1 files changed, 1221 insertions, 0 deletions

diff --git a/gl/lib/glthread/lock.c b/gl/lib/glthread/lock.c
new file mode 100644
index 0000000..a4498cb
--- /dev/null
+++ b/gl/lib/glthread/lock.c
@@ -0,0 +1,1221 @@
+/* Locking in multithreaded situations.
+   Copyright (C) 2005-2019 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3, or (at your option)
+   any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, see <https://www.gnu.org/licenses/>.  */
+
+/* Written by Bruno Haible <bruno@clisp.org>, 2005.
+   Based on GCC's gthr-posix.h, gthr-posix95.h, gthr-solaris.h,
+   gthr-win32.h.  */
+
+#include <config.h>
+
+#include "glthread/lock.h"
+
+/* ========================================================================= */
+
+#if USE_POSIX_THREADS
+
+/* -------------------------- gl_lock_t datatype -------------------------- */
+
+/* ------------------------- gl_rwlock_t datatype ------------------------- */
+
+# if HAVE_PTHREAD_RWLOCK && (HAVE_PTHREAD_RWLOCK_RDLOCK_PREFER_WRITER || (defined PTHREAD_RWLOCK_WRITER_NONRECURSIVE_INITIALIZER_NP && (__GNU_LIBRARY__ > 1)))
+
+#  ifdef PTHREAD_RWLOCK_INITIALIZER
+
+#   if !HAVE_PTHREAD_RWLOCK_RDLOCK_PREFER_WRITER
+     /* glibc with bug https://sourceware.org/bugzilla/show_bug.cgi?id=13701 */
+
+int
+glthread_rwlock_init_for_glibc (pthread_rwlock_t *lock)
+{
+  pthread_rwlockattr_t attributes;
+  int err;
+
+  err = pthread_rwlockattr_init (&attributes);
+  if (err != 0)
+    return err;
+  /* Note: PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP is the only value that
+     causes the writer to be preferred. PTHREAD_RWLOCK_PREFER_WRITER_NP does not
+     do this; see
+     http://man7.org/linux/man-pages/man3/pthread_rwlockattr_setkind_np.3.html */
+  err = pthread_rwlockattr_setkind_np (&attributes,
+                                       PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP);
+  if (err == 0)
+    err = pthread_rwlock_init(lock, &attributes);
+  /* pthread_rwlockattr_destroy always returns 0.  It cannot influence the
+     return value.  */
+  pthread_rwlockattr_destroy (&attributes);
+  return err;
+}
+
+#   endif
+#  else
+
+int
+glthread_rwlock_init_multithreaded (gl_rwlock_t *lock)
+{
+  int err;
+
+  err = pthread_rwlock_init (&lock->rwlock, NULL);
+  if (err != 0)
+    return err;
+  lock->initialized = 1;
+  return 0;
+}
+
+int
+glthread_rwlock_rdlock_multithreaded (gl_rwlock_t *lock)
+{
+  if (!lock->initialized)
+    {
+      int err;
+
+      err = pthread_mutex_lock (&lock->guard);
+      if (err != 0)
+        return err;
+      if (!lock->initialized)
+        {
+          err = glthread_rwlock_init_multithreaded (lock);
+          if (err != 0)
+            {
+              pthread_mutex_unlock (&lock->guard);
+              return err;
+            }
+        }
+      err = pthread_mutex_unlock (&lock->guard);
+      if (err != 0)
+        return err;
+    }
+  return pthread_rwlock_rdlock (&lock->rwlock);
+}
+
+int
+glthread_rwlock_wrlock_multithreaded (gl_rwlock_t *lock)
+{
+  if (!lock->initialized)
+    {
+      int err;
+
+      err = pthread_mutex_lock (&lock->guard);
+      if (err != 0)
+        return err;
+      if (!lock->initialized)
+        {
+          err = glthread_rwlock_init_multithreaded (lock);
+          if (err != 0)
+            {
+              pthread_mutex_unlock (&lock->guard);
+              return err;
+            }
+        }
+      err = pthread_mutex_unlock (&lock->guard);
+      if (err != 0)
+        return err;
+    }
+  return pthread_rwlock_wrlock (&lock->rwlock);
+}
+
+int
+glthread_rwlock_unlock_multithreaded (gl_rwlock_t *lock)
+{
+  if (!lock->initialized)
+    return EINVAL;
+  return pthread_rwlock_unlock (&lock->rwlock);
+}
+
+int
+glthread_rwlock_destroy_multithreaded (gl_rwlock_t *lock)
+{
+  int err;
+
+  if (!lock->initialized)
+    return EINVAL;
+  err = pthread_rwlock_destroy (&lock->rwlock);
+  if (err != 0)
+    return err;
+  lock->initialized = 0;
+  return 0;
+}
+
+#  endif
+
+# else
+
+int
+glthread_rwlock_init_multithreaded (gl_rwlock_t *lock)
+{
