libgo/runtime/chan.c

   1 // Copyright 2009 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 #include "runtime.h"
   6 #include "go-type.h"
   7
   8 #define NOSELGEN        1
   9
  10 static  int32   debug   = 0;
  11
  12 typedef struct  WaitQ   WaitQ;
  13 typedef struct  SudoG   SudoG;
  14 typedef struct  Select  Select;
  15 typedef struct  Scase   Scase;
  16
  17 typedef struct  __go_type_descriptor    Type;
  18 typedef struct  __go_channel_type       ChanType;
  19
  20 struct  SudoG
  21 {
  22         G*      g;              // g and selgen constitute
  23         uint32  selgen;         // a weak pointer to g
  24         SudoG*  link;
  25         byte*   elem;           // data element
  26 };
  27
  28 struct  WaitQ
  29 {
  30         SudoG*  first;
  31         SudoG*  last;
  32 };
  33
  34 struct  Hchan
  35 {
  36         uint32  qcount;                 // total data in the q
  37         uint32  dataqsiz;               // size of the circular q
  38         uint16  elemsize;
  39         bool    closed;
  40         uint8   elemalign;
  41         uint32  sendx;                  // send index
  42         uint32  recvx;                  // receive index
  43         WaitQ   recvq;                  // list of recv waiters
  44         WaitQ   sendq;                  // list of send waiters
  45         Lock;
  46 };
  47
  48 // Buffer follows Hchan immediately in memory.
  49 // chanbuf(c, i) is pointer to the i'th slot in the buffer.
  50 #define chanbuf(c, i) ((byte*)((c)+1)+(uintptr)(c)->elemsize*(i))
  51
  52 enum
  53 {
  54         // Scase.kind
  55         CaseRecv,
  56         CaseSend,
  57         CaseDefault,
  58 };
  59
  60 struct  Scase
  61 {
  62         SudoG   sg;                     // must be first member (cast to Scase)
  63         Hchan*  chan;                   // chan
  64         uint16  kind;
  65         uint16  index;                  // index to return
  66         bool*   receivedp;              // pointer to received bool (recv2)
  67 };
  68
  69 struct  Select
  70 {
  71         uint16  tcase;                  // total count of scase[]
  72         uint16  ncase;                  // currently filled scase[]
  73         uint16* pollorder;              // case poll order
  74         Hchan** lockorder;              // channel lock order
  75         Scase   scase[1];               // one per case (in order of appearance)
  76 };
  77
  78 static  void    dequeueg(WaitQ*);
  79 static  SudoG*  dequeue(WaitQ*);
  80 static  void    enqueue(WaitQ*, SudoG*);
  81
  82 Hchan*
  83 runtime_makechan_c(ChanType *t, int64 hint)
  84 {
  85         Hchan *c;
  86         int32 n;
  87         const Type *elem;
  88
  89         elem = t->__element_type;
  90
  91         if(hint < 0 || (int32)hint != hint || (elem->__size > 0 && (uintptr)hint > ((uintptr)-1) / elem->__size))
  92                 runtime_panicstring("makechan: size out of range");
  93
  94         n = sizeof(*c);
  95
  96         // allocate memory in one call
  97         c = (Hchan*)runtime_mal(n + hint*elem->__size);
  98         c->elemsize = elem->__size;
  99         c->elemalign = elem->__align;
 100         c->dataqsiz = hint;
 101
 102         if(debug)
 103                 runtime_printf("makechan: chan=%p; elemsize=%lld; elemalign=%d; dataqsiz=%d\n",
 104                         c, (long long)elem->__size, elem->__align, c->dataqsiz);
 105
 106         return c;
 107 }
 108
 109 // For reflect
 110 //      func makechan(typ *ChanType, size uint32) (chan)
 111 uintptr reflect_makechan(ChanType *, uint32)
 112   asm ("libgo_reflect.reflect.makechan");
 113
 114 uintptr
 115 reflect_makechan(ChanType *t, uint32 size)
 116 {
 117         void *ret;
 118         Hchan *c;
 119
 120         c = runtime_makechan_c(t, size);
 121         ret = runtime_mal(sizeof(void*));
 122         __builtin_memcpy(ret, &c, sizeof(void*));
 123         return (uintptr)ret;
 124 }
 125
 126 // makechan(t *ChanType, hint int64) (hchan *chan any);
 127 Hchan*
 128 __go_new_channel(ChanType *t, uintptr hint)
 129 {
 130         return runtime_makechan_c(t, hint);
 131 }
 132
 133 Hchan*
 134 __go_new_channel_big(ChanType *t, uint64 hint)
 135 {
 136         return runtime_makechan_c(t, hint);
 137 }
 138
 139 /*
 140  * generic single channel send/recv
 141  * if the bool pointer is nil,
 142  * then the full exchange will
 143  * occur. if pres is not nil,
 144  * then the protocol will not
 145  * sleep but return if it could
 146  * not complete.
