gnulib/import/glthread/lock.c

   1 /* Locking in multithreaded situations.
   2    Copyright (C) 2005-2016 Free Software Foundation, Inc.
   3
   4    This program is free software; you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 3, or (at your option)
   7    any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program; if not, see <http://www.gnu.org/licenses/>.  */
  16
  17 /* Written by Bruno Haible <bruno@clisp.org>, 2005.
  18    Based on GCC's gthr-posix.h, gthr-posix95.h, gthr-solaris.h,
  19    gthr-win32.h.  */
  20
  21 #include <config.h>
  22
  23 #include "glthread/lock.h"
  24
  25 /* ========================================================================= */
  26
  27 #if USE_POSIX_THREADS
  28
  29 /* -------------------------- gl_lock_t datatype -------------------------- */
  30
  31 /* ------------------------- gl_rwlock_t datatype ------------------------- */
  32
  33 # if HAVE_PTHREAD_RWLOCK
  34
  35 #  if !defined PTHREAD_RWLOCK_INITIALIZER
  36
  37 int
  38 glthread_rwlock_init_multithreaded (gl_rwlock_t *lock)
  39 {
  40   int err;
  41
  42   err = pthread_rwlock_init (&lock->rwlock, NULL);
  43   if (err != 0)
  44     return err;
  45   lock->initialized = 1;
  46   return 0;
  47 }
  48
  49 int
  50 glthread_rwlock_rdlock_multithreaded (gl_rwlock_t *lock)
  51 {
  52   if (!lock->initialized)
  53     {
  54       int err;
  55
  56       err = pthread_mutex_lock (&lock->guard);
  57       if (err != 0)
  58         return err;
  59       if (!lock->initialized)
  60         {
  61           err = glthread_rwlock_init_multithreaded (lock);
  62           if (err != 0)
  63             {
  64               pthread_mutex_unlock (&lock->guard);
  65               return err;
  66             }
  67         }
  68       err = pthread_mutex_unlock (&lock->guard);
  69       if (err != 0)
  70         return err;
  71     }
  72   return pthread_rwlock_rdlock (&lock->rwlock);
  73 }
  74
  75 int
  76 glthread_rwlock_wrlock_multithreaded (gl_rwlock_t *lock)
  77 {
  78   if (!lock->initialized)
  79     {
  80       int err;
  81
  82       err = pthread_mutex_lock (&lock->guard);
  83       if (err != 0)
  84         return err;
  85       if (!lock->initialized)
  86         {
  87           err = glthread_rwlock_init_multithreaded (lock);
  88           if (err != 0)
  89             {
  90               pthread_mutex_unlock (&lock->guard);
  91               return err;
  92             }
  93         }
  94       err = pthread_mutex_unlock (&lock->guard);
  95       if (err != 0)
  96         return err;
  97     }
  98   return pthread_rwlock_wrlock (&lock->rwlock);
  99 }
 100
 101 int
 102 glthread_rwlock_unlock_multithreaded (gl_rwlock_t *lock)
 103 {
 104   if (!lock->initialized)
 105     return EINVAL;
 106   return pthread_rwlock_unlock (&lock->rwlock);
 107 }
 108
 109 int
 110 glthread_rwlock_destroy_multithreaded (gl_rwlock_t *lock)
 111 {
 112   int err;
 113
 114   if (!lock->initialized)
 115     return EINVAL;
 116   err = pthread_rwlock_destroy (&lock->rwlock);
 117   if (err != 0)
 118     return err;
 119   lock->initialized = 0;
 120   return 0;
 121 }
 122
 123 #  endif
 124
 125 # else
 126
 127 int
 128 glthread_rwlock_init_multithreaded (gl_rwlock_t *lock)
 129 {
 130   int err;
 131
 132   err = pthread_mutex_init (&lock->lock, NULL);
 133   if (err != 0)
 134     return err;
 135   err = pthread_cond_init (&lock->waiting_readers, NULL);
 136   if (err != 0)
 137     return err;
 138   err = pthread_cond_init (&lock->waiting_writers, NULL);
 139   if (err != 0)
 140     return err;
 141   lock->waiting_writers_count = 0;
 142   lock->runcount = 0;
 143   return 0;
 144 }
 145
 146 int
 147 glthread_rwlock_rdlock_multithreaded (gl_rwlock_t *lock)
 148 {
 149   int err;
 150
 151   err = pthread_mutex_lock (&lock->lock);
