon as created, only main thread is kept alive
-  activeThreads = 1;
+  set_size(1);
   threads[0].state = Thread::SEARCHING;
+  threads[0].threadID = 0;
 
   // Allocate pawn and material hash tables for main thread
   init_hash_tables();
@@ -149,13 +160,13 @@ void ThreadsManager::init() {
   for (int i = 1; i < MAX_THREADS; i++)
   {
       threads[i].state = Thread::INITIALIZING;
-      threadID[i] = i;
+      threads[i].threadID = i;
 
 #if defined(_MSC_VER)
-      bool ok = (CreateThread(NULL, 0, start_routine, (LPVOID)&threadID[i], 0, NULL) != NULL);
+      bool ok = (CreateThread(NULL, 0, start_routine, (LPVOID)&threads[i].threadID , 0, NULL) != NULL);
 #else
       pthread_t pthreadID;
-      bool ok = (pthread_create(&pthreadID, NULL, start_routine, (void*)&threadID[i]) == 0);
+      bool ok = (pthread_create(&pthreadID, NULL, start_routine, (void*)&threads[i].threadID) == 0);
       pthread_detach(pthreadID);
 #endif
       if (!ok)
@@ -174,14 +185,12 @@ void ThreadsManager::init() {
 
 void ThreadsManager::exit() {
 
-  // Force the woken up threads to exit idle_loop() and hence terminate
-  allThreadsShouldExit = true;
-
   for (int i = 0; i < MAX_THREADS; i++)
   {
-      // Wake up all the threads and wait for termination
+      // Wake up all the slave threads and wait for termination
       if (i != 0)
       {
+          threads[i].do_terminate = true;
           threads[i].wake_up();
           while (threads[i].state != Thread::TERMINATED) {}
       }
@@ -318,7 +327,7 @@ 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, sp);
+  masterThread.idle_loop(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.

src/thread.h

@@ -77,16 +77,20 @@ struct Thread {
   void wake_up();
   bool cutoff_occurred() const;
   bool is_available_to(int master) const;
+  void idle_loop(SplitPoint* sp);
 
   SplitPoint splitPoints[MAX_ACTIVE_SPLIT_POINTS];
   MaterialInfoTable materialTable;
   PawnInfoTable pawnTable;
+  int threadID;
   int maxPly;
   Lock sleepLock;
   WaitCondition sleepCond;
   volatile ThreadState state;
   SplitPoint* volatile splitPoint;
   volatile int activeSplitPoints;
+  volatile bool do_sleep;
+  volatile bool do_terminate;
 };
 
 
@@ -105,13 +109,13 @@ public:
   void exit();
   void init_hash_tables();
 
+  bool use_sleeping_threads() const { return useSleepingThreads; }
   int min_split_depth() const { return minimumSplitDepth; }
   int size() const { return activeThreads; }
-  void set_size(int cnt) { activeThreads = cnt; }
 
+  void set_size(int cnt);
   void read_uci_options();
   bool available_slave_exists(int master) const;
-  void idle_loop(int threadID, SplitPoint* sp);
 
   template <bool Fake>
   Value split(Position& pos, SearchStack* ss, Value alpha, Value beta, Value bestValue,
@@ -123,7 +127,6 @@ private:
   int maxThreadsPerSplitPoint;
   int activeThreads;
   bool useSleepingThreads;
-  volatile bool allThreadsShouldExit;
 };
 
 extern ThreadsManager Threads;