Merge branch 'master' into RincewindsHat-patch-1

1 files changed, 377 insertions, 0 deletions

diff --git a/gl/windows-rwlock.c b/gl/windows-rwlock.c
new file mode 100644
index 0000000..7cbd7bb
--- /dev/null
+++ b/gl/windows-rwlock.c
@@ -0,0 +1,377 @@
+/* Read-write locks (native Windows implementation).
+   Copyright (C) 2005-2023 Free Software Foundation, Inc.
+
+   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 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 Lesser General Public License for more details.
+
+   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-win32.h.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include "windows-rwlock.h"
+
+#include <errno.h>
+#include <stdlib.h>
+
+/* Don't assume that UNICODE is not defined.  */
+#undef CreateEvent
+#define CreateEvent CreateEventA
+
+/* In this file, the waitqueues are implemented as circular arrays.  */
+#define glwthread_waitqueue_t glwthread_carray_waitqueue_t
+
+static void
+glwthread_waitqueue_init (glwthread_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
+glwthread_waitqueue_add (glwthread_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
+glwthread_waitqueue_notify_first (glwthread_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
+glwthread_waitqueue_notify_all (glwthread_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
+glwthread_rwlock_init (glwthread_rwlock_t *lock)
+{
+  InitializeCriticalSection (&lock->lock);
+  glwthread_waitqueue_init (&lock->waiting_readers);
+  glwthread_waitqueue_init (&lock->waiting_writers);
+  lock->runcount = 0;
+  lock->guard.done = 1;
+}
+
+int
+glwthread_rwlock_rdlock (glwthread_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.  */
+        glwthread_rwlock_init (lock);
+      else
+        {
+          /* Don't let lock->guard.started grow and wrap around.  */
+          InterlockedDecrement (&lock->guard.started);
+          /* 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 = glwthread_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
+glwthread_rwlock_wrlock (glwthread_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.  */
+        glwthread_rwlock_init (lock);
+      else
+        {
+          /* Don't let lock->guard.started grow and wrap around.  */
+          InterlockedDecrement (&lock->guard.started);
+          /* 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 = glwthread_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
+glwthread_rwlock_tryrdlock (glwthread_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.  */
+        glwthread_rwlock_init (lock);
+      else
+        {
+          /* Don't let lock->guard.started grow and wrap around.  */
+          InterlockedDecrement (&lock->guard.started);
+          /* Yield the CPU while waiting for another thread to finish
+             initializing this lock.  */
+          while (!lock->guard.done)
+            Sleep (0);
+        }
+    }
+  /* It's OK to wait for this critical section, because it is never taken for a
+     long time.  */
+  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 would have to wait for a while.  Return instead.  */
+      LeaveCriticalSection (&lock->lock);
+      return EBUSY;
+    }
+  lock->runcount++;
+  LeaveCriticalSection (&lock->lock);
+  return 0;
+}
+
+int
+glwthread_rwlock_trywrlock (glwthread_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.  */
+        glwthread_rwlock_init (lock);
+      else
+        {
+          /* Don't let lock->guard.started grow and wrap around.  */
+          InterlockedDecrement (&lock->guard.started);
+          /* Yield the CPU while waiting for another thread to finish
+             initializing this lock.  */
+          while (!lock->guard.done)
+            Sleep (0);
+        }
+    }
+  /* It's OK to wait for this critical section, because it is never taken for a
+     long time.  */
+  EnterCriticalSection (&lock->lock);
+  /* Test whether no readers or writers are currently running.  */
+  if (!(lock->runcount == 0))
+    {
+      /* This thread would have to wait for a while.  Return instead.  */
+      LeaveCriticalSection (&lock->lock);
+      return EBUSY;
+    }
+  lock->runcount--; /* runcount becomes -1 */
+  LeaveCriticalSection (&lock->lock);
+  return 0;
+}
+
+int
+glwthread_rwlock_unlock (glwthread_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--;
+          glwthread_waitqueue_notify_first (&lock->waiting_writers);
+        }
+      else
+        {
+          /* Wake up all waiting readers.  */
+          lock->runcount += lock->waiting_readers.count;
+          glwthread_waitqueue_notify_all (&lock->waiting_readers);
+        }
+    }
+  LeaveCriticalSection (&lock->lock);
+  return 0;
+}
+
+int
+glwthread_rwlock_destroy (glwthread_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;
+}