 147  *
 148  * sleep can wake up with g->param == nil
 149  * when a channel involved in the sleep has
 150  * been closed.  it is easiest to loop and re-run
 151  * the operation; we'll see that it's now closed.
 152  */
 153 void
 154 runtime_chansend(ChanType *t, Hchan *c, byte *ep, bool *pres)
 155 {
 156         SudoG *sg;
 157         SudoG mysg;
 158         G* gp;
 159         G* g;
 160
 161         g = runtime_g();
 162
 163         if(c == nil) {
 164                 USED(t);
 165                 if(pres != nil) {
 166                         *pres = false;
 167                         return;
 168                 }
 169                 g->status = Gwaiting;
 170                 g->waitreason = "chan send (nil chan)";
 171                 runtime_gosched();
 172                 return;  // not reached
 173         }
 174
 175         if(runtime_gcwaiting)
 176                 runtime_gosched();
 177
 178         if(debug) {
 179                 runtime_printf("chansend: chan=%p\n", c);
 180         }
 181
 182         runtime_lock(c);
 183         if(c->closed)
 184                 goto closed;
 185
 186         if(c->dataqsiz > 0)
 187                 goto asynch;
 188
 189         sg = dequeue(&c->recvq);
 190         if(sg != nil) {
 191                 runtime_unlock(c);
 192
 193                 gp = sg->g;
 194                 gp->param = sg;
 195                 if(sg->elem != nil)
 196                         runtime_memmove(sg->elem, ep, c->elemsize);
 197                 runtime_ready(gp);
 198
 199                 if(pres != nil)
 200                         *pres = true;
 201                 return;
 202         }
 203
 204         if(pres != nil) {
 205                 runtime_unlock(c);
 206                 *pres = false;
 207                 return;
 208         }
 209
 210         mysg.elem = ep;
 211         mysg.g = g;
 212         mysg.selgen = NOSELGEN;
 213         g->param = nil;
 214         g->status = Gwaiting;
 215         g->waitreason = "chan send";
 216         enqueue(&c->sendq, &mysg);
 217         runtime_unlock(c);
 218         runtime_gosched();
 219
 220         if(g->param == nil) {
 221                 runtime_lock(c);
 222                 if(!c->closed)
 223                         runtime_throw("chansend: spurious wakeup");
 224                 goto closed;
 225         }
 226
 227         return;
 228
 229 asynch:
 230         if(c->closed)
 231                 goto closed;
 232
 233         if(c->qcount >= c->dataqsiz) {
 234                 if(pres != nil) {
 235                         runtime_unlock(c);
 236                         *pres = false;
 237                         return;
 238                 }
 239                 mysg.g = g;
 240                 mysg.elem = nil;
 241                 mysg.selgen = NOSELGEN;
 242                 g->status = Gwaiting;
 243                 g->waitreason = "chan send";
 244                 enqueue(&c->sendq, &mysg);
 245                 runtime_unlock(c);
 246                 runtime_gosched();
 247
 248                 runtime_lock(c);
 249                 goto asynch;
 250         }
 251         runtime_memmove(chanbuf(c, c->sendx), ep, c->elemsize);
 252         if(++c->sendx == c->dataqsiz)
 253                 c->sendx = 0;
 254         c->qcount++;
 255
 256         sg = dequeue(&c->recvq);
 257         if(sg != nil) {
 258                 gp = sg->g;
 259                 runtime_unlock(c);
 260                 runtime_ready(gp);
 261         } else
 262                 runtime_unlock(c);
 263         if(pres != nil)
 264                 *pres = true;
 265         return;
 266
 267 closed:
 268         runtime_unlock(c);
 269         runtime_panicstring("send on closed channel");
 270 }
 271
 272
 273 void
 274 runtime_chanrecv(ChanType *t, Hchan* c, byte *ep, bool *selected, bool *received)
 275 {
 276         SudoG *sg;
 277         SudoG mysg;
 278         G *gp;
 279         G *g;
 280
 281         if(runtime_gcwaiting)
 282                 runtime_gosched();
 283
 284         if(debug)
 285                 runtime_printf("chanrecv: chan=%p\n", c);
 286
 287         g = runtime_g();
 288
 289         if(c == nil) {
 290                 USED(t);
 291                 if(selected != nil) {
 292                         *selected = false;
 293                         return;
 294                 }
 295                 g->status = Gwaiting;
 296                 g->waitreason = "chan receive (nil chan)";
 297                 runtime_gosched();
 298                 return;  // not reached