 152   if (err != 0)
 153     return err;
 154   /* Test whether only readers are currently running, and whether the runcount
 155      field will not overflow.  */
 156   /* POSIX says: "It is implementation-defined whether the calling thread
 157      acquires the lock when a writer does not hold the lock and there are
 158      writers blocked on the lock."  Let's say, no: give the writers a higher
 159      priority.  */
 160   while (!(lock->runcount + 1 > 0 && lock->waiting_writers_count == 0))
 161     {
 162       /* This thread has to wait for a while.  Enqueue it among the
 163          waiting_readers.  */
 164       err = pthread_cond_wait (&lock->waiting_readers, &lock->lock);
 165       if (err != 0)
 166         {
 167           pthread_mutex_unlock (&lock->lock);
 168           return err;
 169         }
 170     }
 171   lock->runcount++;
 172   return pthread_mutex_unlock (&lock->lock);
 173 }
 174
 175 int
 176 glthread_rwlock_wrlock_multithreaded (gl_rwlock_t *lock)
 177 {
 178   int err;
 179
 180   err = pthread_mutex_lock (&lock->lock);
 181   if (err != 0)
 182     return err;
 183   /* Test whether no readers or writers are currently running.  */
 184   while (!(lock->runcount == 0))
 185     {
 186       /* This thread has to wait for a while.  Enqueue it among the
 187          waiting_writers.  */
 188       lock->waiting_writers_count++;
 189       err = pthread_cond_wait (&lock->waiting_writers, &lock->lock);
 190       if (err != 0)
 191         {
 192           lock->waiting_writers_count--;
 193           pthread_mutex_unlock (&lock->lock);
 194           return err;
 195         }
 196       lock->waiting_writers_count--;
 197     }
 198   lock->runcount--; /* runcount becomes -1 */
 199   return pthread_mutex_unlock (&lock->lock);
 200 }
 201
 202 int
 203 glthread_rwlock_unlock_multithreaded (gl_rwlock_t *lock)
 204 {
 205   int err;
 206
 207   err = pthread_mutex_lock (&lock->lock);
 208   if (err != 0)
 209     return err;
 210   if (lock->runcount < 0)
 211     {
 212       /* Drop a writer lock.  */
 213       if (!(lock->runcount == -1))
 214         {
 215           pthread_mutex_unlock (&lock->lock);
 216           return EINVAL;
 217         }
 218       lock->runcount = 0;
 219     }
 220   else
 221     {
 222       /* Drop a reader lock.  */
 223       if (!(lock->runcount > 0))
 224         {
 225           pthread_mutex_unlock (&lock->lock);
 226           return EINVAL;
 227         }
 228       lock->runcount--;
 229     }
 230   if (lock->runcount == 0)
 231     {
 232       /* POSIX recommends that "write locks shall take precedence over read
 233          locks", to avoid "writer starvation".  */
 234       if (lock->waiting_writers_count > 0)
 235         {
 236           /* Wake up one of the waiting writers.  */
 237           err = pthread_cond_signal (&lock->waiting_writers);
 238           if (err != 0)
 239             {
 240               pthread_mutex_unlock (&lock->lock);
 241               return err;
 242             }
 243         }
 244       else
 245         {
 246           /* Wake up all waiting readers.  */
 247           err = pthread_cond_broadcast (&lock->waiting_readers);
 248           if (err != 0)
 249             {
 250               pthread_mutex_unlock (&lock->lock);
 251               return err;
 252             }
 253         }
 254     }
 255   return pthread_mutex_unlock (&lock->lock);
 256 }
 257
 258 int
 259 glthread_rwlock_destroy_multithreaded (gl_rwlock_t *lock)
 260 {
 261   int err;
 262
 263   err = pthread_mutex_destroy (&lock->lock);
 264   if (err != 0)
 265     return err;
 266   err = pthread_cond_destroy (&lock->waiting_readers);
 267   if (err != 0)
 268     return err;
 269   err = pthread_cond_destroy (&lock->waiting_writers);
 270   if (err != 0)
