uct/search.c

   1 #include <assert.h>
   2 #include <math.h>
   3 #include <pthread.h>
   4 #include <signal.h>
   5 #include <stdio.h>
   6 #include <stdlib.h>
   7 #include <string.h>
   8 #include <time.h>
   9
  10 #define DEBUG
  11
  12 #include "debug.h"
  13 #include "distributed/distributed.h"
  14 #include "move.h"
  15 #include "random.h"
  16 #include "timeinfo.h"
  17 #include "uct/dynkomi.h"
  18 #include "uct/internal.h"
  19 #include "uct/search.h"
  20 #include "uct/tree.h"
  21 #include "uct/uct.h"
  22 #include "uct/walk.h"
  23
  24
  25 /* Default number of simulations to perform per move.
  26  * Note that this is now in total over all threads!. */
  27 #define MC_GAMES        80000
  28 static const struct time_info default_ti = {
  29         .period = TT_MOVE,
  30         .dim = TD_GAMES,
  31         .len = { .games = MC_GAMES },
  32 };
  33
  34 /* When terminating UCT search early, the safety margin to add to the
  35  * remaining playout number estimate when deciding whether the result can
  36  * still change. */
  37 #define PLAYOUT_DELTA_SAFEMARGIN 1000
  38
  39 /* Minimal number of simulations to consider early break. */
  40 #define PLAYOUT_EARLY_BREAK_MIN 5000
  41
  42 /* Minimal time to consider early break (in seconds). */
  43 #define TIME_EARLY_BREAK_MIN 1.0
  44
  45
  46 /* Pachi threading structure:
  47  *
  48  * main thread
  49  *   |         main(), GTP communication, ...
  50  *   |         starts and stops the search managed by thread_manager
  51  *   |
  52  * thread_manager
  53  *   |         spawns and collects worker threads
  54  *   |
  55  * worker0
  56  * worker1
  57  * ...
  58  * workerK
  59  *             uct_playouts() loop, doing descend-playout until uct_halt
  60  *
  61  * Another way to look at it is by functions (lines denote thread boundaries):
  62  *
  63  * | uct_genmove()
  64  * | uct_search()            (uct_search_start() .. uct_search_stop())
  65  * | -----------------------
  66  * | spawn_thread_manager()
  67  * | -----------------------
  68  * | spawn_worker()
  69  * V uct_playouts() */
  70
  71 /* Set in thread manager in case the workers should stop. */
  72 volatile sig_atomic_t uct_halt = 0;
  73 /* ID of the thread manager. */
  74 static pthread_t thread_manager;
  75 bool thread_manager_running;
  76
  77 static pthread_mutex_t finish_mutex = PTHREAD_MUTEX_INITIALIZER;
  78 static pthread_cond_t finish_cond = PTHREAD_COND_INITIALIZER;
  79 static volatile int finish_thread;
  80 static pthread_mutex_t finish_serializer = PTHREAD_MUTEX_INITIALIZER;
  81
  82 static void *
  83 spawn_worker(void *ctx_)
  84 {
  85         struct uct_thread_ctx *ctx = ctx_;
  86         /* Setup */
  87         fast_srandom(ctx->seed);
  88         /* Run */
  89         ctx->games = uct_playouts(ctx->u, ctx->b, ctx->color, ctx->t, ctx->ti);
  90         /* Finish */
  91         pthread_mutex_lock(&finish_serializer);
  92         pthread_mutex_lock(&finish_mutex);
  93         finish_thread = ctx->tid;
  94         pthread_cond_signal(&finish_cond);
  95         pthread_mutex_unlock(&finish_mutex);
  96         return ctx;
  97 }
  98
  99 /* Thread manager, controlling worker threads. It must be called with
 100  * finish_mutex lock held, but it will unlock it itself before exiting;
 101  * this is necessary to be completely deadlock-free. */
 102 /* The finish_cond can be signalled for it to stop; in that case,
 103  * the caller should set finish_thread = -1. */
 104 /* After it is started, it will update mctx->t to point at some tree
 105  * used for the actual search, on return
 106  * it will set mctx->games to the number of performed simulations. */
 107 static void *
 108 spawn_thread_manager(void *ctx_)
 109 {
 110         /* In thread_manager, we use only some of the ctx fields. */
 111         struct uct_thread_ctx *mctx = ctx_;
 112         struct uct *u = mctx->u;
 113         struct tree *t = mctx->t;
 114         fast_srandom(mctx->seed);
 115
 116         int played_games = 0;
 117         pthread_t threads[u->threads];
 118         int joined = 0;
 119
 120         uct_halt = 0;
 121
 122         /* Garbage collect the tree by preference when pondering. */
 123         if (u->pondering && t->nodes && t->nodes_size >= t->pruning_threshold) {
 124                 t->root = tree_garbage_collect(t, t->root);
