3 files changed, 528 insertions, 937 deletions

diff --git a/gl/glthread/lock.c b/gl/glthread/lock.c
index f62aa301..44335e32 100644
--- a/gl/glthread/lock.c
+++ b/gl/glthread/lock.c
@@ -1,22 +1,21 @@
 /* Locking in multithreaded situations.
-   Copyright (C) 2005-2013 Free Software Foundation, Inc.
+   Copyright (C) 2005-2021 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 file is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Lesser General Public License as
+   published by the Free Software Foundation; either version 2.1 of the
+   License, or (at your option) any later version.
 
-   This program is distributed in the hope that it will be useful,
+   This file 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.
+   GNU Lesser 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 <http://www.gnu.org/licenses/>.  */
+   You should have received a copy of the GNU Lesser 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.  */
+   Based on GCC's gthr-posix.h, gthr-posix95.h.  */
 
 #include <config.h>
 
@@ -24,15 +23,267 @@
 
 /* ========================================================================= */
 
+#if USE_ISOC_THREADS || USE_ISOC_AND_POSIX_THREADS
+
+/* -------------------------- gl_lock_t datatype -------------------------- */
+
+int
+glthread_lock_init (gl_lock_t *lock)
+{
+  if (mtx_init (&lock->mutex, mtx_plain) != thrd_success)
+    return ENOMEM;
+  lock->init_needed = 0;
+  return 0;
+}
+
+int
+glthread_lock_lock (gl_lock_t *lock)
+{
+  if (lock->init_needed)
+    call_once (&lock->init_once, lock->init_func);
+  if (mtx_lock (&lock->mutex) != thrd_success)
+    return EAGAIN;
+  return 0;
+}
+
+int
+glthread_lock_unlock (gl_lock_t *lock)
+{
+  if (lock->init_needed)
+    call_once (&lock->init_once, lock->init_func);
+  if (mtx_unlock (&lock->mutex) != thrd_success)
+    return EINVAL;
+  return 0;
+}
+
+int
+glthread_lock_destroy (gl_lock_t *lock)
+{
+  if (lock->init_needed)
+    call_once (&lock->init_once, lock->init_func);
+  mtx_destroy (&lock->mutex);
+  return 0;
+}
+
+/* ------------------------- gl_rwlock_t datatype ------------------------- */
+
+int
+glthread_rwlock_init (gl_rwlock_t *lock)
+{
+  if (mtx_init (&lock->lock, mtx_plain) != thrd_success
+      || cnd_init (&lock->waiting_readers) != thrd_success
+      || cnd_init (&lock->waiting_writers) != thrd_success)
+    return ENOMEM;
+  lock->waiting_writers_count = 0;
+  lock->runcount = 0;
+  lock->init_needed = 0;
+  return 0;
+}
+
+int
+glthread_rwlock_rdlock (gl_rwlock_t *lock)
+{
+  if (lock->init_needed)
+    call_once (&lock->init_once, lock->init_func);
+  if (mtx_lock (&lock->lock) != thrd_success)
+    return EAGAIN;
+  /* 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 (cnd_wait (&lock->waiting_readers, &lock->lock) != thrd_success)
+        {
+          mtx_unlock (&lock->lock);
+          return EINVAL;
+        }
+    }
+  lock->runcount++;
+  if (mtx_unlock (&lock->lock) != thrd_success)
+    return EINVAL;
+  return 0;
+}
+
+int
+glthread_rwlock_wrlock (gl_rwlock_t *lock)
+{
+  if (lock->init_needed)
+    call_once (&lock->init_once, lock->init_func);
+  if (mtx_lock (&lock->lock) != thrd_success)
+    return EAGAIN;
+  /* 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 (cnd_wait (&lock->waiting_writers, &lock->lock) != thrd_success)
+        {
+          lock->waiting_writers_count--;
+          mtx_unlock (&lock->lock);
+          return EINVAL;
+        }
+      lock->waiting_writers_count--;
+    }
+  lock->runcount--; /* runcount becomes -1 */
+  if (mtx_unlock (&lock->lock) != thrd_success)
+    return EINVAL;
+  return 0;
+}
+
+int
+glthread_rwlock_unlock (gl_rwlock_t *lock)
+{
+  if (lock->init_needed)
+    call_once (&lock->init_once, lock->init_func);
+  if (mtx_lock (&lock->lock) != thrd_success)
+    return EAGAIN;
+  if (lock->runcount < 0)
+    {
+      /* Drop a writer lock.  */
+      if (!(lock->runcount == -1))
+        {
+          mtx_unlock (&lock->lock);
+          return EINVAL;
+        }
+      lock->runcount = 0;
+    }
+  else
+    {
+      /* Drop a reader lock.  */
+      if (!(lock->runcount > 0))
+        {
+          mtx_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.  */
+          if (cnd_signal (&lock->waiting_writers) != thrd_success)
+            {
+              mtx_unlock (&lock->lock);
+              return EINVAL;
+            }
+        }
+      else
+        {
+          /* Wake up all waiting readers.  */
+          if (cnd_broadcast (&lock->waiting_readers) != thrd_success)
+            {
+              mtx_unlock (&lock->lock);
+              return EINVAL;
+            }
+        }
+    }
+  if (mtx_unlock (&lock->lock) != thrd_success)
+    return EINVAL;
+  return 0;
+}
+
+int
+glthread_rwlock_destroy (gl_rwlock_t *lock)
+{
+  if (lock->init_needed)
+    call_once (&lock->init_once, lock->init_func);
+  mtx_destroy (&lock->lock);
+  cnd_destroy (&lock->waiting_readers);
+  cnd_destroy (&lock->waiting_writers);
+  return 0;
+}
+
+/* --------------------- gl_recursive_lock_t datatype --------------------- */
+
+int
+glthread_recursive_lock_init (gl_recursive_lock_t *lock)
+{
+  if (mtx_init (&lock->mutex, mtx_plain | mtx_recursive) != thrd_success)
+    return ENOMEM;
+  lock->init_needed = 0;
+  return 0;
+}
+
+int
+glthread_recursive_lock_lock (gl_recursive_lock_t *lock)
+{
+  if (lock->init_needed)
+    call_once (&lock->init_once, lock->init_func);
+  if (mtx_lock (&lock->mutex) != thrd_success)
+    return EAGAIN;
+  return 0;
+}
+
+int
+glthread_recursive_lock_unlock (gl_recursive_lock_t *lock)
+{
+  if (lock->init_needed)
+    call_once (&lock->init_once, lock->init_func);
+  if (mtx_unlock (&lock->mutex) != thrd_success)
+    return EINVAL;
+  return 0;
+}
+
+int
+glthread_recursive_lock_destroy (gl_recursive_lock_t *lock)
+{
+  if (lock->init_needed)
+    call_once (&lock->init_once, lock->init_func);
+  mtx_destroy (&lock->mutex);
+  return 0;
+}
+
+/* -------------------------- gl_once_t datatype -------------------------- */
+
+#endif
+
+/* ========================================================================= */
+
 #if USE_POSIX_THREADS
 
