Polymorphic Thread hierarchy

Subclass MainThread and TimerThread and declare
idle_loop() virtual. This allow us to cleanly
remove a good bunch of hacks, relying on C++
polymorphism to do the job.

No functional change.

src/search.cpp

@@ -235,7 +235,7 @@ void Search::think() {
 
   // Set best timer interval to avoid lagging under time pressure. Timer is
   // used to check for remaining available thinking time.
-  Threads.timer_thread()->maxPly = /* Hack: we use maxPly to set timer interval */
+  Threads.timer_thread()->msec =
   Limits.use_time_management() ? std::min(100, std::max(TimeMgr.available_time() / 16, TimerResolution)) :
                   Limits.nodes ? 2 * TimerResolution
                                : 100;
@@ -244,7 +244,7 @@ void Search::think() {
 
   id_loop(RootPos); // Let's start searching !
 
-  Threads.timer_thread()->maxPly = 0; // Stop the timer
+  Threads.timer_thread()->msec = 0; // Stop the timer
   Threads.sleepWhileIdle = true; // Send idle threads to sleep
 
   if (Options["Use Search Log"])
@@ -1655,7 +1655,7 @@ void Thread::idle_loop() {
       // If this thread has been assigned work, launch a search
       if (is_searching)
       {
-          assert(/*!is_finished &&*/ !do_exit);
+          assert(!do_exit);
 
           Threads.mutex.lock();
 

src/thread.cpp

@@ -32,26 +32,23 @@ ThreadPool Threads; // Global object
 namespace { extern "C" {
 
  // start_routine() is the C function which is called when a new thread
- // is launched. It is a wrapper to member function pointed by start_fn.
+ // is launched. It is a wrapper to the virtual function idle_loop().
 
- long start_routine(Thread* th) { (th->*(th->start_fn))(); return 0; }
+ long start_routine(Thread* th) { th->idle_loop(); return 0; }
 
 } }
 
 
 // Thread c'tor starts a newly-created thread of execution that will call
-// the idle loop function pointed by start_fn going immediately to sleep.
+// the the virtual function idle_loop(), going immediately to sleep.
 
-Thread::Thread(Fn fn) : splitPoints() {
+Thread::Thread() : splitPoints() {
 
   is_searching = do_exit = false;
   maxPly = splitPointsCnt = 0;
   curSplitPoint = NULL;
-  start_fn = fn;
   idx = Threads.size();
 
-  is_finished = (fn != &Thread::main_loop); // Avoid a race with start_searching()
-
   if (!thread_create(handle, start_routine, this))
   {
       std::cerr << "Failed to create thread number " << idx << std::endl;
@@ -60,39 +57,37 @@ Thread::Thread(Fn fn) : splitPoints() {
 }
 
 
-// Thread d'tor waits for thread termination before to return.
+// Thread d'tor waits for thread termination before to return
 
 Thread::~Thread() {
 
-  assert(is_finished);
-
   do_exit = true; // Search must be already finished
   notify_one();
   thread_join(handle); // Wait for thread termination
 }
 
 
-// Thread::timer_loop() is where the timer thread waits maxPly milliseconds and
+// TimerThread::idle_loop() is where the timer thread waits msec milliseconds
-// then calls check_time(). If maxPly is 0 thread sleeps until is woken up.
+// and then calls check_time(). If msec is 0 thread sleeps until is woken up.
 extern void check_time();
 
-void Thread::timer_loop() {
+void TimerThread::idle_loop() {
 
   while (!do_exit)
   {
       mutex.lock();
-      while (!maxPly && !do_exit)
+      while (!msec && !do_exit)
-          sleepCondition.wait_for(mutex, maxPly ? maxPly : INT_MAX);
+          sleepCondition.wait_for(mutex, msec ? msec : INT_MAX);
       mutex.unlock();
       check_time();
   }
 }
 
 
-// Thread::main_loop() is where the main thread is parked waiting to be started
+// MainThread::idle_loop() is where the main thread is parked waiting to be started
 // when there is a new search. Main thread will launch all the slave threads.
 
