mingw/share/gettext/intl/lock.c

   1 /* Locking in multithreaded situations.
   2    Copyright (C) 2005-2008 Free Software Foundation, Inc.
   3
   4    This program is free software; you can redistribute it and/or modify it
   5    under the terms of the GNU Library General Public License as published
   6    by the Free Software Foundation; either version 2, 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 GNU
  12    Library General Public License for more details.
  13
  14    You should have received a copy of the GNU Library General Public
  15    License along with this program; if not, write to the Free Software
  16    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
  17    USA.  */
  18
  19 /* Written by Bruno Haible <bruno@clisp.org>, 2005.
  20    Based on GCC's gthr-posix.h, gthr-posix95.h, gthr-solaris.h,
  21    gthr-win32.h.  */
  22
  23 #include <config.h>
  24
  25 #include "lock.h"
  26
  27 /* ========================================================================= */
  28
  29 #if USE_POSIX_THREADS
  30
  31 /* -------------------------- gl_lock_t datatype -------------------------- */
  32
  33 /* ------------------------- gl_rwlock_t datatype ------------------------- */
  34
  35 # if HAVE_PTHREAD_RWLOCK
  36
  37 #  if !defined PTHREAD_RWLOCK_INITIALIZER
  38
  39 int
  40 glthread_rwlock_init_multithreaded (gl_rwlock_t *lock)
  41 {
  42   int err;
  43
  44   err = pthread_rwlock_init (&lock->rwlock, NULL);
  45   if (err != 0)
  46     return err;
  47   lock->initialized = 1;
  48   return 0;
  49 }
  50
  51 int
  52 glthread_rwlock_rdlock_multithreaded (gl_rwlock_t *lock)
  53 {
  54   if (!lock->initialized)
  55     {
  56       int err;
  57
  58       err = pthread_mutex_lock (&lock->guard);
  59       if (err != 0)
  60         return err;
  61       if (!lock->initialized)
  62         {
  63           err = glthread_rwlock_init_multithreaded (lock);
  64           if (err != 0)
  65             {
  66               pthread_mutex_unlock (&lock->guard);
  67               return err;
  68             }
  69         }
  70       err = pthread_mutex_unlock (&lock->guard);
  71       if (err != 0)
  72         return err;
  73     }
  74   return pthread_rwlock_rdlock (&lock->rwlock);
  75 }
  76
  77 int
  78 glthread_rwlock_wrlock_multithreaded (gl_rwlock_t *lock)
  79 {
  80   if (!lock->initialized)
  81     {
  82       int err;
  83
  84       err = pthread_mutex_lock (&lock->guard);
  85       if (err != 0)
  86         return err;
  87       if (!lock->initialized)
  88         {
  89           err = glthread_rwlock_init_multithreaded (lock);
  90           if (err != 0)
  91             {
  92               pthread_mutex_unlock (&lock->guard);
  93               return err;
  94             }
  95         }
  96       err = pthread_mutex_unlock (&lock->guard);
  97       if (err != 0)
  98         return err;
  99     }
 100   return pthread_rwlock_wrlock (&lock->rwlock);
 101 }
 102
 103 int
 104 glthread_rwlock_unlock_multithreaded (gl_rwlock_t *lock)
 105 {
 106   if (!lock->initialized)
 107     return EINVAL;
 108   return pthread_rwlock_unlock (&lock->rwlock);
 109 }
 110
 111 int
 112 glthread_rwlock_destroy_multithreaded (gl_rwlock_t *lock)
 113 {
 114   int err;
 115
 116   if (!lock->initialized)
 117     return EINVAL;
 118   err = pthread_rwlock_destroy (&lock->rwlock);
 119   if (err != 0)
 120     return err;
 121   lock->initialized = 0;
 122   return 0;
 123 }
 124
 125 #  endif
 126
 127 # else
 128
 129 int
 130 glthread_rwlock_init_multithreaded (gl_rwlock_t *lock)
 131 {
 132   int err;
 133
 134   err = pthread_mutex_init (&lock->lock, NULL);
 135   if (err != 0)
 136     return err;
 137   err = pthread_cond_init (&lock->waiting_readers, NULL);
 138   if (err != 0)
 139     return err;
 140   err = pthread_cond_init (&lock->waiting_writers, NULL);
 141   if (err != 0)