+  int err;
+
+  err = pthread_mutex_init (&lock->lock, NULL);
+  if (err != 0)
+    return err;
+  err = pthread_cond_init (&lock->waiting_readers, NULL);
+  if (err != 0)
+    return err;
+  err = pthread_cond_init (&lock->waiting_writers, NULL);
+  if (err != 0)
+    return err;
+  lock->waiting_writers_count = 0;
+  lock->runcount = 0;
+  return 0;
+}
+
+int
+glthread_rwlock_rdlock_multithreaded (gl_rwlock_t *lock)
+{
+  int err;
+
+  err = pthread_mutex_lock (&lock->lock);
+  if (err != 0)
+    return err;
+  /* Test whether only readers are currently running, and whether the runcount
+     field will not overflow, and whether no writer is waiting.  The latter
+     condition is because POSIX recommends that "write locks shall take
+     precedence over read locks", to avoid "writer starvation".  */
+  while (!(lock->runcount + 1 > 0 && lock->waiting_writers_count == 0))
+    {
+      /* This thread has to wait for a while.  Enqueue it among the
+         waiting_readers.  */
+      err = pthread_cond_wait (&lock->waiting_readers, &lock->lock);
+      if (err != 0)
+        {
+          pthread_mutex_unlock (&lock->lock);
+          return err;
+        }
+    }
+  lock->runcount++;
+  return pthread_mutex_unlock (&lock->lock);
+}
+
+int
+glthread_rwlock_wrlock_multithreaded (gl_rwlock_t *lock)
+{
+  int err;
+
+  err = pthread_mutex_lock (&lock->lock);
+  if (err != 0)
+    return err;
+  /* Test whether no readers or writers are currently running.  */
+  while (!(lock->runcount == 0))
+    {
+      /* This thread has to wait for a while.  Enqueue it among the
+         waiting_writers.  */
+      lock->waiting_writers_count++;
+      err = pthread_cond_wait (&lock->waiting_writers, &lock->lock);
+      if (err != 0)
+        {
+          lock->waiting_writers_count--;
+          pthread_mutex_unlock (&lock->lock);
+          return err;
+        }
+      lock->waiting_writers_count--;
+    }
+  lock->runcount--; /* runcount becomes -1 */
+  return pthread_mutex_unlock (&lock->lock);
+}
+
+int
+glthread_rwlock_unlock_multithreaded (gl_rwlock_t *lock)
+{
+  int err;
+
+  err = pthread_mutex_lock (&lock->lock);
+  if (err != 0)
+    return err;
+  if (lock->runcount < 0)
+    {
+      /* Drop a writer lock.  */
+      if (!(lock->runcount == -1))
+        {
+          pthread_mutex_unlock (&lock->lock);
+          return EINVAL;
+        }
+      lock->runcount = 0;
+    }
+  else
+    {
+      /* Drop a reader lock.  */
+      if (!(lock->runcount > 0))
+        {
+          pthread_mutex_unlock (&lock->lock);
+          return EINVAL;
+        }
+      lock->runcount--;
+    }
+  if (lock->runcount == 0)
+    {
+      /* POSIX recommends that "write locks shall take precedence over read
+         locks", to avoid "writer starvation".  */
+      if (lock->waiting_writers_count > 0)
+        {
+          /* Wake up one of the waiting writers.  */
+          err = pthread_cond_signal (&lock->waiting_writers);
+          if (err != 0)
+            {
+              pthread_mutex_unlock (&lock->lock);
+              return err;
+            }
+        }
+      else
+        {
+          /* Wake up all waiting readers.  */
+          err = pthread_cond_broadcast (&lock->waiting_readers);
+          if (err != 0)
+            {
+              pthread_mutex_unlock (&lock->lock);
+              return err;
+            }
+        }
+    }
+  return pthread_mutex_unlock (&lock->lock);
+}
+
+int
+glthread_rwlock_destroy_multithreaded (gl_rwlock_t *lock)
+{
+  int err;
+
+  err = pthread_mutex_destroy (&lock->lock);
+  if (err != 0)
+    return err;
+  err = pthread_cond_destroy (&lock->waiting_readers);
+  if (err != 0)
+    return err;
+  err = pthread_cond_destroy (&lock->waiting_writers);
+  if (err != 0)
+    return err;
+  return 0;
+}
+
+# endif
+
+/* --------------------- gl_recursive_lock_t datatype --------------------- */
+
+# if HAVE_PTHREAD_MUTEX_RECURSIVE
+
+#  if defined PTHREAD_RECURSIVE_MUTEX_INITIALIZER || defined PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP
+
+int
