rts/Sparks.c

   1 /* ---------------------------------------------------------------------------
   2  *
   3  * (c) The GHC Team, 2000-2006
   4  *
   5  * Sparking support for PARALLEL_HASKELL and THREADED_RTS versions of the RTS.
   6  *
   7  * -------------------------------------------------------------------------*/
   8
   9 #include "PosixSource.h"
  10 #include "Rts.h"
  11 #include "Storage.h"
  12 #include "Schedule.h"
  13 #include "SchedAPI.h"
  14 #include "RtsFlags.h"
  15 #include "RtsUtils.h"
  16 #include "ParTicky.h"
  17 # if defined(PARALLEL_HASKELL)
  18 # include "ParallelRts.h"
  19 # include "GranSimRts.h"   // for GR_...
  20 # elif defined(GRAN)
  21 # include "GranSimRts.h"
  22 # endif
  23 #include "Sparks.h"
  24 #include "Trace.h"
  25
  26 #if defined(THREADED_RTS) || defined(PARALLEL_HASKELL)
  27
  28 static INLINE_ME void bump_hd (StgSparkPool *p)
  29 { p->hd++; if (p->hd == p->lim) p->hd = p->base; }
  30
  31 static INLINE_ME void bump_tl (StgSparkPool *p)
  32 { p->tl++; if (p->tl == p->lim) p->tl = p->base; }
  33
  34 /* -----------------------------------------------------------------------------
  35  *
  36  * Initialising spark pools.
  37  *
  38  * -------------------------------------------------------------------------- */
  39
  40 static void
  41 initSparkPool(StgSparkPool *pool)
  42 {
  43     pool->base = stgMallocBytes(RtsFlags.ParFlags.maxLocalSparks
  44                                 * sizeof(StgClosure *),
  45                                 "initSparkPools");
  46     pool->lim = pool->base + RtsFlags.ParFlags.maxLocalSparks;
  47     pool->hd  = pool->base;
  48     pool->tl  = pool->base;
  49 }
  50
  51 void
  52 initSparkPools( void )
  53 {
  54 #ifdef THREADED_RTS
  55     /* walk over the capabilities, allocating a spark pool for each one */
  56     nat i;
  57     for (i = 0; i < n_capabilities; i++) {
  58         initSparkPool(&capabilities[i].r.rSparks);
  59     }
  60 #else
  61     /* allocate a single spark pool */
  62     initSparkPool(&MainCapability.r.rSparks);
  63 #endif
  64 }
  65
  66 void
  67 freeSparkPool(StgSparkPool *pool) {
  68     stgFree(pool->base);
  69 }
  70
  71 /* -----------------------------------------------------------------------------
  72  *
  73  * findSpark: find a spark on the current Capability that we can fork
  74  * into a thread.
  75  *
  76  * -------------------------------------------------------------------------- */
  77
  78 StgClosure *
  79 findSpark (Capability *cap)
  80 {
  81     StgSparkPool *pool;
  82     StgClosure *spark;
  83
  84     pool = &(cap->r.rSparks);
  85     ASSERT_SPARK_POOL_INVARIANTS(pool);
  86
  87     while (pool->hd != pool->tl) {
  88         spark = *pool->hd;
  89         bump_hd(pool);
  90         if (closure_SHOULD_SPARK(spark)) {
  91 #ifdef GRAN
  92             if (RtsFlags.ParFlags.ParStats.Sparks)
  93                 DumpRawGranEvent(CURRENT_PROC, CURRENT_PROC,
  94                                  GR_STEALING, ((StgTSO *)NULL), spark,
  95                                  0, 0 /* spark_queue_len(ADVISORY_POOL) */);
  96 #endif
  97             return spark;
  98         }
  99     }
 100     // spark pool is now empty
 101     return NULL;
 102 }
 103
 104 /* -----------------------------------------------------------------------------
 105  *
 106  * Turn a spark into a real thread
 107  *
 108  * -------------------------------------------------------------------------- */
 109
 110 void
 111 createSparkThread (Capability *cap, StgClosure *p)
 112 {
 113     StgTSO *tso;
 114
 115     tso = createGenThread (cap, RtsFlags.GcFlags.initialStkSize, p);
 116     appendToRunQueue(cap,tso);
 117 }
 118
 119 /* -----------------------------------------------------------------------------
 120  *
 121  * Create a new spark
 122  *
 123  * -------------------------------------------------------------------------- */
 124
 125 #define DISCARD_NEW
 126
 127 StgInt
 128 newSpark (StgRegTable *reg, StgClosure *p)
 129 {
 130     StgSparkPool *pool = &(reg->rSparks);
 131
 132     /* I am not sure whether this is the right thing to do.
