glib/glib/gthread-win32.c

/* GLIB - Library of useful routines for C programming
 * Copyright (C) 1995-1997  Peter Mattis, Spencer Kimball and Josh MacDonald
 *
 * gthread.c: solaris thread system implementation
 * Copyright 1998-2001 Sebastian Wilhelmi; University of Karlsruhe
 * Copyright 2001 Hans Breuer
 *
 * This library 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 of the License, or (at your option) any later version.
 *
 * This library 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 library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

/*
 * Modified by the GLib Team and others 1997-2000.  See the AUTHORS
 * file for a list of people on the GLib Team.  See the ChangeLog
 * files for a list of changes.  These files are distributed with
 * GLib at ftp://ftp.gtk.org/pub/gtk/.
 */

/* The GMutex and GCond implementations in this file are some of the
 * lowest-level code in GLib.  All other parts of GLib (messages,
 * memory, slices, etc) assume that they can freely use these facilities
 * without risking recursion.
 *
 * As such, these functions are NOT permitted to call any other part of
 * GLib.
 *
 * The thread manipulation functions (create, exit, join, etc.) have
 * more freedom -- they can do as they please.
 */

#include "config.h"

#include "gthread.h"
#include "gthreadprivate.h"
#include "gslice.h"

#include <windows.h>

#include <process.h>
#include <stdlib.h>
#include <stdio.h>

static void
g_thread_abort (gint         status,
                const gchar *function)
{
  fprintf (stderr, "GLib (gthread-win32.c): Unexpected error from C library during '%s': %s.  Aborting.\n",
           strerror (status), function);
  abort ();
}

/* Starting with Vista and Windows 2008, we have access to the
 * CONDITION_VARIABLE and SRWLock primatives on Windows, which are
 * pretty reasonable approximations of the primatives specified in
 * POSIX 2001 (pthread_cond_t and pthread_mutex_t respectively).
 *
 * Both of these types are structs containing a single pointer.  That
 * pointer is used as an atomic bitfield to support user-space mutexes
 * that only get the kernel involved in cases of contention (similar
 * to how futex()-based mutexes work on Linux).  The biggest advantage
 * of these new types is that they can be statically initialised to
 * zero.  This allows us to use them directly and still support:
 *
 *   GMutex mutex = G_MUTEX_INIT;
 *
 * and
 *
 *   GCond cond = G_COND_INIT;
 *
 * Unfortunately, Windows XP lacks these facilities and GLib still
 * needs to support Windows XP.  Our approach here is as follows:
 *
 *   - avoid depending on structure declarations at compile-time by
 *     declaring our own GMutex and GCond strutures to be
 *     ABI-compatible with SRWLock and CONDITION_VARIABLE and using
 *     those instead
 *
 *   - avoid a hard dependency on the symbols used to manipulate these
 *     structures by doing a dynamic lookup of those symbols at
 *     runtime
 *
 *   - if the symbols are not available, emulate them using other
 *     primatives
 *
 * Using this approach also allows us to easily build a GLib that lacks
 * support for Windows XP or to remove this code entirely when XP is no
 * longer supported (end of line is currently April 8, 2014).
 */
typedef struct
{
  void     (__stdcall * CallThisOnThreadExit)        (void);              /* fake */

  void     (__stdcall * InitializeSRWLock)           (gpointer lock);
  void     (__stdcall * DeleteSRWLock)               (gpointer lock);     /* fake */
  void     (__stdcall * AcquireSRWLockExclusive)     (gpointer lock);
  BOOLEAN  (__stdcall * TryAcquireSRWLockExclusive)  (gpointer lock);
  void     (__stdcall * ReleaseSRWLockExclusive)     (gpointer lock);
  void     (__stdcall * AcquireSRWLockShared)        (gpointer lock);
  BOOLEAN  (__stdcall * TryAcquireSRWLockShared)     (gpointer lock);
  void     (__stdcall * ReleaseSRWLockShared)        (gpointer lock);

  void     (__stdcall * InitializeConditionVariable) (gpointer cond);
  void     (__stdcall * DeleteConditionVariable)     (gpointer cond);     /* fake */
  BOOL     (__stdcall * SleepConditionVariableSRW)   (gpointer cond,
                                                      gpointer lock,
                                                      DWORD    timeout,
                                                      ULONG    flags);
  void     (__stdcall * WakeAllConditionVariable)    (gpointer cond);
  void     (__stdcall * WakeConditionVariable)       (gpointer cond);
} GThreadImplVtable;

static GThreadImplVtable g_thread_impl_vtable;