+glthread_recursive_lock_init_multithreaded (gl_recursive_lock_t *lock)
+{
+  pthread_mutexattr_t attributes;
+  int err;
+
+  err = pthread_mutexattr_init (&attributes);
+  if (err != 0)
+    return err;
+  err = pthread_mutexattr_settype (&attributes, PTHREAD_MUTEX_RECURSIVE);
+  if (err != 0)
+    {
+      pthread_mutexattr_destroy (&attributes);
+      return err;
+    }
+  err = pthread_mutex_init (lock, &attributes);
+  if (err != 0)
+    {
+      pthread_mutexattr_destroy (&attributes);
+      return err;
+    }
+  err = pthread_mutexattr_destroy (&attributes);
+  if (err != 0)
+    return err;
+  return 0;
+}
+
+#  else
+
+int
+glthread_recursive_lock_init_multithreaded (gl_recursive_lock_t *lock)
+{
+  pthread_mutexattr_t attributes;
+  int err;
+
+  err = pthread_mutexattr_init (&attributes);
+  if (err != 0)
+    return err;
+  err = pthread_mutexattr_settype (&attributes, PTHREAD_MUTEX_RECURSIVE);
+  if (err != 0)
+    {
+      pthread_mutexattr_destroy (&attributes);
+      return err;
+    }
+  err = pthread_mutex_init (&lock->recmutex, &attributes);
+  if (err != 0)
+    {
+      pthread_mutexattr_destroy (&attributes);
+      return err;
+    }
+  err = pthread_mutexattr_destroy (&attributes);
+  if (err != 0)
+    return err;
+  lock->initialized = 1;
+  return 0;
+}
+
+int
+glthread_recursive_lock_lock_multithreaded (gl_recursive_lock_t *lock)
+{
+  if (!lock->initialized)
+    {
+      int err;
+
+      err = pthread_mutex_lock (&lock->guard);
+      if (err != 0)
+        return err;
+      if (!lock->initialized)
+        {
+          err = glthread_recursive_lock_init_multithreaded (lock);
+          if (err != 0)
+            {
+              pthread_mutex_unlock (&lock->guard);
+              return err;
+            }
+        }
+      err = pthread_mutex_unlock (&lock->guard);
+      if (err != 0)
+        return err;
+    }
+  return pthread_mutex_lock (&lock->recmutex);
+}
+
+int
+glthread_recursive_lock_unlock_multithreaded (gl_recursive_lock_t *lock)
+{
+  if (!lock->initialized)
+    return EINVAL;
+  return pthread_mutex_unlock (&lock->recmutex);
+}
+
+int
+glthread_recursive_lock_destroy_multithreaded (gl_recursive_lock_t *lock)
+{
+  int err;
+
+  if (!lock->initialized)
+    return EINVAL;
+  err = pthread_mutex_destroy (&lock->recmutex);
+  if (err != 0)
+    return err;
+  lock->initialized = 0;
+  return 0;
+}
+
+#  endif
+
+# else
+
+int
+glthread_recursive_lock_init_multithreaded (gl_recursive_lock_t *lock)
+{
+  int err;
+
+  err = pthread_mutex_init (&lock->mutex, NULL);
+  if (err != 0)
+    return err;
+  lock->owner = (pthread_t) 0;
+  lock->depth = 0;
+  return 0;
+}
+
+int
+glthread_recursive_lock_lock_multithreaded (gl_recursive_lock_t *lock)
+{
+  pthread_t self = pthread_self ();
+  if (lock->owner != self)
+    {
+      int err;
+
+      err = pthread_mutex_lock (&lock->mutex);
+      if (err != 0)
+        return err;
+      lock->owner = self;
+    }
+  if (++(lock->depth) == 0) /* wraparound? */
+    {
+      lock->depth--;
+      return EAGAIN;
+    }
+  return 0;
+}
+
+int
+glthread_recursive_lock_unlock_multithreaded (gl_recursive_lock_t *lock)
+{
+  if (lock->owner != pthread_self ())
+    return EPERM;
+  if (lock->depth == 0)
+    return EINVAL;
+  if (--(lock->depth) == 0)
+    {
+      lock->owner = (pthread_t) 0;
+      return pthread_mutex_unlock (&lock->mutex);
+    }
+  else
+    return 0;
+}
+
+int
+glthread_recursive_lock_destroy_multithreaded (gl_recursive_lock_t *lock)
+{
+  if (lock->owner != (pthread_t) 0)
+    return EBUSY;
+  return pthread_mutex_destroy (&lock->mutex);
+}
+
+# endif
+
+/* -------------------------- gl_once_t datatype -------------------------- */
+
+static const pthread_once_t fresh_once = PTHREAD_ONCE_INIT;
+
+int
+glthread_once_singlethreaded (pthread_once_t *once_control)
+{
+  /* We don't know whether pthread_once_t is an integer type, a floating-point
+     type, a pointer type, or a structure type.  */
+  char *firstbyte = (char *)once_control;
+  if (*firstbyte == *(const char *)&fresh_once)
+    {