 271     return err;
 272   return 0;
 273 }
 274
 275 # endif
 276
 277 /* --------------------- gl_recursive_lock_t datatype --------------------- */
 278
 279 # if HAVE_PTHREAD_MUTEX_RECURSIVE
 280
 281 #  if defined PTHREAD_RECURSIVE_MUTEX_INITIALIZER || defined PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP
 282
 283 int
 284 glthread_recursive_lock_init_multithreaded (gl_recursive_lock_t *lock)
 285 {
 286   pthread_mutexattr_t attributes;
 287   int err;
 288
 289   err = pthread_mutexattr_init (&attributes);
 290   if (err != 0)
 291     return err;
 292   err = pthread_mutexattr_settype (&attributes, PTHREAD_MUTEX_RECURSIVE);
 293   if (err != 0)
 294     {
 295       pthread_mutexattr_destroy (&attributes);
 296       return err;
 297     }
 298   err = pthread_mutex_init (lock, &attributes);
 299   if (err != 0)
 300     {
 301       pthread_mutexattr_destroy (&attributes);
 302       return err;
 303     }
 304   err = pthread_mutexattr_destroy (&attributes);
 305   if (err != 0)
 306     return err;
 307   return 0;
 308 }
 309
 310 #  else
 311
 312 int
 313 glthread_recursive_lock_init_multithreaded (gl_recursive_lock_t *lock)
 314 {
 315   pthread_mutexattr_t attributes;
 316   int err;
 317
 318   err = pthread_mutexattr_init (&attributes);
 319   if (err != 0)
 320     return err;
 321   err = pthread_mutexattr_settype (&attributes, PTHREAD_MUTEX_RECURSIVE);
 322   if (err != 0)
 323     {
 324       pthread_mutexattr_destroy (&attributes);
 325       return err;
 326     }
 327   err = pthread_mutex_init (&lock->recmutex, &attributes);
 328   if (err != 0)
 329     {
 330       pthread_mutexattr_destroy (&attributes);
 331       return err;
 332     }
 333   err = pthread_mutexattr_destroy (&attributes);
 334   if (err != 0)
 335     return err;
 336   lock->initialized = 1;
 337   return 0;
 338 }
 339
 340 int
 341 glthread_recursive_lock_lock_multithreaded (gl_recursive_lock_t *lock)
 342 {
 343   if (!lock->initialized)
 344     {
 345       int err;
 346
 347       err = pthread_mutex_lock (&lock->guard);
 348       if (err != 0)
 349         return err;
 350       if (!lock->initialized)
 351         {
 352           err = glthread_recursive_lock_init_multithreaded (lock);
 353           if (err != 0)
 354             {
 355               pthread_mutex_unlock (&lock->guard);
 356               return err;
 357             }
 358         }
 359       err = pthread_mutex_unlock (&lock->guard);
 360       if (err != 0)
 361         return err;
 362     }
 363   return pthread_mutex_lock (&lock->recmutex);
 364 }
 365
 366 int
 367 glthread_recursive_lock_unlock_multithreaded (gl_recursive_lock_t *lock)
 368 {
 369   if (!lock->initialized)
 370     return EINVAL;
 371   return pthread_mutex_unlock (&lock->recmutex);
 372 }
 373
 374 int
 375 glthread_recursive_lock_destroy_multithreaded (gl_recursive_lock_t *lock)
 376 {
 377   int err;
 378
 379   if (!lock->initialized)
 380     return EINVAL;
 381   err = pthread_mutex_destroy (&lock->recmutex);
 382   if (err != 0)
 383     return err;
 384   lock->initialized = 0;
 385   return 0;
 386 }
 387
 388 #  endif
 389
 390 # else
 391
 392 int
 393 glthread_recursive_lock_init_multithreaded (gl_recursive_lock_t *lock)
 394 {
 395   int err;
 396
 397   err = pthread_mutex_init (&lock->mutex, NULL);
 398   if (err != 0)
 399     return err;
 400   lock->owner = (pthread_t) 0;
 401   lock->depth = 0;
 402   return 0;
 403 }
 404
 405 int
 406 glthread_recursive_lock_lock_multithreaded (gl_recursive_lock_t *lock)
 407 {
 408   pthread_t self = pthread_self ();
 409   if (lock->owner != self)
 410     {
 411       int err;
 412
 413       err = pthread_mutex_lock (&lock->mutex);
 414       if (err != 0)
 415         return err;
 416       lock->owner = self;
 417     }
 418   if (++(lock->depth) == 0) /* wraparound? */