 133      * Maybe it is better to exploit the tag information
 134      * instead of throwing it away?
 135      */
 136     p = UNTAG_CLOSURE(p);
 137
 138     ASSERT_SPARK_POOL_INVARIANTS(pool);
 139
 140     if (closure_SHOULD_SPARK(p)) {
 141 #ifdef DISCARD_NEW
 142         StgClosure **new_tl;
 143         new_tl = pool->tl + 1;
 144         if (new_tl == pool->lim) { new_tl = pool->base; }
 145         if (new_tl != pool->hd) {
 146             *pool->tl = p;
 147             pool->tl = new_tl;
 148         } else if (!closure_SHOULD_SPARK(*pool->hd)) {
 149             // if the old closure is not sparkable, discard it and
 150             // keep the new one.  Otherwise, keep the old one.
 151             *pool->tl = p;
 152             bump_hd(pool);
 153         }
 154 #else  /* DISCARD OLD */
 155         *pool->tl = p;
 156         bump_tl(pool);
 157         if (pool->tl == pool->hd) { bump_hd(pool); }
 158 #endif
 159     }
 160
 161     ASSERT_SPARK_POOL_INVARIANTS(pool);
 162     return 1;
 163 }
 164
 165 /* -----------------------------------------------------------------------------
 166  * Mark all nodes pointed to by sparks in the spark queues (for GC) Does an
 167  * implicit slide i.e. after marking all sparks are at the beginning of the
 168  * spark pool and the spark pool only contains sparkable closures
 169  * -------------------------------------------------------------------------- */
 170
 171 void
 172 markSparkQueue (evac_fn evac, void *user, Capability *cap)
 173 {
 174     StgClosure **sparkp, **to_sparkp;
 175     nat n, pruned_sparks; // stats only
 176     StgSparkPool *pool;
 177
 178     PAR_TICKY_MARK_SPARK_QUEUE_START();
 179
 180     n = 0;
 181     pruned_sparks = 0;
 182
 183     pool = &(cap->r.rSparks);
 184
 185     ASSERT_SPARK_POOL_INVARIANTS(pool);
 186
 187 #if defined(PARALLEL_HASKELL)
 188     // stats only
 189     n = 0;
 190     pruned_sparks = 0;
 191 #endif
 192
 193     sparkp = pool->hd;
 194     to_sparkp = pool->hd;
 195     while (sparkp != pool->tl) {
 196         ASSERT(*sparkp!=NULL);
 197         ASSERT(LOOKS_LIKE_CLOSURE_PTR(((StgClosure *)*sparkp)));
 198         // ToDo?: statistics gathering here (also for GUM!)
 199         if (closure_SHOULD_SPARK(*sparkp)) {
 200             evac(user, sparkp);
 201             *to_sparkp++ = *sparkp;
 202             if (to_sparkp == pool->lim) {
 203                 to_sparkp = pool->base;
 204             }
 205             n++;
 206         } else {
 207             pruned_sparks++;
 208         }
 209         sparkp++;
 210         if (sparkp == pool->lim) {
 211             sparkp = pool->base;
 212         }
 213     }
 214     pool->tl = to_sparkp;
 215
 216     PAR_TICKY_MARK_SPARK_QUEUE_END(n);
 217
 218 #if defined(PARALLEL_HASKELL)
 219     debugTrace(DEBUG_sched,
 220                "marked %d sparks and pruned %d sparks on [%x]",
 221                n, pruned_sparks, mytid);
 222 #else
 223     debugTrace(DEBUG_sched,
 224                "marked %d sparks and pruned %d sparks",
 225                n, pruned_sparks);
 226 #endif
 227
 228     debugTrace(DEBUG_sched,
 229                "new spark queue len=%d; (hd=%p; tl=%p)\n",
 230                sparkPoolSize(pool), pool->hd, pool->tl);
 231 }
 232
 233 #else
 234
 235 StgInt
 236 newSpark (StgRegTable *reg STG_UNUSED, StgClosure *p STG_UNUSED)
 237 {
 238     /* nothing */
 239     return 1;
 240 }
 241
 242
 243 #endif /* PARALLEL_HASKELL || THREADED_RTS */
 244
 245
 246 /* -----------------------------------------------------------------------------
 247  *
 248  * GRAN & PARALLEL_HASKELL stuff beyond here.