 299         }
 300
 301         runtime_lock(c);
 302         if(c->dataqsiz > 0)
 303                 goto asynch;
 304
 305         if(c->closed)
 306                 goto closed;
 307
 308         sg = dequeue(&c->sendq);
 309         if(sg != nil) {
 310                 runtime_unlock(c);
 311
 312                 if(ep != nil)
 313                         runtime_memmove(ep, sg->elem, c->elemsize);
 314                 gp = sg->g;
 315                 gp->param = sg;
 316                 runtime_ready(gp);
 317
 318                 if(selected != nil)
 319                         *selected = true;
 320                 if(received != nil)
 321                         *received = true;
 322                 return;
 323         }
 324
 325         if(selected != nil) {
 326                 runtime_unlock(c);
 327                 *selected = false;
 328                 return;
 329         }
 330
 331         mysg.elem = ep;
 332         mysg.g = g;
 333         mysg.selgen = NOSELGEN;
 334         g->param = nil;
 335         g->status = Gwaiting;
 336         g->waitreason = "chan receive";
 337         enqueue(&c->recvq, &mysg);
 338         runtime_unlock(c);
 339         runtime_gosched();
 340
 341         if(g->param == nil) {
 342                 runtime_lock(c);
 343                 if(!c->closed)
 344                         runtime_throw("chanrecv: spurious wakeup");
 345                 goto closed;
 346         }
 347
 348         if(received != nil)
 349                 *received = true;
 350         return;
 351
 352 asynch:
 353         if(c->qcount <= 0) {
 354                 if(c->closed)
 355                         goto closed;
 356
 357                 if(selected != nil) {
 358                         runtime_unlock(c);
 359                         *selected = false;
 360                         if(received != nil)
 361                                 *received = false;
 362                         return;
 363                 }
 364                 mysg.g = g;
 365                 mysg.elem = nil;
 366                 mysg.selgen = NOSELGEN;
 367                 g->status = Gwaiting;
 368                 g->waitreason = "chan receive";
 369                 enqueue(&c->recvq, &mysg);
 370                 runtime_unlock(c);
 371                 runtime_gosched();
 372
 373                 runtime_lock(c);
 374                 goto asynch;
 375         }
 376         if(ep != nil)
 377                 runtime_memmove(ep, chanbuf(c, c->recvx), c->elemsize);
 378         runtime_memclr(chanbuf(c, c->recvx), c->elemsize);
 379         if(++c->recvx == c->dataqsiz)
 380                 c->recvx = 0;
 381         c->qcount--;
 382
 383         sg = dequeue(&c->sendq);
 384         if(sg != nil) {
 385                 gp = sg->g;
 386                 runtime_unlock(c);
 387                 runtime_ready(gp);
 388         } else
 389                 runtime_unlock(c);
 390
 391         if(selected != nil)
 392                 *selected = true;
 393         if(received != nil)
 394                 *received = true;
 395         return;
 396
 397 closed:
 398         if(ep != nil)
 399                 runtime_memclr(ep, c->elemsize);
 400         if(selected != nil)
 401                 *selected = true;
 402         if(received != nil)
 403                 *received = false;
 404         runtime_unlock(c);
 405 }
 406
 407 // The compiler generates a call to __go_send_small to send a value 8
 408 // bytes or smaller.
 409 void
 410 __go_send_small(ChanType *t, Hchan* c, uint64 val)
 411 {
 412         byte b[sizeof(uint64)];
 413
 414         runtime_memclr(b, sizeof(uint64));
 415         __builtin_memcpy(b, &val, t->__element_type->__size);
 416         runtime_chansend(t, c, b, nil);
 417 }
 418
 419 // The compiler generates a call to __go_send_big to send a value
 420 // larger than 8 bytes or smaller.
 421 void
 422 __go_send_big(ChanType *t, Hchan* c, byte* p)
 423 {
 424         runtime_chansend(t, c, p, nil);
 425 }
 426
 427 // The compiler generates a call to __go_receive_small to receive a
 428 // value 8 bytes or smaller.
 429 uint64
 430 __go_receive_small(ChanType *t, Hchan* c)
 431 {
 432         union {
 433                 byte b[sizeof(uint64)];
 434                 uint64 v;
 435         } u;
 436
 437         u.v = 0;
 438         runtime_chanrecv(t, c, u.b, nil, nil);
 439         return u.v;
 440 }
 441
 442 // The compiler generates a call to __go_receive_big to receive a
 443 // value larger than 8 bytes.