/* {{{1 GMutex */
void
g_mutex_init (GMutex *mutex)
{
  g_thread_impl_vtable.InitializeSRWLock (mutex);
}

void
g_mutex_clear (GMutex *mutex)
{
  if (g_thread_impl_vtable.DeleteSRWLock != NULL)
    g_thread_impl_vtable.DeleteSRWLock (mutex);
}

void
g_mutex_lock (GMutex *mutex)
{
  g_thread_impl_vtable.AcquireSRWLockExclusive (mutex);
}

gboolean
g_mutex_trylock (GMutex *mutex)
{
  return g_thread_impl_vtable.TryAcquireSRWLockExclusive (mutex);
}

void
g_mutex_unlock (GMutex *mutex)
{
  g_thread_impl_vtable.ReleaseSRWLockExclusive (mutex);
}

/* {{{1 GRecMutex */

static CRITICAL_SECTION *
g_rec_mutex_impl_new (void)
{
  CRITICAL_SECTION *cs;

  cs = g_slice_new (CRITICAL_SECTION);
  InitializeCriticalSection (cs);

  return cs;
}

static void
g_rec_mutex_impl_free (CRITICAL_SECTION *cs)
{
  DeleteCriticalSection (cs);
  g_slice_free (CRITICAL_SECTION, cs);
}

static CRITICAL_SECTION *
g_rec_mutex_get_impl (GRecMutex *mutex)
{
  CRITICAL_SECTION *impl = mutex->impl;

  if G_UNLIKELY (mutex->impl == NULL)
    {
      impl = g_rec_mutex_impl_new ();
      if (InterlockedCompareExchangePointer (&mutex->impl, impl, NULL) != NULL)
        g_rec_mutex_impl_free (impl);
      impl = mutex->impl;
    }

  return impl;
}

void
g_rec_mutex_init (GRecMutex *mutex)
{
  mutex->impl = g_rec_mutex_impl_new ();
}

void
g_rec_mutex_clear (GRecMutex *mutex)
{
  if (mutex->impl)
    g_rec_mutex_impl_free (mutex->impl);
}

void
g_rec_mutex_lock (GRecMutex *mutex)
{
  EnterCriticalSection (g_rec_mutex_get_impl (mutex));
}

void
g_rec_mutex_unlock (GRecMutex *mutex)
{
  LeaveCriticalSection (mutex->impl);
}

gboolean
g_rec_mutex_trylock (GRecMutex *mutex)
{
  return TryEnterCriticalSection (g_rec_mutex_get_impl (mutex));
}

/* {{{1 GRWLock */

void
g_rw_lock_init (GRWLock *lock)
{
  g_thread_impl_vtable.InitializeSRWLock (lock);
}

void
g_rw_lock_clear (GRWLock *lock)
{
  if (g_thread_impl_vtable.DeleteSRWLock != NULL)
    g_thread_impl_vtable.DeleteSRWLock (lock);
}

void
g_rw_lock_writer_lock (GRWLock *lock)
{
  g_thread_impl_vtable.AcquireSRWLockExclusive (lock);
}

gboolean
g_rw_lock_writer_trylock (GRWLock *lock)
{
  return g_thread_impl_vtable.TryAcquireSRWLockExclusive (lock);
}

void
g_rw_lock_writer_unlock (GRWLock *lock)
{
  g_thread_impl_vtable.ReleaseSRWLockExclusive (lock);
}

void
g_rw_lock_reader_lock (GRWLock *lock)
{
  g_thread_impl_vtable.AcquireSRWLockShared (lock);
}

gboolean
g_rw_lock_reader_trylock (GRWLock *lock)
{
  return g_thread_impl_vtable.TryAcquireSRWLockShared (lock);
}

void
g_rw_lock_reader_unlock (GRWLock *lock)
{
  g_thread_impl_vtable.ReleaseSRWLockShared (lock);
}

