qobject: Simplify QObject

The QObject hierarchy is small enough, and unlikely to grow further
(since we only use it to map to JSON and already cover all JSON
types), that we can simplify things by not tracking a separate
vtable, but just inline the code element of the vtable QType
directly into QObject (renamed to type), and track a separate array
of destroy functions.  We can drop qnull_destroy_obj() in the
process.

The remaining QObject subclasses must export their destructor.

This also has the nice benefit of moving the typename 'QType'
out of the way, so that the next patch can repurpose it for a
nicer name for 'qtype_code'.

The various objects are still the same size (so no change in cache
line pressure), but now have less indirection (although I didn't
bother benchmarking to see if there is a noticeable speedup, as
we don't have hard evidence that this was in a performance hotspot
in the first place).

A future patch could drop the refcnt size to 32 bits for a smaller
struct on 64-bit architectures, if desired (we have limits on the
largest JSON that we are willing to parse, and will probably never
need to take full advantage of a 64-bit refcnt).

Suggested-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1449033659-25497-2-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

9 files changed, 48 insertions, 66 deletions

diff --git a/qobject/Makefile.objs b/qobject/Makefile.objs
index 0031e8b..bed5508 100644
--- a/qobject/Makefile.objs
+++ b/qobject/Makefile.objs
@@ -1,2 +1,2 @@
 util-obj-y = qnull.o qint.o qstring.o qdict.o qlist.o qfloat.o qbool.o
-util-obj-y += qjson.o json-lexer.o json-streamer.o json-parser.o
+util-obj-y += qjson.o qobject.o json-lexer.o json-streamer.o json-parser.o
diff --git a/qobject/qbool.c b/qobject/qbool.c
index bc6535f..856c743 100644
--- a/qobject/qbool.c
+++ b/qobject/qbool.c
@@ -15,13 +15,6 @@
 #include "qapi/qmp/qobject.h"
 #include "qemu-common.h"
 
-static void qbool_destroy_obj(QObject *obj);
-
-static const QType qbool_type = {
-    .code = QTYPE_QBOOL,
-    .destroy = qbool_destroy_obj,
-};
-
 /**
  * qbool_from_bool(): Create a new QBool from a bool
  *
@@ -32,8 +25,8 @@ QBool *qbool_from_bool(bool value)
     QBool *qb;
 
     qb = g_malloc(sizeof(*qb));
+    qobject_init(QOBJECT(qb), QTYPE_QBOOL);
     qb->value = value;
-    QOBJECT_INIT(qb, &qbool_type);
 
     return qb;
 }
@@ -61,7 +54,7 @@ QBool *qobject_to_qbool(const QObject *obj)
  * qbool_destroy_obj(): Free all memory allocated by a
  * QBool object
  */
-static void qbool_destroy_obj(QObject *obj)
+void qbool_destroy_obj(QObject *obj)
 {
     assert(obj != NULL);
     g_free(qobject_to_qbool(obj));
diff --git a/qobject/qdict.c b/qobject/qdict.c
index 2d67bf1..eeade15 100644
--- a/qobject/qdict.c
+++ b/qobject/qdict.c
@@ -19,13 +19,6 @@
 #include "qemu/queue.h"
 #include "qemu-common.h"
 
-static void qdict_destroy_obj(QObject *obj);
-
-static const QType qdict_type = {
-    .code = QTYPE_QDICT,
-    .destroy = qdict_destroy_obj,
-};
-
 /**
  * qdict_new(): Create a new QDict
  *
@@ -36,7 +29,7 @@ QDict *qdict_new(void)
     QDict *qdict;
 
     qdict = g_malloc0(sizeof(*qdict));
-    QOBJECT_INIT(qdict, &qdict_type);
+    qobject_init(QOBJECT(qdict), QTYPE_QDICT);
 
     return qdict;
 }
@@ -441,7 +434,7 @@ void qdict_del(QDict *qdict, const char *key)
 /**
  * qdict_destroy_obj(): Free all the memory allocated by a QDict
  */
-static void qdict_destroy_obj(QObject *obj)
+void qdict_destroy_obj(QObject *obj)
 {
     int i;
     QDict *qdict;
diff --git a/qobject/qfloat.c b/qobject/qfloat.c
index c865163..87d89a7 100644
--- a/qobject/qfloat.c
+++ b/qobject/qfloat.c
@@ -15,13 +15,6 @@
 #include "qapi/qmp/qobject.h"
 #include "qemu-common.h"
 