 125         }
 126
 127         /* Spawn threads... */
 128         for (int ti = 0; ti < u->threads; ti++) {
 129                 struct uct_thread_ctx *ctx = malloc2(sizeof(*ctx));
 130                 ctx->u = u; ctx->b = mctx->b; ctx->color = mctx->color;
 131                 mctx->t = ctx->t = t;
 132                 ctx->tid = ti; ctx->seed = fast_random(65536) + ti;
 133                 ctx->ti = mctx->ti;
 134                 pthread_create(&threads[ti], NULL, spawn_worker, ctx);
 135                 if (UDEBUGL(3))
 136                         fprintf(stderr, "Spawned worker %d\n", ti);
 137         }
 138
 139         /* ...and collect them back: */
 140         while (joined < u->threads) {
 141                 /* Wait for some thread to finish... */
 142                 pthread_cond_wait(&finish_cond, &finish_mutex);
 143                 if (finish_thread < 0) {
 144                         /* Stop-by-caller. Tell the workers to wrap up
 145                          * and unblock them from terminating. */
 146                         uct_halt = 1;
 147                         /* We need to make sure the workers do not complete
 148                          * the termination sequence before we get officially
 149                          * stopped - their wake and the stop wake could get
 150                          * coalesced. */
 151                         pthread_mutex_unlock(&finish_serializer);
 152                         continue;
 153                 }
 154                 /* ...and gather its remnants. */
 155                 struct uct_thread_ctx *ctx;
 156                 pthread_join(threads[finish_thread], (void **) &ctx);
 157                 played_games += ctx->games;
 158                 joined++;
 159                 free(ctx);
 160                 if (UDEBUGL(3))
 161                         fprintf(stderr, "Joined worker %d\n", finish_thread);
 162                 pthread_mutex_unlock(&finish_serializer);
 163         }
 164
 165         pthread_mutex_unlock(&finish_mutex);
 166
 167         mctx->games = played_games;
 168         return mctx;
 169 }
 170
 171
 172 /*** THREAD MANAGER end */
 173
 174 /*** Search infrastructure: */
 175
 176
 177 int
 178 uct_search_games(struct uct_search_state *s)
 179 {
 180         return s->ctx->t->root->u.playouts;
 181 }
 182
 183 void
 184 uct_search_start(struct uct *u, struct board *b, enum stone color,
 185                  struct tree *t, struct time_info *ti,
 186                  struct uct_search_state *s)
 187 {
 188         /* Set up search state. */
 189         s->base_playouts = s->last_dynkomi = s->last_print = t->root->u.playouts;
 190         s->print_interval = u->reportfreq * u->threads;
 191         s->fullmem = false;
 192
 193         if (ti) {
 194                 if (ti->period == TT_NULL) *ti = default_ti;
 195                 time_stop_conditions(ti, b, u->fuseki_end, u->yose_start, u->max_maintime_ratio, &s->stop);
 196         }
 197
 198         /* Fire up the tree search thread manager, which will in turn
 199          * spawn the searching threads. */
 200         assert(u->threads > 0);
 201         assert(!thread_manager_running);
 202         static struct uct_thread_ctx mctx;
 203         mctx = (struct uct_thread_ctx) { .u = u, .b = b, .color = color, .t = t, .seed = fast_random(65536), .ti = ti };
 204         s->ctx = &mctx;
 205         pthread_mutex_lock(&finish_serializer);
 206         pthread_mutex_lock(&finish_mutex);
 207         pthread_create(&thread_manager, NULL, spawn_thread_manager, s->ctx);
 208         thread_manager_running = true;
 209 }
 210
 211 struct uct_thread_ctx *
 212 uct_search_stop(void)
 213 {
 214         assert(thread_manager_running);
 215
 216         /* Signal thread manager to stop the workers. */
 217         pthread_mutex_lock(&finish_mutex);
 218         finish_thread = -1;
 219         pthread_cond_signal(&finish_cond);
 220         pthread_mutex_unlock(&finish_mutex);
 221
 222         /* Collect the thread manager. */
 223         struct uct_thread_ctx *pctx;
 224         thread_manager_running = false;
 225         pthread_join(thread_manager, (void **) &pctx);
 226         return pctx;
 227 }
 228
 229
 230 void
 231 uct_search_progress(struct uct *u, struct board *b, enum stone color,