 444 void
 445 __go_receive_big(ChanType *t, Hchan* c, byte* p)
 446 {
 447         runtime_chanrecv(t, c, p, nil, nil);
 448 }
 449
 450 _Bool runtime_chanrecv2(ChanType *t, Hchan* c, byte* p)
 451   __asm__("runtime.chanrecv2");
 452
 453 _Bool
 454 runtime_chanrecv2(ChanType *t, Hchan* c, byte* p)
 455 {
 456         bool received;
 457
 458         runtime_chanrecv(t, c, p, nil, &received);
 459         return received;
 460 }
 461
 462 // func selectnbsend(c chan any, elem any) bool
 463 //
 464 // compiler implements
 465 //
 466 //      select {
 467 //      case c <- v:
 468 //              ... foo
 469 //      default:
 470 //              ... bar
 471 //      }
 472 //
 473 // as
 474 //
 475 //      if selectnbsend(c, v) {
 476 //              ... foo
 477 //      } else {
 478 //              ... bar
 479 //      }
 480 //
 481 _Bool
 482 runtime_selectnbsend(ChanType *t, Hchan *c, byte *p)
 483 {
 484         bool res;
 485
 486         runtime_chansend(t, c, p, &res);
 487         return res;
 488 }
 489
 490 // func selectnbrecv(elem *any, c chan any) bool
 491 //
 492 // compiler implements
 493 //
 494 //      select {
 495 //      case v = <-c:
 496 //              ... foo
 497 //      default:
 498 //              ... bar
 499 //      }
 500 //
 501 // as
 502 //
 503 //      if selectnbrecv(&v, c) {
 504 //              ... foo
 505 //      } else {
 506 //              ... bar
 507 //      }
 508 //
 509 _Bool
 510 runtime_selectnbrecv(ChanType *t, byte *v, Hchan *c)
 511 {
 512         bool selected;
 513
 514         runtime_chanrecv(t, c, v, &selected, nil);
 515         return selected;
 516 }
 517
 518 // func selectnbrecv2(elem *any, ok *bool, c chan any) bool
 519 //
 520 // compiler implements
 521 //
 522 //      select {
 523 //      case v, ok = <-c:
 524 //              ... foo
 525 //      default:
 526 //              ... bar
 527 //      }
 528 //
 529 // as
 530 //
 531 //      if c != nil && selectnbrecv2(&v, &ok, c) {
 532 //              ... foo
 533 //      } else {
 534 //              ... bar
 535 //      }
 536 //
 537 _Bool
 538 runtime_selectnbrecv2(ChanType *t, byte *v, _Bool *received, Hchan *c)
 539 {
 540         bool selected;
 541         bool r;
 542
 543         r = false;
 544         runtime_chanrecv(t, c, v, &selected, received == nil ? nil : &r);
 545         if(received != nil)
 546                 *received = r;
 547         return selected;
 548 }
 549
 550 // For reflect:
 551 //      func chansend(c chan, val iword, nb bool) (selected bool)
 552 // where an iword is the same word an interface value would use:
 553 // the actual data if it fits, or else a pointer to the data.
 554
 555 _Bool reflect_chansend(ChanType *, Hchan *, uintptr, _Bool)
 556   __asm__("libgo_reflect.reflect.chansend");
 557
 558 _Bool
 559 reflect_chansend(ChanType *t, Hchan *c, uintptr val, _Bool nb)
 560 {
 561         bool selected;
 562         bool *sp;
 563         byte *vp;
 564
 565         if(nb) {
 566                 selected = false;
 567                 sp = (bool*)&selected;
 568         } else {
 569                 selected = true;
 570                 sp = nil;
 571         }
 572         if(__go_is_pointer_type(t->__element_type))
 573                 vp = (byte*)&val;
 574         else
 575                 vp = (byte*)val;
 576         runtime_chansend(t, c, vp, sp);
 577         return selected;
 578 }
 579
 580 // For reflect:
 581 //      func chanrecv(c chan, nb bool) (val iword, selected, received bool)
 582 // where an iword is the same word an interface value would use:
 583 // the actual data if it fits, or else a pointer to the data.
