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/* grefcount.c: Reference counting
*
* Copyright 2018 Emmanuele Bassi
*
* 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 2.1 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, see <http://www.gnu.org/licenses/>.
*/
/**
* SECTION:refcount
* @Title: Reference counting
* @Short_description: Reference counting types and functions
*
* Reference counting is a garbage collection mechanism that is based on
* assigning a counter to a data type, or any memory area; the counter is
* increased whenever a new reference to that data type is acquired, and
* decreased whenever the reference is released. Once the last reference
* is released, the resources associated to that data type are freed.
*
* GLib uses reference counting in many of its data types, and provides
* the #grefcount and #gatomicrefcount types to implement safe and atomic
* reference counting semantics in new data types.
*
* It is important to note that #grefcount and #gatomicrefcount should be
* considered completely opaque types; you should always use the provided
* API to increase and decrease the counters, and you should never check
* their content directly, or compare their content with other values.
*
* Since: 2.58
*/
#include "config.h"
#include "grefcount.h"
#include "gatomic.h"
#include "gmessages.h"
/**
* grefcount:
*
* A type for implementing non-atomic reference count semantics.
*
* Use g_ref_count_init() to initialize it; g_ref_count_inc() to
* increase the counter, and g_ref_count_dec() to decrease it.
*
* It is safe to use #grefcount only if you're expecting to operate
* on the reference counter from a single thread. It is entirely up
* to you to ensure that all reference count changes happen in the
* same thread.
*
* See also: #gatomicrefcount
*
* Since: 2.58
*/
/**
* gatomicrefcount:
*
* A type for implementing atomic reference count semantics.
*
* Use g_atomic_ref_count_init() to initialize it; g_atomic_ref_count_inc()
* to increase the counter, and g_atomic_ref_count_dec() to decrease it.
*
* It is safe to use #gatomicrefcount if you're expecting to operate on the
* reference counter from multiple threads.
*
* See also: #grefcount
*
* Since: 2.58
*/
/**
* g_ref_count_init:
* @rc: the address of a reference count variable
*
* Initializes a reference count variable.
*
* Since: 2.58
*/
void
(g_ref_count_init) (grefcount *rc)
{
g_return_if_fail (rc != NULL);
/* Non-atomic refcounting is implemented using the negative range
* of signed integers:
*
* G_MININT Z¯< 0 > Z⁺ G_MAXINT
* |----------------------------|----------------------------|
*
* Acquiring a reference moves us towards MININT, and releasing a
* reference moves us towards 0.
*/
*rc = -1;
}
/**
* g_ref_count_inc:
* @rc: the address of a reference count variable
*
* Increases the reference count.
*
* Since: 2.58
*/
void
(g_ref_count_inc) (grefcount *rc)
{
grefcount rrc;
g_return_if_fail (rc != NULL);
rrc = *rc;
g_return_if_fail (rrc < 0);
/* Check for saturation */
if (rrc == G_MININT)
{
g_critical ("Reference count %p has reached saturation", rc);
return;
}
rrc -= 1;
*rc = rrc;
}
/**
* g_ref_count_dec:
* @rc: the address of a reference count variable
*
* Decreases the reference count.
*
* Returns: %TRUE if the reference count reached 0, and %FALSE otherwise
*
* Since: 2.58
*/
gboolean
(g_ref_count_dec) (grefcount *rc)
{
grefcount rrc;
g_return_val_if_fail (rc != NULL, FALSE);
rrc = *rc;
g_return_val_if_fail (rrc < 0, FALSE);
rrc += 1;
if (rrc == 0)
return TRUE;
*rc = rrc;
return FALSE;
}
/**
* g_ref_count_compare:
* @rc: the address of a reference count variable
* @val: the value to compare
*
* Compares the current value of @rc with @val.
*
* Returns: %TRUE if the reference count is the same
* as the given value
*
* Since: 2.58
*/
gboolean
(g_ref_count_compare) (grefcount *rc,
gint val)
{
grefcount rrc;
g_return_val_if_fail (rc != NULL, FALSE);
g_return_val_if_fail (val >= 0, FALSE);
rrc = *rc;
if (val == G_MAXINT)
return rrc == G_MININT;
return rrc == -val;
}
/**
* g_atomic_ref_count_init:
* @arc: the address of an atomic reference count variable
*
* Atomically initializes a reference count variable.
*
* Since: 2.58
*/
void
(g_atomic_ref_count_init) (gatomicrefcount *arc)
{
g_return_if_fail (arc != NULL);
/* Atomic refcounting is implemented using the positive range
* of signed integers:
*
* G_MININT Z¯< 0 > Z⁺ G_MAXINT
* |----------------------------|----------------------------|
*
* Acquiring a reference moves us towards MAXINT, and releasing a
* reference moves us towards 0.
*/
g_atomic_int_set (arc, 1);
}
/**
* g_atomic_ref_count_inc:
* @arc: the address of an atomic reference count variable
*
* Atomically increases the reference count.
*
* Since: 2.58
*/
void
(g_atomic_ref_count_inc) (gatomicrefcount *arc)
{
g_return_if_fail (arc != NULL);
g_return_if_fail (g_atomic_int_get (arc) > 0);
if (g_atomic_int_get (arc) == G_MAXINT)
{
g_critical ("Reference count has reached saturation");
return;
}
g_atomic_int_inc (arc);
}
/**
* g_atomic_ref_count_dec:
* @arc: the address of an atomic reference count variable
*
* Atomically decreases the reference count.
*
* Returns: %TRUE if the reference count reached 0, and %FALSE otherwise
*
* Since: 2.58
*/
gboolean
(g_atomic_ref_count_dec) (gatomicrefcount *arc)
{
g_return_val_if_fail (arc != NULL, FALSE);
g_return_val_if_fail (g_atomic_int_get (arc) > 0, FALSE);
return g_atomic_int_dec_and_test (arc);
}
/**
* g_atomic_ref_count_compare:
* @arc: the address of an atomic reference count variable
* @val: the value to compare
*
* Atomically compares the current value of @arc with @val.
*
* Returns: %TRUE if the reference count is the same
* as the given value
*
* Since: 2.58
*/
gboolean
(g_atomic_ref_count_compare) (gatomicrefcount *arc,
gint val)
{
g_return_val_if_fail (arc != NULL, FALSE);
g_return_val_if_fail (val >= 0, FALSE);
return g_atomic_int_get (arc) == val;
}