/*

 * Copyright © 2011 Ryan Lortie

 *

 * 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

 * licence, 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.

 *

 * Author: Ryan Lortie <desrt@desrt.ca>

 */

#include "config.h"

#include "gatomic.h"

/**

 * SECTION:atomic_operations

 * @title: Atomic Operations

 * @short_description: basic atomic integer and pointer operations

 * @see_also: #GMutex

 *

 * The following is a collection of compiler macros to provide atomic

 * access to integer and pointer-sized values.

 *

 * The macros that have 'int' in the name will operate on pointers to

 * #gint and #guint.  The macros with 'pointer' in the name will operate

 * on pointers to any pointer-sized value, including #gsize.  There is

 * no support for 64bit operations on platforms with 32bit pointers

 * because it is not generally possible to perform these operations

 * atomically.

 *

 * The get, set and exchange operations for integers and pointers

 * nominally operate on #gint and #gpointer, respectively.  Of the

 * arithmetic operations, the 'add' operation operates on (and returns)

 * signed integer values (#gint and #gssize) and the 'and', 'or', and

 * 'xor' operations operate on (and return) unsigned integer values

 * (#guint and #gsize).

 *

 * All of the operations act as a full compiler and (where appropriate)

 * hardware memory barrier.  Acquire and release or producer and

 * consumer barrier semantics are not available through this API.

 *

 * It is very important that all accesses to a particular integer or

 * pointer be performed using only this API and that different sizes of

 * operation are not mixed or used on overlapping memory regions.  Never

 * read or assign directly from or to a value -- always use this API.

 *

 * For simple reference counting purposes you should use

 * g_atomic_int_inc() and g_atomic_int_dec_and_test().  Other uses that

 * fall outside of simple reference counting patterns are prone to

 * subtle bugs and occasionally undefined behaviour.  It is also worth

 * noting that since all of these operations require global

 * synchronisation of the entire machine, they can be quite slow.  In

 * the case of performing multiple atomic operations it can often be

 * faster to simply acquire a mutex lock around the critical area,

 * perform the operations normally and then release the lock.

 **/

/**

 * G_ATOMIC_LOCK_FREE:

 *

 * This macro is defined if the atomic operations of GLib are

 * implemented using real hardware atomic operations.  This means that

 * the GLib atomic API can be used between processes and safely mixed

 * with other (hardware) atomic APIs.

 *

 * If this macro is not defined, the atomic operations may be

 * emulated using a mutex.  In that case, the GLib atomic operations are

 * only atomic relative to themselves and within a single process.

 **/

/* NOTE CAREFULLY:

 *

 * This file is the lowest-level part of GLib.

 *

 * Other lowlevel parts of GLib (threads, slice allocator, g_malloc,

 * messages, etc) call into these functions and macros to get work done.

 *

 * As such, these functions can not call back into any part of GLib

 * without risking recursion.

 */

#ifdef G_ATOMIC_LOCK_FREE

/* if G_ATOMIC_LOCK_FREE was defined by ./configure then we MUST

 * implement the atomic operations in a lock-free manner.

 */

#if defined (__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4)

/**

 * g_atomic_int_get:

 * @atomic: a pointer to a #gint or #guint

 *

 * Gets the current value of @atomic.

 *

 * This call acts as a full compiler and hardware

 * memory barrier (before the get).

 *

 * Returns: the value of the integer

 *

 * Since: 2.4

 **/

gint

(g_atomic_int_get) (volatile gint *atomic)

{

  return g_atomic_int_get (atomic);

}

/**

 * g_atomic_int_set:

 * @atomic: a pointer to a #gint or #guint

 * @newval: a new value to store

 *

 * Sets the value of @atomic to @newval.

 *

 * This call acts as a full compiler and hardware

 * memory barrier (after the set).

 *

 * Since: 2.4

 */

void

(g_atomic_int_set) (volatile gint *atomic,

                    gint           newval)

{

  g_atomic_int_set (atomic, newval);

}

/**

 * g_atomic_int_inc:

 * @atomic: a pointer to a #gint or #guint

 *

 * Increments the value of @atomic by 1.