 584
 585 struct chanrecv_ret
 586 {
 587         uintptr val;
 588         _Bool selected;
 589         _Bool received;
 590 };
 591
 592 struct chanrecv_ret reflect_chanrecv(ChanType *, Hchan *, _Bool)
 593   __asm__("libgo_reflect.reflect.chanrecv");
 594
 595 struct chanrecv_ret
 596 reflect_chanrecv(ChanType *t, Hchan *c, _Bool nb)
 597 {
 598         struct chanrecv_ret ret;
 599         byte *vp;
 600         bool *sp;
 601         bool selected;
 602         bool received;
 603
 604         if(nb) {
 605                 selected = false;
 606                 sp = &selected;
 607         } else {
 608                 ret.selected = true;
 609                 sp = nil;
 610         }
 611         received = false;
 612         if(__go_is_pointer_type(t->__element_type)) {
 613                 vp = (byte*)&ret.val;
 614         } else {
 615                 vp = runtime_mal(t->__element_type->__size);
 616                 ret.val = (uintptr)vp;
 617         }
 618         runtime_chanrecv(t, c, vp, sp, &received);
 619         if(nb)
 620                 ret.selected = selected;
 621         ret.received = received;
 622         return ret;
 623 }
 624
 625 static void newselect(int32, Select**);
 626
 627 // newselect(size uint32) (sel *byte);
 628
 629 void* runtime_newselect(int) __asm__("runtime.newselect");
 630
 631 void*
 632 runtime_newselect(int size)
 633 {
 634         Select *sel;
 635
 636         newselect(size, &sel);
 637         return (void*)sel;
 638 }
 639
 640 static void
 641 newselect(int32 size, Select **selp)
 642 {
 643         int32 n;
 644         Select *sel;
 645
 646         n = 0;
 647         if(size > 1)
 648                 n = size-1;
 649
 650         sel = runtime_mal(sizeof(*sel) +
 651                 n*sizeof(sel->scase[0]) +
 652                 size*sizeof(sel->lockorder[0]) +
 653                 size*sizeof(sel->pollorder[0]));
 654
 655         sel->tcase = size;
 656         sel->ncase = 0;
 657         sel->pollorder = (void*)(sel->scase + size);
 658         sel->lockorder = (void*)(sel->pollorder + size);
 659         *selp = sel;
 660
 661         if(debug)
 662                 runtime_printf("newselect s=%p size=%d\n", sel, size);
 663 }
 664
 665 // cut in half to give stack a chance to split
 666 static void selectsend(Select *sel, Hchan *c, int index, void *elem);
 667
 668 // selectsend(sel *byte, hchan *chan any, elem *any) (selected bool);
 669
 670 void runtime_selectsend(Select *, Hchan *, void *, int)
 671   __asm__("runtime.selectsend");
 672
 673 void
 674 runtime_selectsend(Select *sel, Hchan *c, void *elem, int index)
 675 {
 676         // nil cases do not compete
 677         if(c == nil)
 678                 return;
 679
 680         selectsend(sel, c, index, elem);
 681 }
 682
 683 static void
 684 selectsend(Select *sel, Hchan *c, int index, void *elem)
 685 {
 686         int32 i;
 687         Scase *cas;
 688
 689         i = sel->ncase;
 690         if(i >= sel->tcase)
 691                 runtime_throw("selectsend: too many cases");
 692         sel->ncase = i+1;
 693         cas = &sel->scase[i];
 694
 695         cas->index = index;
 696         cas->chan = c;
 697         cas->kind = CaseSend;
 698         cas->sg.elem = elem;
 699
 700         if(debug)
 701                 runtime_printf("selectsend s=%p index=%d chan=%p\n",
 702                         sel, cas->index, cas->chan);
 703 }
 704
 705 // cut in half to give stack a chance to split
 706 static void selectrecv(Select *sel, Hchan *c, int index, void *elem, bool*);
 707
 708 // selectrecv(sel *byte, hchan *chan any, elem *any) (selected bool);
 709
 710 void runtime_selectrecv(Select *, Hchan *, void *, int)
 711   __asm__("runtime.selectrecv");
 712
 713 void
 714 runtime_selectrecv(Select *sel, Hchan *c, void *elem, int index)
 715 {
 716         // nil cases do not compete
 717         if(c == nil)
 718                 return;
 719
 720         selectrecv(sel, c, index, elem, nil);
 721 }
 722
 723 // selectrecv2(sel *byte, hchan *chan any, elem *any, received *bool) (selected bool);
 724
 725 void runtime_selectrecv2(Select *, Hchan *, void *, bool *, int)
 726   __asm__("runtime.selectrecv2");
 727
 728 void
 729 runtime_selectrecv2(Select *sel, Hchan *c, void *elem, bool *received, int index)
 730 {
 731         // nil cases do not compete
 732         if(c == nil)
 733                 return;
 734
 735         selectrecv(sel, c, index, elem, received);
 736 }
 737
 738 static void
 739 selectrecv(Select *sel, Hchan *c, int index, void *elem, bool *received)
 740 {
 741         int32 i;
 742         Scase *cas;
 743
 744         i = sel->ncase;
 745         if(i >= sel->tcase)
 746                 runtime_throw("selectrecv: too many cases");
 747         sel->ncase = i+1;
 748         cas = &sel->scase[i];
 749         cas->index = index;
 750         cas->chan = c;
 751
 752         cas->kind = CaseRecv;