 419     {
 420       lock->depth--;
 421       return EAGAIN;
 422     }
 423   return 0;
 424 }
 425
 426 int
 427 glthread_recursive_lock_unlock_multithreaded (gl_recursive_lock_t *lock)
 428 {
 429   if (lock->owner != pthread_self ())
 430     return EPERM;
 431   if (lock->depth == 0)
 432     return EINVAL;
 433   if (--(lock->depth) == 0)
 434     {
 435       lock->owner = (pthread_t) 0;
 436       return pthread_mutex_unlock (&lock->mutex);
 437     }
 438   else
 439     return 0;
 440 }
 441
 442 int
 443 glthread_recursive_lock_destroy_multithreaded (gl_recursive_lock_t *lock)
 444 {
 445   if (lock->owner != (pthread_t) 0)
 446     return EBUSY;
 447   return pthread_mutex_destroy (&lock->mutex);
 448 }
 449
 450 # endif
 451
 452 /* -------------------------- gl_once_t datatype -------------------------- */
 453
 454 static const pthread_once_t fresh_once = PTHREAD_ONCE_INIT;
 455
 456 int
 457 glthread_once_singlethreaded (pthread_once_t *once_control)
 458 {
 459   /* We don't know whether pthread_once_t is an integer type, a floating-point
 460      type, a pointer type, or a structure type.  */
 461   char *firstbyte = (char *)once_control;
 462   if (*firstbyte == *(const char *)&fresh_once)
 463     {
 464       /* First time use of once_control.  Invert the first byte.  */
 465       *firstbyte = ~ *(const char *)&fresh_once;
 466       return 1;
 467     }
 468   else
 469     return 0;
 470 }
 471
 472 #endif
 473
 474 /* ========================================================================= */
 475
 476 #if USE_PTH_THREADS
 477
 478 /* Use the GNU Pth threads library.  */
 479
 480 /* -------------------------- gl_lock_t datatype -------------------------- */
 481
 482 /* ------------------------- gl_rwlock_t datatype ------------------------- */
 483
 484 /* --------------------- gl_recursive_lock_t datatype --------------------- */
 485
 486 /* -------------------------- gl_once_t datatype -------------------------- */
 487
 488 static void
 489 glthread_once_call (void *arg)
 490 {
 491   void (**gl_once_temp_addr) (void) = (void (**) (void)) arg;
 492   void (*initfunction) (void) = *gl_once_temp_addr;
 493   initfunction ();
 494 }
 495
 496 int
 497 glthread_once_multithreaded (pth_once_t *once_control, void (*initfunction) (void))
 498 {
 499   void (*temp) (void) = initfunction;
 500   return (!pth_once (once_control, glthread_once_call, &temp) ? errno : 0);
 501 }
 502
 503 int
 504 glthread_once_singlethreaded (pth_once_t *once_control)
 505 {
 506   /* We know that pth_once_t is an integer type.  */
 507   if (*once_control == PTH_ONCE_INIT)
 508     {
 509       /* First time use of once_control.  Invert the marker.  */
 510       *once_control = ~ PTH_ONCE_INIT;
 511       return 1;
 512     }
 513   else
 514     return 0;
 515 }
 516
 517 #endif
 518
 519 /* ========================================================================= */
 520
 521 #if USE_SOLARIS_THREADS
 522
 523 /* Use the old Solaris threads library.  */
 524
 525 /* -------------------------- gl_lock_t datatype -------------------------- */
 526
 527 /* ------------------------- gl_rwlock_t datatype ------------------------- */
 528
 529 /* --------------------- gl_recursive_lock_t datatype --------------------- */
 530
 531 int
 532 glthread_recursive_lock_init_multithreaded (gl_recursive_lock_t *lock)
 533 {
 534   int err;
 535
 536   err = mutex_init (&lock->mutex, USYNC_THREAD, NULL);
 537   if (err != 0)
 538     return err;
 539   lock->owner = (thread_t) 0;
 540   lock->depth = 0;
 541   return 0;
 542 }
 543
 544 int
 545 glthread_recursive_lock_lock_multithreaded (gl_recursive_lock_t *lock)
 546 {
 547   thread_t self = thr_self ();
 548   if (lock->owner != self)
 549     {
 550       int err;
 551
 552       err = mutex_lock (&lock->mutex);