-void Thread::main_loop() {
+void MainThread::idle_loop() {
 
   while (true)
   {
@@ -121,8 +116,7 @@ void Thread::main_loop() {
 }
 
 
-// Thread::notify_one() wakes up the thread, normally at the beginning of the
+// Thread::notify_one() wakes up the thread, normally at split time
-// search or, if "sleeping threads" is used at split time.
 
 void Thread::notify_one() {
 
@@ -184,9 +178,9 @@ bool Thread::is_available_to(Thread* master) const {
 
 void ThreadPool::init() {
 
-  timer = new Thread(&Thread::timer_loop);
-  threads.push_back(new Thread(&Thread::main_loop));
   sleepWhileIdle = true;
+  timer = new TimerThread();
+  threads.push_back(new MainThread());
   read_uci_options();
 }
 
@@ -216,7 +210,7 @@ void ThreadPool::read_uci_options() {
   assert(requested > 0);
 
   while (threads.size() < requested)
-      threads.push_back(new Thread(&Thread::idle_loop));
+      threads.push_back(new Thread());
 
   while (threads.size() > requested)
   {
@@ -319,7 +313,7 @@ Value ThreadPool::split(Position& pos, Stack* ss, Value alpha, Value beta,
   // their work at this split point.
   if (slavesCnt || Fake)
   {
-      master->idle_loop();
+      master->Thread::idle_loop(); // Force a call to base class idle_loop()
 
       // In helpful master concept a master can help only a sub-tree of its split
       // point, and because here is all finished is not possible master is booked.
@@ -354,7 +348,7 @@ template Value ThreadPool::split<true>(Position&, Stack*, Value, Value, Value, M
 
 void ThreadPool::wait_for_search_finished() {
 
-  Thread* t = main_thread();
+  MainThread* t = main_thread();
   t->mutex.lock();
   while (!t->is_finished) sleepCondition.wait(t->mutex);
   t->mutex.unlock();

src/thread.h

@@ -93,18 +93,14 @@ struct SplitPoint {
 
 class Thread {
 
-  typedef void (Thread::* Fn) (); // Pointer to member function
-
 public:
-  Thread(Fn fn);
+  Thread();
- ~Thread();
+  virtual ~Thread();
 
+  virtual void idle_loop();
   void notify_one();
   bool cutoff_occurred() const;
   bool is_available_to(Thread* master) const;
-  void idle_loop();
-  void main_loop();
-  void timer_loop();
   void wait_for(volatile const bool& b);
 
   SplitPoint splitPoints[MAX_SPLITPOINTS_PER_THREAD];
@@ -116,14 +112,24 @@ public:
   Mutex mutex;
   ConditionVariable sleepCondition;
   NativeHandle handle;
-  Fn start_fn;
   SplitPoint* volatile curSplitPoint;
   volatile int splitPointsCnt;
   volatile bool is_searching;
-  volatile bool is_finished;
   volatile bool do_exit;
 };
 
+struct TimerThread : public Thread {
+  TimerThread() : msec(0) {}
+  virtual void idle_loop();
+  int msec;
+};
+
+struct MainThread : public Thread {
+  MainThread() : is_finished(false) {} // Avoid a race with start_searching()
+  virtual void idle_loop();
+  volatile bool is_finished;
+};
+
 
 /// ThreadPool class handles all the threads related stuff like init, starting,
 /// parking and, the most important, launching a slave thread at a split point.
@@ -138,8 +144,8 @@ public:
   Thread& operator[](size_t id) { return *threads[id]; }
   int min_split_depth() const { return minimumSplitDepth; }
   size_t size() const { return threads.size(); }
-  Thread* main_thread() { return threads[0]; }
+  MainThread* main_thread() { return static_cast<MainThread*>(threads[0]); }
-  Thread* timer_thread() { return timer; }
+  TimerThread* timer_thread() { return timer; }
 
   void read_uci_options();
   bool available_slave_exists(Thread* master) const;
@@ -152,10 +158,11 @@ public:
               Depth depth, Move threatMove, int moveCount, MovePicker& mp, int nodeType);
 private:
   friend class Thread;
+  friend struct MainThread;
   friend void check_time();
 
   std::vector<Thread*> threads;
-  Thread* timer;
+  TimerThread* timer;
   Mutex mutex;
   ConditionVariable sleepCondition;
   Depth minimumSplitDepth;