 753         cas->sg.elem = elem;
 754         cas->receivedp = received;
 755
 756         if(debug)
 757                 runtime_printf("selectrecv s=%p index=%d chan=%p\n",
 758                         sel, cas->index, cas->chan);
 759 }
 760
 761 // cut in half to give stack a chance to split
 762 static void selectdefault(Select*, int);
 763
 764 // selectdefault(sel *byte) (selected bool);
 765
 766 void runtime_selectdefault(Select *, int) __asm__("runtime.selectdefault");
 767
 768 void
 769 runtime_selectdefault(Select *sel, int index)
 770 {
 771         selectdefault(sel, index);
 772 }
 773
 774 static void
 775 selectdefault(Select *sel, int index)
 776 {
 777         int32 i;
 778         Scase *cas;
 779
 780         i = sel->ncase;
 781         if(i >= sel->tcase)
 782                 runtime_throw("selectdefault: too many cases");
 783         sel->ncase = i+1;
 784         cas = &sel->scase[i];
 785         cas->index = index;
 786         cas->chan = nil;
 787
 788         cas->kind = CaseDefault;
 789
 790         if(debug)
 791                 runtime_printf("selectdefault s=%p index=%d\n",
 792                         sel, cas->index);
 793 }
 794
 795 static void
 796 sellock(Select *sel)
 797 {
 798         uint32 i;
 799         Hchan *c, *c0;
 800
 801         c = nil;
 802         for(i=0; i<sel->ncase; i++) {
 803                 c0 = sel->lockorder[i];
 804                 if(c0 && c0 != c) {
 805                         c = sel->lockorder[i];
 806                         runtime_lock(c);
 807                 }
 808         }
 809 }
 810
 811 static void
 812 selunlock(Select *sel)
 813 {
 814         uint32 i;
 815         Hchan *c, *c0;
 816
 817         c = nil;
 818         for(i=sel->ncase; i-->0;) {
 819                 c0 = sel->lockorder[i];
 820                 if(c0 && c0 != c) {
 821                         c = c0;
 822                         runtime_unlock(c);
 823                 }
 824         }
 825 }
 826
 827 void
 828 runtime_block(void)
 829 {
 830         G *g;
 831
 832         g = runtime_g();
 833         g->status = Gwaiting;   // forever
 834         g->waitreason = "select (no cases)";
 835         runtime_gosched();
 836 }
 837
 838 static int selectgo(Select**);
 839
 840 // selectgo(sel *byte);
 841
 842 int runtime_selectgo(Select *) __asm__("runtime.selectgo");
 843
 844 int
 845 runtime_selectgo(Select *sel)
 846 {
 847         return selectgo(&sel);
 848 }
 849
 850 static int
 851 selectgo(Select **selp)
 852 {
 853         Select *sel;
 854         uint32 o, i, j;
 855         Scase *cas, *dfl;
 856         Hchan *c;
 857         SudoG *sg;
 858         G *gp;
 859         int index;
 860         G *g;
 861
 862         sel = *selp;
 863         if(runtime_gcwaiting)
 864                 runtime_gosched();
 865
 866         if(debug)
 867                 runtime_printf("select: sel=%p\n", sel);
 868
 869         g = runtime_g();
 870
 871         // The compiler rewrites selects that statically have
 872         // only 0 or 1 cases plus default into simpler constructs.
 873         // The only way we can end up with such small sel->ncase
 874         // values here is for a larger select in which most channels
 875         // have been nilled out.  The general code handles those
 876         // cases correctly, and they are rare enough not to bother
 877         // optimizing (and needing to test).
 878
 879         // generate permuted order
 880         for(i=0; i<sel->ncase; i++)
 881                 sel->pollorder[i] = i;
 882         for(i=1; i<sel->ncase; i++) {
 883                 o = sel->pollorder[i];
 884                 j = runtime_fastrand1()%(i+1);
 885                 sel->pollorder[i] = sel->pollorder[j];
 886                 sel->pollorder[j] = o;
 887         }
 888
 889         // sort the cases by Hchan address to get the locking order.
 890         for(i=0; i<sel->ncase; i++) {
 891                 c = sel->scase[i].chan;
 892                 for(j=i; j>0 && sel->lockorder[j-1] >= c; j--)
 893                         sel->lockorder[j] = sel->lockorder[j-1];
 894                 sel->lockorder[j] = c;
 895         }
 896         sellock(sel);
 897
 898 loop:
 899         // pass 1 - look for something already waiting
 900         dfl = nil;
 901         for(i=0; i<sel->ncase; i++) {
 902                 o = sel->pollorder[i];
 903                 cas = &sel->scase[o];
 904                 c = cas->chan;
 905
 906                 switch(cas->kind) {
 907                 case CaseRecv:
 908                         if(c->dataqsiz > 0) {
 909                                 if(c->qcount > 0)
 910                                         goto asyncrecv;
 911                         } else {
 912                                 sg = dequeue(&c->sendq);
 913                                 if(sg != nil)
 914                                         goto syncrecv;
 915                         }