 553       if (err != 0)
 554         return err;
 555       lock->owner = self;
 556     }
 557   if (++(lock->depth) == 0) /* wraparound? */
 558     {
 559       lock->depth--;
 560       return EAGAIN;
 561     }
 562   return 0;
 563 }
 564
 565 int
 566 glthread_recursive_lock_unlock_multithreaded (gl_recursive_lock_t *lock)
 567 {
 568   if (lock->owner != thr_self ())
 569     return EPERM;
 570   if (lock->depth == 0)
 571     return EINVAL;
 572   if (--(lock->depth) == 0)
 573     {
 574       lock->owner = (thread_t) 0;
 575       return mutex_unlock (&lock->mutex);
 576     }
 577   else
 578     return 0;
 579 }
 580
 581 int
 582 glthread_recursive_lock_destroy_multithreaded (gl_recursive_lock_t *lock)
 583 {
 584   if (lock->owner != (thread_t) 0)
 585     return EBUSY;
 586   return mutex_destroy (&lock->mutex);
 587 }
 588
 589 /* -------------------------- gl_once_t datatype -------------------------- */
 590
 591 int
 592 glthread_once_multithreaded (gl_once_t *once_control, void (*initfunction) (void))
 593 {
 594   if (!once_control->inited)
 595     {
 596       int err;
 597
 598       /* Use the mutex to guarantee that if another thread is already calling
 599          the initfunction, this thread waits until it's finished.  */
 600       err = mutex_lock (&once_control->mutex);
 601       if (err != 0)
 602         return err;
 603       if (!once_control->inited)
 604         {
 605           once_control->inited = 1;
 606           initfunction ();
 607         }
 608       return mutex_unlock (&once_control->mutex);
 609     }
 610   else
 611     return 0;
 612 }
 613
 614 int
 615 glthread_once_singlethreaded (gl_once_t *once_control)
 616 {
 617   /* We know that gl_once_t contains an integer type.  */
 618   if (!once_control->inited)
 619     {
 620       /* First time use of once_control.  Invert the marker.  */
 621       once_control->inited = ~ 0;
 622       return 1;
 623     }
 624   else
 625     return 0;
 626 }
 627
 628 #endif
 629
 630 /* ========================================================================= */
 631
 632 #if USE_WINDOWS_THREADS
 633
 634 /* -------------------------- gl_lock_t datatype -------------------------- */
 635
 636 void
 637 glthread_lock_init_func (gl_lock_t *lock)
 638 {
 639   InitializeCriticalSection (&lock->lock);
 640   lock->guard.done = 1;
 641 }
 642
 643 int
 644 glthread_lock_lock_func (gl_lock_t *lock)
 645 {
 646   if (!lock->guard.done)
 647     {
 648       if (InterlockedIncrement (&lock->guard.started) == 0)
 649         /* This thread is the first one to need this lock.  Initialize it.  */
 650         glthread_lock_init (lock);
 651       else
 652         /* Yield the CPU while waiting for another thread to finish
 653            initializing this lock.  */
 654         while (!lock->guard.done)
 655           Sleep (0);
 656     }
 657   EnterCriticalSection (&lock->lock);
 658   return 0;
 659 }
 660
 661 int
 662 glthread_lock_unlock_func (gl_lock_t *lock)
 663 {
 664   if (!lock->guard.done)
 665     return EINVAL;
 666   LeaveCriticalSection (&lock->lock);
 667   return 0;
 668 }
 669
 670 int
 671 glthread_lock_destroy_func (gl_lock_t *lock)
 672 {
 673   if (!lock->guard.done)
 674     return EINVAL;
 675   DeleteCriticalSection (&lock->lock);
 676   lock->guard.done = 0;
 677   return 0;
 678 }
 679
 680 /* ------------------------- gl_rwlock_t datatype ------------------------- */
 681
 682 /* In this file, the waitqueues are implemented as circular arrays.  */
 683 #define gl_waitqueue_t gl_carray_waitqueue_t
 684
 685 static void
 686 gl_waitqueue_init (gl_waitqueue_t *wq)
 687 {
 688   wq->array = NULL;
 689   wq->count = 0;
 690   wq->alloc = 0;
 691   wq->offset = 0;
 692 }
 693
 694 /* Enqueues the current thread, represented by an event, in a wait queue.