 142     return err;
 143   lock->waiting_writers_count = 0;
 144   lock->runcount = 0;
 145   return 0;
 146 }
 147
 148 int
 149 glthread_rwlock_rdlock_multithreaded (gl_rwlock_t *lock)
 150 {
 151   int err;
 152
 153   err = pthread_mutex_lock (&lock->lock);
 154   if (err != 0)
 155     return err;
 156   /* Test whether only readers are currently running, and whether the runcount
 157      field will not overflow.  */
 158   /* POSIX says: "It is implementation-defined whether the calling thread
 159      acquires the lock when a writer does not hold the lock and there are
 160      writers blocked on the lock."  Let's say, no: give the writers a higher
 161      priority.  */
 162   while (!(lock->runcount + 1 > 0 && lock->waiting_writers_count == 0))
 163     {
 164       /* This thread has to wait for a while.  Enqueue it among the
 165          waiting_readers.  */
 166       err = pthread_cond_wait (&lock->waiting_readers, &lock->lock);
 167       if (err != 0)
 168         {
 169           pthread_mutex_unlock (&lock->lock);
 170           return err;
 171         }
 172     }
 173   lock->runcount++;
 174   return pthread_mutex_unlock (&lock->lock);
 175 }
 176
 177 int
 178 glthread_rwlock_wrlock_multithreaded (gl_rwlock_t *lock)
 179 {
 180   int err;
 181
 182   err = pthread_mutex_lock (&lock->lock);
 183   if (err != 0)
 184     return err;
 185   /* Test whether no readers or writers are currently running.  */
 186   while (!(lock->runcount == 0))
 187     {
 188       /* This thread has to wait for a while.  Enqueue it among the
 189          waiting_writers.  */
 190       lock->waiting_writers_count++;
 191       err = pthread_cond_wait (&lock->waiting_writers, &lock->lock);
 192       if (err != 0)
 193         {
 194           lock->waiting_writers_count--;
 195           pthread_mutex_unlock (&lock->lock);
 196           return err;
 197         }
 198       lock->waiting_writers_count--;
 199     }
 200   lock->runcount--; /* runcount becomes -1 */
 201   return pthread_mutex_unlock (&lock->lock);
 202 }
 203
 204 int
 205 glthread_rwlock_unlock_multithreaded (gl_rwlock_t *lock)
 206 {
 207   int err;
 208
 209   err = pthread_mutex_lock (&lock->lock);
 210   if (err != 0)
 211     return err;
 212   if (lock->runcount < 0)
 213     {
 214       /* Drop a writer lock.  */
 215       if (!(lock->runcount == -1))
 216         {
 217           pthread_mutex_unlock (&lock->lock);
 218           return EINVAL;
 219         }
 220       lock->runcount = 0;
 221     }
 222   else
 223     {
 224       /* Drop a reader lock.  */
 225       if (!(lock->runcount > 0))
 226         {
 227           pthread_mutex_unlock (&lock->lock);
 228           return EINVAL;
 229         }
 230       lock->runcount--;
 231     }
 232   if (lock->runcount == 0)
 233     {
 234       /* POSIX recommends that "write locks shall take precedence over read
 235          locks", to avoid "writer starvation".  */
 236       if (lock->waiting_writers_count > 0)
 237         {
 238           /* Wake up one of the waiting writers.  */
 239           err = pthread_cond_signal (&lock->waiting_writers);
 240           if (err != 0)
 241             {
 242               pthread_mutex_unlock (&lock->lock);
 243               return err;
 244             }
 245         }
 246       else
 247         {
 248           /* Wake up all waiting readers.  */
 249           err = pthread_cond_broadcast (&lock->waiting_readers);
 250           if (err != 0)
 251             {
 252               pthread_mutex_unlock (&lock->lock);
 253               return err;
 254             }
 255         }
 256     }
 257   return pthread_mutex_unlock (&lock->lock);
 258 }
 259
 260 int
 261 glthread_rwlock_destroy_multithreaded (gl_rwlock_t *lock)
 262 {
 263   int err;
 264
 265   err = pthread_mutex_destroy (&lock->lock);
 266   if (err != 0)
 267     return err;