 249  *
 250  * -------------------------------------------------------------------------- */
 251
 252 #if defined(PARALLEL_HASKELL) || defined(GRAN)
 253
 254 static void slide_spark_pool( StgSparkPool *pool );
 255
 256 rtsBool
 257 add_to_spark_queue( StgClosure *closure, StgSparkPool *pool )
 258 {
 259   if (pool->tl == pool->lim)
 260     slide_spark_pool(pool);
 261
 262   if (closure_SHOULD_SPARK(closure) &&
 263       pool->tl < pool->lim) {
 264     *(pool->tl++) = closure;
 265
 266 #if defined(PARALLEL_HASKELL)
 267     // collect parallel global statistics (currently done together with GC stats)
 268     if (RtsFlags.ParFlags.ParStats.Global &&
 269         RtsFlags.GcFlags.giveStats > NO_GC_STATS) {
 270       // debugBelch("Creating spark for %x @ %11.2f\n", closure, usertime());
 271       globalParStats.tot_sparks_created++;
 272     }
 273 #endif
 274     return rtsTrue;
 275   } else {
 276 #if defined(PARALLEL_HASKELL)
 277     // collect parallel global statistics (currently done together with GC stats)
 278     if (RtsFlags.ParFlags.ParStats.Global &&
 279         RtsFlags.GcFlags.giveStats > NO_GC_STATS) {
 280       //debugBelch("Ignoring spark for %x @ %11.2f\n", closure, usertime());
 281       globalParStats.tot_sparks_ignored++;
 282     }
 283 #endif
 284     return rtsFalse;
 285   }
 286 }
 287
 288 static void
 289 slide_spark_pool( StgSparkPool *pool )
 290 {
 291   StgClosure **sparkp, **to_sparkp;
 292
 293   sparkp = pool->hd;
 294   to_sparkp = pool->base;
 295   while (sparkp < pool->tl) {
 296     ASSERT(to_sparkp<=sparkp);
 297     ASSERT(*sparkp!=NULL);
 298     ASSERT(LOOKS_LIKE_GHC_INFO((*sparkp)->header.info));
 299
 300     if (closure_SHOULD_SPARK(*sparkp)) {
 301       *to_sparkp++ = *sparkp++;
 302     } else {
 303       sparkp++;
 304     }
 305   }
 306   pool->hd = pool->base;
 307   pool->tl = to_sparkp;
 308 }
 309
 310 void
 311 disposeSpark(spark)
 312 StgClosure *spark;
 313 {
 314 #if !defined(THREADED_RTS)
 315   Capability *cap;
 316   StgSparkPool *pool;
 317
 318   cap = &MainRegTable;
 319   pool = &(cap->rSparks);
 320   ASSERT(pool->hd <= pool->tl && pool->tl <= pool->lim);
 321 #endif
 322   ASSERT(spark != (StgClosure *)NULL);
 323   /* Do nothing */
 324 }
 325
 326
 327 #elif defined(GRAN)
 328
 329 /*
 330    Search the spark queue of the proc in event for a spark that's worth
 331    turning into a thread
 332    (was gimme_spark in the old RTS)
 333 */
 334 void
 335 findLocalSpark (rtsEvent *event, rtsBool *found_res, rtsSparkQ *spark_res)
 336 {
 337    PEs proc = event->proc,       /* proc to search for work */
 338        creator = event->creator; /* proc that requested work */
 339    StgClosure* node;
 340    rtsBool found;
 341    rtsSparkQ spark_of_non_local_node = NULL,
 342              spark_of_non_local_node_prev = NULL,
 343              low_priority_spark = NULL,
 344              low_priority_spark_prev = NULL,
 345              spark = NULL, prev = NULL;
 346
 347    /* Choose a spark from the local spark queue */
 348    prev = (rtsSpark*)NULL;
 349    spark = pending_sparks_hds[proc];
 350    found = rtsFalse;
 351
 352    // ToDo: check this code & implement local sparking !! -- HWL
 353    while (!found && spark != (rtsSpark*)NULL)
 354      {
 355        ASSERT((prev!=(rtsSpark*)NULL || spark==pending_sparks_hds[proc]) &&
 356               (prev==(rtsSpark*)NULL || prev->next==spark) &&
 357               (spark->prev==prev));
 358        node = spark->node;
 359        if (!closure_SHOULD_SPARK(node))
 360          {
 361            IF_GRAN_DEBUG(checkSparkQ,
 362                          debugBelch("^^ pruning spark %p (node %p) in gimme_spark",
 363                                spark, node));
 364
 365            if (RtsFlags.GranFlags.GranSimStats.Sparks)
 366              DumpRawGranEvent(proc, (PEs)0, SP_PRUNED,(StgTSO*)NULL,