 695    Returns INVALID_HANDLE_VALUE if an allocation failure occurs.  */
 696 static HANDLE
 697 gl_waitqueue_add (gl_waitqueue_t *wq)
 698 {
 699   HANDLE event;
 700   unsigned int index;
 701
 702   if (wq->count == wq->alloc)
 703     {
 704       unsigned int new_alloc = 2 * wq->alloc + 1;
 705       HANDLE *new_array =
 706         (HANDLE *) realloc (wq->array, new_alloc * sizeof (HANDLE));
 707       if (new_array == NULL)
 708         /* No more memory.  */
 709         return INVALID_HANDLE_VALUE;
 710       /* Now is a good opportunity to rotate the array so that its contents
 711          starts at offset 0.  */
 712       if (wq->offset > 0)
 713         {
 714           unsigned int old_count = wq->count;
 715           unsigned int old_alloc = wq->alloc;
 716           unsigned int old_offset = wq->offset;
 717           unsigned int i;
 718           if (old_offset + old_count > old_alloc)
 719             {
 720               unsigned int limit = old_offset + old_count - old_alloc;
 721               for (i = 0; i < limit; i++)
 722                 new_array[old_alloc + i] = new_array[i];
 723             }
 724           for (i = 0; i < old_count; i++)
 725             new_array[i] = new_array[old_offset + i];
 726           wq->offset = 0;
 727         }
 728       wq->array = new_array;
 729       wq->alloc = new_alloc;
 730     }
 731   /* Whether the created event is a manual-reset one or an auto-reset one,
 732      does not matter, since we will wait on it only once.  */
 733   event = CreateEvent (NULL, TRUE, FALSE, NULL);
 734   if (event == INVALID_HANDLE_VALUE)
 735     /* No way to allocate an event.  */
 736     return INVALID_HANDLE_VALUE;
 737   index = wq->offset + wq->count;
 738   if (index >= wq->alloc)
 739     index -= wq->alloc;
 740   wq->array[index] = event;
 741   wq->count++;
 742   return event;
 743 }
 744
 745 /* Notifies the first thread from a wait queue and dequeues it.  */
 746 static void
 747 gl_waitqueue_notify_first (gl_waitqueue_t *wq)
 748 {
 749   SetEvent (wq->array[wq->offset + 0]);
 750   wq->offset++;
 751   wq->count--;
 752   if (wq->count == 0 || wq->offset == wq->alloc)
 753     wq->offset = 0;
 754 }
 755
 756 /* Notifies all threads from a wait queue and dequeues them all.  */
 757 static void
 758 gl_waitqueue_notify_all (gl_waitqueue_t *wq)
 759 {
 760   unsigned int i;
 761
 762   for (i = 0; i < wq->count; i++)
 763     {
 764       unsigned int index = wq->offset + i;
 765       if (index >= wq->alloc)
 766         index -= wq->alloc;
 767       SetEvent (wq->array[index]);
 768     }
 769   wq->count = 0;
 770   wq->offset = 0;
 771 }
 772
 773 void
 774 glthread_rwlock_init_func (gl_rwlock_t *lock)
 775 {
 776   InitializeCriticalSection (&lock->lock);
 777   gl_waitqueue_init (&lock->waiting_readers);
 778   gl_waitqueue_init (&lock->waiting_writers);
 779   lock->runcount = 0;
 780   lock->guard.done = 1;
 781 }
 782
 783 int
 784 glthread_rwlock_rdlock_func (gl_rwlock_t *lock)
 785 {
 786   if (!lock->guard.done)
 787     {
 788       if (InterlockedIncrement (&lock->guard.started) == 0)
 789         /* This thread is the first one to need this lock.  Initialize it.  */
 790         glthread_rwlock_init (lock);
 791       else
 792         /* Yield the CPU while waiting for another thread to finish
 793            initializing this lock.  */
 794         while (!lock->guard.done)
 795           Sleep (0);
 796     }
 797   EnterCriticalSection (&lock->lock);
 798   /* Test whether only readers are currently running, and whether the runcount
 799      field will not overflow.  */
 800   if (!(lock->runcount + 1 > 0))
 801     {
 802       /* This thread has to wait for a while.  Enqueue it among the
 803          waiting_readers.  */
 804       HANDLE event = gl_waitqueue_add (&lock->waiting_readers);
 805       if (event != INVALID_HANDLE_VALUE)
 806         {
 807           DWORD result;
 808           LeaveCriticalSection (&lock->lock);
 809           /* Wait until another thread signals this event.  */
 810           result = WaitForSingleObject (event, INFINITE);