/* {{{1 GCond */
void
g_cond_init (GCond *cond)
{
  g_thread_impl_vtable.InitializeConditionVariable (cond);
}

void
g_cond_clear (GCond *cond)
{
  if (g_thread_impl_vtable.DeleteConditionVariable)
    g_thread_impl_vtable.DeleteConditionVariable (cond);
}

void
g_cond_signal (GCond *cond)
{
  g_thread_impl_vtable.WakeConditionVariable (cond);
}

void
g_cond_broadcast (GCond *cond)
{
  g_thread_impl_vtable.WakeAllConditionVariable (cond);
}

void
g_cond_wait (GCond  *cond,
             GMutex *entered_mutex)
{
  g_thread_impl_vtable.SleepConditionVariableSRW (cond, entered_mutex, INFINITE, 0);
}

gboolean
g_cond_timedwait (GCond  *cond,
                  GMutex *entered_mutex,
                  gint64  abs_time)
{
  gint64 span;
  FILETIME ft;
  gint64 now;

  GetSystemTimeAsFileTime (&ft);
  memmove (&now, &ft, sizeof (FILETIME));

  now -= G_GINT64_CONSTANT (116444736000000000);
  now /= 10;

  span = abs_time - now;

  if G_UNLIKELY (span < 0)
    span = 0;

  if G_UNLIKELY (span > G_GINT64_CONSTANT (1000) * G_MAXINT32)
    span = INFINITE;

  return g_thread_impl_vtable.SleepConditionVariableSRW (cond, entered_mutex, span / 1000, 0);
}

gboolean
g_cond_timed_wait (GCond    *cond,
                   GMutex   *entered_mutex,
                   GTimeVal *abs_time)
{
  if (abs_time)
    {
      gint64 micros;

      micros = abs_time->tv_sec;
      micros *= 1000000;
      micros += abs_time->tv_usec;

      return g_cond_timedwait (cond, entered_mutex, micros);
    }
  else
    {
      g_cond_wait (cond, entered_mutex);
      return TRUE;
    }
}

/* {{{1 GPrivate */

typedef struct _GPrivateDestructor GPrivateDestructor;

struct _GPrivateDestructor
{
  DWORD               index;
  GDestroyNotify      notify;
  GPrivateDestructor *next;
};

static GPrivateDestructor * volatile g_private_destructors;
static CRITICAL_SECTION g_private_lock;

static DWORD
g_private_get_impl (GPrivate *key)
{
  DWORD impl = (DWORD) key->p;

  if G_UNLIKELY (impl == 0)
    {
      EnterCriticalSection (&g_private_lock);
      impl = (DWORD) key->p;
      if (impl == 0)
        {
          GPrivateDestructor *destructor;

          impl = TlsAlloc ();

          if (impl == TLS_OUT_OF_INDEXES)
            g_thread_abort (0, "TlsAlloc");

          if (key->notify != NULL)
            {
              destructor = malloc (sizeof (GPrivateDestructor));
              if G_UNLIKELY (destructor == NULL)
                g_thread_abort (errno, "malloc");
              destructor->index = impl;
              destructor->notify = key->notify;
              destructor->next = g_private_destructors;

              /* We need to do an atomic store due to the unlocked
               * access to the destructor list from the thread exit
               * function.
               *
               * It can double as a sanity check...
               */
              if (InterlockedCompareExchangePointer (&g_private_destructors, destructor,
                                                     destructor->next) != destructor->next)
                g_thread_abort (0, "g_private_get_impl(1)");
            }