 268   err = pthread_cond_destroy (&lock->waiting_readers);
 269   if (err != 0)
 270     return err;
 271   err = pthread_cond_destroy (&lock->waiting_writers);
 272   if (err != 0)
 273     return err;
 274   return 0;
 275 }
 276
 277 # endif
 278
 279 /* --------------------- gl_recursive_lock_t datatype --------------------- */
 280
 281 # if HAVE_PTHREAD_MUTEX_RECURSIVE
 282
 283 #  if defined PTHREAD_RECURSIVE_MUTEX_INITIALIZER || defined PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP
 284
 285 int
 286 glthread_recursive_lock_init_multithreaded (gl_recursive_lock_t *lock)
 287 {
 288   pthread_mutexattr_t attributes;
 289   int err;
 290
 291   err = pthread_mutexattr_init (&attributes);
 292   if (err != 0)
 293     return err;
 294   err = pthread_mutexattr_settype (&attributes, PTHREAD_MUTEX_RECURSIVE);
 295   if (err != 0)
 296     {
 297       pthread_mutexattr_destroy (&attributes);
 298       return err;
 299     }
 300   err = pthread_mutex_init (lock, &attributes);
 301   if (err != 0)
 302     {
 303       pthread_mutexattr_destroy (&attributes);
 304       return err;
 305     }
 306   err = pthread_mutexattr_destroy (&attributes);
 307   if (err != 0)
 308     return err;
 309   return 0;
 310 }
 311
 312 #  else
 313
 314 int
 315 glthread_recursive_lock_init_multithreaded (gl_recursive_lock_t *lock)
 316 {
 317   pthread_mutexattr_t attributes;
 318   int err;
 319
 320   err = pthread_mutexattr_init (&attributes);
 321   if (err != 0)
 322     return err;
 323   err = pthread_mutexattr_settype (&attributes, PTHREAD_MUTEX_RECURSIVE);
 324   if (err != 0)
 325     {
 326       pthread_mutexattr_destroy (&attributes);
 327       return err;
 328     }
 329   err = pthread_mutex_init (&lock->recmutex, &attributes);
 330   if (err != 0)
 331     {
 332       pthread_mutexattr_destroy (&attributes);
 333       return err;
 334     }
 335   err = pthread_mutexattr_destroy (&attributes);
 336   if (err != 0)
 337     return err;
 338   lock->initialized = 1;
 339   return 0;
 340 }
 341
 342 int
 343 glthread_recursive_lock_lock_multithreaded (gl_recursive_lock_t *lock)
 344 {
 345   if (!lock->initialized)
 346     {
 347       int err;
 348
 349       err = pthread_mutex_lock (&lock->guard);
 350       if (err != 0)
 351         return err;
 352       if (!lock->initialized)
 353         {
 354           err = glthread_recursive_lock_init_multithreaded (lock);
 355           if (err != 0)
 356             {
 357               pthread_mutex_unlock (&lock->guard);
 358               return err;
 359             }
 360         }
 361       err = pthread_mutex_unlock (&lock->guard);
 362       if (err != 0)
 363         return err;
 364     }
 365   return pthread_mutex_lock (&lock->recmutex);
 366 }
 367
 368 int
 369 glthread_recursive_lock_unlock_multithreaded (gl_recursive_lock_t *lock)
 370 {
 371   if (!lock->initialized)
 372     return EINVAL;
 373   return pthread_mutex_unlock (&lock->recmutex);
 374 }
 375
 376 int
 377 glthread_recursive_lock_destroy_multithreaded (gl_recursive_lock_t *lock)
 378 {
 379   int err;
 380
 381   if (!lock->initialized)
 382     return EINVAL;
 383   err = pthread_mutex_destroy (&lock->recmutex);
 384   if (err != 0)
 385     return err;
 386   lock->initialized = 0;
 387   return 0;
 388 }
 389
 390 #  endif
 391
 392 # else
 393
 394 int
 395 glthread_recursive_lock_init_multithreaded (gl_recursive_lock_t *lock)
 396 {
 397   int err;
 398
 399   err = pthread_mutex_init (&lock->mutex, NULL);
 400   if (err != 0)
 401     return err;
 402   lock->owner = (pthread_t) 0;
 403   lock->depth = 0;
 404   return 0;
 405 }
 406
 407 int
 408 glthread_recursive_lock_lock_multithreaded (gl_recursive_lock_t *lock)
 409 {
 410   pthread_t self = pthread_self ();
 411   if (lock->owner != self)
 412     {
 413       int err;
 414
 415       err = pthread_mutex_lock (&lock->mutex);