 /* -------------------------- gl_lock_t datatype -------------------------- */
 
 /* ------------------------- gl_rwlock_t datatype ------------------------- */
 
-# if HAVE_PTHREAD_RWLOCK
+# if HAVE_PTHREAD_RWLOCK && (HAVE_PTHREAD_RWLOCK_RDLOCK_PREFER_WRITER || (defined PTHREAD_RWLOCK_WRITER_NONRECURSIVE_INITIALIZER_NP && (__GNU_LIBRARY__ > 1)))
+
+#  if defined PTHREAD_RWLOCK_INITIALIZER || defined PTHREAD_RWLOCK_INITIALIZER_NP
+
+#   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;
 
-#  if !defined PTHREAD_RWLOCK_INITIALIZER
+  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)
@@ -152,11 +403,9 @@ glthread_rwlock_rdlock_multithreaded (gl_rwlock_t *lock)
   if (err != 0)
     return err;
   /* Test whether only readers are currently running, and whether the runcount
-     field will not overflow.  */
-  /* POSIX says: "It is implementation-defined whether the calling thread
-     acquires the lock when a writer does not hold the lock and there are
-     writers blocked on the lock."  Let's say, no: give the writers a higher
-     priority.  */
+     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
@@ -469,161 +718,25 @@ glthread_once_singlethreaded (pthread_once_t *once_control)
     return 0;
 }
 
-#endif
-
-/* ========================================================================= */
-
-#if USE_PTH_THREADS
-
-/* Use the GNU Pth threads library.  */
-
-/* -------------------------- gl_lock_t datatype -------------------------- */
-
-/* ------------------------- gl_rwlock_t datatype ------------------------- */
-
-/* --------------------- 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 --------------------- */
+# if !(PTHREAD_IN_USE_DETECTION_HARD || USE_POSIX_THREADS_WEAK)
 
 int
-glthread_recursive_lock_init_multithreaded (gl_recursive_lock_t *lock)
+glthread_once_multithreaded (pthread_once_t *once_control,
+                             void (*init_function) (void))
 {
-  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 = pthread_once (once_control, init_function);
+  if (err == ENOSYS)
     {
-      int err;
-
-      err = mutex_lock (&lock->mutex);
-      if (err != 0)
-        return err;
-      lock->owner = self;
+      /* This happens on FreeBSD 11: The pthread_once function in libc returns
+         ENOSYS.  */
+      if (glthread_once_singlethreaded (once_control))
+        init_function ();
+      return 0;
     }
-  if (++(lock->depth) == 0) /* wraparound? */
-    {
-      lock->depth--;
-      return EAGAIN;
-    }
-  return 0;
+  return err;
 }
 
-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
 
 #endif
 
@@ -631,427 +744,6 @@ glthread_once_singlethreaded (gl_once_t *once_control)
 
 #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.  */
-  if (!(lock->runcount + 1 > 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
 
 /* ========================================================================= */
diff --git a/gl/glthread/lock.h b/gl/glthread/lock.h
index d20bbdef..cc4c5193 100644
--- a/gl/glthread/lock.h
+++ b/gl/glthread/lock.h
@@ -1,22 +1,21 @@
 /* Locking in multithreaded situations.
-   Copyright (C) 2005-2013 Free Software Foundation, Inc.
+   Copyright (C) 2005-2021 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 file is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Lesser General Public License as
+   published by the Free Software Foundation; either version 2.1 of the
+   License, or (at your option) any later version.
 