 *

 * Think of this operation as an atomic version of

 * <literal>{ *@atomic += 1; }</literal>

 *

 * This call acts as a full compiler and hardware memory barrier.

 *

 * Since: 2.4

 **/

void

(g_atomic_int_inc) (volatile gint *atomic)

{

  g_atomic_int_inc (atomic);

}

/**

 * g_atomic_int_dec_and_test:

 * @atomic: a pointer to a #gint or #guint

 *

 * Decrements the value of @atomic by 1.

 *

 * Think of this operation as an atomic version of

 * <literal>{ *@atomic -= 1; return (*@atomic == 0); }</literal>

 *

 * This call acts as a full compiler and hardware memory barrier.

 *

 * Returns: %TRUE if the resultant value is zero

 *

 * Since: 2.4

 **/

gboolean

(g_atomic_int_dec_and_test) (volatile gint *atomic)

{

  return g_atomic_int_dec_and_test (atomic);

}

/**

 * g_atomic_int_compare_and_exchange:

 * @atomic: a pointer to a #gint or #guint

 * @oldval: the value to compare with

 * @newval: the value to conditionally replace with

 *

 * Compares @atomic to @oldval and, if equal, sets it to @newval.

 * If @atomic was not equal to @oldval then no change occurs.

 *

 * This compare and exchange is done atomically.

 *

 * Think of this operation as an atomic version of

 * <literal>{ if (*@atomic == @oldval) { *@atomic = @newval; return TRUE; } else return FALSE; }</literal>

 *

 * This call acts as a full compiler and hardware memory barrier.

 *

 * Returns: %TRUE if the exchange took place

 *

 * Since: 2.4

 **/

gboolean

(g_atomic_int_compare_and_exchange) (volatile gint *atomic,

                                     gint           oldval,

                                     gint           newval)

{

  return g_atomic_int_compare_and_exchange (atomic, oldval, newval);

}

/**

 * g_atomic_int_add:

 * @atomic: a pointer to a #gint or #guint

 * @val: the value to add

 *

 * Atomically adds @val to the value of @atomic.

 *

 * Think of this operation as an atomic version of

 * <literal>{ tmp = *atomic; *@atomic += @val; return tmp; }</literal>

 *

 * This call acts as a full compiler and hardware memory barrier.

 *

 * Before version 2.30, this function did not return a value

 * (but g_atomic_int_exchange_and_add() did, and had the same meaning).

 *

 * Returns: the value of @atomic before the add, signed

 *

 * Since: 2.4

 **/

gint

(g_atomic_int_add) (volatile gint *atomic,

                    gint           val)

{

  return g_atomic_int_add (atomic, val);

}

/**

 * g_atomic_int_and:

 * @atomic: a pointer to a #gint or #guint

 * @val: the value to 'and'

 *

 * Performs an atomic bitwise 'and' of the value of @atomic and @val,

 * storing the result back in @atomic.

 *

 * This call acts as a full compiler and hardware memory barrier.

 *

 * Think of this operation as an atomic version of

 * <literal>{ tmp = *atomic; *@atomic &= @val; return tmp; }</literal>

 *

 * Returns: the value of @atomic before the operation, unsigned

 *

 * Since: 2.30

 **/

guint

(g_atomic_int_and) (volatile guint *atomic,

                    guint           val)

{

  return g_atomic_int_and (atomic, val);

}

/**

 * g_atomic_int_or:

 * @atomic: a pointer to a #gint or #guint

 * @val: the value to 'or'

 *

 * Performs an atomic bitwise 'or' of the value of @atomic and @val,

 * storing the result back in @atomic.

 *

 * Think of this operation as an atomic version of

 * <literal>{ tmp = *atomic; *@atomic |= @val; return tmp; }</literal>

 *

 * This call acts as a full compiler and hardware memory barrier.