          /* Ditto, due to the unlocked access on the fast path */
          if (InterlockedCompareExchangePointer (&key->p, impl, NULL) != NULL)
            g_thread_abort (0, "g_private_get_impl(2)");
        }
      LeaveCriticalSection (&g_private_lock);
    }

  return impl;
}

gpointer
g_private_get (GPrivate *key)
{
  return TlsGetValue (g_private_get_impl (key));
}

void
g_private_set (GPrivate *key,
               gpointer  value)
{
  TlsSetValue (g_private_get_impl (key), value);
}

void
g_private_replace (GPrivate *key,
                   gpointer  value)
{
  DWORD impl = g_private_get_impl (key);
  gpointer old;

  old = TlsGetValue (impl);
  if (old && key->notify)
    key->notify (old);
  TlsSetValue (impl, value);
}

/* {{{1 GThread */

#include "glib.h"
#include "gthreadprivate.h"

#define win32_check_for_error(what) G_STMT_START{			\
  if (!(what))								\
    g_error ("file %s: line %d (%s): error %s during %s",		\
	     __FILE__, __LINE__, G_STRFUNC,				\
	     g_win32_error_message (GetLastError ()), #what);		\
  }G_STMT_END

#define G_MUTEX_SIZE (sizeof (gpointer))

static DWORD g_thread_self_tls;

typedef BOOL (__stdcall *GTryEnterCriticalSectionFunc) (CRITICAL_SECTION *);

typedef struct _GThreadData GThreadData;
struct _GThreadData
{
  GThreadFunc func;
  gpointer data;
  HANDLE thread;
  gboolean joinable;
};

void
g_system_thread_self (gpointer thread)
{
  GThreadData *self = TlsGetValue (g_thread_self_tls);

  if (!self)
    {
      /* This should only happen for the main thread! */
      HANDLE handle = GetCurrentThread ();
      HANDLE process = GetCurrentProcess ();
      self = g_new (GThreadData, 1);
      win32_check_for_error (DuplicateHandle (process, handle, process,
					      &self->thread, 0, FALSE,
					      DUPLICATE_SAME_ACCESS));
      win32_check_for_error (TlsSetValue (g_thread_self_tls, self));
      self->func = NULL;
      self->data = NULL;
      self->joinable = FALSE;
    }

  *(GThreadData **)thread = self;
}

void
g_system_thread_exit (void)
{
  GThreadData *self = TlsGetValue (g_thread_self_tls);
  gboolean dtors_called;

  do
    {
      GPrivateDestructor *dtor;

      /* We go by the POSIX book on this one.
       *
       * If we call a destructor then there is a chance that some new
       * TLS variables got set by code called in that destructor.
       *
       * Loop until nothing is left.
       */
      dtors_called = FALSE;

      for (dtor = g_private_destructors; dtor; dtor = dtor->next)
        {
          gpointer value;

          value = TlsGetValue (dtor->index);
          if (value != NULL && dtor->notify != NULL)
            {
              /* POSIX says to clear this before the call */
              TlsSetValue (dtor->index, NULL);
              dtor->notify (value);
              dtors_called = TRUE;
            }
        }
    }
  while (dtors_called);

  if (self)
    {
      if (!self->joinable)
	{
	  win32_check_for_error (CloseHandle (self->thread));
	  g_free (self);
	}
      win32_check_for_error (TlsSetValue (g_thread_self_tls, NULL));
    }

  if (g_thread_impl_vtable.CallThisOnThreadExit)
    g_thread_impl_vtable.CallThisOnThreadExit ();