-   This program is distributed in the hope that it will be useful,
+   This file 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.
+   GNU Lesser 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 <http://www.gnu.org/licenses/>.  */
+   You should have received a copy of the GNU Lesser 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.  */
+   Based on GCC's gthr-posix.h, gthr-posix95.h, gthr-win32.h.  */
 
 /* This file contains locking primitives for use with a given thread library.
    It does not contain primitives for creating threads or for other
@@ -81,6 +80,127 @@
 #include <errno.h>
 #include <stdlib.h>
 
+#if !defined c11_threads_in_use
+# if HAVE_THREADS_H && USE_POSIX_THREADS_FROM_LIBC
+#  define c11_threads_in_use() 1
+# elif HAVE_THREADS_H && USE_POSIX_THREADS_WEAK
+#  include <threads.h>
+#  pragma weak thrd_exit
+#  define c11_threads_in_use() (thrd_exit != NULL)
+# else
+#  define c11_threads_in_use() 0
+# endif
+#endif
+
+/* ========================================================================= */
+
+#if USE_ISOC_THREADS || USE_ISOC_AND_POSIX_THREADS
+
+/* Use the ISO C threads library.  */
+
+# include <threads.h>
+
+# ifdef __cplusplus
+extern "C" {
+# endif
+
+/* -------------------------- gl_lock_t datatype -------------------------- */
+
+typedef struct
+        {
+          int volatile init_needed;
+          once_flag init_once;
+          void (*init_func) (void);
+          mtx_t mutex;
+        }
+        gl_lock_t;
+# define gl_lock_define(STORAGECLASS, NAME) \
+    STORAGECLASS gl_lock_t NAME;
+# define gl_lock_define_initialized(STORAGECLASS, NAME) \
+    static void _atomic_init_##NAME (void);       \
+    STORAGECLASS gl_lock_t NAME =                 \
+      { 1, ONCE_FLAG_INIT, _atomic_init_##NAME }; \
+    static void _atomic_init_##NAME (void)        \
+    {                                             \
+      if (glthread_lock_init (&(NAME)))           \
+        abort ();                                 \
+    }
+extern int glthread_lock_init (gl_lock_t *lock);
+extern int glthread_lock_lock (gl_lock_t *lock);
+extern int glthread_lock_unlock (gl_lock_t *lock);
+extern int glthread_lock_destroy (gl_lock_t *lock);
+
+/* ------------------------- gl_rwlock_t datatype ------------------------- */
+
+typedef struct
+        {
+          int volatile init_needed;
+          once_flag init_once;
+          void (*init_func) (void);
+          mtx_t lock; /* protects the remaining fields */
+          cnd_t waiting_readers; /* waiting readers */
+          cnd_t waiting_writers; /* waiting writers */
+          unsigned int waiting_writers_count; /* number of waiting writers */
+          int runcount; /* number of readers running, or -1 when a writer runs */
+        }
+        gl_rwlock_t;
+# define gl_rwlock_define(STORAGECLASS, NAME) \
+    STORAGECLASS gl_rwlock_t NAME;
+# define gl_rwlock_define_initialized(STORAGECLASS, NAME) \
+    static void _atomic_init_##NAME (void);       \
+    STORAGECLASS gl_rwlock_t NAME =               \
+      { 1, ONCE_FLAG_INIT, _atomic_init_##NAME }; \
+    static void _atomic_init_##NAME (void)        \
+    {                                             \
+      if (glthread_rwlock_init (&(NAME)))         \
+        abort ();                                 \
+    }
+extern int glthread_rwlock_init (gl_rwlock_t *lock);
+extern int glthread_rwlock_rdlock (gl_rwlock_t *lock);
+extern int glthread_rwlock_wrlock (gl_rwlock_t *lock);
+extern int glthread_rwlock_unlock (gl_rwlock_t *lock);
+extern int glthread_rwlock_destroy (gl_rwlock_t *lock);
+
+/* --------------------- gl_recursive_lock_t datatype --------------------- */
+
+typedef struct
+        {
+          int volatile init_needed;
+          once_flag init_once;
+          void (*init_func) (void);
+          mtx_t mutex;
+        }
+        gl_recursive_lock_t;
+# define gl_recursive_lock_define(STORAGECLASS, NAME) \
+    STORAGECLASS gl_recursive_lock_t NAME;
+# define gl_recursive_lock_define_initialized(STORAGECLASS, NAME) \
+    static void _atomic_init_##NAME (void);       \
+    STORAGECLASS gl_recursive_lock_t NAME =       \
+      { 1, ONCE_FLAG_INIT, _atomic_init_##NAME }; \
+    static void _atomic_init_##NAME (void)        \
+    {                                             \
+      if (glthread_recursive_lock_init (&(NAME))) \
+        abort ();                                 \
+    }
+extern int glthread_recursive_lock_init (gl_recursive_lock_t *lock);
+extern int glthread_recursive_lock_lock (gl_recursive_lock_t *lock);
+extern int glthread_recursive_lock_unlock (gl_recursive_lock_t *lock);
+extern int glthread_recursive_lock_destroy (gl_recursive_lock_t *lock);
+
+/* -------------------------- gl_once_t datatype -------------------------- */
+
+typedef once_flag gl_once_t;
+# define gl_once_define(STORAGECLASS, NAME) \
+    STORAGECLASS once_flag NAME = ONCE_FLAG_INIT;
+# define glthread_once(ONCE_CONTROL, INITFUNCTION) \
+    (call_once (ONCE_CONTROL, INITFUNCTION), 0)
+
+# ifdef __cplusplus
+}
+# endif
+
+#endif
+
 /* ========================================================================= */
 