+      /* First time use of once_control.  Invert the first byte.  */
+      *firstbyte = ~ *(const char *)&fresh_once;
+      return 1;
+    }
+  else
+    return 0;
+}
+
+#endif
+
+/* ========================================================================= */
+
+#if USE_PTH_THREADS
+
+/* Use the GNU Pth threads library.  */
+
+/* -------------------------- gl_lock_t datatype -------------------------- */
+
+/* ------------------------- gl_rwlock_t datatype ------------------------- */
+
+# if !HAVE_PTH_RWLOCK_ACQUIRE_PREFER_WRITER
+
+int
+glthread_rwlock_init_multithreaded (gl_rwlock_t *lock)
+{
+  if (!pth_mutex_init (&lock->lock))
+    return errno;
+  if (!pth_cond_init (&lock->waiting_readers))
+    return errno;
+  if (!pth_cond_init (&lock->waiting_writers))
+    return errno;
+  lock->waiting_writers_count = 0;
+  lock->runcount = 0;
+  lock->initialized = 1;
+  return 0;
+}
+
+int
+glthread_rwlock_rdlock_multithreaded (gl_rwlock_t *lock)
+{
+  if (!lock->initialized)
+    glthread_rwlock_init_multithreaded (lock);
+  if (!pth_mutex_acquire (&lock->lock, 0, NULL))
+    return errno;
+  /* Test whether only readers are currently running, and whether the runcount
+     field will not overflow, and whether no writer is waiting.  The latter
+     condition is because POSIX recommends that "write locks shall take
+     precedence over read locks", to avoid "writer starvation".  */
+  while (!(lock->runcount + 1 > 0 && lock->waiting_writers_count == 0))
+    {
+      /* This thread has to wait for a while.  Enqueue it among the
+         waiting_readers.  */
+      if (!pth_cond_await (&lock->waiting_readers, &lock->lock, NULL))
+        {
+          int err = errno;
+          pth_mutex_release (&lock->lock);
+          return err;
+        }
+    }
+  lock->runcount++;
+  return (!pth_mutex_release (&lock->lock) ? errno : 0);
+}
+
+int
+glthread_rwlock_wrlock_multithreaded (gl_rwlock_t *lock)
+{
+  if (!lock->initialized)
+    glthread_rwlock_init_multithreaded (lock);
+  if (!pth_mutex_acquire (&lock->lock, 0, NULL))
+    return errno;
+  /* Test whether no readers or writers are currently running.  */
+  while (!(lock->runcount == 0))
+    {
+      /* This thread has to wait for a while.  Enqueue it among the
+         waiting_writers.  */
+      lock->waiting_writers_count++;
+      if (!pth_cond_await (&lock->waiting_writers, &lock->lock, NULL))
+        {
+          int err = errno;
+          lock->waiting_writers_count--;
+          pth_mutex_release (&lock->lock);
+          return err;
+        }
+      lock->waiting_writers_count--;
+    }
+  lock->runcount--; /* runcount becomes -1 */
+  return (!pth_mutex_release (&lock->lock) ? errno : 0);
+}
+
+int
+glthread_rwlock_unlock_multithreaded (gl_rwlock_t *lock)
+{
+  int err;
+
+  if (!lock->initialized)
+    return EINVAL;
+  if (!pth_mutex_acquire (&lock->lock, 0, NULL))
+    return errno;
+  if (lock->runcount < 0)
+    {
+      /* Drop a writer lock.  */
+      if (!(lock->runcount == -1))
+        {
+          pth_mutex_release (&lock->lock);
+          return EINVAL;
+        }
+      lock->runcount = 0;
+    }
+  else
+    {
+      /* Drop a reader lock.  */
+      if (!(lock->runcount > 0))
+        {
+          pth_mutex_release (&lock->lock);
+          return EINVAL;
+        }
+      lock->runcount--;
+    }
+  if (lock->runcount == 0)
+    {
+      /* POSIX recommends that "write locks shall take precedence over read
+         locks", to avoid "writer starvation".  */
+      if (lock->waiting_writers_count > 0)
+        {
+          /* Wake up one of the waiting writers.  */
+          if (!pth_cond_notify (&lock->waiting_writers, FALSE))
+            {
+              int err = errno;
+              pth_mutex_release (&lock->lock);
+              return err;
+            }
+        }
+      else
+        {
+          /* Wake up all waiting readers.  */
+          if (!pth_cond_notify (&lock->waiting_readers, TRUE))
+            {
+              int err = errno;
+              pth_mutex_release (&lock->lock);
+              return err;
+            }
+        }