 367                               spark->node, spark->name, spark_queue_len(proc));
 368
 369            ASSERT(spark != (rtsSpark*)NULL);
 370            ASSERT(SparksAvail>0);
 371            --SparksAvail;
 372
 373            ASSERT(prev==(rtsSpark*)NULL || prev->next==spark);
 374            spark = delete_from_sparkq (spark, proc, rtsTrue);
 375            if (spark != (rtsSpark*)NULL)
 376              prev = spark->prev;
 377            continue;
 378          }
 379        /* -- node should eventually be sparked */
 380        else if (RtsFlags.GranFlags.PreferSparksOfLocalNodes &&
 381                !IS_LOCAL_TO(PROCS(node),CurrentProc))
 382          {
 383            barf("Local sparking not yet implemented");
 384
 385            /* Remember first low priority spark */
 386            if (spark_of_non_local_node==(rtsSpark*)NULL) {
 387              spark_of_non_local_node_prev = prev;
 388              spark_of_non_local_node = spark;
 389               }
 390
 391            if (spark->next == (rtsSpark*)NULL) {
 392              /* ASSERT(spark==SparkQueueTl);  just for testing */
 393              prev = spark_of_non_local_node_prev;
 394              spark = spark_of_non_local_node;
 395              found = rtsTrue;
 396              break;
 397            }
 398
 399 # if defined(GRAN) && defined(GRAN_CHECK)
 400            /* Should never happen; just for testing
 401            if (spark==pending_sparks_tl) {
 402              debugBelch("ReSchedule: Last spark != SparkQueueTl\n");
 403                 stg_exit(EXIT_FAILURE);
 404                 } */
 405 # endif
 406            prev = spark;
 407            spark = spark->next;
 408            ASSERT(SparksAvail>0);
 409            --SparksAvail;
 410            continue;
 411          }
 412        else if ( RtsFlags.GranFlags.DoPrioritySparking ||
 413                  (spark->gran_info >= RtsFlags.GranFlags.SparkPriority2) )
 414          {
 415            if (RtsFlags.GranFlags.DoPrioritySparking)
 416              barf("Priority sparking not yet implemented");
 417
 418            found = rtsTrue;
 419          }
 420 #if 0
 421        else /* only used if SparkPriority2 is defined */
 422          {
 423            /* ToDo: fix the code below and re-integrate it */
 424            /* Remember first low priority spark */
 425            if (low_priority_spark==(rtsSpark*)NULL) {
 426              low_priority_spark_prev = prev;
 427              low_priority_spark = spark;
 428            }
 429
 430            if (spark->next == (rtsSpark*)NULL) {
 431                 /* ASSERT(spark==spark_queue_tl);  just for testing */
 432              prev = low_priority_spark_prev;
 433              spark = low_priority_spark;
 434              found = rtsTrue;       /* take low pri spark => rc is 2  */
 435              break;
 436            }
 437
 438            /* Should never happen; just for testing
 439            if (spark==pending_sparks_tl) {
 440              debugBelch("ReSchedule: Last spark != SparkQueueTl\n");
 441                 stg_exit(EXIT_FAILURE);
 442              break;
 443            } */
 444            prev = spark;
 445            spark = spark->next;
 446
 447            IF_GRAN_DEBUG(pri,
 448                          debugBelch("++ Ignoring spark of priority %u (SparkPriority=%u); node=%p; name=%u\n",
 449                                spark->gran_info, RtsFlags.GranFlags.SparkPriority,
 450                                spark->node, spark->name);)
 451            }
 452 #endif
 453    }  /* while (spark!=NULL && !found) */
 454
 455    *spark_res = spark;
 456    *found_res = found;
 457 }
 458
 459 /*
 460   Turn the spark into a thread.
 461   In GranSim this basically means scheduling a StartThread event for the
 462   node pointed to by the spark at some point in the future.