 #if USE_POSIX_THREADS
@@ -139,13 +259,25 @@ extern int glthread_in_use (void);
 #  pragma weak pthread_mutexattr_init
 #  pragma weak pthread_mutexattr_settype
 #  pragma weak pthread_mutexattr_destroy
+#  pragma weak pthread_rwlockattr_init
+#  if __GNU_LIBRARY__ > 1
+#   pragma weak pthread_rwlockattr_setkind_np
+#  endif
+#  pragma weak pthread_rwlockattr_destroy
 #  ifndef pthread_self
 #   pragma weak pthread_self
 #  endif
 
 #  if !PTHREAD_IN_USE_DETECTION_HARD
-#   pragma weak pthread_cancel
-#   define pthread_in_use() (pthread_cancel != NULL)
+    /* Considering all platforms with USE_POSIX_THREADS_WEAK, only few symbols
+       can be used to determine whether libpthread is in use.  These are:
+         pthread_mutexattr_gettype
+         pthread_rwlockattr_destroy
+         pthread_rwlockattr_init
+     */
+#   pragma weak pthread_mutexattr_gettype
+#   define pthread_in_use() \
+      (pthread_mutexattr_gettype != NULL || c11_threads_in_use ())
 #  endif
 
 # else
@@ -176,19 +308,32 @@ typedef pthread_mutex_t gl_lock_t;
 
 /* ------------------------- gl_rwlock_t datatype ------------------------- */
 
-# if HAVE_PTHREAD_RWLOCK
+# 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 defined PTHREAD_RWLOCK_INITIALIZER || defined PTHREAD_RWLOCK_INITIALIZER_NP
 