 416       if (err != 0)
 417         return err;
 418       lock->owner = self;
 419     }
 420   if (++(lock->depth) == 0) /* wraparound? */
 421     {
 422       lock->depth--;
 423       return EAGAIN;
 424     }
 425   return 0;
 426 }
 427
 428 int
 429 glthread_recursive_lock_unlock_multithreaded (gl_recursive_lock_t *lock)
 430 {
 431   if (lock->owner != pthread_self ())
 432     return EPERM;
 433   if (lock->depth == 0)
 434     return EINVAL;
 435   if (--(lock->depth) == 0)
 436     {
 437       lock->owner = (pthread_t) 0;
 438       return pthread_mutex_unlock (&lock->mutex);
 439     }
 440   else
 441     return 0;
 442 }
 443
 444 int
 445 glthread_recursive_lock_destroy_multithreaded (gl_recursive_lock_t *lock)
 446 {
 447   if (lock->owner != (pthread_t) 0)
 448     return EBUSY;
 449   return pthread_mutex_destroy (&lock->mutex);
 450 }
 451
 452 # endif
 453
 454 /* -------------------------- gl_once_t datatype -------------------------- */
 455
 456 static const pthread_once_t fresh_once = PTHREAD_ONCE_INIT;
 457
 458 int
 459 glthread_once_singlethreaded (pthread_once_t *once_control)
 460 {
 461   /* We don't know whether pthread_once_t is an integer type, a floating-point
 462      type, a pointer type, or a structure type.  */
 463   char *firstbyte = (char *)once_control;
 464   if (*firstbyte == *(const char *)&fresh_once)
 465     {
 466       /* First time use of once_control.  Invert the first byte.  */
 467       *firstbyte = ~ *(const char *)&fresh_once;
 468       return 1;
 469     }
 470   else
 471     return 0;
 472 }
 473
 474 #endif
 475
 476 /* ========================================================================= */
 477
 478 #if USE_PTH_THREADS
 479
 480 /* Use the GNU Pth threads library.  */
 481
 482 /* -------------------------- gl_lock_t datatype -------------------------- */
 483
 484 /* ------------------------- gl_rwlock_t datatype ------------------------- */
 485
 486 /* --------------------- gl_recursive_lock_t datatype --------------------- */
 487
 488 /* -------------------------- gl_once_t datatype -------------------------- */
 489
 490 static void
 491 glthread_once_call (void *arg)
 492 {
 493   void (**gl_once_temp_addr) (void) = (void (**) (void)) arg;
 494   void (*initfunction) (void) = *gl_once_temp_addr;
 495   initfunction ();
 496 }
 497
 498 int
 499 glthread_once_multithreaded (pth_once_t *once_control, void (*initfunction) (void))
 500 {
 501   void (*temp) (void) = initfunction;
 502   return (!pth_once (once_control, glthread_once_call, &temp) ? errno : 0);
 503 }
 504
 505 int
 506 glthread_once_singlethreaded (pth_once_t *once_control)
 507 {
 508   /* We know that pth_once_t is an integer type.  */
 509   if (*once_control == PTH_ONCE_INIT)
 510     {
 511       /* First time use of once_control.  Invert the marker.  */
 512       *once_control = ~ PTH_ONCE_INIT;
 513       return 1;
 514     }
 515   else
 516     return 0;
 517 }
 518
 519 #endif
 520
 521 /* ========================================================================= */
 522
 523 #if USE_SOLARIS_THREADS
 524
 525 /* Use the old Solaris threads library.  */
 526
 527 /* -------------------------- gl_lock_t datatype -------------------------- */
 528
 529 /* ------------------------- gl_rwlock_t datatype ------------------------- */
 530
 531 /* --------------------- gl_recursive_lock_t datatype --------------------- */
 532
 533 int
 534 glthread_recursive_lock_init_multithreaded (gl_recursive_lock_t *lock)
 535 {
 536   int err;
 537
 538   err = mutex_init (&lock->mutex, USYNC_THREAD, NULL);
 539   if (err != 0)
 540     return err;
 541   lock->owner = (thread_t) 0;
 542   lock->depth = 0;
 543   return 0;
 544 }
 545
 546 int
 547 glthread_recursive_lock_lock_multithreaded (gl_recursive_lock_t *lock)
 548 {
 549   thread_t self = thr_self ();
 550   if (lock->owner != self)
 551     {