 *

 * Returns: the value of @atomic before the operation, unsigned

 *

 * Since: 2.30

 **/

guint

(g_atomic_int_or) (volatile guint *atomic,

                   guint           val)

{

  return g_atomic_int_or (atomic, val);

}

/**

 * g_atomic_int_xor:

 * @atomic: a pointer to a #gint or #guint

 * @val: the value to 'xor'

 *

 * Performs an atomic bitwise 'xor' of the value of @atomic and @val,

 * storing the result back in @atomic.

 *

 * Think of this operation as an atomic version of

 * <literal>{ tmp = *atomic; *@atomic ^= @val; return tmp; }</literal>

 *

 * This call acts as a full compiler and hardware memory barrier.

 *

 * Returns: the value of @atomic before the operation, unsigned

 *

 * Since: 2.30

 **/

guint

(g_atomic_int_xor) (volatile guint *atomic,

                    guint           val)

{

  return g_atomic_int_xor (atomic, val);

}

/**

 * g_atomic_pointer_get:

 * @atomic: a pointer to a #gpointer-sized value

 *

 * Gets the current value of @atomic.

 *

 * This call acts as a full compiler and hardware

 * memory barrier (before the get).

 *

 * Returns: the value of the pointer

 *

 * Since: 2.4

 **/

gpointer

(g_atomic_pointer_get) (volatile void *atomic)

{

  return g_atomic_pointer_get ((volatile gpointer *) atomic);

}

/**

 * g_atomic_pointer_set:

 * @atomic: a pointer to a #gpointer-sized value

 * @newval: a new value to store

 *

 * Sets the value of @atomic to @newval.

 *

 * This call acts as a full compiler and hardware

 * memory barrier (after the set).

 *

 * Since: 2.4

 **/

void

(g_atomic_pointer_set) (volatile void *atomic,

                        gpointer       newval)

{

  g_atomic_pointer_set ((volatile gpointer *) atomic, newval);

}

/**

 * g_atomic_pointer_compare_and_exchange:

 * @atomic: a pointer to a #gpointer-sized value

 * @oldval: the value to compare with

 * @newval: the value to conditionally replace with

 *

 * Compares @atomic to @oldval and, if equal, sets it to @newval.

 * If @atomic was not equal to @oldval then no change occurs.

 *

 * This compare and exchange is done atomically.

 *

 * Think of this operation as an atomic version of

 * <literal>{ if (*@atomic == @oldval) { *@atomic = @newval; return TRUE; } else return FALSE; }</literal>

 *

 * This call acts as a full compiler and hardware memory barrier.

 *

 * Returns: %TRUE if the exchange took place

 *

 * Since: 2.4

 **/

gboolean

(g_atomic_pointer_compare_and_exchange) (volatile void *atomic,

                                         gpointer       oldval,

                                         gpointer       newval)

{

  return g_atomic_pointer_compare_and_exchange ((volatile gpointer *) atomic,

                                                oldval, newval);

}

/**

 * g_atomic_pointer_add:

 * @atomic: a pointer to a #gpointer-sized value

 * @val: the value to add

 *

 * Atomically adds @val to the value of @atomic.

 *

 * Think of this operation as an atomic version of

 * <literal>{ tmp = *atomic; *@atomic += @val; return tmp; }</literal>

 *

 * This call acts as a full compiler and hardware memory barrier.

 *

 * Returns: the value of @atomic before the add, signed

 *

 * Since: 2.30

 **/

gssize

(g_atomic_pointer_add) (volatile void *atomic,

                        gssize         val)

{

  return g_atomic_pointer_add ((volatile gpointer *) atomic, val);

}

/**

 * g_atomic_pointer_and:

 * @atomic: a pointer to a #gpointer-sized value

 * @val: the value to 'and'

 *

 * Performs an atomic bitwise 'and' of the value of @atomic and @val,

 * storing the result back in @atomic.