  _endthreadex (0);
}

static guint __stdcall
g_thread_proxy (gpointer data)
{
  GThreadData *self = (GThreadData*) data;

  win32_check_for_error (TlsSetValue (g_thread_self_tls, self));

  self->func (self->data);

  g_system_thread_exit ();

  g_assert_not_reached ();

  return 0;
}

void
g_system_thread_create (GThreadFunc       func,
                        gpointer          data,
                        gulong            stack_size,
                        gboolean          joinable,
                        gpointer          thread,
                        GError          **error)
{
  guint ignore;
  GThreadData *retval;

  g_return_if_fail (func);

  retval = g_new(GThreadData, 1);
  retval->func = func;
  retval->data = data;

  retval->joinable = joinable;

  retval->thread = (HANDLE) _beginthreadex (NULL, stack_size, g_thread_proxy,
					    retval, 0, &ignore);

  if (retval->thread == NULL)
    {
      gchar *win_error = g_win32_error_message (GetLastError ());
      g_set_error (error, G_THREAD_ERROR, G_THREAD_ERROR_AGAIN,
                   "Error creating thread: %s", win_error);
      g_free (retval);
      g_free (win_error);
      return;
    }

  *(GThreadData **)thread = retval;
}

void
g_thread_yield (void)
{
  Sleep(0);
}

void
g_system_thread_join (gpointer thread)
{
  GThreadData *target = *(GThreadData **)thread;

  g_return_if_fail (target->joinable);

  win32_check_for_error (WAIT_FAILED !=
			 WaitForSingleObject (target->thread, INFINITE));

  win32_check_for_error (CloseHandle (target->thread));
  g_free (target);
}

gboolean
g_system_thread_equal (gpointer thread1,
                       gpointer thread2)
{
   return ((GSystemThread*)thread1)->dummy_pointer == ((GSystemThread*)thread2)->dummy_pointer;
}

/* {{{1 SRWLock and CONDITION_VARIABLE emulation (for Windows XP) */

static CRITICAL_SECTION g_thread_xp_lock;
static DWORD            g_thread_xp_waiter_tls;

/* {{{2 GThreadWaiter utility class for CONDITION_VARIABLE emulation */
typedef struct _GThreadXpWaiter GThreadXpWaiter;
struct _GThreadXpWaiter
{
  HANDLE                    event;
  volatile GThreadXpWaiter *next;
};

static GThreadXpWaiter *
g_thread_xp_waiter_get (void)
{
  GThreadXpWaiter *waiter;

  waiter = TlsGetValue (g_thread_xp_waiter_tls);

  if G_UNLIKELY (waiter == NULL)
    {
      waiter = malloc (sizeof (GThreadXpWaiter));
      if (waiter == NULL)
        g_thread_abort (GetLastError (), "malloc");
      waiter->event = CreateEvent (0, FALSE, FALSE, NULL);
      if (waiter->event == NULL)
        g_thread_abort (GetLastError (), "CreateEvent");

      TlsSetValue (g_thread_xp_waiter_tls, waiter);
    }

  return waiter;
}

static void __stdcall
g_thread_xp_CallThisOnThreadExit (void)
{
  GThreadXpWaiter *waiter;

  waiter = TlsGetValue (g_thread_xp_waiter_tls);

  if (waiter != NULL)
    {
      TlsSetValue (g_thread_xp_waiter_tls, NULL);
      CloseHandle (waiter->event);
      free (waiter);
    }
}

/* {{{2 SRWLock emulation */
typedef struct
{
  CRITICAL_SECTION  writer_lock;
  gboolean          ever_shared;    /* protected by writer_lock */
  gboolean          writer_locked;  /* protected by writer_lock */

  /* below is only ever touched if ever_shared becomes true */
  CRITICAL_SECTION  atomicity;
  GThreadXpWaiter  *queued_writer; /* protected by atomicity lock */
  gint              num_readers;   /* protected by atomicity lock */
} GThreadSRWLock;

static void __stdcall
g_thread_xp_InitializeSRWLock (gpointer mutex)
{
  *(GThreadSRWLock * volatile *) mutex = NULL;
}

static void __stdcall
g_thread_xp_DeleteSRWLock (gpointer mutex)
{
  GThreadSRWLock *lock = *(GThreadSRWLock * volatile *) mutex;

  if (lock)
    {
      if (lock->ever_shared)
        DeleteCriticalSection (&lock->atomicity);