 811           if (result == WAIT_FAILED || result == WAIT_TIMEOUT)
 812             abort ();
 813           CloseHandle (event);
 814           /* The thread which signalled the event already did the bookkeeping:
 815              removed us from the waiting_readers, incremented lock->runcount.  */
 816           if (!(lock->runcount > 0))
 817             abort ();
 818           return 0;
 819         }
 820       else
 821         {
 822           /* Allocation failure.  Weird.  */
 823           do
 824             {
 825               LeaveCriticalSection (&lock->lock);
 826               Sleep (1);
 827               EnterCriticalSection (&lock->lock);
 828             }
 829           while (!(lock->runcount + 1 > 0));
 830         }
 831     }
 832   lock->runcount++;
 833   LeaveCriticalSection (&lock->lock);
 834   return 0;
 835 }
 836
 837 int
 838 glthread_rwlock_wrlock_func (gl_rwlock_t *lock)
 839 {
 840   if (!lock->guard.done)
 841     {
 842       if (InterlockedIncrement (&lock->guard.started) == 0)
 843         /* This thread is the first one to need this lock.  Initialize it.  */
 844         glthread_rwlock_init (lock);
 845       else
 846         /* Yield the CPU while waiting for another thread to finish
 847            initializing this lock.  */
 848         while (!lock->guard.done)
 849           Sleep (0);
 850     }
 851   EnterCriticalSection (&lock->lock);
 852   /* Test whether no readers or writers are currently running.  */
 853   if (!(lock->runcount == 0))
 854     {
 855       /* This thread has to wait for a while.  Enqueue it among the
 856          waiting_writers.  */
 857       HANDLE event = gl_waitqueue_add (&lock->waiting_writers);
 858       if (event != INVALID_HANDLE_VALUE)
 859         {
 860           DWORD result;
 861           LeaveCriticalSection (&lock->lock);
 862           /* Wait until another thread signals this event.  */
 863           result = WaitForSingleObject (event, INFINITE);
 864           if (result == WAIT_FAILED || result == WAIT_TIMEOUT)
 865             abort ();
 866           CloseHandle (event);
 867           /* The thread which signalled the event already did the bookkeeping:
 868              removed us from the waiting_writers, set lock->runcount = -1.  */
 869           if (!(lock->runcount == -1))
 870             abort ();
 871           return 0;
 872         }
 873       else
 874         {
 875           /* Allocation failure.  Weird.  */
 876           do
 877             {
 878               LeaveCriticalSection (&lock->lock);
 879               Sleep (1);
 880               EnterCriticalSection (&lock->lock);
 881             }
 882           while (!(lock->runcount == 0));
 883         }
 884     }
 885   lock->runcount--; /* runcount becomes -1 */
 886   LeaveCriticalSection (&lock->lock);
 887   return 0;
 888 }
 889
 890 int
 891 glthread_rwlock_unlock_func (gl_rwlock_t *lock)
 892 {
 893   if (!lock->guard.done)
 894     return EINVAL;
 895   EnterCriticalSection (&lock->lock);
 896   if (lock->runcount < 0)
 897     {
 898       /* Drop a writer lock.  */
 899       if (!(lock->runcount == -1))
 900         abort ();
 901       lock->runcount = 0;
 902     }
 903   else
 904     {
 905       /* Drop a reader lock.  */
 906       if (!(lock->runcount > 0))
 907         {
 908           LeaveCriticalSection (&lock->lock);
 909           return EPERM;
 910         }
 911       lock->runcount--;
 912     }
 913   if (lock->runcount == 0)
 914     {
 915       /* POSIX recommends that "write locks shall take precedence over read
 916          locks", to avoid "writer starvation".  */
 917       if (lock->waiting_writers.count > 0)
 918         {
 919           /* Wake up one of the waiting writers.  */
 920           lock->runcount--;
 921           gl_waitqueue_notify_first (&lock->waiting_writers);
 922         }
 923       else
 924         {
 925           /* Wake up all waiting readers.  */
 926           lock->runcount += lock->waiting_readers.count;
 927           gl_waitqueue_notify_all (&lock->waiting_readers);