 *

 * Think of this operation as an atomic version of

 * <literal>{ tmp = *atomic; *@atomic &= @val; return tmp; }</literal>

 *

 * This call acts as a full compiler and hardware memory barrier.

 *

 * Returns: the value of @atomic before the operation, unsigned

 *

 * Since: 2.30

 **/

gsize

(g_atomic_pointer_and) (volatile void *atomic,

                        gsize          val)

{

  return g_atomic_pointer_and ((volatile gpointer *) atomic, val);

}

/**

 * g_atomic_pointer_or:

 * @atomic: a pointer to a #gpointer-sized value

 * @val: the value to 'or'

 *

 * Performs an atomic bitwise 'or' of the value of @atomic and @val,

 * storing the result back in @atomic.

 *

 * Think of this operation as an atomic version of

 * <literal>{ tmp = *atomic; *@atomic |= @val; return tmp; }</literal>

 *

 * This call acts as a full compiler and hardware memory barrier.

 *

 * Returns: the value of @atomic before the operation, unsigned

 *

 * Since: 2.30

 **/

gsize

(g_atomic_pointer_or) (volatile void *atomic,

                       gsize          val)

{

  return g_atomic_pointer_or ((volatile gpointer *) atomic, val);

}

/**

 * g_atomic_pointer_xor:

 * @atomic: a pointer to a #gpointer-sized value

 * @val: the value to 'xor'

 *

 * Performs an atomic bitwise 'xor' of the value of @atomic and @val,

 * storing the result back in @atomic.

 *

 * Think of this operation as an atomic version of

 * <literal>{ tmp = *atomic; *@atomic ^= @val; return tmp; }</literal>

 *

 * This call acts as a full compiler and hardware memory barrier.

 *

 * Returns: the value of @atomic before the operation, unsigned

 *

 * Since: 2.30

 **/

gsize

(g_atomic_pointer_xor) (volatile void *atomic,

                        gsize          val)

{

  return g_atomic_pointer_xor ((volatile gpointer *) atomic, val);

}

#elif defined (G_PLATFORM_WIN32)

#include <windows.h>

#if !defined(_M_AMD64) && !defined (_M_IA64) && !defined(_M_X64)

#define InterlockedAnd _InterlockedAnd

#define InterlockedOr _InterlockedOr

#define InterlockedXor _InterlockedXor

#endif

/*

 * http://msdn.microsoft.com/en-us/library/ms684122(v=vs.85).aspx

 */

gint

(g_atomic_int_get) (volatile gint *atomic)

{

  MemoryBarrier ();

  return *atomic;

}

void

(g_atomic_int_set) (volatile gint *atomic,

                    gint           newval)

{

  *atomic = newval;

  MemoryBarrier ();

}

void

(g_atomic_int_inc) (volatile gint *atomic)

{

  InterlockedIncrement (atomic);

}

gboolean

(g_atomic_int_dec_and_test) (volatile gint *atomic)

{

  return InterlockedDecrement (atomic) == 0;

}

gboolean

(g_atomic_int_compare_and_exchange) (volatile gint *atomic,

                                     gint           oldval,

                                     gint           newval)

{

  return InterlockedCompareExchange (atomic, newval, oldval) == oldval;

}

gint

(g_atomic_int_add) (volatile gint *atomic,

                    gint           val)

{

  return InterlockedExchangeAdd (atomic, val);

}

guint

(g_atomic_int_and) (volatile guint *atomic,

                    guint           val)

{

  return InterlockedAnd (atomic, val);

}

guint

(g_atomic_int_or) (volatile guint *atomic,

                   guint           val)

{

  return InterlockedOr (atomic, val);

}

guint

(g_atomic_int_xor) (volatile guint *atomic,

                    guint           val)

{

  return InterlockedXor (atomic, val);

}

gpointer

(g_atomic_pointer_get) (volatile void *atomic)

{

  volatile gpointer *ptr = atomic;

  MemoryBarrier ();

  return *ptr;

}

void

(g_atomic_pointer_set) (volatile void *atomic,

                        gpointer       newval)