 463   (was munch_spark in the old RTS)
 464 */
 465 rtsBool
 466 activateSpark (rtsEvent *event, rtsSparkQ spark)
 467 {
 468   PEs proc = event->proc,       /* proc to search for work */
 469       creator = event->creator; /* proc that requested work */
 470   StgTSO* tso;
 471   StgClosure* node;
 472   rtsTime spark_arrival_time;
 473
 474   /*
 475      We've found a node on PE proc requested by PE creator.
 476      If proc==creator we can turn the spark into a thread immediately;
 477      otherwise we schedule a MoveSpark event on the requesting PE
 478   */
 479
 480   /* DaH Qu' yIchen */
 481   if (proc!=creator) {
 482
 483     /* only possible if we simulate GUM style fishing */
 484     ASSERT(RtsFlags.GranFlags.Fishing);
 485
 486     /* Message packing costs for sending a Fish; qeq jabbI'ID */
 487     CurrentTime[proc] += RtsFlags.GranFlags.Costs.mpacktime;
 488
 489     if (RtsFlags.GranFlags.GranSimStats.Sparks)
 490       DumpRawGranEvent(proc, (PEs)0, SP_EXPORTED,
 491                        (StgTSO*)NULL, spark->node,
 492                        spark->name, spark_queue_len(proc));
 493
 494     /* time of the spark arrival on the remote PE */
 495     spark_arrival_time = CurrentTime[proc] + RtsFlags.GranFlags.Costs.latency;
 496
 497     new_event(creator, proc, spark_arrival_time,
 498               MoveSpark,
 499               (StgTSO*)NULL, spark->node, spark);
 500
 501     CurrentTime[proc] += RtsFlags.GranFlags.Costs.mtidytime;
 502
 503   } else { /* proc==creator i.e. turn the spark into a thread */
 504
 505     if ( RtsFlags.GranFlags.GranSimStats.Global &&
 506          spark->gran_info < RtsFlags.GranFlags.SparkPriority2 ) {
 507
 508       globalGranStats.tot_low_pri_sparks++;
 509       IF_GRAN_DEBUG(pri,
 510                     debugBelch("++ No high priority spark available; low priority (%u) spark chosen: node=%p; name=%u\n",
 511                           spark->gran_info,
 512                           spark->node, spark->name));
 513     }
 514
 515     CurrentTime[proc] += RtsFlags.GranFlags.Costs.threadcreatetime;
 516
 517     node = spark->node;
 518
 519 # if 0
 520     /* ToDo: fix the GC interface and move to StartThread handling-- HWL */
 521     if (GARBAGE COLLECTION IS NECESSARY) {
 522       /* Some kind of backoff needed here in case there's too little heap */
 523 #  if defined(GRAN_CHECK) && defined(GRAN)
 524       if (RtsFlags.GcFlags.giveStats)
 525         fprintf(RtsFlags.GcFlags.statsFile,"***** vIS Qu' chen veQ boSwI'; spark=%p, node=%p;  name=%u\n",
 526                 /* (found==2 ? "no hi pri spark" : "hi pri spark"), */
 527                 spark, node, spark->name);
 528 #  endif
 529       new_event(CurrentProc, CurrentProc, CurrentTime[CurrentProc]+1,
 530                   FindWork,
 531                   (StgTSO*)NULL, (StgClosure*)NULL, (rtsSpark*)NULL);
 532       barf("//// activateSpark: out of heap ; ToDo: call GarbageCollect()");
 533       GarbageCollect(GetRoots, rtsFalse);
 534       // HWL old: ReallyPerformThreadGC(TSO_HS+TSO_CTS_SIZE,rtsFalse);
 535       // HWL old: SAVE_Hp -= TSO_HS+TSO_CTS_SIZE;
 536       spark = NULL;
 537       return; /* was: continue; */ /* to the next event, eventually */
 538     }
 539 # endif
 540
 541     if (RtsFlags.GranFlags.GranSimStats.Sparks)
 542       DumpRawGranEvent(CurrentProc,(PEs)0,SP_USED,(StgTSO*)NULL,
 543                        spark->node, spark->name,
 544                        spark_queue_len(CurrentProc));
 545
 546     new_event(proc, proc, CurrentTime[proc],
 547               StartThread,
 548               END_TSO_QUEUE, node, spark); // (rtsSpark*)NULL);
 549
 550     procStatus[proc] = Starting;
 551   }
 552 }
 553
 554 /* -------------------------------------------------------------------------
 555    This is the main point where handling granularity information comes into
 556    play.