 232                     struct tree *t, struct time_info *ti,
 233                     struct uct_search_state *s, int i)
 234 {
 235         struct uct_thread_ctx *ctx = s->ctx;
 236
 237         /* Adjust dynkomi? */
 238         int di = u->dynkomi_interval * u->threads;
 239         if (ctx->t->use_extra_komi && u->dynkomi->permove
 240             && !u->pondering && di
 241             && i > s->last_dynkomi + di) {
 242                 s->last_dynkomi += di;
 243                 floating_t old_dynkomi = ctx->t->extra_komi;
 244                 ctx->t->extra_komi = u->dynkomi->permove(u->dynkomi, b, ctx->t);
 245                 if (UDEBUGL(3) && old_dynkomi != ctx->t->extra_komi)
 246                         fprintf(stderr, "dynkomi adjusted (%f -> %f)\n",
 247                                 old_dynkomi, ctx->t->extra_komi);
 248         }
 249
 250         /* Print progress? */
 251         if (i - s->last_print > s->print_interval) {
 252                 s->last_print += s->print_interval; // keep the numbers tidy
 253                 uct_progress_status(u, ctx->t, color, s->last_print, NULL);
 254         }
 255
 256         if (!s->fullmem && ctx->t->nodes_size > u->max_tree_size) {
 257                 if (UDEBUGL(2))
 258                         fprintf(stderr, "memory limit hit (%lu > %lu)\n",
 259                                 ctx->t->nodes_size, u->max_tree_size);
 260                 s->fullmem = true;
 261         }
 262 }
 263
 264
 265 /* Determine whether we should terminate the search early. */
 266 static bool
 267 uct_search_stop_early(struct uct *u, struct tree *t, struct board *b,
 268                 struct time_info *ti, struct time_stop *stop,
 269                 struct tree_node *best, struct tree_node *best2,
 270                 int played, bool fullmem)
 271 {
 272         /* If the memory is full, stop immediately. Since the tree
 273          * cannot grow anymore, some non-well-expanded nodes will
 274          * quickly take over with extremely high ratio since the
 275          * counters are not properly simulated (just as if we use
 276          * non-UCT MonteCarlo). */
 277         /* (XXX: A proper solution would be to prune the tree
 278          * on the spot.) */
 279         if (fullmem)
 280                 return true;
 281
 282         /* Think at least 100ms to avoid a random move. This is particularly
 283          * important in distributed mode, where this function is called frequently. */
 284         double elapsed = 0.0;
 285         if (ti->dim == TD_WALLTIME) {
 286                 elapsed = time_now() - ti->len.t.timer_start;
 287                 if (elapsed < TREE_BUSYWAIT_INTERVAL) return false;
 288         }
 289
 290         /* Break early if we estimate the second-best move cannot
 291          * catch up in assigned time anymore. We use all our time
 292          * if we are in byoyomi with single stone remaining in our
 293          * period, however - it's better to pre-ponder. */
 294         bool time_indulgent = (!ti->len.t.main_time && ti->len.t.byoyomi_stones == 1);
 295         if (best2 && ti->dim == TD_WALLTIME
 296             && played >= PLAYOUT_EARLY_BREAK_MIN && !time_indulgent) {
 297                 double remaining = stop->worst.time - elapsed;
 298                 double pps = ((double)played) / elapsed;
 299                 double estplayouts = remaining * pps + PLAYOUT_DELTA_SAFEMARGIN;
 300                 if (best->u.playouts > best2->u.playouts + estplayouts) {
 301                         if (UDEBUGL(2))
 302                                 fprintf(stderr, "Early stop, result cannot change: "
 303                                         "best %d, best2 %d, estimated %f simulations to go (%d/%f=%f pps)\n",
 304                                         best->u.playouts, best2->u.playouts, estplayouts, played, elapsed, pps);
 305                         return true;
 306                 }
 307         }
 308
 309         /* Early break in won situation. */
 310         if (best->u.playouts >= PLAYOUT_EARLY_BREAK_MIN
 311             && (ti->dim != TD_WALLTIME || elapsed > TIME_EARLY_BREAK_MIN)
 312             && tree_node_get_value(t, 1, best->u.value) >= u->sure_win_threshold) {
 313                 return true;
 314         }
 315
 316         return false;
 317 }
 318