+    }
+  return (!pth_mutex_release (&lock->lock) ? errno : 0);
+}
+
+int
+glthread_rwlock_destroy_multithreaded (gl_rwlock_t *lock)
+{
+  lock->initialized = 0;
+  return 0;
+}
+
+# endif
+
+/* --------------------- gl_recursive_lock_t datatype --------------------- */
+
+/* -------------------------- gl_once_t datatype -------------------------- */
+
+static void
+glthread_once_call (void *arg)
+{
+  void (**gl_once_temp_addr) (void) = (void (**) (void)) arg;
+  void (*initfunction) (void) = *gl_once_temp_addr;
+  initfunction ();
+}
+
+int
+glthread_once_multithreaded (pth_once_t *once_control, void (*initfunction) (void))
+{
+  void (*temp) (void) = initfunction;
+  return (!pth_once (once_control, glthread_once_call, &temp) ? errno : 0);
+}
+
+int
+glthread_once_singlethreaded (pth_once_t *once_control)
+{
+  /* We know that pth_once_t is an integer type.  */
+  if (*once_control == PTH_ONCE_INIT)
+    {
+      /* First time use of once_control.  Invert the marker.  */
+      *once_control = ~ PTH_ONCE_INIT;
+      return 1;
+    }
+  else
+    return 0;
+}
+
+#endif
+
+/* ========================================================================= */
+
+#if USE_SOLARIS_THREADS
+
+/* Use the old Solaris threads library.  */
+
+/* -------------------------- gl_lock_t datatype -------------------------- */
+
+/* ------------------------- gl_rwlock_t datatype ------------------------- */
+
+/* --------------------- gl_recursive_lock_t datatype --------------------- */
+
+int
+glthread_recursive_lock_init_multithreaded (gl_recursive_lock_t *lock)
+{
+  int err;
+
+  err = mutex_init (&lock->mutex, USYNC_THREAD, NULL);
+  if (err != 0)
+    return err;
+  lock->owner = (thread_t) 0;
+  lock->depth = 0;
+  return 0;
+}
+
+int
+glthread_recursive_lock_lock_multithreaded (gl_recursive_lock_t *lock)
+{
+  thread_t self = thr_self ();
+  if (lock->owner != self)
+    {
+      int err;
+
+      err = mutex_lock (&lock->mutex);
+      if (err != 0)
+        return err;
+      lock->owner = self;
+    }
+  if (++(lock->depth) == 0) /* wraparound? */
+    {
+      lock->depth--;
+      return EAGAIN;
+    }
+  return 0;
+}
+
+int
+glthread_recursive_lock_unlock_multithreaded (gl_recursive_lock_t *lock)
+{
+  if (lock->owner != thr_self ())
+    return EPERM;
+  if (lock->depth == 0)
+    return EINVAL;
+  if (--(lock->depth) == 0)
+    {
+      lock->owner = (thread_t) 0;
+      return mutex_unlock (&lock->mutex);
+    }
+  else
+    return 0;
+}
+
+int
+glthread_recursive_lock_destroy_multithreaded (gl_recursive_lock_t *lock)
+{
+  if (lock->owner != (thread_t) 0)
+    return EBUSY;
+  return mutex_destroy (&lock->mutex);
+}
+
+/* -------------------------- gl_once_t datatype -------------------------- */
+
+int
+glthread_once_multithreaded (gl_once_t *once_control, void (*initfunction) (void))
+{
+  if (!once_control->inited)
+    {
+      int err;
+
+      /* Use the mutex to guarantee that if another thread is already calling
+         the initfunction, this thread waits until it's finished.  */
+      err = mutex_lock (&once_control->mutex);
+      if (err != 0)
+        return err;
+      if (!once_control->inited)
+        {
+          once_control->inited = 1;
+          initfunction ();
+        }
+      return mutex_unlock (&once_control->mutex);
+    }
+  else
+    return 0;
+}
+
+int
+glthread_once_singlethreaded (gl_once_t *once_control)
+{
+  /* We know that gl_once_t contains an integer type.  */
+  if (!once_control->inited)
+    {
+      /* First time use of once_control.  Invert the marker.  */
+      once_control->inited = ~ 0;
+      return 1;
+    }
+  else
+    return 0;
+}
+
+#endif
+
+/* ========================================================================= */
+
+#if USE_WINDOWS_THREADS
+
+/* -------------------------- gl_lock_t datatype -------------------------- */
+
+void
+glthread_lock_init_func (gl_lock_t *lock)
+{
+  InitializeCriticalSection (&lock->lock);
+  lock->guard.done = 1;
+}
+
+int
+glthread_lock_lock_func (gl_lock_t *lock)
+{
+  if (!lock->guard.done)
+    {
