Set timer to a fixed interval

And remove a complex (and broken) formula.

Indeed previous code was broken in case of TC with big
time increments where available_time() was too similar
to total time yielding to many time losses, so for instance:

go wtime 2600 winc 2600
info nodes 4432770 time 2601 <-- time forfeit!

maximum search time = 2530 ms
available_time = 2300 ms

For a reference and further details see:

https://groups.google.com/forum/?fromgroups=#!topic/fishcooking/dCPAvQDcm2E

Speed tested with bench disabling timer alltogheter vs timer set at
max resolution, showed we have no speed regressions both in single
core and when using all physical cores.

No functional change.

src/search.cpp

@@ -55,9 +55,6 @@ namespace {
   // Set to true to force running with one thread. Used for debugging
   const bool FakeSplit = false;
 
-  // This is the minimum interval in msec between two check_time() calls
-  const int TimerResolution = 5;
-
   // Different node types, used as template parameter
   enum NodeType { Root, PV, NonPV, SplitPointRoot, SplitPointPV, SplitPointNonPV };
 
@@ -243,19 +240,12 @@ void Search::think() {
       Threads[i]->maxPly = 0;
 
   Threads.sleepWhileIdle = Options["Idle Threads Sleep"];
-
-  // Set best timer interval to avoid lagging under time pressure. Timer is
-  // used to check for remaining available thinking time.
-  Threads.timer->msec =
-  Limits.use_time_management() ? std::min(100, std::max(TimeMgr.available_time() / 16, TimerResolution)) :
-                  Limits.nodes ? 2 * TimerResolution
-                               : 100;
-
+  Threads.timer->run = true;
   Threads.timer->notify_one(); // Wake up the recurring timer
 
   id_loop(RootPos); // Let's start searching !
 
-  Threads.timer->msec = 0; // Stop the timer
+  Threads.timer->run = false; // Stop the timer
   Threads.sleepWhileIdle = true; // Send idle threads to sleep
 
   if (Options["Write Search Log"])
@@ -1764,7 +1754,7 @@ void check_time() {
                          && !Signals.failedLowAtRoot
                          &&  elapsed > TimeMgr.available_time();
 
-  bool noMoreTime =   elapsed > TimeMgr.maximum_time() - 2 * TimerResolution
+  bool noMoreTime =   elapsed > TimeMgr.maximum_time() - 2 * TimerThread::Resolution
                    || stillAtFirstMove;
 
   if (   (Limits.use_time_management() && noMoreTime)

src/thread.cpp

@@ -101,11 +101,11 @@ void TimerThread::idle_loop() {
       mutex.lock();
 
       if (!exit)
-          sleepCondition.wait_for(mutex, msec ? msec : INT_MAX);
+          sleepCondition.wait_for(mutex, run ? Resolution : INT_MAX);
 
       mutex.unlock();
 
-      if (msec)
+      if (run)
           check_time();
   }
 }

src/thread.h

@@ -143,9 +143,10 @@ struct MainThread : public Thread {
 };
 
 struct TimerThread : public ThreadBase {
-  TimerThread() : msec(0) {}
+  TimerThread() : run(false) {}
   virtual void idle_loop();
-  int msec;
+  bool run;
+  static const int Resolution = 5; // msec between two check_time() calls
 };