 557    ------------------------------------------------------------------------- */
 558
 559 #define MAX_RAND_PRI    100
 560
 561 /*
 562    Granularity info transformers.
 563    Applied to the GRAN_INFO field of a spark.
 564 */
 565 STATIC_INLINE nat  ID(nat x) { return(x); };
 566 STATIC_INLINE nat  INV(nat x) { return(-x); };
 567 STATIC_INLINE nat  IGNORE(nat x) { return (0); };
 568 STATIC_INLINE nat  RAND(nat x) { return ((random() % MAX_RAND_PRI) + 1); }
 569
 570 /* NB: size_info and par_info are currently unused (what a shame!) -- HWL */
 571 rtsSpark *
 572 newSpark(node,name,gran_info,size_info,par_info,local)
 573 StgClosure *node;
 574 nat name, gran_info, size_info, par_info, local;
 575 {
 576   nat pri;
 577   rtsSpark *newspark;
 578
 579   pri = RtsFlags.GranFlags.RandomPriorities ? RAND(gran_info) :
 580         RtsFlags.GranFlags.InversePriorities ? INV(gran_info) :
 581         RtsFlags.GranFlags.IgnorePriorities ? IGNORE(gran_info) :
 582                            ID(gran_info);
 583
 584   if ( RtsFlags.GranFlags.SparkPriority!=0 &&
 585        pri<RtsFlags.GranFlags.SparkPriority ) {
 586     IF_GRAN_DEBUG(pri,
 587       debugBelch(",, NewSpark: Ignoring spark of priority %u (SparkPriority=%u); node=%#x; name=%u\n",
 588               pri, RtsFlags.GranFlags.SparkPriority, node, name));
 589     return ((rtsSpark*)NULL);
 590   }
 591
 592   newspark = (rtsSpark*) stgMallocBytes(sizeof(rtsSpark), "NewSpark");
 593   newspark->prev = newspark->next = (rtsSpark*)NULL;
 594   newspark->node = node;
 595   newspark->name = (name==1) ? CurrentTSO->gran.sparkname : name;
 596   newspark->gran_info = pri;
 597   newspark->global = !local;      /* Check that with parAt, parAtAbs !!*/
 598
 599   if (RtsFlags.GranFlags.GranSimStats.Global) {
 600     globalGranStats.tot_sparks_created++;
 601     globalGranStats.sparks_created_on_PE[CurrentProc]++;
 602   }
 603
 604   return(newspark);
 605 }
 606
 607 void
 608 disposeSpark(spark)
 609 rtsSpark *spark;
 610 {
 611   ASSERT(spark!=NULL);
 612   stgFree(spark);
 613 }
 614
 615 void
 616 disposeSparkQ(spark)
 617 rtsSparkQ spark;
 618 {
 619   if (spark==NULL)
 620     return;
 621
 622   disposeSparkQ(spark->next);
 623
 624 # ifdef GRAN_CHECK
 625   if (SparksAvail < 0) {
 626     debugBelch("disposeSparkQ: SparksAvail<0 after disposing sparkq @ %p\n", &spark);
 627     print_spark(spark);
 628   }
 629 # endif
 630
 631   stgFree(spark);
 632 }
 633
 634 /*
 635    With PrioritySparking add_to_spark_queue performs an insert sort to keep
 636    the spark queue sorted. Otherwise the spark is just added to the end of
 637    the queue.