      DeleteCriticalSection (&lock->writer_lock);
      free (lock);
    }
}

static GThreadSRWLock * __stdcall
g_thread_xp_get_srwlock (GThreadSRWLock * volatile *lock)
{
  GThreadSRWLock *result;

  /* It looks like we're missing some barriers here, but this code only
   * ever runs on Windows XP, which in turn only ever runs on hardware
   * with a relatively rigid memory model.  The 'volatile' will take
   * care of the compiler.
   */
  result = *lock;

  if G_UNLIKELY (result == NULL)
    {
      EnterCriticalSection (&g_thread_xp_lock);

      result = malloc (sizeof (GThreadSRWLock));

      if (result == NULL)
        g_thread_abort (errno, "malloc");

      InitializeCriticalSection (&result->writer_lock);
      result->writer_locked = FALSE;
      result->ever_shared = FALSE;
      *lock = result;

      LeaveCriticalSection (&g_thread_xp_lock);
    }

  return result;
}

static void __stdcall
g_thread_xp_AcquireSRWLockExclusive (gpointer mutex)
{
  GThreadSRWLock *lock = g_thread_xp_get_srwlock (mutex);

  EnterCriticalSection (&lock->writer_lock);

  /* CRITICAL_SECTION is reentrant, but SRWLock is not.
   * Detect the deadlock that would occur on later Windows version.
   */
  g_assert (!lock->writer_locked);
  lock->writer_locked = TRUE;

  if (lock->ever_shared)
    {
      GThreadXpWaiter *waiter = NULL;

      EnterCriticalSection (&lock->atomicity);
      if (lock->num_readers > 0)
        lock->queued_writer = waiter = g_thread_xp_waiter_get ();
      LeaveCriticalSection (&lock->atomicity);

      if (waiter != NULL)
        WaitForSingleObject (waiter->event, INFINITE);

      lock->queued_writer = NULL;
    }
}

static BOOLEAN __stdcall
g_thread_xp_TryAcquireSRWLockExclusive (gpointer mutex)
{
  GThreadSRWLock *lock = g_thread_xp_get_srwlock (mutex);

  if (!TryEnterCriticalSection (&lock->writer_lock))
    return FALSE;

  /* CRITICAL_SECTION is reentrant, but SRWLock is not.
   * Ensure that this properly returns FALSE (as SRWLock would).
   */
  if G_UNLIKELY (lock->writer_locked)
    {
      LeaveCriticalSection (&lock->writer_lock);
      return FALSE;
    }

  lock->writer_locked = TRUE;

  if (lock->ever_shared)
    {
      gboolean available;

      EnterCriticalSection (&lock->atomicity);
      available = lock->num_readers == 0;
      LeaveCriticalSection (&lock->atomicity);

      if (!available)
        {
          LeaveCriticalSection (&lock->writer_lock);
          return FALSE;
        }
    }

  return TRUE;
}

static void __stdcall
g_thread_xp_ReleaseSRWLockExclusive (gpointer mutex)
{
  GThreadSRWLock *lock = *(GThreadSRWLock * volatile *) mutex;

  lock->writer_locked = FALSE;

  /* We need this until we fix some weird parts of GLib that try to
   * unlock freshly-allocated mutexes.
   */
  if (lock != NULL)
    LeaveCriticalSection (&lock->writer_lock);
}

static void
g_thread_xp_srwlock_become_reader (GThreadSRWLock *lock)
{
  if G_UNLIKELY (!lock->ever_shared)
    {
      InitializeCriticalSection (&lock->atomicity);
      lock->queued_writer = NULL;
      lock->num_readers = 0;

      lock->ever_shared = TRUE;
    }

  EnterCriticalSection (&lock->atomicity);
  lock->num_readers++;
  LeaveCriticalSection (&lock->atomicity);
}

static void __stdcall
g_thread_xp_AcquireSRWLockShared (gpointer mutex)
{
  GThreadSRWLock *lock = g_thread_xp_get_srwlock (mutex);

  EnterCriticalSection (&lock->writer_lock);