 typedef pthread_rwlock_t gl_rwlock_t;
 #   define gl_rwlock_define(STORAGECLASS, NAME) \
       STORAGECLASS pthread_rwlock_t NAME;
 #   define gl_rwlock_define_initialized(STORAGECLASS, NAME) \
       STORAGECLASS pthread_rwlock_t NAME = gl_rwlock_initializer;
-#   define gl_rwlock_initializer \
-      PTHREAD_RWLOCK_INITIALIZER
-#   define glthread_rwlock_init(LOCK) \
-      (pthread_in_use () ? pthread_rwlock_init (LOCK, NULL) : 0)
+#   if HAVE_PTHREAD_RWLOCK_RDLOCK_PREFER_WRITER
+#    if defined PTHREAD_RWLOCK_INITIALIZER
+#     define gl_rwlock_initializer \
+        PTHREAD_RWLOCK_INITIALIZER
+#    else
+#     define gl_rwlock_initializer \
+        PTHREAD_RWLOCK_INITIALIZER_NP
+#    endif
+#    define glthread_rwlock_init(LOCK) \
+       (pthread_in_use () ? pthread_rwlock_init (LOCK, NULL) : 0)
+#   else /* glibc with bug https://sourceware.org/bugzilla/show_bug.cgi?id=13701 */
+#    define gl_rwlock_initializer \
+       PTHREAD_RWLOCK_WRITER_NONRECURSIVE_INITIALIZER_NP
+#    define glthread_rwlock_init(LOCK) \
+       (pthread_in_use () ? glthread_rwlock_init_for_glibc (LOCK) : 0)
+extern int glthread_rwlock_init_for_glibc (pthread_rwlock_t *lock);
+#   endif
 #   define glthread_rwlock_rdlock(LOCK) \
       (pthread_in_use () ? pthread_rwlock_rdlock (LOCK) : 0)
 #   define glthread_rwlock_wrlock(LOCK) \
@@ -362,248 +507,20 @@ extern int glthread_recursive_lock_destroy_multithreaded (gl_recursive_lock_t *l
 typedef pthread_once_t gl_once_t;
 # define gl_once_define(STORAGECLASS, NAME) \
     STORAGECLASS pthread_once_t NAME = PTHREAD_ONCE_INIT;
-# define glthread_once(ONCE_CONTROL, INITFUNCTION) \
-    (pthread_in_use ()                                                         \
-     ? pthread_once (ONCE_CONTROL, INITFUNCTION)                               \
-     : (glthread_once_singlethreaded (ONCE_CONTROL) ? (INITFUNCTION (), 0) : 0))
-extern int glthread_once_singlethreaded (pthread_once_t *once_control);
-
-# ifdef __cplusplus
-}
-# endif
-
-#endif
-
-/* ========================================================================= */
-
-#if USE_PTH_THREADS
-
-/* Use the GNU Pth threads library.  */
-
-# include <pth.h>
-
-# ifdef __cplusplus
-extern "C" {
-# endif
-
-# if USE_PTH_THREADS_WEAK
-
-/* Use weak references to the GNU Pth threads library.  */
-
-#  pragma weak pth_mutex_init
-#  pragma weak pth_mutex_acquire
-#  pragma weak pth_mutex_release
-#  pragma weak pth_rwlock_init
-#  pragma weak pth_rwlock_acquire
-#  pragma weak pth_rwlock_release
-#  pragma weak pth_once
-
-#  pragma weak pth_cancel
-#  define pth_in_use() (pth_cancel != NULL)
-
+# if PTHREAD_IN_USE_DETECTION_HARD || USE_POSIX_THREADS_WEAK
+#  define glthread_once(ONCE_CONTROL, INITFUNCTION) \
+     (pthread_in_use ()                                                        \
+      ? pthread_once (ONCE_CONTROL, INITFUNCTION)                              \
+      : (glthread_once_singlethreaded (ONCE_CONTROL) ? (INITFUNCTION (), 0) : 0))
 # else
-
-#  define pth_in_use() 1
-
+#  define glthread_once(ONCE_CONTROL, INITFUNCTION) \
+     (pthread_in_use ()                                                        \
+      ? glthread_once_multithreaded (ONCE_CONTROL, INITFUNCTION)               \
+      : (glthread_once_singlethreaded (ONCE_CONTROL) ? (INITFUNCTION (), 0) : 0))
+extern int glthread_once_multithreaded (pthread_once_t *once_control,
+                                        void (*init_function) (void));
 # endif
-
-/* -------------------------- gl_lock_t datatype -------------------------- */
-
-typedef pth_mutex_t gl_lock_t;
-# define gl_lock_define(STORAGECLASS, NAME) \
-    STORAGECLASS pth_mutex_t NAME;
-# define gl_lock_define_initialized(STORAGECLASS, NAME) \
-    STORAGECLASS pth_mutex_t NAME = gl_lock_initializer;
-# define gl_lock_initializer \
-    PTH_MUTEX_INIT
-# define glthread_lock_init(LOCK) \
-    (pth_in_use () && !pth_mutex_init (LOCK) ? errno : 0)
-# define glthread_lock_lock(LOCK) \
-    (pth_in_use () && !pth_mutex_acquire (LOCK, 0, NULL) ? errno : 0)
-# define glthread_lock_unlock(LOCK) \
-    (pth_in_use () && !pth_mutex_release (LOCK) ? errno : 0)
-# define glthread_lock_destroy(LOCK) \
-    ((void)(LOCK), 0)
-
-/* ------------------------- gl_rwlock_t datatype ------------------------- */
-
-typedef pth_rwlock_t gl_rwlock_t;
-#  define gl_rwlock_define(STORAGECLASS, NAME) \
-     STORAGECLASS pth_rwlock_t NAME;
-#  define gl_rwlock_define_initialized(STORAGECLASS, NAME) \
-     STORAGECLASS pth_rwlock_t NAME = gl_rwlock_initializer;
-#  define gl_rwlock_initializer \
-     PTH_RWLOCK_INIT
-#  define glthread_rwlock_init(LOCK) \
-     (pth_in_use () && !pth_rwlock_init (LOCK) ? errno : 0)
-#  define glthread_rwlock_rdlock(LOCK) \
-     (pth_in_use () && !pth_rwlock_acquire (LOCK, PTH_RWLOCK_RD, 0, NULL) ? errno : 0)
-#  define glthread_rwlock_wrlock(LOCK) \
-     (pth_in_use () && !pth_rwlock_acquire (LOCK, PTH_RWLOCK_RW, 0, NULL) ? errno : 0)
-#  define glthread_rwlock_unlock(LOCK) \
-     (pth_in_use () && !pth_rwlock_release (LOCK) ? errno : 0)
-#  define glthread_rwlock_destroy(LOCK) \
-     ((void)(LOCK), 0)
-
-/* --------------------- gl_recursive_lock_t datatype --------------------- */
-
-/* In Pth, mutexes are recursive by default.  */
-typedef pth_mutex_t gl_recursive_lock_t;
-#  define gl_recursive_lock_define(STORAGECLASS, NAME) \
-     STORAGECLASS pth_mutex_t NAME;
-#  define gl_recursive_lock_define_initialized(STORAGECLASS, NAME) \
-     STORAGECLASS pth_mutex_t NAME = gl_recursive_lock_initializer;
-#  define gl_recursive_lock_initializer \
-     PTH_MUTEX_INIT
-#  define glthread_recursive_lock_init(LOCK) \
-     (pth_in_use () && !pth_mutex_init (LOCK) ? errno : 0)