{

  volatile gpointer *ptr = atomic;

  *ptr = newval;

  MemoryBarrier ();

}

gboolean

(g_atomic_pointer_compare_and_exchange) (volatile void *atomic,

                                         gpointer       oldval,

                                         gpointer       newval)

{

  return InterlockedCompareExchangePointer (atomic, newval, oldval) == oldval;

}

gssize

(g_atomic_pointer_add) (volatile void *atomic,

                        gssize         val)

{

#if GLIB_SIZEOF_VOID_P == 8

  return InterlockedExchangeAdd64 (atomic, val);

#else

  return InterlockedExchangeAdd (atomic, val);

#endif

}

gsize

(g_atomic_pointer_and) (volatile void *atomic,

                        gsize          val)

{

#if GLIB_SIZEOF_VOID_P == 8

  return InterlockedAnd64 (atomic, val);

#else

  return InterlockedAnd (atomic, val);

#endif

}

gsize

(g_atomic_pointer_or) (volatile void *atomic,

                       gsize          val)

{

#if GLIB_SIZEOF_VOID_P == 8

  return InterlockedOr64 (atomic, val);

#else

  return InterlockedOr (atomic, val);

#endif

}

gsize

(g_atomic_pointer_xor) (volatile void *atomic,

                        gsize          val)

{

#if GLIB_SIZEOF_VOID_P == 8

  return InterlockedXor64 (atomic, val);

#else

  return InterlockedXor (atomic, val);

#endif

}

#else

/* This error occurs when ./configure decided that we should be capable

 * of lock-free atomics but we find at compile-time that we are not.

 */

#error G_ATOMIC_LOCK_FREE defined, but incapable of lock-free atomics.

#endif /* defined (__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4) */

#else /* G_ATOMIC_LOCK_FREE */

/* We are not permitted to call into any GLib functions from here, so we

 * can not use GMutex.

 *

 * Fortunately, we already take care of the Windows case above, and all

 * non-Windows platforms on which glib runs have pthreads.  Use those.

 */

#include <pthread.h>

static pthread_mutex_t g_atomic_lock = PTHREAD_MUTEX_INITIALIZER;

gint

(g_atomic_int_get) (volatile gint *atomic)

{

  gint value;

  pthread_mutex_lock (&g_atomic_lock);

  value = *atomic;

  pthread_mutex_unlock (&g_atomic_lock);

  return value;

}

void

(g_atomic_int_set) (volatile gint *atomic,

                    gint           value)

{

  pthread_mutex_lock (&g_atomic_lock);

  *atomic = value;

  pthread_mutex_unlock (&g_atomic_lock);

}

void

(g_atomic_int_inc) (volatile gint *atomic)

{

  pthread_mutex_lock (&g_atomic_lock);

  (*atomic)++;

  pthread_mutex_unlock (&g_atomic_lock);

}

gboolean

(g_atomic_int_dec_and_test) (volatile gint *atomic)

{

  gboolean is_zero;

  pthread_mutex_lock (&g_atomic_lock);

  is_zero = --(*atomic) == 0;

  pthread_mutex_unlock (&g_atomic_lock);

  return is_zero;

}

gboolean

(g_atomic_int_compare_and_exchange) (volatile gint *atomic,

                                     gint           oldval,

                                     gint           newval)

{

  gboolean success;

  pthread_mutex_lock (&g_atomic_lock);

  if ((success = (*atomic == oldval)))

    *atomic = newval;

  pthread_mutex_unlock (&g_atomic_lock);

  return success;

}

gint

(g_atomic_int_add) (volatile gint *atomic,

                    gint           val)

{

  gint oldval;

  pthread_mutex_lock (&g_atomic_lock);

  oldval = *atomic;

  *atomic = oldval + val;

  pthread_mutex_unlock (&g_atomic_lock);

  return oldval;

}

guint

(g_atomic_int_and) (volatile guint *atomic,

                    guint           val)