 552       int err;
 553
 554       err = mutex_lock (&lock->mutex);
 555       if (err != 0)
 556         return err;
 557       lock->owner = self;
 558     }
 559   if (++(lock->depth) == 0) /* wraparound? */
 560     {
 561       lock->depth--;
 562       return EAGAIN;
 563     }
 564   return 0;
 565 }
 566
 567 int
 568 glthread_recursive_lock_unlock_multithreaded (gl_recursive_lock_t *lock)
 569 {
 570   if (lock->owner != thr_self ())
 571     return EPERM;
 572   if (lock->depth == 0)
 573     return EINVAL;
 574   if (--(lock->depth) == 0)
 575     {
 576       lock->owner = (thread_t) 0;
 577       return mutex_unlock (&lock->mutex);
 578     }
 579   else
 580     return 0;
 581 }
 582
 583 int
 584 glthread_recursive_lock_destroy_multithreaded (gl_recursive_lock_t *lock)
 585 {
 586   if (lock->owner != (thread_t) 0)
 587     return EBUSY;
 588   return mutex_destroy (&lock->mutex);
 589 }
 590
 591 /* -------------------------- gl_once_t datatype -------------------------- */
 592
 593 int
 594 glthread_once_multithreaded (gl_once_t *once_control, void (*initfunction) (void))
 595 {
 596   if (!once_control->inited)
 597     {
 598       int err;
 599
 600       /* Use the mutex to guarantee that if another thread is already calling
 601          the initfunction, this thread waits until it's finished.  */
 602       err = mutex_lock (&once_control->mutex);
 603       if (err != 0)
 604         return err;
 605       if (!once_control->inited)
 606         {
 607           once_control->inited = 1;
 608           initfunction ();
 609         }
 610       return mutex_unlock (&once_control->mutex);
 611     }
 612   else
 613     return 0;
 614 }
 615
 616 int
 617 glthread_once_singlethreaded (gl_once_t *once_control)
 618 {
 619   /* We know that gl_once_t contains an integer type.  */
 620   if (!once_control->inited)
 621     {
 622       /* First time use of once_control.  Invert the marker.  */
 623       once_control->inited = ~ 0;
 624       return 1;
 625     }
 626   else
 627     return 0;
 628 }
 629
 630 #endif
 631
 632 /* ========================================================================= */
 633
 634 #if USE_WIN32_THREADS
 635
 636 /* -------------------------- gl_lock_t datatype -------------------------- */
 637
 638 void
 639 glthread_lock_init_func (gl_lock_t *lock)
 640 {
 641   InitializeCriticalSection (&lock->lock);
 642   lock->guard.done = 1;
 643 }
 644
 645 int
 646 glthread_lock_lock_func (gl_lock_t *lock)
 647 {
 648   if (!lock->guard.done)
 649     {
 650       if (InterlockedIncrement (&lock->guard.started) == 0)
 651         /* This thread is the first one to need this lock.  Initialize it.  */
 652         glthread_lock_init (lock);
 653       else
 654         /* Yield the CPU while waiting for another thread to finish
 655            initializing this lock.  */
 656         while (!lock->guard.done)
 657           Sleep (0);
 658     }
 659   EnterCriticalSection (&lock->lock);
 660   return 0;
 661 }
 662
 663 int
 664 glthread_lock_unlock_func (gl_lock_t *lock)
 665 {
 666   if (!lock->guard.done)
 667     return EINVAL;
 668   LeaveCriticalSection (&lock->lock);
 669   return 0;
 670 }
 671
 672 int
 673 glthread_lock_destroy_func (gl_lock_t *lock)
 674 {
 675   if (!lock->guard.done)
 676     return EINVAL;
 677   DeleteCriticalSection (&lock->lock);
 678   lock->guard.done = 0;
 679   return 0;
 680 }
 681
 682 /* ------------------------- gl_rwlock_t datatype ------------------------- */
 683
 684 /* In this file, the waitqueues are implemented as circular arrays.  */
 685 #define gl_waitqueue_t gl_carray_waitqueue_t
 686
 687 static inline void
 688 gl_waitqueue_init (gl_waitqueue_t *wq)
 689 {
 690   wq->array = NULL;
 691   wq->count = 0;
 692   wq->alloc = 0;
 693   wq->offset = 0;
 694 }
 695
 696 /* Enqueues the current thread, represented by an event, in a wait queue.