-#  define glthread_recursive_lock_lock(LOCK) \
-     (pth_in_use () && !pth_mutex_acquire (LOCK, 0, NULL) ? errno : 0)
-#  define glthread_recursive_lock_unlock(LOCK) \
-     (pth_in_use () && !pth_mutex_release (LOCK) ? errno : 0)
-#  define glthread_recursive_lock_destroy(LOCK) \
-     ((void)(LOCK), 0)
-
-/* -------------------------- gl_once_t datatype -------------------------- */
-
-typedef pth_once_t gl_once_t;
-# define gl_once_define(STORAGECLASS, NAME) \
-    STORAGECLASS pth_once_t NAME = PTH_ONCE_INIT;
-# define glthread_once(ONCE_CONTROL, INITFUNCTION) \
-    (pth_in_use ()                                                             \
-     ? glthread_once_multithreaded (ONCE_CONTROL, INITFUNCTION)                \
-     : (glthread_once_singlethreaded (ONCE_CONTROL) ? (INITFUNCTION (), 0) : 0))
-extern int glthread_once_multithreaded (pth_once_t *once_control, void (*initfunction) (void));
-extern int glthread_once_singlethreaded (pth_once_t *once_control);
-
-# ifdef __cplusplus
-}
-# endif
-
-#endif
-
-/* ========================================================================= */
-
-#if USE_SOLARIS_THREADS
-
-/* Use the old Solaris threads library.  */
-
-# include <thread.h>
-# include <synch.h>
-
-# ifdef __cplusplus
-extern "C" {
-# endif
-
-# if USE_SOLARIS_THREADS_WEAK
-
-/* Use weak references to the old Solaris threads library.  */
-
-#  pragma weak mutex_init
-#  pragma weak mutex_lock
-#  pragma weak mutex_unlock
-#  pragma weak mutex_destroy
-#  pragma weak rwlock_init
-#  pragma weak rw_rdlock
-#  pragma weak rw_wrlock
-#  pragma weak rw_unlock
-#  pragma weak rwlock_destroy
-#  pragma weak thr_self
-
-#  pragma weak thr_suspend
-#  define thread_in_use() (thr_suspend != NULL)
-
-# else
-
-#  define thread_in_use() 1
-
-# endif
-
-/* -------------------------- gl_lock_t datatype -------------------------- */
-
-typedef mutex_t gl_lock_t;
-# define gl_lock_define(STORAGECLASS, NAME) \
-    STORAGECLASS mutex_t NAME;
-# define gl_lock_define_initialized(STORAGECLASS, NAME) \
-    STORAGECLASS mutex_t NAME = gl_lock_initializer;
-# define gl_lock_initializer \
-    DEFAULTMUTEX
-# define glthread_lock_init(LOCK) \
-    (thread_in_use () ? mutex_init (LOCK, USYNC_THREAD, NULL) : 0)
-# define glthread_lock_lock(LOCK) \
-    (thread_in_use () ? mutex_lock (LOCK) : 0)
-# define glthread_lock_unlock(LOCK) \
-    (thread_in_use () ? mutex_unlock (LOCK) : 0)
-# define glthread_lock_destroy(LOCK) \
-    (thread_in_use () ? mutex_destroy (LOCK) : 0)
-
-/* ------------------------- gl_rwlock_t datatype ------------------------- */
-
-typedef rwlock_t gl_rwlock_t;
-# define gl_rwlock_define(STORAGECLASS, NAME) \
-    STORAGECLASS rwlock_t NAME;
-# define gl_rwlock_define_initialized(STORAGECLASS, NAME) \
-    STORAGECLASS rwlock_t NAME = gl_rwlock_initializer;
-# define gl_rwlock_initializer \
-    DEFAULTRWLOCK
-# define glthread_rwlock_init(LOCK) \
-    (thread_in_use () ? rwlock_init (LOCK, USYNC_THREAD, NULL) : 0)
-# define glthread_rwlock_rdlock(LOCK) \
-    (thread_in_use () ? rw_rdlock (LOCK) : 0)
-# define glthread_rwlock_wrlock(LOCK) \
-    (thread_in_use () ? rw_wrlock (LOCK) : 0)
-# define glthread_rwlock_unlock(LOCK) \
-    (thread_in_use () ? rw_unlock (LOCK) : 0)
-# define glthread_rwlock_destroy(LOCK) \
-    (thread_in_use () ? rwlock_destroy (LOCK) : 0)
-
-/* --------------------- gl_recursive_lock_t datatype --------------------- */
-
-/* Old Solaris threads did not have recursive locks.
-   We have to implement them ourselves.  */
-
-typedef struct
-        {
-          mutex_t mutex;
-          thread_t owner;
-          unsigned long depth;
-        }
-        gl_recursive_lock_t;
-# define gl_recursive_lock_define(STORAGECLASS, NAME) \
-    STORAGECLASS gl_recursive_lock_t NAME;
-# define gl_recursive_lock_define_initialized(STORAGECLASS, NAME) \
-    STORAGECLASS gl_recursive_lock_t NAME = gl_recursive_lock_initializer;
-# define gl_recursive_lock_initializer \
-    { DEFAULTMUTEX, (thread_t) 0, 0 }
-# define glthread_recursive_lock_init(LOCK) \
-    (thread_in_use () ? glthread_recursive_lock_init_multithreaded (LOCK) : 0)
-# define glthread_recursive_lock_lock(LOCK) \
-    (thread_in_use () ? glthread_recursive_lock_lock_multithreaded (LOCK) : 0)
-# define glthread_recursive_lock_unlock(LOCK) \
-    (thread_in_use () ? glthread_recursive_lock_unlock_multithreaded (LOCK) : 0)
-# define glthread_recursive_lock_destroy(LOCK) \
-    (thread_in_use () ? glthread_recursive_lock_destroy_multithreaded (LOCK) : 0)
-extern int glthread_recursive_lock_init_multithreaded (gl_recursive_lock_t *lock);
-extern int glthread_recursive_lock_lock_multithreaded (gl_recursive_lock_t *lock);
-extern int glthread_recursive_lock_unlock_multithreaded (gl_recursive_lock_t *lock);
-extern int glthread_recursive_lock_destroy_multithreaded (gl_recursive_lock_t *lock);
-
-/* -------------------------- gl_once_t datatype -------------------------- */
-
-typedef struct
-        {
-          volatile int inited;
-          mutex_t mutex;
-        }
-        gl_once_t;
-# define gl_once_define(STORAGECLASS, NAME) \
-    STORAGECLASS gl_once_t NAME = { 0, DEFAULTMUTEX };
-# define glthread_once(ONCE_CONTROL, INITFUNCTION) \
-    (thread_in_use ()                                                          \
-     ? glthread_once_multithreaded (ONCE_CONTROL, INITFUNCTION)                \
-     : (glthread_once_singlethreaded (ONCE_CONTROL) ? (INITFUNCTION (), 0) : 0))
-extern int glthread_once_multithreaded (gl_once_t *once_control, void (*initfunction) (void));
-extern int glthread_once_singlethreaded (gl_once_t *once_control);
+extern int glthread_once_singlethreaded (pthread_once_t *once_control);
 
