[glib/wip/ebassi/rc-new: 1/4] Add reference counting types

[Emmanuele Bassi <ebassi src gnome org>]

commit c0955ef68d3914a904d05f079a3043bb473d8c60
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Wed Jan 17 16:38:45 2018 +0000

    Add reference counting types
    
    We have a common pattern for reference counting in GLib, but we always
    implement it with ad hoc code. This is a good chance at trying to
    standardise the implementation and make it public, so that other code
    using GLib can take advantage of shared behaviour and semantics.
    
    Instead of simply taking an integer variable, we should create type
    aliases, to immediately distinguish the reference counting semantics of
    the code; we can handle mixing atomic reference counting with a
    non-atomic type (and vice versa) by using differently signed values for
    the atomic and non-atomic cases.

 docs/reference/glib/glib-docs.xml     |    1 +
 docs/reference/glib/glib-sections.txt |   15 +++
 glib/Makefile.am                      |    2 +
 glib/glib.h                           |    1 +
 glib/grefcount.c                      |  194 +++++++++++++++++++++++++++++++++
 glib/grefcount.h                      |   51 +++++++++
 glib/gtypes.h                         |    3 +
 glib/meson.build                      |    2 +
 8 files changed, 269 insertions(+), 0 deletions(-)
---
diff --git a/docs/reference/glib/glib-docs.xml b/docs/reference/glib/glib-docs.xml
index a0716c1..26cdafb 100644
--- a/docs/reference/glib/glib-docs.xml
+++ b/docs/reference/glib/glib-docs.xml
@@ -119,6 +119,7 @@
     <xi:include href="xml/gvariant.xml"/>
     <xi:include href="gvariant-varargs.xml"/>
     <xi:include href="gvariant-text.xml"/>
+    <xi:include href="xml/refcount.xml"/>
   </chapter>
 