-static void qfloat_destroy_obj(QObject *obj);
-
-static const QType qfloat_type = {
-    .code = QTYPE_QFLOAT,
-    .destroy = qfloat_destroy_obj,
-};
-
 /**
  * qfloat_from_int(): Create a new QFloat from a float
  *
@@ -32,8 +25,8 @@ QFloat *qfloat_from_double(double value)
     QFloat *qf;
 
     qf = g_malloc(sizeof(*qf));
+    qobject_init(QOBJECT(qf), QTYPE_QFLOAT);
     qf->value = value;
-    QOBJECT_INIT(qf, &qfloat_type);
 
     return qf;
 }
@@ -61,7 +54,7 @@ QFloat *qobject_to_qfloat(const QObject *obj)
  * qfloat_destroy_obj(): Free all memory allocated by a
  * QFloat object
  */
-static void qfloat_destroy_obj(QObject *obj)
+void qfloat_destroy_obj(QObject *obj)
 {
     assert(obj != NULL);
     g_free(qobject_to_qfloat(obj));
diff --git a/qobject/qint.c b/qobject/qint.c
index 999688e..7cba9ad 100644
--- a/qobject/qint.c
+++ b/qobject/qint.c
@@ -14,13 +14,6 @@
 #include "qapi/qmp/qobject.h"
 #include "qemu-common.h"
 
-static void qint_destroy_obj(QObject *obj);
-
-static const QType qint_type = {
-    .code = QTYPE_QINT,
-    .destroy = qint_destroy_obj,
-};
-
 /**
  * qint_from_int(): Create a new QInt from an int64_t
  *
@@ -31,8 +24,8 @@ QInt *qint_from_int(int64_t value)
     QInt *qi;
 
     qi = g_malloc(sizeof(*qi));
+    qobject_init(QOBJECT(qi), QTYPE_QINT);
     qi->value = value;
-    QOBJECT_INIT(qi, &qint_type);
 
     return qi;
 }
@@ -60,7 +53,7 @@ QInt *qobject_to_qint(const QObject *obj)
  * qint_destroy_obj(): Free all memory allocated by a
  * QInt object
  */
-static void qint_destroy_obj(QObject *obj)
+void qint_destroy_obj(QObject *obj)
 {
     assert(obj != NULL);
     g_free(qobject_to_qint(obj));
diff --git a/qobject/qlist.c b/qobject/qlist.c
index 298003a..3c045ae 100644
--- a/qobject/qlist.c
+++ b/qobject/qlist.c
@@ -15,13 +15,6 @@
 #include "qemu/queue.h"
 #include "qemu-common.h"
 
-static void qlist_destroy_obj(QObject *obj);
-
-static const QType qlist_type = {
-    .code = QTYPE_QLIST,
-    .destroy = qlist_destroy_obj,
-};
- 
 /**
  * qlist_new(): Create a new QList
  *
@@ -32,8 +25,8 @@ QList *qlist_new(void)
     QList *qlist;
 
     qlist = g_malloc(sizeof(*qlist));
+    qobject_init(QOBJECT(qlist), QTYPE_QLIST);
     QTAILQ_INIT(&qlist->head);
-    QOBJECT_INIT(qlist, &qlist_type);
 
     return qlist;
 }
@@ -151,7 +144,7 @@ QList *qobject_to_qlist(const QObject *obj)
 /**
  * qlist_destroy_obj(): Free all the memory allocated by a QList
  */
-static void qlist_destroy_obj(QObject *obj)
+void qlist_destroy_obj(QObject *obj)
 {
     QList *qlist;
     QListEntry *entry, *next_entry;
diff --git a/qobject/qnull.c b/qobject/qnull.c
index 9873e26..5f7ba4d 100644
--- a/qobject/qnull.c
+++ b/qobject/qnull.c
@@ -13,17 +13,7 @@
 #include "qemu-common.h"
 #include "qapi/qmp/qobject.h"
 