 697    Returns INVALID_HANDLE_VALUE if an allocation failure occurs.  */
 698 static HANDLE
 699 gl_waitqueue_add (gl_waitqueue_t *wq)
 700 {
 701   HANDLE event;
 702   unsigned int index;
 703
 704   if (wq->count == wq->alloc)
 705     {
 706       unsigned int new_alloc = 2 * wq->alloc + 1;
 707       HANDLE *new_array =
 708         (HANDLE *) realloc (wq->array, new_alloc * sizeof (HANDLE));
 709       if (new_array == NULL)
 710         /* No more memory.  */
 711         return INVALID_HANDLE_VALUE;
 712       /* Now is a good opportunity to rotate the array so that its contents
 713          starts at offset 0.  */
 714       if (wq->offset > 0)
 715         {
 716           unsigned int old_count = wq->count;
 717           unsigned int old_alloc = wq->alloc;
 718           unsigned int old_offset = wq->offset;
 719           unsigned int i;
 720           if (old_offset + old_count > old_alloc)
 721             {
 722               unsigned int limit = old_offset + old_count - old_alloc;
 723               for (i = 0; i < limit; i++)
 724                 new_array[old_alloc + i] = new_array[i];
 725             }
 726           for (i = 0; i < old_count; i++)
 727             new_array[i] = new_array[old_offset + i];
 728           wq->offset = 0;
 729         }
 730       wq->array = new_array;
 731       wq->alloc = new_alloc;
 732     }
 733   /* Whether the created event is a manual-reset one or an auto-reset one,
 734      does not matter, since we will wait on it only once.  */
 735   event = CreateEvent (NULL, TRUE, FALSE, NULL);
 736   if (event == INVALID_HANDLE_VALUE)
 737     /* No way to allocate an event.  */
 738     return INVALID_HANDLE_VALUE;
 739   index = wq->offset + wq->count;
 740   if (index >= wq->alloc)
 741     index -= wq->alloc;
 742   wq->array[index] = event;
 743   wq->count++;
 744   return event;
 745 }
 746
 747 /* Notifies the first thread from a wait queue and dequeues it.  */
 748 static inline void
 749 gl_waitqueue_notify_first (gl_waitqueue_t *wq)
 750 {
 751   SetEvent (wq->array[wq->offset + 0]);
 752   wq->offset++;
 753   wq->count--;
 754   if (wq->count == 0 || wq->offset == wq->alloc)
 755     wq->offset = 0;
 756 }
 757
 758 /* Notifies all threads from a wait queue and dequeues them all.  */
 759 static inline void
 760 gl_waitqueue_notify_all (gl_waitqueue_t *wq)
 761 {
 762   unsigned int i;
 763
 764   for (i = 0; i < wq->count; i++)
 765     {
 766       unsigned int index = wq->offset + i;
 767       if (index >= wq->alloc)
 768         index -= wq->alloc;
 769       SetEvent (wq->array[index]);
 770     }
 771   wq->count = 0;
 772   wq->offset = 0;
 773 }
 774
 775 void
 776 glthread_rwlock_init_func (gl_rwlock_t *lock)
 777 {
 778   InitializeCriticalSection (&lock->lock);
 779   gl_waitqueue_init (&lock->waiting_readers);
 780   gl_waitqueue_init (&lock->waiting_writers);
 781   lock->runcount = 0;
 782   lock->guard.done = 1;
 783 }
 784
 785 int
 786 glthread_rwlock_rdlock_func (gl_rwlock_t *lock)
 787 {
 788   if (!lock->guard.done)
 789     {
 790       if (InterlockedIncrement (&lock->guard.started) == 0)
 791         /* This thread is the first one to need this lock.  Initialize it.  */
 792         glthread_rwlock_init (lock);
 793       else
 794         /* Yield the CPU while waiting for another thread to finish
 795            initializing this lock.  */
 796         while (!lock->guard.done)
 797           Sleep (0);
 798     }
 799   EnterCriticalSection (&lock->lock);
 800   /* Test whether only readers are currently running, and whether the runcount
 801      field will not overflow.  */
 802   if (!(lock->runcount + 1 > 0))
 803     {
 804       /* This thread has to wait for a while.  Enqueue it among the
 805          waiting_readers.  */
 806       HANDLE event = gl_waitqueue_add (&lock->waiting_readers);
 807       if (event != INVALID_HANDLE_VALUE)
 808         {
 809           DWORD result;
 810           LeaveCriticalSection (&lock->lock);
 811           /* Wait until another thread signals this event.  */