   <chapter id="deprecated">
diff --git a/docs/reference/glib/glib-sections.txt b/docs/reference/glib/glib-sections.txt
index dd1d5de..641a33a 100644
--- a/docs/reference/glib/glib-sections.txt
+++ b/docs/reference/glib/glib-sections.txt
@@ -3440,3 +3440,18 @@ g_hostname_is_ip_address
 g_uuid_string_is_valid
 g_uuid_string_random
 </SECTION>
+
+<SECTION>
+<FILE>refcount</FILE>
+grefcount
+g_ref_count_init
+g_ref_count_inc
+g_ref_count_dec
+g_ref_count_compare
+<SUBSECTION>
+gatomicrefcount
+g_atomic_ref_count_init
+g_atomic_ref_count_inc
+g_atomic_ref_count_dec
+g_atomic_ref_count_compare
+</SECTION>
diff --git a/glib/Makefile.am b/glib/Makefile.am
index 8da549c..6be9d98 100644
--- a/glib/Makefile.am
+++ b/glib/Makefile.am
@@ -153,6 +153,7 @@ libglib_2_0_la_SOURCES =    \
        gquark.c                \
        gqueue.c                \
        grand.c                 \
+       grefcount.c             \
        gregex.c                \
        gscanner.c              \
        gscripttable.h          \
@@ -287,6 +288,7 @@ glibsubinclude_HEADERS = \
        gquark.h        \
        gqueue.h        \
        grand.h         \
+       grefcount.h     \
        gregex.h        \
        gscanner.h      \
        gsequence.h     \
diff --git a/glib/glib.h b/glib/glib.h
index 4f5a7f7..84299c4 100644
--- a/glib/glib.h
+++ b/glib/glib.h
@@ -69,6 +69,7 @@
 #include <glib/gquark.h>
 #include <glib/gqueue.h>
 #include <glib/grand.h>
+#include <glib/grefcount.h>
 #include <glib/gregex.h>
 #include <glib/gscanner.h>
 #include <glib/gsequence.h>
diff --git a/glib/grefcount.c b/glib/grefcount.c
new file mode 100644
index 0000000..ca0c06e
--- /dev/null
+++ b/glib/grefcount.c
@@ -0,0 +1,194 @@
+/*
+ * Copyright 2017  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
+ *
+ * FIXME
+ */
+
+#include "config.h"
+
+#include "grefcount.h"
+
+#include "gatomic.h"
+#include "gmessages.h"
+
+/**
+ * g_ref_count_init:
+ * @rc: the address of a reference count variable
+ *
+ * Initializes a reference count variable.
+ *
+ * Since: 2.56
+ */
+void
+g_ref_count_init (grefcount *rc)
+{
+  g_return_if_fail (rc != NULL);
+
+  *rc = -1;
+}
+
+/**
+ * g_ref_count_inc:
+ * @rc: the address of a reference count variable
+ *
+ * Increases the reference count.
+ *
+ * Since: 2.56
+ */
+void
+g_ref_count_inc (grefcount *rc)
+{
+  g_return_if_fail (rc != NULL);
+
+  grefcount rrc = *rc;
+
+  g_return_if_fail (rrc < 0);
+
+  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: 2.56
+ */
+gboolean
+g_ref_count_dec (grefcount *rc)
+{
+  g_return_val_if_fail (rc != NULL, FALSE);
+
+  grefcount rrc = *rc;
+  g_return_val_if_fail (rrc < 0, FALSE);
+
+  rrc += 1;
+
+  *rc = rrc;
+
+  if (rrc == 0)
+    return TRUE;
+
+  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: 2.56
+ */
+gboolean
+g_ref_count_compare (grefcount *rc,
+                     gint       val)
+{
+  g_return_val_if_fail (rc != NULL, FALSE);
+
+  grefcount rrc = *rc;
+
+  return rrc == val;
+}
+
+/**
+ * g_atomic_ref_count_init:
+ * @arc: the address of an atomic reference count variable
+ *
+ * Atomically initializes a reference count variable.
+ *
+ * Since: 2.56
+ */
+void
+g_atomic_ref_count_init (gatomicrefcount *arc)
+{
+  g_return_if_fail (arc != NULL);
+
+  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: 2.56
+ */
+void
+g_atomic_ref_count_inc (gatomicrefcount *arc)
+{
+  g_return_if_fail (arc != NULL);
+  g_return_if_fail (g_atomic_int_get (arc) > 0);
+
+  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: 2.56
+ */
+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: 2.56
+ */
+gboolean
+g_atomic_ref_count_compare (gatomicrefcount *arc,
+                            gint             val)
+{
+  g_return_val_if_fail (arc != NULL, FALSE);
+
+  return g_atomic_int_get (arc) == val;
+}
+
diff --git a/glib/grefcount.h b/glib/grefcount.h
new file mode 100644
index 0000000..f73001b
--- /dev/null
+++ b/glib/grefcount.h
@@ -0,0 +1,51 @@
+/*
+ * Copyright 2017  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/>.
+ */
+
+#ifndef __GREFCOUNT_H__
+#define __GREFCOUNT_H__
+
+#if !defined (__GLIB_H_INSIDE__) && !defined (GLIB_COMPILATION)
+#error "Only <glib.h> can be included directly."
+#endif
+
+#include <glib/gtypes.h>
+
+G_BEGIN_DECLS
+
+GLIB_AVAILABLE_IN_2_56
+void            g_ref_count_init                (grefcount       *rc);
+GLIB_AVAILABLE_IN_2_56
+void            g_ref_count_inc                 (grefcount       *rc);
+GLIB_AVAILABLE_IN_2_56
+gboolean        g_ref_count_dec                 (grefcount       *rc);
+GLIB_AVAILABLE_IN_2_56
+gboolean        g_ref_count_compare             (grefcount       *rc,
+                                                 gint             val);
+
+GLIB_AVAILABLE_IN_2_56
+void            g_atomic_ref_count_init         (gatomicrefcount *arc);
+GLIB_AVAILABLE_IN_2_56
+void            g_atomic_ref_count_inc          (gatomicrefcount *arc);
+GLIB_AVAILABLE_IN_2_56
+gboolean        g_atomic_ref_count_dec          (gatomicrefcount *arc);
+GLIB_AVAILABLE_IN_2_56
+gboolean        g_atomic_ref_count_compare      (gatomicrefcount *arc,
+                                                 gint             val);
+
+G_END_DECLS
+
+#endif /* __GREFCOUNT_H__ */
diff --git a/glib/gtypes.h b/glib/gtypes.h
index 047ac62..e0a3283 100644
--- a/glib/gtypes.h
+++ b/glib/gtypes.h
@@ -510,6 +510,9 @@ struct _GTimeVal
   glong tv_usec;
 };
 
+typedef gint            grefcount;
+typedef volatile gint   gatomicrefcount;
+
 G_END_DECLS
 
 /* We prefix variable declarations so they can
diff --git a/glib/meson.build b/glib/meson.build
index add29d0..8797e3c 100644
--- a/glib/meson.build
+++ b/glib/meson.build
@@ -76,6 +76,7 @@ glib_sub_headers = files(
   'gquark.h',
   'gqueue.h',
   'grand.h',
+  'grefcount.h',
   'gregex.h',
   'gscanner.h',
   'gsequence.h',
@@ -159,6 +160,7 @@ glib_sources = files(
   'gquark.c',
   'gqueue.c',
   'grand.c',
+  'grefcount.c',
   'gregex.c',
   'gscanner.c',
   'gsequence.c',