+      if (InterlockedIncrement (&lock->guard.started) == 0)
+        /* This thread is the first one to need this lock.  Initialize it.  */
+        glthread_lock_init (lock);
+      else
+        /* Yield the CPU while waiting for another thread to finish
+           initializing this lock.  */
+        while (!lock->guard.done)
+          Sleep (0);
+    }
+  EnterCriticalSection (&lock->lock);
+  return 0;
+}
+
+int
+glthread_lock_unlock_func (gl_lock_t *lock)
+{
+  if (!lock->guard.done)
+    return EINVAL;
+  LeaveCriticalSection (&lock->lock);
+  return 0;
+}
+
+int
+glthread_lock_destroy_func (gl_lock_t *lock)
+{
+  if (!lock->guard.done)
+    return EINVAL;
+  DeleteCriticalSection (&lock->lock);
+  lock->guard.done = 0;
+  return 0;
+}
+
+/* ------------------------- gl_rwlock_t datatype ------------------------- */
+
+/* In this file, the waitqueues are implemented as circular arrays.  */
+#define gl_waitqueue_t gl_carray_waitqueue_t
+
+static void
+gl_waitqueue_init (gl_waitqueue_t *wq)
+{
+  wq->array = NULL;
+  wq->count = 0;
+  wq->alloc = 0;
+  wq->offset = 0;
+}
+
+/* Enqueues the current thread, represented by an event, in a wait queue.
+   Returns INVALID_HANDLE_VALUE if an allocation failure occurs.  */
+static HANDLE
+gl_waitqueue_add (gl_waitqueue_t *wq)
+{
+  HANDLE event;
+  unsigned int index;
+
+  if (wq->count == wq->alloc)
+    {
+      unsigned int new_alloc = 2 * wq->alloc + 1;
+      HANDLE *new_array =
+        (HANDLE *) realloc (wq->array, new_alloc * sizeof (HANDLE));
+      if (new_array == NULL)
+        /* No more memory.  */
+        return INVALID_HANDLE_VALUE;
+      /* Now is a good opportunity to rotate the array so that its contents
+         starts at offset 0.  */
+      if (wq->offset > 0)
+        {
+          unsigned int old_count = wq->count;
+          unsigned int old_alloc = wq->alloc;
+          unsigned int old_offset = wq->offset;
+          unsigned int i;
+          if (old_offset + old_count > old_alloc)
+            {
+              unsigned int limit = old_offset + old_count - old_alloc;
+              for (i = 0; i < limit; i++)
+                new_array[old_alloc + i] = new_array[i];
+            }
+          for (i = 0; i < old_count; i++)
+            new_array[i] = new_array[old_offset + i];
+          wq->offset = 0;
+        }
+      wq->array = new_array;
+      wq->alloc = new_alloc;
+    }
+  /* Whether the created event is a manual-reset one or an auto-reset one,
+     does not matter, since we will wait on it only once.  */
+  event = CreateEvent (NULL, TRUE, FALSE, NULL);
+  if (event == INVALID_HANDLE_VALUE)
+    /* No way to allocate an event.  */
+    return INVALID_HANDLE_VALUE;
+  index = wq->offset + wq->count;
+  if (index >= wq->alloc)
+    index -= wq->alloc;
+  wq->array[index] = event;
+  wq->count++;
+  return event;
+}
+
+/* Notifies the first thread from a wait queue and dequeues it.  */
+static void
+gl_waitqueue_notify_first (gl_waitqueue_t *wq)
+{
+  SetEvent (wq->array[wq->offset + 0]);
+  wq->offset++;
+  wq->count--;
+  if (wq->count == 0 || wq->offset == wq->alloc)
+    wq->offset = 0;
+}
+
+/* Notifies all threads from a wait queue and dequeues them all.  */
+static void
+gl_waitqueue_notify_all (gl_waitqueue_t *wq)
+{
+  unsigned int i;
+
+  for (i = 0; i < wq->count; i++)
+    {
+      unsigned int index = wq->offset + i;
+      if (index >= wq->alloc)
+        index -= wq->alloc;
+      SetEvent (wq->array[index]);
+    }
+  wq->count = 0;
+  wq->offset = 0;
+}
+
+void
+glthread_rwlock_init_func (gl_rwlock_t *lock)
+{
+  InitializeCriticalSection (&lock->lock);
+  gl_waitqueue_init (&lock->waiting_readers);
+  gl_waitqueue_init (&lock->waiting_writers);
+  lock->runcount = 0;
+  lock->guard.done = 1;
+}
+
+int
+glthread_rwlock_rdlock_func (gl_rwlock_t *lock)
+{
+  if (!lock->guard.done)
+    {
+      if (InterlockedIncrement (&lock->guard.started) == 0)
+        /* This thread is the first one to need this lock.  Initialize it.  */
+        glthread_rwlock_init (lock);
+      else
+        /* Yield the CPU while waiting for another thread to finish