 812           result = WaitForSingleObject (event, INFINITE);
 813           if (result == WAIT_FAILED || result == WAIT_TIMEOUT)
 814             abort ();
 815           CloseHandle (event);
 816           /* The thread which signalled the event already did the bookkeeping:
 817              removed us from the waiting_readers, incremented lock->runcount.  */
 818           if (!(lock->runcount > 0))
 819             abort ();
 820           return 0;
 821         }
 822       else
 823         {
 824           /* Allocation failure.  Weird.  */
 825           do
 826             {
 827               LeaveCriticalSection (&lock->lock);
 828               Sleep (1);
 829               EnterCriticalSection (&lock->lock);
 830             }
 831           while (!(lock->runcount + 1 > 0));
 832         }
 833     }
 834   lock->runcount++;
 835   LeaveCriticalSection (&lock->lock);
 836   return 0;
 837 }
 838
 839 int
 840 glthread_rwlock_wrlock_func (gl_rwlock_t *lock)
 841 {
 842   if (!lock->guard.done)
 843     {
 844       if (InterlockedIncrement (&lock->guard.started) == 0)
 845         /* This thread is the first one to need this lock.  Initialize it.  */
 846         glthread_rwlock_init (lock);
 847       else
 848         /* Yield the CPU while waiting for another thread to finish
 849            initializing this lock.  */
 850         while (!lock->guard.done)
 851           Sleep (0);
 852     }
 853   EnterCriticalSection (&lock->lock);
 854   /* Test whether no readers or writers are currently running.  */
 855   if (!(lock->runcount == 0))
 856     {
 857       /* This thread has to wait for a while.  Enqueue it among the
 858          waiting_writers.  */
 859       HANDLE event = gl_waitqueue_add (&lock->waiting_writers);
 860       if (event != INVALID_HANDLE_VALUE)
 861         {
 862           DWORD result;
 863           LeaveCriticalSection (&lock->lock);
 864           /* Wait until another thread signals this event.  */
 865           result = WaitForSingleObject (event, INFINITE);
 866           if (result == WAIT_FAILED || result == WAIT_TIMEOUT)
 867             abort ();
 868           CloseHandle (event);
 869           /* The thread which signalled the event already did the bookkeeping:
 870              removed us from the waiting_writers, set lock->runcount = -1.  */
 871           if (!(lock->runcount == -1))
 872             abort ();
 873           return 0;
 874         }
 875       else
 876         {
 877           /* Allocation failure.  Weird.  */
 878           do
 879             {
 880               LeaveCriticalSection (&lock->lock);
 881               Sleep (1);
 882               EnterCriticalSection (&lock->lock);
 883             }
 884           while (!(lock->runcount == 0));
 885         }
 886     }
 887   lock->runcount--; /* runcount becomes -1 */
 888   LeaveCriticalSection (&lock->lock);
 889   return 0;
 890 }
 891
 892 int
 893 glthread_rwlock_unlock_func (gl_rwlock_t *lock)
 894 {
 895   if (!lock->guard.done)
 896     return EINVAL;
 897   EnterCriticalSection (&lock->lock);
 898   if (lock->runcount < 0)
 899     {
 900       /* Drop a writer lock.  */
 901       if (!(lock->runcount == -1))
 902         abort ();
 903       lock->runcount = 0;
 904     }
 905   else
 906     {
 907       /* Drop a reader lock.  */
 908       if (!(lock->runcount > 0))
 909         {
 910           LeaveCriticalSection (&lock->lock);
 911           return EPERM;
 912         }
 913       lock->runcount--;
 914     }
 915   if (lock->runcount == 0)
 916     {
 917       /* POSIX recommends that "write locks shall take precedence over read
 918          locks", to avoid "writer starvation".  */
 919       if (lock->waiting_writers.count > 0)
 920         {
 921           /* Wake up one of the waiting writers.  */
 922           lock->runcount--;
 923           gl_waitqueue_notify_first (&lock->waiting_writers);
 924         }
 925       else
 926         {
 927           /* Wake up all waiting readers.  */
 928           lock->runcount += lock->waiting_readers.count;
 929           gl_waitqueue_notify_all (&lock->waiting_readers);