 928         }
 929     }
 930   LeaveCriticalSection (&lock->lock);
 931   return 0;
 932 }
 933
 934 int
 935 glthread_rwlock_destroy_func (gl_rwlock_t *lock)
 936 {
 937   if (!lock->guard.done)
 938     return EINVAL;
 939   if (lock->runcount != 0)
 940     return EBUSY;
 941   DeleteCriticalSection (&lock->lock);
 942   if (lock->waiting_readers.array != NULL)
 943     free (lock->waiting_readers.array);
 944   if (lock->waiting_writers.array != NULL)
 945     free (lock->waiting_writers.array);
 946   lock->guard.done = 0;
 947   return 0;
 948 }
 949
 950 /* --------------------- gl_recursive_lock_t datatype --------------------- */
 951
 952 void
 953 glthread_recursive_lock_init_func (gl_recursive_lock_t *lock)
 954 {
 955   lock->owner = 0;
 956   lock->depth = 0;
 957   InitializeCriticalSection (&lock->lock);
 958   lock->guard.done = 1;
 959 }
 960
 961 int
 962 glthread_recursive_lock_lock_func (gl_recursive_lock_t *lock)
 963 {
 964   if (!lock->guard.done)
 965     {
 966       if (InterlockedIncrement (&lock->guard.started) == 0)
 967         /* This thread is the first one to need this lock.  Initialize it.  */
 968         glthread_recursive_lock_init (lock);
 969       else
 970         /* Yield the CPU while waiting for another thread to finish
 971            initializing this lock.  */
 972         while (!lock->guard.done)
 973           Sleep (0);
 974     }
 975   {
 976     DWORD self = GetCurrentThreadId ();
 977     if (lock->owner != self)
 978       {
 979         EnterCriticalSection (&lock->lock);
 980         lock->owner = self;
 981       }
 982     if (++(lock->depth) == 0) /* wraparound? */
 983       {
 984         lock->depth--;
 985         return EAGAIN;
 986       }
 987   }
 988   return 0;
 989 }
 990
 991 int
 992 glthread_recursive_lock_unlock_func (gl_recursive_lock_t *lock)
 993 {
 994   if (lock->owner != GetCurrentThreadId ())
 995     return EPERM;
 996   if (lock->depth == 0)
 997     return EINVAL;
 998   if (--(lock->depth) == 0)
 999     {
1000       lock->owner = 0;
1001       LeaveCriticalSection (&lock->lock);
1002     }
1003   return 0;
1004 }
1005
1006 int
1007 glthread_recursive_lock_destroy_func (gl_recursive_lock_t *lock)
1008 {
1009   if (lock->owner != 0)
1010     return EBUSY;
1011   DeleteCriticalSection (&lock->lock);
1012   lock->guard.done = 0;
1013   return 0;
1014 }
1015
1016 /* -------------------------- gl_once_t datatype -------------------------- */
1017
1018 void
1019 glthread_once_func (gl_once_t *once_control, void (*initfunction) (void))
1020 {
1021   if (once_control->inited <= 0)
1022     {
1023       if (InterlockedIncrement (&once_control->started) == 0)
1024         {
1025           /* This thread is the first one to come to this once_control.  */
1026           InitializeCriticalSection (&once_control->lock);
1027           EnterCriticalSection (&once_control->lock);
1028           once_control->inited = 0;
1029           initfunction ();
1030           once_control->inited = 1;
1031           LeaveCriticalSection (&once_control->lock);
1032         }
1033       else
1034         {
1035           /* Undo last operation.  */
1036           InterlockedDecrement (&once_control->started);
1037           /* Some other thread has already started the initialization.
1038              Yield the CPU while waiting for the other thread to finish
1039              initializing and taking the lock.  */
1040           while (once_control->inited < 0)
1041             Sleep (0);
1042           if (once_control->inited <= 0)
1043             {
1044               /* Take the lock.  This blocks until the other thread has
1045                  finished calling the initfunction.  */
1046               EnterCriticalSection (&once_control->lock);
1047               LeaveCriticalSection (&once_control->lock);
1048               if (!(once_control->inited > 0))
1049                 abort ();
1050             }
1051         }
1052     }
1053 }
1054
1055 #endif
1056
1057 /* ========================================================================= */