 # ifdef __cplusplus
 }
@@ -618,6 +535,11 @@ extern int glthread_once_singlethreaded (gl_once_t *once_control);
 # define WIN32_LEAN_AND_MEAN  /* avoid including junk */
 # include <windows.h>
 
+# include "windows-mutex.h"
+# include "windows-rwlock.h"
+# include "windows-recmutex.h"
+# include "windows-once.h"
+
 # ifdef __cplusplus
 extern "C" {
 # endif
@@ -633,127 +555,69 @@ extern "C" {
 /* There is no way to statically initialize a CRITICAL_SECTION.  It needs
    to be done lazily, once only.  For this we need spinlocks.  */
 
-typedef struct { volatile int done; volatile long started; } gl_spinlock_t;
-
 /* -------------------------- gl_lock_t datatype -------------------------- */
 
-typedef struct
-        {
-          gl_spinlock_t guard; /* protects the initialization */
-          CRITICAL_SECTION lock;
-        }
-        gl_lock_t;
+typedef glwthread_mutex_t gl_lock_t;
 # define gl_lock_define(STORAGECLASS, NAME) \
     STORAGECLASS gl_lock_t NAME;
 # define gl_lock_define_initialized(STORAGECLASS, NAME) \
     STORAGECLASS gl_lock_t NAME = gl_lock_initializer;
 # define gl_lock_initializer \
-    { { 0, -1 } }
+    GLWTHREAD_MUTEX_INIT
 # define glthread_lock_init(LOCK) \
-    (glthread_lock_init_func (LOCK), 0)
+    (glwthread_mutex_init (LOCK), 0)
 # define glthread_lock_lock(LOCK) \
-    glthread_lock_lock_func (LOCK)
+    glwthread_mutex_lock (LOCK)
 # define glthread_lock_unlock(LOCK) \
-    glthread_lock_unlock_func (LOCK)
+    glwthread_mutex_unlock (LOCK)
 # define glthread_lock_destroy(LOCK) \
-    glthread_lock_destroy_func (LOCK)
-extern void glthread_lock_init_func (gl_lock_t *lock);
-extern int glthread_lock_lock_func (gl_lock_t *lock);
-extern int glthread_lock_unlock_func (gl_lock_t *lock);
-extern int glthread_lock_destroy_func (gl_lock_t *lock);
+    glwthread_mutex_destroy (LOCK)
 
 /* ------------------------- gl_rwlock_t datatype ------------------------- */
 
-/* It is impossible to implement read-write locks using plain locks, without
-   introducing an extra thread dedicated to managing read-write locks.
-   Therefore here we need to use the low-level Event type.  */
-
-typedef struct
-        {
-          HANDLE *array; /* array of waiting threads, each represented by an event */
-          unsigned int count; /* number of waiting threads */
-          unsigned int alloc; /* length of allocated array */
-          unsigned int offset; /* index of first waiting thread in array */
-        }
-        gl_carray_waitqueue_t;
-typedef struct
-        {
-          gl_spinlock_t guard; /* protects the initialization */
-          CRITICAL_SECTION lock; /* protects the remaining fields */
-          gl_carray_waitqueue_t waiting_readers; /* waiting readers */
-          gl_carray_waitqueue_t waiting_writers; /* waiting writers */
-          int runcount; /* number of readers running, or -1 when a writer runs */
-        }
-        gl_rwlock_t;
+typedef glwthread_rwlock_t gl_rwlock_t;
 # define gl_rwlock_define(STORAGECLASS, NAME) \
     STORAGECLASS gl_rwlock_t NAME;
 # define gl_rwlock_define_initialized(STORAGECLASS, NAME) \
     STORAGECLASS gl_rwlock_t NAME = gl_rwlock_initializer;
 # define gl_rwlock_initializer \
-    { { 0, -1 } }
+    GLWTHREAD_RWLOCK_INIT
 # define glthread_rwlock_init(LOCK) \
-    (glthread_rwlock_init_func (LOCK), 0)
+    (glwthread_rwlock_init (LOCK), 0)
 # define glthread_rwlock_rdlock(LOCK) \
-    glthread_rwlock_rdlock_func (LOCK)
+    glwthread_rwlock_rdlock (LOCK)
 # define glthread_rwlock_wrlock(LOCK) \
-    glthread_rwlock_wrlock_func (LOCK)
+    glwthread_rwlock_wrlock (LOCK)
 # define glthread_rwlock_unlock(LOCK) \
-    glthread_rwlock_unlock_func (LOCK)
+    glwthread_rwlock_unlock (LOCK)
 # define glthread_rwlock_destroy(LOCK) \
-    glthread_rwlock_destroy_func (LOCK)
-extern void glthread_rwlock_init_func (gl_rwlock_t *lock);
-extern int glthread_rwlock_rdlock_func (gl_rwlock_t *lock);
-extern int glthread_rwlock_wrlock_func (gl_rwlock_t *lock);
-extern int glthread_rwlock_unlock_func (gl_rwlock_t *lock);
-extern int glthread_rwlock_destroy_func (gl_rwlock_t *lock);
+    glwthread_rwlock_destroy (LOCK)
 