 916                         if(c->closed)
 917                                 goto rclose;
 918                         break;
 919
 920                 case CaseSend:
 921                         if(c->closed)
 922                                 goto sclose;
 923                         if(c->dataqsiz > 0) {
 924                                 if(c->qcount < c->dataqsiz)
 925                                         goto asyncsend;
 926                         } else {
 927                                 sg = dequeue(&c->recvq);
 928                                 if(sg != nil)
 929                                         goto syncsend;
 930                         }
 931                         break;
 932
 933                 case CaseDefault:
 934                         dfl = cas;
 935                         break;
 936                 }
 937         }
 938
 939         if(dfl != nil) {
 940                 selunlock(sel);
 941                 cas = dfl;
 942                 goto retc;
 943         }
 944
 945
 946         // pass 2 - enqueue on all chans
 947         for(i=0; i<sel->ncase; i++) {
 948                 o = sel->pollorder[i];
 949                 cas = &sel->scase[o];
 950                 c = cas->chan;
 951                 sg = &cas->sg;
 952                 sg->g = g;
 953                 sg->selgen = g->selgen;
 954
 955                 switch(cas->kind) {
 956                 case CaseRecv:
 957                         enqueue(&c->recvq, sg);
 958                         break;
 959
 960                 case CaseSend:
 961                         enqueue(&c->sendq, sg);
 962                         break;
 963                 }
 964         }
 965
 966         g->param = nil;
 967         g->status = Gwaiting;
 968         g->waitreason = "select";
 969         selunlock(sel);
 970         runtime_gosched();
 971
 972         sellock(sel);
 973         sg = g->param;
 974
 975         // pass 3 - dequeue from unsuccessful chans
 976         // otherwise they stack up on quiet channels
 977         for(i=0; i<sel->ncase; i++) {
 978                 cas = &sel->scase[i];
 979                 if(cas != (Scase*)sg) {
 980                         c = cas->chan;
 981                         if(cas->kind == CaseSend)
 982                                 dequeueg(&c->sendq);
 983                         else
 984                                 dequeueg(&c->recvq);
 985                 }
 986         }
 987
 988         if(sg == nil)
 989                 goto loop;
 990
 991         cas = (Scase*)sg;
 992         c = cas->chan;
 993
 994         if(c->dataqsiz > 0)
 995                 runtime_throw("selectgo: shouldnt happen");
 996
 997         if(debug)
 998                 runtime_printf("wait-return: sel=%p c=%p cas=%p kind=%d\n",
 999                         sel, c, cas, cas->kind);
1000
1001         if(cas->kind == CaseRecv) {
1002                 if(cas->receivedp != nil)
1003                         *cas->receivedp = true;
1004         }
1005
1006         selunlock(sel);
1007         goto retc;
1008
1009 asyncrecv:
1010         // can receive from buffer
1011         if(cas->receivedp != nil)
1012                 *cas->receivedp = true;
1013         if(cas->sg.elem != nil)
1014                 runtime_memmove(cas->sg.elem, chanbuf(c, c->recvx), c->elemsize);
1015         runtime_memclr(chanbuf(c, c->recvx), c->elemsize);
1016         if(++c->recvx == c->dataqsiz)
1017                 c->recvx = 0;
1018         c->qcount--;
1019         sg = dequeue(&c->sendq);
1020         if(sg != nil) {
1021                 gp = sg->g;
1022                 selunlock(sel);
1023                 runtime_ready(gp);
1024         } else {
1025                 selunlock(sel);
1026         }
1027         goto retc;
1028
1029 asyncsend:
1030         // can send to buffer
1031         runtime_memmove(chanbuf(c, c->sendx), cas->sg.elem, c->elemsize);
1032         if(++c->sendx == c->dataqsiz)
1033                 c->sendx = 0;
1034         c->qcount++;
1035         sg = dequeue(&c->recvq);
1036         if(sg != nil) {
1037                 gp = sg->g;
1038                 selunlock(sel);
1039                 runtime_ready(gp);
1040         } else {
1041                 selunlock(sel);
1042         }
1043         goto retc;
1044
1045 syncrecv:
1046         // can receive from sleeping sender (sg)
1047         selunlock(sel);
1048         if(debug)
1049                 runtime_printf("syncrecv: sel=%p c=%p o=%d\n", sel, c, o);
1050         if(cas->receivedp != nil)
1051                 *cas->receivedp = true;
1052         if(cas->sg.elem != nil)
1053                 runtime_memmove(cas->sg.elem, sg->elem, c->elemsize);
1054         gp = sg->g;
1055         gp->param = sg;
1056         runtime_ready(gp);
1057         goto retc;
1058
1059 rclose:
1060         // read at end of closed channel
1061         selunlock(sel);
1062         if(cas->receivedp != nil)