 930         }
 931     }
 932   LeaveCriticalSection (&lock->lock);
 933   return 0;
 934 }
 935
 936 int
 937 glthread_rwlock_destroy_func (gl_rwlock_t *lock)
 938 {
 939   if (!lock->guard.done)
 940     return EINVAL;
 941   if (lock->runcount != 0)
 942     return EBUSY;
 943   DeleteCriticalSection (&lock->lock);
 944   if (lock->waiting_readers.array != NULL)
 945     free (lock->waiting_readers.array);
 946   if (lock->waiting_writers.array != NULL)
 947     free (lock->waiting_writers.array);
 948   lock->guard.done = 0;
 949   return 0;
 950 }
 951
 952 /* --------------------- gl_recursive_lock_t datatype --------------------- */
 953
 954 void
 955 glthread_recursive_lock_init_func (gl_recursive_lock_t *lock)
 956 {
 957   lock->owner = 0;
 958   lock->depth = 0;
 959   InitializeCriticalSection (&lock->lock);
 960   lock->guard.done = 1;
 961 }
 962
 963 int
 964 glthread_recursive_lock_lock_func (gl_recursive_lock_t *lock)
 965 {
 966   if (!lock->guard.done)
 967     {
 968       if (InterlockedIncrement (&lock->guard.started) == 0)
 969         /* This thread is the first one to need this lock.  Initialize it.  */
 970         glthread_recursive_lock_init (lock);
 971       else
 972         /* Yield the CPU while waiting for another thread to finish
 973            initializing this lock.  */
 974         while (!lock->guard.done)
 975           Sleep (0);
 976     }
 977   {
 978     DWORD self = GetCurrentThreadId ();
 979     if (lock->owner != self)
 980       {
 981         EnterCriticalSection (&lock->lock);
 982         lock->owner = self;
 983       }
 984     if (++(lock->depth) == 0) /* wraparound? */
 985       {
 986         lock->depth--;
 987         return EAGAIN;
 988       }
 989   }
 990   return 0;
 991 }
 992
 993 int
 994 glthread_recursive_lock_unlock_func (gl_recursive_lock_t *lock)
 995 {
 996   if (lock->owner != GetCurrentThreadId ())
 997     return EPERM;
 998   if (lock->depth == 0)
 999     return EINVAL;
1000   if (--(lock->depth) == 0)
1001     {
1002       lock->owner = 0;
1003       LeaveCriticalSection (&lock->lock);
1004     }
1005   return 0;
1006 }
1007
1008 int
1009 glthread_recursive_lock_destroy_func (gl_recursive_lock_t *lock)
1010 {
1011   if (lock->owner != 0)
1012     return EBUSY;
1013   DeleteCriticalSection (&lock->lock);
1014   lock->guard.done = 0;
1015   return 0;
1016 }
1017
1018 /* -------------------------- gl_once_t datatype -------------------------- */
1019
1020 void
1021 glthread_once_func (gl_once_t *once_control, void (*initfunction) (void))
1022 {
1023   if (once_control->inited <= 0)
1024     {
1025       if (InterlockedIncrement (&once_control->started) == 0)
1026         {
1027           /* This thread is the first one to come to this once_control.  */
1028           InitializeCriticalSection (&once_control->lock);
1029           EnterCriticalSection (&once_control->lock);
1030           once_control->inited = 0;
1031           initfunction ();
1032           once_control->inited = 1;
1033           LeaveCriticalSection (&once_control->lock);
1034         }
1035       else
1036         {
1037           /* Undo last operation.  */
1038           InterlockedDecrement (&once_control->started);
1039           /* Some other thread has already started the initialization.
1040              Yield the CPU while waiting for the other thread to finish
1041              initializing and taking the lock.  */
1042           while (once_control->inited < 0)
1043             Sleep (0);
1044           if (once_control->inited <= 0)
1045             {
1046               /* Take the lock.  This blocks until the other thread has
1047                  finished calling the initfunction.  */
1048               EnterCriticalSection (&once_control->lock);
1049               LeaveCriticalSection (&once_control->lock);
1050               if (!(once_control->inited > 0))
1051                 abort ();
1052             }
1053         }
1054     }
1055 }
1056
1057 #endif
1058
1059 /* ========================================================================= */