 638 */
 639
 640 void
 641 add_to_spark_queue(spark)
 642 rtsSpark *spark;
 643 {
 644   rtsSpark *prev = NULL, *next = NULL;
 645   nat count = 0;
 646   rtsBool found = rtsFalse;
 647
 648   if ( spark == (rtsSpark *)NULL ) {
 649     return;
 650   }
 651
 652   if (RtsFlags.GranFlags.DoPrioritySparking && (spark->gran_info != 0) ) {
 653     /* Priority sparking is enabled i.e. spark queues must be sorted */
 654
 655     for (prev = NULL, next = pending_sparks_hd, count=0;
 656          (next != NULL) &&
 657          !(found = (spark->gran_info >= next->gran_info));
 658          prev = next, next = next->next, count++)
 659      {}
 660
 661   } else {   /* 'utQo' */
 662     /* Priority sparking is disabled */
 663
 664     found = rtsFalse;   /* to add it at the end */
 665
 666   }
 667
 668   if (found) {
 669     /* next points to the first spark with a gran_info smaller than that
 670        of spark; therefore, add spark before next into the spark queue */
 671     spark->next = next;
 672     if ( next == NULL ) {
 673       pending_sparks_tl = spark;
 674     } else {
 675       next->prev = spark;
 676     }
 677     spark->prev = prev;
 678     if ( prev == NULL ) {
 679       pending_sparks_hd = spark;
 680     } else {
 681       prev->next = spark;
 682     }
 683   } else {  /* (RtsFlags.GranFlags.DoPrioritySparking && !found) || !DoPrioritySparking */
 684     /* add the spark at the end of the spark queue */
 685     spark->next = NULL;
 686     spark->prev = pending_sparks_tl;
 687     if (pending_sparks_hd == NULL)
 688       pending_sparks_hd = spark;
 689     else
 690       pending_sparks_tl->next = spark;
 691     pending_sparks_tl = spark;
 692   }
 693   ++SparksAvail;
 694
 695   /* add costs for search in priority sparking */
 696   if (RtsFlags.GranFlags.DoPrioritySparking) {
 697     CurrentTime[CurrentProc] += count * RtsFlags.GranFlags.Costs.pri_spark_overhead;
 698   }
 699
 700   IF_GRAN_DEBUG(checkSparkQ,
 701                 debugBelch("++ Spark stats after adding spark %p (node %p) to queue on PE %d",
 702                       spark, spark->node, CurrentProc);
 703                 print_sparkq_stats());
 704
 705 #  if defined(GRAN_CHECK)
 706   if (RtsFlags.GranFlags.Debug.checkSparkQ) {
 707     for (prev = NULL, next =  pending_sparks_hd;
 708          (next != NULL);
 709          prev = next, next = next->next)
 710       {}
 711     if ( (prev!=NULL) && (prev!=pending_sparks_tl) )
 712       debugBelch("SparkQ inconsistency after adding spark %p: (PE %u) pending_sparks_tl (%p) not end of queue (%p)\n",
 713               spark,CurrentProc,
 714               pending_sparks_tl, prev);
 715   }
 716 #  endif
 717
 718 #  if defined(GRAN_CHECK)
 719   /* Check if the sparkq is still sorted. Just for testing, really!  */
 720   if ( RtsFlags.GranFlags.Debug.checkSparkQ &&
 721        RtsFlags.GranFlags.Debug.pri ) {
 722     rtsBool sorted = rtsTrue;
 723     rtsSpark *prev, *next;
 724
 725     if (pending_sparks_hd == NULL ||
 726         pending_sparks_hd->next == NULL ) {
 727       /* just 1 elem => ok */
 728     } else {
 729       for (prev = pending_sparks_hd,
 730            next = pending_sparks_hd->next;
 731            (next != NULL) ;
 732            prev = next, next = next->next) {
 733         sorted = sorted &&
 734                  (prev->gran_info >= next->gran_info);
 735       }
 736     }
 737     if (!sorted) {
 738       debugBelch("ghuH: SPARKQ on PE %d is not sorted:\n",
 739               CurrentProc);
 740       print_sparkq(CurrentProc);
 741     }
 742   }
 743 #  endif
 744 }
 745
 746 nat
 747 spark_queue_len(proc)
 748 PEs proc;
 749 {
 750  rtsSpark *prev, *spark;                     /* prev only for testing !! */
 751  nat len;
 752
 753  for (len = 0, prev = NULL, spark = pending_sparks_hds[proc];
 754       spark != NULL;
 755       len++, prev = spark, spark = spark->next)
 756    {}
 757
 758 #  if defined(GRAN_CHECK)
 759   if ( RtsFlags.GranFlags.Debug.checkSparkQ )
 760     if ( (prev!=NULL) && (prev!=pending_sparks_tls[proc]) )
 761       debugBelch("ERROR in spark_queue_len: (PE %u) pending_sparks_tl (%p) not end of queue (%p)\n",
 762               proc, pending_sparks_tls[proc], prev);
 763 #  endif
 764
 765  return (len);
 766 }
 767
 768 /*
 769    Take spark out of the spark queue on PE p and nuke the spark. Adjusts
 770    hd and tl pointers of the spark queue. Returns a pointer to the next
 771    spark in the queue.