+           initializing this lock.  */
+        while (!lock->guard.done)
+          Sleep (0);
+    }
+  EnterCriticalSection (&lock->lock);
+  /* Test whether only readers are currently running, and whether the runcount
+     field will not overflow, and whether no writer is waiting.  The latter
+     condition is because POSIX recommends that "write locks shall take
+     precedence over read locks", to avoid "writer starvation".  */
+  if (!(lock->runcount + 1 > 0 && lock->waiting_writers.count == 0))
+    {
+      /* This thread has to wait for a while.  Enqueue it among the
+         waiting_readers.  */
+      HANDLE event = gl_waitqueue_add (&lock->waiting_readers);
+      if (event != INVALID_HANDLE_VALUE)
+        {
+          DWORD result;
+          LeaveCriticalSection (&lock->lock);
+          /* Wait until another thread signals this event.  */
+          result = WaitForSingleObject (event, INFINITE);
+          if (result == WAIT_FAILED || result == WAIT_TIMEOUT)
+            abort ();
+          CloseHandle (event);
+          /* The thread which signalled the event already did the bookkeeping:
+             removed us from the waiting_readers, incremented lock->runcount.  */
+          if (!(lock->runcount > 0))
+            abort ();
+          return 0;
+        }
+      else
+        {
+          /* Allocation failure.  Weird.  */
+          do
+            {
+              LeaveCriticalSection (&lock->lock);
+              Sleep (1);
+              EnterCriticalSection (&lock->lock);
+            }
+          while (!(lock->runcount + 1 > 0));
+        }
+    }
+  lock->runcount++;
+  LeaveCriticalSection (&lock->lock);
+  return 0;
+}
+
+int
+glthread_rwlock_wrlock_func (gl_rwlock_t *lock)
+{
+  if (!lock->guard.done)
+    {
+      if (InterlockedIncrement (&lock->guard.started) == 0)
+        /* This thread is the first one to need this lock.  Initialize it.  */
+        glthread_rwlock_init (lock);
+      else
+        /* Yield the CPU while waiting for another thread to finish
+           initializing this lock.  */
+        while (!lock->guard.done)
+          Sleep (0);
+    }
+  EnterCriticalSection (&lock->lock);
+  /* Test whether no readers or writers are currently running.  */
+  if (!(lock->runcount == 0))
+    {
+      /* This thread has to wait for a while.  Enqueue it among the
+         waiting_writers.  */
+      HANDLE event = gl_waitqueue_add (&lock->waiting_writers);
+      if (event != INVALID_HANDLE_VALUE)
+        {
+          DWORD result;
+          LeaveCriticalSection (&lock->lock);
+          /* Wait until another thread signals this event.  */
+          result = WaitForSingleObject (event, INFINITE);
+          if (result == WAIT_FAILED || result == WAIT_TIMEOUT)
+            abort ();
+          CloseHandle (event);
+          /* The thread which signalled the event already did the bookkeeping:
+             removed us from the waiting_writers, set lock->runcount = -1.  */
+          if (!(lock->runcount == -1))
+            abort ();
+          return 0;
+        }
+      else
+        {
+          /* Allocation failure.  Weird.  */
+          do
+            {
+              LeaveCriticalSection (&lock->lock);
+              Sleep (1);
+              EnterCriticalSection (&lock->lock);
+            }
+          while (!(lock->runcount == 0));
+        }
+    }
+  lock->runcount--; /* runcount becomes -1 */
+  LeaveCriticalSection (&lock->lock);
+  return 0;
+}
+
+int
+glthread_rwlock_unlock_func (gl_rwlock_t *lock)
+{
+  if (!lock->guard.done)
+    return EINVAL;
+  EnterCriticalSection (&lock->lock);
+  if (lock->runcount < 0)
+    {
+      /* Drop a writer lock.  */
+      if (!(lock->runcount == -1))
+        abort ();
+      lock->runcount = 0;
+    }
+  else
+    {
+      /* Drop a reader lock.  */
+      if (!(lock->runcount > 0))
+        {
+          LeaveCriticalSection (&lock->lock);
+          return EPERM;
+        }
+      lock->runcount--;
+    }
+  if (lock->runcount == 0)
+    {