 /* --------------------- gl_recursive_lock_t datatype --------------------- */
 
-/* The native Windows documentation says that CRITICAL_SECTION already
-   implements a recursive lock.  But we need not rely on it: It's easy to
-   implement a recursive lock without this assumption.  */
-
-typedef struct
-        {
-          gl_spinlock_t guard; /* protects the initialization */
-          DWORD owner;
-          unsigned long depth;
-          CRITICAL_SECTION lock;
-        }
-        gl_recursive_lock_t;
+typedef glwthread_recmutex_t gl_recursive_lock_t;
 # define gl_recursive_lock_define(STORAGECLASS, NAME) \
     STORAGECLASS gl_recursive_lock_t NAME;
 # define gl_recursive_lock_define_initialized(STORAGECLASS, NAME) \
     STORAGECLASS gl_recursive_lock_t NAME = gl_recursive_lock_initializer;
 # define gl_recursive_lock_initializer \
-    { { 0, -1 }, 0, 0 }
+    GLWTHREAD_RECMUTEX_INIT
 # define glthread_recursive_lock_init(LOCK) \
-    (glthread_recursive_lock_init_func (LOCK), 0)
+    (glwthread_recmutex_init (LOCK), 0)
 # define glthread_recursive_lock_lock(LOCK) \
-    glthread_recursive_lock_lock_func (LOCK)
+    glwthread_recmutex_lock (LOCK)
 # define glthread_recursive_lock_unlock(LOCK) \
-    glthread_recursive_lock_unlock_func (LOCK)
+    glwthread_recmutex_unlock (LOCK)
 # define glthread_recursive_lock_destroy(LOCK) \
-    glthread_recursive_lock_destroy_func (LOCK)
-extern void glthread_recursive_lock_init_func (gl_recursive_lock_t *lock);
-extern int glthread_recursive_lock_lock_func (gl_recursive_lock_t *lock);
-extern int glthread_recursive_lock_unlock_func (gl_recursive_lock_t *lock);
-extern int glthread_recursive_lock_destroy_func (gl_recursive_lock_t *lock);
+    glwthread_recmutex_destroy (LOCK)
 
 /* -------------------------- gl_once_t datatype -------------------------- */
 
-typedef struct
-        {
-          volatile int inited;
-          volatile long started;
-          CRITICAL_SECTION lock;
-        }
-        gl_once_t;
+typedef glwthread_once_t gl_once_t;
 # define gl_once_define(STORAGECLASS, NAME) \
-    STORAGECLASS gl_once_t NAME = { -1, -1 };
+    STORAGECLASS gl_once_t NAME = GLWTHREAD_ONCE_INIT;
 # define glthread_once(ONCE_CONTROL, INITFUNCTION) \
-    (glthread_once_func (ONCE_CONTROL, INITFUNCTION), 0)
-extern void glthread_once_func (gl_once_t *once_control, void (*initfunction) (void));
+    (glwthread_once (ONCE_CONTROL, INITFUNCTION), 0)
 
 # ifdef __cplusplus
 }
@@ -763,7 +627,7 @@ extern void glthread_once_func (gl_once_t *once_control, void (*initfunction) (v
 
 /* ========================================================================= */
 
-#if !(USE_POSIX_THREADS || USE_PTH_THREADS || USE_SOLARIS_THREADS || USE_WINDOWS_THREADS)
+#if !(USE_ISOC_THREADS || USE_POSIX_THREADS || USE_ISOC_AND_POSIX_THREADS || USE_WINDOWS_THREADS)
 
 /* Provide dummy implementation if threads are not supported.  */
 
diff --git a/gl/glthread/threadlib.c b/gl/glthread/threadlib.c
index b4476573..793bc694 100644
--- a/gl/glthread/threadlib.c
+++ b/gl/glthread/threadlib.c
@@ -1,18 +1,18 @@
 /* Multithreading primitives.
-   Copyright (C) 2005-2013 Free Software Foundation, Inc.
+   Copyright (C) 2005-2021 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 file is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Lesser General Public License as
+   published by the Free Software Foundation; either version 2.1 of the
+   License, or (at your option) any later version.
 
-   This program is distributed in the hope that it will be useful,
+   This file 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.
+   GNU Lesser 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 <http://www.gnu.org/licenses/>.  */
+   You should have received a copy of the GNU Lesser General Public License
+   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
 
 /* Written by Bruno Haible <bruno@clisp.org>, 2005.  */
 
@@ -20,15 +20,48 @@
 
 /* ========================================================================= */
 
-#if USE_POSIX_THREADS
+#if USE_POSIX_THREADS || USE_ISOC_AND_POSIX_THREADS
 
 /* Use the POSIX threads library.  */
 
+# include <errno.h>
 # include <pthread.h>
 # include <stdlib.h>
 
 # if PTHREAD_IN_USE_DETECTION_HARD
 
+#  if defined __FreeBSD__ || defined __DragonFly__                 /* FreeBSD */
+
+/* Test using pthread_key_create.  */
+
+int
+glthread_in_use (void)
+{
+  static int tested;
+  static int result; /* 1: linked with -lpthread, 0: only with libc */
+
+  if (!tested)
+    {
+      pthread_key_t key;
+      int err = pthread_key_create (&key, NULL);
+
+      if (err == ENOSYS)
+        result = 0;
+      else
+        {
+          result = 1;
+          if (err == 0)
+            pthread_key_delete (key);
+        }
+      tested = 1;
+    }
+  return result;
+}
+
+#  else                                                     /* Solaris, HP-UX */
+
+/* Test using pthread_create.  */
+
 /* The function to be executed by a dummy thread.  */
 static void *
 dummy_thread_func (void *arg)
@@ -62,6 +95,8 @@ glthread_in_use (void)
   return result;
 }
 
+#  endif
+
 # endif
 
 #endif