-static void qnull_destroy_obj(QObject *obj)
-{
-    assert(0);
-}
-
-static const QType qnull_type = {
-    .code = QTYPE_QNULL,
-    .destroy = qnull_destroy_obj,
-};
-
 QObject qnull_ = {
-    .type = &qnull_type,
+    .type = QTYPE_QNULL,
     .refcnt = 1,
 };
diff --git a/qobject/qobject.c b/qobject/qobject.c
new file mode 100644
index 0000000..1df315a
--- /dev/null
+++ b/qobject/qobject.c
@@ -0,0 +1,34 @@
+/*
+ * QObject
+ *
+ * Copyright (C) 2015 Red Hat, Inc.
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2.1
+ * or later.  See the COPYING.LIB file in the top-level directory.
+ */
+
+#include "qemu-common.h"
+#include "qapi/qmp/qbool.h"
+#include "qapi/qmp/qdict.h"
+#include "qapi/qmp/qfloat.h"
+#include "qapi/qmp/qint.h"
+#include "qapi/qmp/qlist.h"
+#include "qapi/qmp/qstring.h"
+
+static void (*qdestroy[QTYPE_MAX])(QObject *) = {
+    [QTYPE_NONE] = NULL,               /* No such object exists */
+    [QTYPE_QNULL] = NULL,              /* qnull_ is indestructible */
+    [QTYPE_QINT] = qint_destroy_obj,
+    [QTYPE_QSTRING] = qstring_destroy_obj,
+    [QTYPE_QDICT] = qdict_destroy_obj,
+    [QTYPE_QLIST] = qlist_destroy_obj,
+    [QTYPE_QFLOAT] = qfloat_destroy_obj,
+    [QTYPE_QBOOL] = qbool_destroy_obj,
+};
+
+void qobject_destroy(QObject *obj)
+{
+    assert(!obj->refcnt);
+    assert(QTYPE_QNULL < obj->type && obj->type < QTYPE_MAX);
+    qdestroy[obj->type](obj);
+}
diff --git a/qobject/qstring.c b/qobject/qstring.c
index cb72dfb..f44c5c4 100644
--- a/qobject/qstring.c
+++ b/qobject/qstring.c
@@ -14,13 +14,6 @@
 #include "qapi/qmp/qstring.h"
 #include "qemu-common.h"
 
-static void qstring_destroy_obj(QObject *obj);
-
-static const QType qstring_type = {
-    .code = QTYPE_QSTRING,
-    .destroy = qstring_destroy_obj,
-};
-
 /**
  * qstring_new(): Create a new empty QString
  *
@@ -49,6 +42,7 @@ QString *qstring_from_substr(const char *str, int start, int end)
     QString *qstring;
 
     qstring = g_malloc(sizeof(*qstring));
+    qobject_init(QOBJECT(qstring), QTYPE_QSTRING);
 
     qstring->length = end - start + 1;
     qstring->capacity = qstring->length;
@@ -57,7 +51,6 @@ QString *qstring_from_substr(const char *str, int start, int end)
     memcpy(qstring->string, str + start, qstring->length);
     qstring->string[qstring->length] = 0;
 
-    QOBJECT_INIT(qstring, &qstring_type);
 
     return qstring;
 }
@@ -138,7 +131,7 @@ const char *qstring_get_str(const QString *qstring)
  * qstring_destroy_obj(): Free all memory allocated by a QString
  * object
  */
-static void qstring_destroy_obj(QObject *obj)
+void qstring_destroy_obj(QObject *obj)
 {
     QString *qs;