1063                 *cas->receivedp = false;
1064         if(cas->sg.elem != nil)
1065                 runtime_memclr(cas->sg.elem, c->elemsize);
1066         goto retc;
1067
1068 syncsend:
1069         // can send to sleeping receiver (sg)
1070         selunlock(sel);
1071         if(debug)
1072                 runtime_printf("syncsend: sel=%p c=%p o=%d\n", sel, c, o);
1073         if(sg->elem != nil)
1074                 runtime_memmove(sg->elem, cas->sg.elem, c->elemsize);
1075         gp = sg->g;
1076         gp->param = sg;
1077         runtime_ready(gp);
1078
1079 retc:
1080         // return index corresponding to chosen case
1081         index = cas->index;
1082         runtime_free(sel);
1083         return index;
1084
1085 sclose:
1086         // send on closed channel
1087         selunlock(sel);
1088         runtime_panicstring("send on closed channel");
1089         return 0;  // not reached
1090 }
1091
1092 // closechan(sel *byte);
1093 void
1094 runtime_closechan(Hchan *c)
1095 {
1096         SudoG *sg;
1097         G* gp;
1098
1099         if(c == nil)
1100                 runtime_panicstring("close of nil channel");
1101
1102         if(runtime_gcwaiting)
1103                 runtime_gosched();
1104
1105         runtime_lock(c);
1106         if(c->closed) {
1107                 runtime_unlock(c);
1108                 runtime_panicstring("close of closed channel");
1109         }
1110
1111         c->closed = true;
1112
1113         // release all readers
1114         for(;;) {
1115                 sg = dequeue(&c->recvq);
1116                 if(sg == nil)
1117                         break;
1118                 gp = sg->g;
1119                 gp->param = nil;
1120                 runtime_ready(gp);
1121         }
1122
1123         // release all writers
1124         for(;;) {
1125                 sg = dequeue(&c->sendq);
1126                 if(sg == nil)
1127                         break;
1128                 gp = sg->g;
1129                 gp->param = nil;
1130                 runtime_ready(gp);
1131         }
1132
1133         runtime_unlock(c);
1134 }
1135
1136 void
1137 __go_builtin_close(Hchan *c)
1138 {
1139         runtime_closechan(c);
1140 }
1141
1142 // For reflect
1143 //      func chanclose(c chan)
1144
1145 void reflect_chanclose(uintptr) __asm__("libgo_reflect.reflect.chanclose");
1146
1147 void
1148 reflect_chanclose(uintptr c)
1149 {
1150         runtime_closechan((Hchan*)c);
1151 }
1152
1153 // For reflect
1154 //      func chanlen(c chan) (len int32)
1155
1156 int32 reflect_chanlen(uintptr) __asm__("libgo_reflect.reflect.chanlen");
1157
1158 int32
1159 reflect_chanlen(uintptr ca)
1160 {
1161         Hchan *c;
1162         int32 len;
1163
1164         c = (Hchan*)ca;
1165         if(c == nil)
1166                 len = 0;
1167         else
1168                 len = c->qcount;
1169         return len;
1170 }
1171
1172 int
1173 __go_chan_len(Hchan *c)
1174 {
1175         return reflect_chanlen((uintptr)c);
1176 }
1177
1178 // For reflect
1179 //      func chancap(c chan) (cap int32)
1180
1181 int32 reflect_chancap(uintptr) __asm__("libgo_reflect.reflect.chancap");
1182
1183 int32
1184 reflect_chancap(uintptr ca)
1185 {
1186         Hchan *c;
1187         int32 cap;
1188
1189         c = (Hchan*)ca;
1190         if(c == nil)
1191                 cap = 0;
1192         else
1193                 cap = c->dataqsiz;
1194         return cap;
1195 }
1196
1197 int
1198 __go_chan_cap(Hchan *c)
1199 {
1200         return reflect_chancap((uintptr)c);
1201 }
1202
1203 static SudoG*
1204 dequeue(WaitQ *q)
1205 {
1206         SudoG *sgp;
1207
1208 loop:
1209         sgp = q->first;
1210         if(sgp == nil)
1211                 return nil;
1212         q->first = sgp->link;
1213
1214         // if sgp is stale, ignore it
1215         if(sgp->selgen != NOSELGEN &&
1216                 (sgp->selgen != sgp->g->selgen ||
1217                 !runtime_cas(&sgp->g->selgen, sgp->selgen, sgp->selgen + 2))) {
1218                 //prints("INVALID PSEUDOG POINTER\n");
1219                 goto loop;
1220         }
1221
1222         return sgp;
1223 }
1224
1225 static void
1226 dequeueg(WaitQ *q)
1227 {
1228         SudoG **l, *sgp, *prevsgp;
1229         G *g;
1230
1231         g = runtime_g();
1232         prevsgp = nil;
1233         for(l=&q->first; (sgp=*l) != nil; l=&sgp->link, prevsgp=sgp) {
1234                 if(sgp->g == g) {
1235                         *l = sgp->link;
1236                         if(q->last == sgp)
1237                                 q->last = prevsgp;
1238                         break;
1239                 }
1240         }
1241 }
1242
1243 static void
1244 enqueue(WaitQ *q, SudoG *sgp)
1245 {
1246         sgp->link = nil;
1247         if(q->first == nil) {
1248                 q->first = sgp;
1249                 q->last = sgp;
1250                 return;
1251         }
1252         q->last->link = sgp;
1253         q->last = sgp;
1254 }