 319 /* Determine whether we should terminate the search later than expected. */
 320 static bool
 321 uct_search_keep_looking(struct uct *u, struct tree *t, struct board *b,
 322                 struct time_info *ti, struct time_stop *stop,
 323                 struct tree_node *best, struct tree_node *best2,
 324                 struct tree_node *bestr, struct tree_node *winner, int i)
 325 {
 326         if (!best) {
 327                 if (UDEBUGL(2))
 328                         fprintf(stderr, "Did not find best move, still trying...\n");
 329                 return true;
 330         }
 331
 332         /* Do not waste time if we are winning. Spend up to worst time if
 333          * we are unsure, but only desired time if we are sure of winning. */
 334         floating_t beta = 2 * (tree_node_get_value(t, 1, best->u.value) - 0.5);
 335         if (ti->dim == TD_WALLTIME && beta > 0) {
 336                 double good_enough = stop->desired.time * beta + stop->worst.time * (1 - beta);
 337                 double elapsed = time_now() - ti->len.t.timer_start;
 338                 if (elapsed > good_enough) return false;
 339         }
 340
 341         if (u->best2_ratio > 0) {
 342                 /* Check best/best2 simulations ratio. If the
 343                  * two best moves give very similar results,
 344                  * keep simulating. */
 345                 if (best2 && best2->u.playouts
 346                     && (double)best->u.playouts / best2->u.playouts < u->best2_ratio) {
 347                         if (UDEBUGL(2))
 348                                 fprintf(stderr, "Best2 ratio %f < threshold %f\n",
 349                                         (double)best->u.playouts / best2->u.playouts,
 350                                         u->best2_ratio);
 351                         return true;
 352                 }
 353         }
 354
 355         if (u->bestr_ratio > 0) {
 356                 /* Check best, best_best value difference. If the best move
 357                  * and its best child do not give similar enough results,
 358                  * keep simulating. */
 359                 if (bestr && bestr->u.playouts
 360                     && fabs((double)best->u.value - bestr->u.value) > u->bestr_ratio) {
 361                         if (UDEBUGL(2))
 362                                 fprintf(stderr, "Bestr delta %f > threshold %f\n",
 363                                         fabs((double)best->u.value - bestr->u.value),
 364                                         u->bestr_ratio);
 365                         return true;
 366                 }
 367         }
 368
 369         if (winner && winner != best) {
 370                 /* Keep simulating if best explored
 371                  * does not have also highest value. */
 372                 if (UDEBUGL(2))
 373                         fprintf(stderr, "[%d] best %3s [%d] %f != winner %3s [%d] %f\n", i,
 374                                 coord2sstr(node_coord(best), t->board),
 375                                 best->u.playouts, tree_node_get_value(t, 1, best->u.value),
 376                                 coord2sstr(node_coord(winner), t->board),
 377                                 winner->u.playouts, tree_node_get_value(t, 1, winner->u.value));
 378                 return true;
 379         }
 380
 381         /* No reason to keep simulating, bye. */
 382         return false;
 383 }
 384
 385 bool
 386 uct_search_check_stop(struct uct *u, struct board *b, enum stone color,
 387                       struct tree *t, struct time_info *ti,
 388                       struct uct_search_state *s, int i)
 389 {
 390         struct uct_thread_ctx *ctx = s->ctx;
 391
 392         /* Never consider stopping if we played too few simulations.
 393          * Maybe we risk losing on time when playing in super-extreme
 394          * time pressure but the tree is going to be just too messed
 395          * up otherwise - we might even play invalid suicides or pass
 396          * when we mustn't. */
 397         assert(!(ti->dim == TD_GAMES && ti->len.games < GJ_MINGAMES));
 398         if (i < GJ_MINGAMES)
 399                 return false;
 400
 401         struct tree_node *best = NULL;
 402         struct tree_node *best2 = NULL; // Second-best move.
 403         struct tree_node *bestr = NULL; // best's best child.
