Simplify pondering time management (#1899)

stopOnPonderhit is used to stop search quickly on a ponderhit. It is set by mainThread as part of its time management. However, master employs it as a signal between mainThread and the UCI thread. This is not necessary, it is sufficient for the UCI thread to signal that pondering finished, and mainThread should do its usual time-keeping job, and in this case stop immediately.

This patch implements this, removing stopOnPonderHit as an atomic variable from the ThreadPool,
and moving it as a normal variable to mainThread, reducing its scope. In MainThread::check_time() the search is stopped immediately if ponder switches to false, and the variable stopOnPonderHit is set.

Furthermore, ponder has been moved to mainThread, as the variable is only used to exchange signals between the UCI thread and mainThread.

The version has been tested locally (as fishtest doesn't support ponder):

Score of ponderSimp vs master: 2616 - 2528 - 8630 [0.503] 13774
Elo difference: 2.22 +/- 3.54

which indicates no regression.

No functional change.

diff --git a/src/search.cpp b/src/search.cpp
index 4a1a352349f966ecf5efd224540dc894bd9821ff..99985fde53b4f74acd5d0ac562a2f7e2b452b045 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -227,10 +227,9 @@ void MainThread::search() {
   // Threads.stop. However, if we are pondering or in an infinite search,
   // the UCI protocol states that we shouldn't print the best move before the
   // GUI sends a "stop" or "ponderhit" command. We therefore simply wait here
-  // until the GUI sends one of those commands (which also raises Threads.stop).
-  Threads.stopOnPonderhit = true;
+  // until the GUI sends one of those commands.
 
-  while (!Threads.stop && (Threads.ponder || Limits.infinite))
+  while (!Threads.stop && (ponder || Limits.infinite))
   {} // Busy wait for a stop or a ponder reset
 
   // Stop the threads if not already stopped (also raise the stop if
@@ -448,7 +447,7 @@ void Thread::search() {
                   {
                       failedHighCnt = 0;
                       failedLow = true;
-                      Threads.stopOnPonderhit = false;
+                      mainThread->stopOnPonderhit = false;
                   }
               }
               else if (bestValue >= beta)
@@ -497,7 +496,7 @@ void Thread::search() {
       // Do we have time for the next iteration? Can we stop searching now?
       if (    Limits.use_time_management()
           && !Threads.stop
-          && !Threads.stopOnPonderhit)
+          && !mainThread->stopOnPonderhit)
       {
           double fallingEval = (306 + 119 * failedLow + 6 * (mainThread->previousScore - bestValue)) / 581.0;
           fallingEval        = std::max(0.5, std::min(1.5, fallingEval));
@@ -515,8 +514,8 @@ void Thread::search() {
           {
               // If we are allowed to ponder do not stop the search now but
               // keep pondering until the GUI sends "ponderhit" or "stop".
-              if (Threads.ponder)
-                  Threads.stopOnPonderhit = true;
+              if (mainThread->ponder)
+                  mainThread->stopOnPonderhit = true;
               else
                   Threads.stop = true;
           }
@@ -1595,10 +1594,10 @@ void MainThread::check_time() {
   }
 
   // We should not stop pondering until told so by the GUI
-  if (Threads.ponder)
+  if (ponder)
       return;
 
-  if (   (Limits.use_time_management() && elapsed > Time.maximum() - 10)
+  if (   (Limits.use_time_management() && (elapsed > Time.maximum() - 10 || stopOnPonderhit))
       || (Limits.movetime && elapsed >= Limits.movetime)
       || (Limits.nodes && Threads.nodes_searched() >= (uint64_t)Limits.nodes))
       Threads.stop = true;

diff --git a/src/thread.cpp b/src/thread.cpp
index f88e359b0373436db1f6c445f72f4b04448667e7..6c1d729987d90bb237f0b0c9034d78d19aa2d7f0 100644 (file)
--- a/src/thread.cpp
+++ b/src/thread.cpp
@@ -162,8 +162,8 @@ void ThreadPool::start_thinking(Position& pos, StateListPtr& states,
 
   main()->wait_for_search_finished();
 
-  stopOnPonderhit = stop = false;
-  ponder = ponderMode;
+  main()->stopOnPonderhit = stop = false;
+  main()->ponder = ponderMode;
   Search::Limits = limits;
   Search::RootMoves rootMoves;
 

diff --git a/src/thread.h b/src/thread.h
index e377e992d6852e0a041ef770b9db91f25178213b..686441cb52c2c1e506b57043e947ec4052c68e8e 100644 (file)
--- a/src/thread.h
+++ b/src/thread.h
@@ -88,6 +88,8 @@ struct MainThread : public Thread {
   double bestMoveChanges, previousTimeReduction;
   Value previousScore;
   int callsCnt;
+  bool stopOnPonderhit;
+  std::atomic_bool ponder;
 };
 
 
@@ -105,7 +107,7 @@ struct ThreadPool : public std::vector<Thread*> {
   uint64_t nodes_searched() const { return accumulate(&Thread::nodes); }
   uint64_t tb_hits()        const { return accumulate(&Thread::tbHits); }
 
-  std::atomic_bool stop, ponder, stopOnPonderhit;
+  std::atomic_bool stop;
 
 private:
   StateListPtr setupStates;

diff --git a/src/uci.cpp b/src/uci.cpp
index 36d359c6ff1c1228c2225cb8b0685facf537b2f8..739cf34347f497782c16526d64849b9058a237f7 100644 (file)
--- a/src/uci.cpp
+++ b/src/uci.cpp
@@ -207,18 +207,16 @@ void UCI::loop(int argc, char* argv[]) {
       token.clear(); // Avoid a stale if getline() returns empty or blank line
       is >> skipws >> token;
 
-      // The GUI sends 'ponderhit' to tell us the user has played the expected move.
-      // So 'ponderhit' will be sent if we were told to ponder on the same move the
-      // user has played. We should continue searching but switch from pondering to
-      // normal search. In case Threads.stopOnPonderhit is set we are waiting for
-      // 'ponderhit' to stop the search, for instance if max search depth is reached.
       if (    token == "quit"
-          ||  token == "stop"
-          || (token == "ponderhit" && Threads.stopOnPonderhit))
+          ||  token == "stop")
           Threads.stop = true;
 
+      // The GUI sends 'ponderhit' to tell us the user has played the expected move.
+      // So 'ponderhit' will be sent if we were told to ponder on the same move the
+      // user has played. We should continue searching but switch from pondering to
+      // normal search.
       else if (token == "ponderhit")
-          Threads.ponder = false; // Switch to normal search
+          Threads.main()->ponder = false; // Switch to normal search
 
       else if (token == "uci")
           sync_cout << "id name " << engine_info(true)