object.c

/* Copyright (c) 2013 The Squash Authors
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use, copy,
 * modify, merge, publish, distribute, sublicense, and/or sell copies
 * of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 *
 * Authors:
 *   Evan Nemerson <evan@nemerson.com>
 */

#include <assert.h>

#include "internal.h"

#if defined(__GNUC__) || defined(__clang__) || defined(__INTEL_COMPILER)
#  define squash_atomic_inc(var) __sync_fetch_and_add(var, 1)
#  define squash_atomic_dec(var) __sync_fetch_and_sub(var, 1)
#  define squash_atomic_cas(var, orig, val) __sync_val_compare_and_swap(var, orig, val)
#elif defined(_WIN32)
#  define squash_atomic_cas(var, orig, val) InterlockedCompareExchange(var, orig, val)
#else
SQUASH_MTX_DEFINE(atomic_ref)

static unsigned int
squash_atomic_cas (volatile unsigned int* var,
                   unsigned int orig,
                   unsigned int val) {
  unsigned int res;

  SQUASH_MTX_LOCK(atomic_ref);
  res = *var;
  if (res == orig)
    *var = val;
  SQUASH_MTX_UNLOCK(atomic_ref);

  return res;
}
#endif

#if !defined(squash_atomic_inc)
static unsigned int
squash_atomic_inc (volatile unsigned int* var) {
  while (true) {
    unsigned int tmp = *var;
    if (squash_atomic_cas (var, tmp, tmp + 1) == tmp) {
      return tmp;
    }
  }
}
#endif /* defined(squash_atomic_inc) */

#if !defined(squash_atomic_dec)
static unsigned int
squash_atomic_dec (volatile unsigned int* var) {
  while (true) {
    unsigned int tmp = *var;
    assert (tmp > 0);
    if (squash_atomic_cas (var, tmp, tmp - 1) == tmp) {
      return tmp;
    }
  }
}
#endif /* defined(squash_atomic_dec) */

void*
squash_object_ref (void* obj) {
  SquashObject* object = (SquashObject*) obj;

  if (object == NULL)
    return object;

  if (object->is_floating) {
    if (squash_atomic_cas (&(object->is_floating), 1, 0) == 0) {
      squash_atomic_inc (&(object->ref_count));
    }
  } else {
    squash_atomic_inc (&(object->ref_count));
  }

  return obj;
}

void*
squash_object_ref_sink (void* obj) {
  SquashObject* object = (SquashObject*) obj;

  if (object == NULL)
    return object;

  return (squash_atomic_cas (&(object->is_floating), 1, 0) == 1) ? obj : NULL;
}

void*
squash_object_unref (void* obj) {
  SquashObject* object = (SquashObject*) obj;

  if (object == NULL)
    return object;

  unsigned int ref_count = squash_atomic_dec (&(object->ref_count));

  if (ref_count == 1) {
    if (object->destroy_notify != NULL) {
      object->destroy_notify (obj);
    }
    return NULL;
  } else {
    return NULL;
  }
}

unsigned int
squash_object_get_ref_count (void* obj) {
  if (obj == NULL)
    return 0;

  return ((SquashObject*) obj)->ref_count;
}

void
squash_object_init (void* obj, bool is_floating, SquashDestroyNotify destroy_notify) {
  SquashObject* object = (SquashObject*) obj;

  assert (object != NULL);

  object->ref_count = 1;
  object->is_floating = is_floating;
  object->destroy_notify = destroy_notify;
}

void
squash_object_destroy (void* obj) {
  assert (obj != NULL);
}