{

  guint oldval;

  pthread_mutex_lock (&g_atomic_lock);

  oldval = *atomic;

  *atomic = oldval & val;

  pthread_mutex_unlock (&g_atomic_lock);

  return oldval;

}

guint

(g_atomic_int_or) (volatile guint *atomic,

                   guint           val)

{

  guint oldval;

  pthread_mutex_lock (&g_atomic_lock);

  oldval = *atomic;

  *atomic = oldval | val;

  pthread_mutex_unlock (&g_atomic_lock);

  return oldval;

}

guint

(g_atomic_int_xor) (volatile guint *atomic,

                    guint           val)

{

  guint oldval;

  pthread_mutex_lock (&g_atomic_lock);

  oldval = *atomic;

  *atomic = oldval ^ val;

  pthread_mutex_unlock (&g_atomic_lock);

  return oldval;

}

gpointer

(g_atomic_pointer_get) (volatile void *atomic)

{

  volatile gpointer *ptr = atomic;

  gpointer value;

  pthread_mutex_lock (&g_atomic_lock);

  value = *ptr;

  pthread_mutex_unlock (&g_atomic_lock);

  return value;

}

void

(g_atomic_pointer_set) (volatile void *atomic,

                        gpointer       newval)

{

  volatile gpointer *ptr = atomic;

  pthread_mutex_lock (&g_atomic_lock);

  *ptr = newval;

  pthread_mutex_unlock (&g_atomic_lock);

}

gboolean

(g_atomic_pointer_compare_and_exchange) (volatile void *atomic,

                                         gpointer       oldval,

                                         gpointer       newval)

{

  volatile gpointer *ptr = atomic;

  gboolean success;

  pthread_mutex_lock (&g_atomic_lock);

  if ((success = (*ptr == oldval)))

    *ptr = newval;

  pthread_mutex_unlock (&g_atomic_lock);

  return success;

}

gssize

(g_atomic_pointer_add) (volatile void *atomic,

                        gssize         val)

{

  volatile gssize *ptr = atomic;

  gssize oldval;

  pthread_mutex_lock (&g_atomic_lock);

  oldval = *ptr;

  *ptr = oldval + val;

  pthread_mutex_unlock (&g_atomic_lock);

  return oldval;

}

gsize

(g_atomic_pointer_and) (volatile void *atomic,

                        gsize          val)

{

  volatile gsize *ptr = atomic;

  gsize oldval;

  pthread_mutex_lock (&g_atomic_lock);

  oldval = *ptr;

  *ptr = oldval & val;

  pthread_mutex_unlock (&g_atomic_lock);

  return oldval;

}

gsize

(g_atomic_pointer_or) (volatile void *atomic,

                       gsize          val)

{

  volatile gsize *ptr = atomic;

  gsize oldval;

  pthread_mutex_lock (&g_atomic_lock);

  oldval = *ptr;

  *ptr = oldval | val;

  pthread_mutex_unlock (&g_atomic_lock);

  return oldval;

}

gsize

(g_atomic_pointer_xor) (volatile void *atomic,

                        gsize          val)

{

  volatile gsize *ptr = atomic;

  gsize oldval;

  pthread_mutex_lock (&g_atomic_lock);

  oldval = *ptr;

  *ptr = oldval ^ val;

  pthread_mutex_unlock (&g_atomic_lock);

  return oldval;

}

#endif

/**

 * g_atomic_int_exchange_and_add:

 * @atomic: a pointer to a #gint

 * @val: the value to add

 *

 * This function existed before g_atomic_int_add() returned the prior

 * value of the integer (which it now does).  It is retained only for

 * compatibility reasons.  Don't use this function in new code.

 *

 * Returns: the value of @atomic before the add, signed

 * Since: 2.4

 * Deprecated: 2.30: Use g_atomic_int_add() instead.

 **/

gint

g_atomic_int_exchange_and_add (volatile gint *atomic,

                               gint           val)

{

  return (g_atomic_int_add) (atomic, val);

}