  /* See g_thread_xp_AcquireSRWLockExclusive */
  g_assert (!lock->writer_locked);

  g_thread_xp_srwlock_become_reader (lock);

  LeaveCriticalSection (&lock->writer_lock);
}

static BOOLEAN __stdcall
g_thread_xp_TryAcquireSRWLockShared (gpointer mutex)
{
  GThreadSRWLock *lock = g_thread_xp_get_srwlock (mutex);

  if (!TryEnterCriticalSection (&lock->writer_lock))
    return FALSE;

  /* See g_thread_xp_AcquireSRWLockExclusive */
  if G_UNLIKELY (lock->writer_locked)
    {
      LeaveCriticalSection (&lock->writer_lock);
      return FALSE;
    }

  g_thread_xp_srwlock_become_reader (lock);

  LeaveCriticalSection (&lock->writer_lock);

  return TRUE;
}

static void __stdcall
g_thread_xp_ReleaseSRWLockShared (gpointer mutex)
{
  GThreadSRWLock *lock = g_thread_xp_get_srwlock (mutex);

  EnterCriticalSection (&lock->atomicity);

  lock->num_readers--;

  if (lock->num_readers == 0 && lock->queued_writer)
    SetEvent (lock->queued_writer->event);

  LeaveCriticalSection (&lock->atomicity);
}

/* {{{2 CONDITION_VARIABLE emulation */
typedef struct
{
  volatile GThreadXpWaiter  *first;
  volatile GThreadXpWaiter **last_ptr;
} GThreadXpCONDITION_VARIABLE;

static void __stdcall
g_thread_xp_InitializeConditionVariable (gpointer cond)
{
  *(GThreadXpCONDITION_VARIABLE * volatile *) cond = NULL;
}

static void __stdcall
g_thread_xp_DeleteConditionVariable (gpointer cond)
{
  GThreadXpCONDITION_VARIABLE *cv = *(GThreadXpCONDITION_VARIABLE * volatile *) cond;

  if (cv)
    free (cv);
}

static GThreadXpCONDITION_VARIABLE * __stdcall
g_thread_xp_get_condition_variable (GThreadXpCONDITION_VARIABLE * volatile *cond)
{
  GThreadXpCONDITION_VARIABLE *result;

  /* It looks like we're missing some barriers here, but this code only
   * ever runs on Windows XP, which in turn only ever runs on hardware
   * with a relatively rigid memory model.  The 'volatile' will take
   * care of the compiler.
   */
  result = *cond;

  if G_UNLIKELY (result == NULL)
    {
      result = malloc (sizeof (GThreadXpCONDITION_VARIABLE));

      if (result == NULL)
        g_thread_abort (errno, "malloc");

      result->first = NULL;
      result->last_ptr = &result->first;

      if (InterlockedCompareExchangePointer (cond, result, NULL) != NULL)
        {
          free (result);
          result = *cond;
        }
    }

  return result;
}

static BOOL __stdcall
g_thread_xp_SleepConditionVariableSRW (gpointer cond,
                                       gpointer mutex,
                                       DWORD    timeout,
                                       ULONG    flags)
{
  GThreadXpCONDITION_VARIABLE *cv = g_thread_xp_get_condition_variable (cond);
  GThreadXpWaiter *waiter = g_thread_xp_waiter_get ();
  DWORD status;

  waiter->next = NULL;

  EnterCriticalSection (&g_thread_xp_lock);
  *cv->last_ptr = waiter;
  cv->last_ptr = &waiter->next;
  LeaveCriticalSection (&g_thread_xp_lock);

  g_mutex_unlock (mutex);
  status = WaitForSingleObject (waiter->event, timeout);

  if (status != WAIT_TIMEOUT && status != WAIT_OBJECT_0)
    g_thread_abort (GetLastError (), "WaitForSingleObject");

  g_mutex_lock (mutex);

  return status == WAIT_OBJECT_0;
}

static void __stdcall
g_thread_xp_WakeConditionVariable (gpointer cond)
{
  GThreadXpCONDITION_VARIABLE *cv = g_thread_xp_get_condition_variable (cond);
  volatile GThreadXpWaiter *waiter;