 772 */
 773 rtsSpark *
 774 delete_from_sparkq (spark, p, dispose_too)     /* unlink and dispose spark */
 775 rtsSpark *spark;
 776 PEs p;
 777 rtsBool dispose_too;
 778 {
 779   rtsSpark *new_spark;
 780
 781   if (spark==NULL)
 782     barf("delete_from_sparkq: trying to delete NULL spark\n");
 783
 784 #  if defined(GRAN_CHECK)
 785   if ( RtsFlags.GranFlags.Debug.checkSparkQ ) {
 786     debugBelch("## |%p:%p| (%p)<-spark=%p->(%p) <-(%p)\n",
 787             pending_sparks_hd, pending_sparks_tl,
 788             spark->prev, spark, spark->next,
 789             (spark->next==NULL ? 0 : spark->next->prev));
 790   }
 791 #  endif
 792
 793   if (spark->prev==NULL) {
 794     /* spark is first spark of queue => adjust hd pointer */
 795     ASSERT(pending_sparks_hds[p]==spark);
 796     pending_sparks_hds[p] = spark->next;
 797   } else {
 798     spark->prev->next = spark->next;
 799   }
 800   if (spark->next==NULL) {
 801     ASSERT(pending_sparks_tls[p]==spark);
 802     /* spark is first spark of queue => adjust tl pointer */
 803     pending_sparks_tls[p] = spark->prev;
 804   } else {
 805     spark->next->prev = spark->prev;
 806   }
 807   new_spark = spark->next;
 808
 809 #  if defined(GRAN_CHECK)
 810   if ( RtsFlags.GranFlags.Debug.checkSparkQ ) {
 811     debugBelch("## |%p:%p| (%p)<-spark=%p->(%p) <-(%p); spark=%p will be deleted NOW \n",
 812             pending_sparks_hd, pending_sparks_tl,
 813             spark->prev, spark, spark->next,
 814             (spark->next==NULL ? 0 : spark->next->prev), spark);
 815   }
 816 #  endif
 817
 818   if (dispose_too)
 819     disposeSpark(spark);
 820
 821   return new_spark;
 822 }
 823
 824 /* Mark all nodes pointed to by sparks in the spark queues (for GC) */
 825 void
 826 markSparkQueue(void)
 827 {
 828   StgClosure *MarkRoot(StgClosure *root); // prototype
 829   PEs p;
 830   rtsSpark *sp;
 831
 832   for (p=0; p<RtsFlags.GranFlags.proc; p++)
 833     for (sp=pending_sparks_hds[p]; sp!=NULL; sp=sp->next) {
 834       ASSERT(sp->node!=NULL);
 835       ASSERT(LOOKS_LIKE_GHC_INFO(sp->node->header.info));
 836       // ToDo?: statistics gathering here (also for GUM!)
 837       sp->node = (StgClosure *)MarkRoot(sp->node);
 838     }
 839
 840   IF_DEBUG(gc,
 841            debugBelch("markSparkQueue: spark statistics at start of GC:");
 842            print_sparkq_stats());
 843 }
 844
 845 void
 846 print_spark(spark)
 847 rtsSpark *spark;
 848 {
 849   char str[16];
 850
 851   if (spark==NULL) {
 852     debugBelch("Spark: NIL\n");
 853     return;
 854   } else {
 855     sprintf(str,
 856             ((spark->node==NULL) ? "______" : "%#6lx"),
 857             stgCast(StgPtr,spark->node));
 858
 859     debugBelch("Spark: Node %8s, Name %#6x, Global %5s, Creator %5x, Prev %6p, Next %6p\n",
 860             str, spark->name,
 861             ((spark->global)==rtsTrue?"True":"False"), spark->creator,
 862             spark->prev, spark->next);
 863   }
 864 }
 865
 866 void
 867 print_sparkq(proc)
 868 PEs proc;
 869 // rtsSpark *hd;
 870 {
 871   rtsSpark *x = pending_sparks_hds[proc];
 872
 873   debugBelch("Spark Queue of PE %d with root at %p:\n", proc, x);
 874   for (; x!=(rtsSpark*)NULL; x=x->next) {
 875     print_spark(x);
 876   }
 877 }
 878
 879 /*
 880    Print a statistics of all spark queues.
 881 */
 882 void
 883 print_sparkq_stats(void)
 884 {
 885   PEs p;
 886
 887   debugBelch("SparkQs: [");
 888   for (p=0; p<RtsFlags.GranFlags.proc; p++)
 889     debugBelch(", PE %d: %d", p, spark_queue_len(p));
 890   debugBelch("\n");
 891 }
 892
 893 #endif