Refactor global variables

This aims to remove some of the annoying global structure which Stockfish has.

Overall there is no major elo regression to be expected.

Non regression SMP STC (paused, early version):
https://tests.stockfishchess.org/tests/view/65983d7979aa8af82b9608f1
LLR: 0.23 (-2.94,2.94) <-1.75,0.25>
Total: 76232 W: 19035 L: 19096 D: 38101
Ptnml(0-2): 92, 8735, 20515, 8690, 84

Non regression STC (early version):
https://tests.stockfishchess.org/tests/view/6595b3a479aa8af82b95da7f
LLR: 2.93 (-2.94,2.94) <-1.75,0.25>
Total: 185344 W: 47027 L: 46972 D: 91345
Ptnml(0-2): 571, 21285, 48943, 21264, 609

Non regression SMP STC:
https://tests.stockfishchess.org/tests/view/65a0715c79aa8af82b96b7e4
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 142936 W: 35761 L: 35662 D: 71513
Ptnml(0-2): 209, 16400, 38135, 16531, 193

These global structures/variables add hidden dependencies and allow data
to be mutable from where it shouldn't it be (i.e. options). They also
prevent Stockfish from internal selfplay, which would be a nice thing to
be able to do, i.e. instantiate two Stockfish instances and let them
play against each other. It will also allow us to make Stockfish a
library, which can be easier used on other platforms.

For consistency with the old search code, `thisThread` has been kept,
even though it is not strictly necessary anymore. This the first major
refactor of this kind (in recent time), and future changes are required,
to achieve the previously described goals. This includes cleaning up the
dependencies, transforming the network to be self contained and coming
up with a plan to deal with proper tablebase memory management (see
comments for more information on this).

The removal of these global structures has been discussed in parts with
Vondele and Sopel.

closes https://github.com/official-stockfish/Stockfish/pull/4968

No functional change

src/timeman.cpp

@@ -19,30 +19,47 @@
 #include "timeman.h"
 
 #include <algorithm>
+#include <cassert>
 #include <cmath>
+#include <cstdint>
 
 #include "search.h"
-#include "uci.h"
+#include "ucioption.h"
 
 namespace Stockfish {
 
-TimeManagement Time;  // Our global time management object
 
+TimePoint TimeManagement::optimum() const { return optimumTime; }
+TimePoint TimeManagement::maximum() const { return maximumTime; }
+TimePoint TimeManagement::elapsed(size_t nodes) const {
+    return useNodesTime ? TimePoint(nodes) : now() - startTime;
+}
+
+void TimeManagement::clear() {
+    availableNodes = 0;  // When in 'nodes as time' mode
+}
+
+void TimeManagement::advance_nodes_time(std::int64_t nodes) {
+    assert(useNodesTime);
+    availableNodes += nodes;
+}
 
 // Called at the beginning of the search and calculates
 // the bounds of time allowed for the current game ply. We currently support:
 //      1) x basetime (+ z increment)
 //      2) x moves in y seconds (+ z increment)
-void TimeManagement::init(Search::LimitsType& limits, Color us, int ply) {
-
+void TimeManagement::init(Search::LimitsType& limits,
+                          Color               us,
+                          int                 ply,
+                          const OptionsMap&   options) {
     // If we have no time, no need to initialize TM, except for the start time,
     // which is used by movetime.
     startTime = limits.startTime;
     if (limits.time[us] == 0)
         return;
 
-    TimePoint moveOverhead = TimePoint(Options["Move Overhead"]);
-    TimePoint npmsec       = TimePoint(Options["nodestime"]);
+    TimePoint moveOverhead = TimePoint(options["Move Overhead"]);
+    TimePoint npmsec       = TimePoint(options["nodestime"]);
 
     // optScale is a percentage of available time to use for the current move.
     // maxScale is a multiplier applied to optimumTime.
@@ -54,6 +71,8 @@ void TimeManagement::init(Search::LimitsType& limits, Color us, int ply) {
     // must be much lower than the real engine speed.
     if (npmsec)
     {
+        useNodesTime = true;
+
         if (!availableNodes)                            // Only once at game start
             availableNodes = npmsec * limits.time[us];  // Time is in msec
 
@@ -100,7 +119,7 @@ void TimeManagement::init(Search::LimitsType& limits, Color us, int ply) {
     maximumTime =
       TimePoint(std::min(0.84 * limits.time[us] - moveOverhead, maxScale * optimumTime)) - 10;
 
-    if (Options["Ponder"])
+    if (options["Ponder"])
         optimumTime += optimumTime / 4;
 }