  EnterCriticalSection (&g_thread_xp_lock);
  waiter = cv->first;
  if (waiter != NULL)
    {
      cv->first = waiter->next;
      if (cv->first == NULL)
        cv->last_ptr = &cv->first;
    }
  LeaveCriticalSection (&g_thread_xp_lock);

  if (waiter != NULL)
    SetEvent (waiter->event);
}

static void __stdcall
g_thread_xp_WakeAllConditionVariable (gpointer cond)
{
  GThreadXpCONDITION_VARIABLE *cv = g_thread_xp_get_condition_variable (cond);
  volatile GThreadXpWaiter *waiter;

  EnterCriticalSection (&g_thread_xp_lock);
  waiter = cv->first;
  cv->first = NULL;
  cv->last_ptr = &cv->first;
  LeaveCriticalSection (&g_thread_xp_lock);

  while (waiter != NULL)
    {
      volatile GThreadXpWaiter *next;

      next = waiter->next;
      SetEvent (waiter->event);
      waiter = next;
    }
}

/* {{{2 XP Setup */
static void
g_thread_xp_init (void)
{
  static const GThreadImplVtable g_thread_xp_impl_vtable = {
    g_thread_xp_CallThisOnThreadExit,
    g_thread_xp_InitializeSRWLock,
    g_thread_xp_DeleteSRWLock,
    g_thread_xp_AcquireSRWLockExclusive,
    g_thread_xp_TryAcquireSRWLockExclusive,
    g_thread_xp_ReleaseSRWLockExclusive,
    g_thread_xp_AcquireSRWLockShared,
    g_thread_xp_TryAcquireSRWLockShared,
    g_thread_xp_ReleaseSRWLockShared,
    g_thread_xp_InitializeConditionVariable,
    g_thread_xp_DeleteConditionVariable,
    g_thread_xp_SleepConditionVariableSRW,
    g_thread_xp_WakeAllConditionVariable,
    g_thread_xp_WakeConditionVariable
  };

  InitializeCriticalSection (&g_thread_xp_lock);
  g_thread_xp_waiter_tls = TlsAlloc ();

  g_thread_impl_vtable = g_thread_xp_impl_vtable;
}

/* {{{1 Epilogue */

static gboolean
g_thread_lookup_native_funcs (void)
{
  GThreadImplVtable native_vtable = { 0, };
  HMODULE kernel32;

  kernel32 = GetModuleHandle ("KERNEL32.DLL");

  if (kernel32 == NULL)
    return FALSE;

#define GET_FUNC(name) if ((native_vtable.name = (void *) GetProcAddress (kernel32, #name)) == NULL) return FALSE
  GET_FUNC(InitializeSRWLock);
  GET_FUNC(AcquireSRWLockExclusive);
  GET_FUNC(TryAcquireSRWLockExclusive);
  GET_FUNC(ReleaseSRWLockExclusive);
  GET_FUNC(AcquireSRWLockShared);
  GET_FUNC(TryAcquireSRWLockShared);
  GET_FUNC(ReleaseSRWLockShared);

  GET_FUNC(InitializeConditionVariable);
  GET_FUNC(SleepConditionVariableSRW);
  GET_FUNC(WakeAllConditionVariable);
  GET_FUNC(WakeConditionVariable);
#undef GET_FUNC

  g_thread_impl_vtable = native_vtable;

  return TRUE;
}

G_GNUC_INTERNAL void
g_thread_DllMain (void)
{
  if (g_thread_lookup_native_funcs ())
    fprintf (stderr, "(debug) GThread using native mode\n");
  else
    {
      fprintf (stderr, "(debug) GThread using Windows XP mode\n");
      g_thread_xp_init ();
    }

  win32_check_for_error (TLS_OUT_OF_INDEXES != (g_thread_self_tls = TlsAlloc ()));
  InitializeCriticalSection (&g_private_lock);
}

/* vim:set foldmethod=marker: */