 404         struct tree_node *winner = NULL;
 405
 406         best = u->policy->choose(u->policy, ctx->t->root, b, color, resign);
 407         if (best) best2 = u->policy->choose(u->policy, ctx->t->root, b, color, node_coord(best));
 408
 409         /* Possibly stop search early if it's no use to try on. */
 410         int played = u->played_all + i - s->base_playouts;
 411         if (best && uct_search_stop_early(u, ctx->t, b, ti, &s->stop, best, best2, played, s->fullmem))
 412                 return true;
 413
 414         /* Check against time settings. */
 415         bool desired_done;
 416         if (ti->dim == TD_WALLTIME) {
 417                 double elapsed = time_now() - ti->len.t.timer_start;
 418                 if (elapsed > s->stop.worst.time) return true;
 419                 desired_done = elapsed > s->stop.desired.time;
 420
 421         } else { assert(ti->dim == TD_GAMES);
 422                 if (i > s->stop.worst.playouts) return true;
 423                 desired_done = i > s->stop.desired.playouts;
 424         }
 425
 426         /* We want to stop simulating, but are willing to keep trying
 427          * if we aren't completely sure about the winner yet. */
 428         if (desired_done) {
 429                 if (u->policy->winner && u->policy->evaluate) {
 430                         struct uct_descent descent = { .node = ctx->t->root };
 431                         u->policy->winner(u->policy, ctx->t, &descent);
 432                         winner = descent.node;
 433                 }
 434                 if (best)
 435                         bestr = u->policy->choose(u->policy, best, b, stone_other(color), resign);
 436                 if (!uct_search_keep_looking(u, ctx->t, b, ti, &s->stop, best, best2, bestr, winner, i))
 437                         return true;
 438         }
 439
 440         /* TODO: Early break if best->variance goes under threshold
 441          * and we already have enough playouts (possibly thanks to tbook
 442          * or to pondering)? */
 443         return false;
 444 }
 445
 446
 447 struct tree_node *
 448 uct_search_result(struct uct *u, struct board *b, enum stone color,
 449                   bool pass_all_alive, int played_games, int base_playouts,
 450                   coord_t *best_coord)
 451 {
 452         /* Choose the best move from the tree. */
 453         struct tree_node *best = u->policy->choose(u->policy, u->t->root, b, color, resign);
 454         if (!best) {
 455                 *best_coord = pass;
 456                 return NULL;
 457         }
 458         *best_coord = node_coord(best);
 459         if (UDEBUGL(1))
 460                 fprintf(stderr, "*** WINNER is %s (%d,%d) with score %1.4f (%d/%d:%d/%d games), extra komi %f\n",
 461                         coord2sstr(node_coord(best), b), coord_x(node_coord(best), b), coord_y(node_coord(best), b),
 462                         tree_node_get_value(u->t, 1, best->u.value), best->u.playouts,
 463                         u->t->root->u.playouts, u->t->root->u.playouts - base_playouts, played_games,
 464                         u->t->extra_komi);
 465
 466         /* Do not resign if we're so short of time that evaluation of best
 467          * move is completely unreliable, we might be winning actually.
 468          * In this case best is almost random but still better than resign.
 469          * Also do not resign if we are getting bad results while actually
 470          * giving away extra komi points (dynkomi). */
 471         if (tree_node_get_value(u->t, 1, best->u.value) < u->resign_threshold
 472             && !is_pass(node_coord(best)) && best->u.playouts > GJ_MINGAMES
 473             && (!u->t->use_extra_komi || komi_by_color(u->t->extra_komi, color) < 0.5)) {
 474                 *best_coord = resign;
 475                 return NULL;
 476         }
 477
 478         /* If the opponent just passed and we win counting, always
 479          * pass as well. For option stones_only, we pass only when there
 480          * there is nothing else to do, to show how to maximize score. */
 481         if (b->moves > 1 && is_pass(b->last_move.coord) && b->rules != RULES_STONES_ONLY) {
 482                 if (uct_pass_is_safe(u, b, color, pass_all_alive)) {
 483                         if (UDEBUGL(0))
 484                                 fprintf(stderr, "<Will rather pass, looks safe enough; score %f>\n",
 485                                         board_official_score(b, NULL) / 2);
 486                         *best_coord = pass;
 487                         best = u->t->root->children; // pass is the first child
 488                         assert(is_pass(node_coord(best)));
 489                         return best;
 490                 } else {
 491                         if (UDEBUGL(3))
 492                                 fprintf(stderr, "Refusing to pass, unsafe; pass_all_alive %d, ownermap #playouts %d, raw score %f\n",
 493                                         pass_all_alive, u->ownermap.playouts,
 494                                         board_official_score(b, NULL) / 2);
 495                 }
 496         }
 497
 498         return best;
 499 }