+      /* POSIX recommends that "write locks shall take precedence over read
+         locks", to avoid "writer starvation".  */
+      if (lock->waiting_writers.count > 0)
+        {
+          /* Wake up one of the waiting writers.  */
+          lock->runcount--;
+          gl_waitqueue_notify_first (&lock->waiting_writers);
+        }
+      else
+        {
+          /* Wake up all waiting readers.  */
+          lock->runcount += lock->waiting_readers.count;
+          gl_waitqueue_notify_all (&lock->waiting_readers);
+        }
+    }
+  LeaveCriticalSection (&lock->lock);
+  return 0;
+}
+
+int
+glthread_rwlock_destroy_func (gl_rwlock_t *lock)
+{
+  if (!lock->guard.done)
+    return EINVAL;
+  if (lock->runcount != 0)
+    return EBUSY;
+  DeleteCriticalSection (&lock->lock);
+  if (lock->waiting_readers.array != NULL)
+    free (lock->waiting_readers.array);
+  if (lock->waiting_writers.array != NULL)
+    free (lock->waiting_writers.array);
+  lock->guard.done = 0;
+  return 0;
+}
+
+/* --------------------- gl_recursive_lock_t datatype --------------------- */
+
+void
+glthread_recursive_lock_init_func (gl_recursive_lock_t *lock)
+{
+  lock->owner = 0;
+  lock->depth = 0;
+  InitializeCriticalSection (&lock->lock);
+  lock->guard.done = 1;
+}
+
+int
+glthread_recursive_lock_lock_func (gl_recursive_lock_t *lock)
+{
+  if (!lock->guard.done)
+    {
+      if (InterlockedIncrement (&lock->guard.started) == 0)
+        /* This thread is the first one to need this lock.  Initialize it.  */
+        glthread_recursive_lock_init (lock);
+      else
+        /* Yield the CPU while waiting for another thread to finish
+           initializing this lock.  */
+        while (!lock->guard.done)
+          Sleep (0);
+    }
+  {
+    DWORD self = GetCurrentThreadId ();
+    if (lock->owner != self)
+      {
+        EnterCriticalSection (&lock->lock);
+        lock->owner = self;
+      }
+    if (++(lock->depth) == 0) /* wraparound? */
+      {
+        lock->depth--;
+        return EAGAIN;
+      }
+  }
+  return 0;
+}
+
+int
+glthread_recursive_lock_unlock_func (gl_recursive_lock_t *lock)
+{
+  if (lock->owner != GetCurrentThreadId ())
+    return EPERM;
+  if (lock->depth == 0)
+    return EINVAL;
+  if (--(lock->depth) == 0)
+    {
+      lock->owner = 0;
+      LeaveCriticalSection (&lock->lock);
+    }
+  return 0;
+}
+
+int
+glthread_recursive_lock_destroy_func (gl_recursive_lock_t *lock)
+{
+  if (lock->owner != 0)
+    return EBUSY;
+  DeleteCriticalSection (&lock->lock);
+  lock->guard.done = 0;
+  return 0;
+}
+
+/* -------------------------- gl_once_t datatype -------------------------- */
+
+void
+glthread_once_func (gl_once_t *once_control, void (*initfunction) (void))
+{
+  if (once_control->inited <= 0)
+    {
+      if (InterlockedIncrement (&once_control->started) == 0)
+        {
+          /* This thread is the first one to come to this once_control.  */
+          InitializeCriticalSection (&once_control->lock);
+          EnterCriticalSection (&once_control->lock);
+          once_control->inited = 0;
+          initfunction ();
+          once_control->inited = 1;
+          LeaveCriticalSection (&once_control->lock);
+        }
+      else
+        {
+          /* Undo last operation.  */
+          InterlockedDecrement (&once_control->started);
+          /* Some other thread has already started the initialization.
+             Yield the CPU while waiting for the other thread to finish
+             initializing and taking the lock.  */
+          while (once_control->inited < 0)
+            Sleep (0);
+          if (once_control->inited <= 0)
+            {
+              /* Take the lock.  This blocks until the other thread has
+                 finished calling the initfunction.  */
+              EnterCriticalSection (&once_control->lock);
+              LeaveCriticalSection (&once_control->lock);
+              if (!(once_control->inited > 0))
+                abort ();
+            }
+        }
+    }
+}
+
+#endif
+
+/* ========================================================================= */