bus: break reference cycle between bus and messages

Because messages in the read and write queues hold a reference on the
bus, and the bus holds a reference on each of them, we would never
free the bus if the read or write queues were not empty. Explicitly
substract the number of messages in those queue from the bus reference
count when deciding whether to free or not.

A simple test which creates and unrefs simple objects is added.

diff --git a/src/libsystemd-bus/test-bus-cleanup.c b/src/libsystemd-bus/test-bus-cleanup.c
new file mode 100644 (file)
index 0000000..d8ddb84
--- /dev/null
+++ b/src/libsystemd-bus/test-bus-cleanup.c
@@ -0,0 +1,80 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright 2013 Zbigniew Jędrzejewski-Szmek
+
+  systemd 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.
+
+  systemd 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 systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <stdio.h>
+
+#include "sd-bus.h"
+#include "bus-util.h"
+#include "bus-internal.h"
+#include "bus-message.h"
+#include "refcnt.h"
+
+static void test_bus_new(void) {
+        _cleanup_bus_unref_ sd_bus *bus = NULL;
+
+        assert_se(sd_bus_new(&bus) == 0);
+        printf("after new: refcount %u\n", REFCNT_GET(bus->n_ref));
+}
+
+static void test_bus_open(void) {
+        _cleanup_bus_unref_ sd_bus *bus = NULL;
+
+        assert_se(sd_bus_open_system(&bus) >= 0);
+        printf("after open: refcount %u\n", REFCNT_GET(bus->n_ref));
+}
+
+static void test_bus_new_method_call(void) {
+        sd_bus *bus = NULL;
+        _cleanup_bus_message_unref_ sd_bus_message *m = NULL;
+
+        assert_se(sd_bus_open_system(&bus) >= 0);
+
+        assert_se(sd_bus_message_new_method_call(bus, "a.service.name", "/an/object/path", "an.interface.name", "AMethodName", &m) >= 0);
+
+        printf("after message_new_method_call: refcount %u\n", REFCNT_GET(bus->n_ref));
+
+        sd_bus_unref(bus);
+        printf("after bus_unref: refcount %u\n", m->n_ref);
+}
+
+static void test_bus_new_signal(void) {
+        sd_bus *bus = NULL;
+        _cleanup_bus_message_unref_ sd_bus_message *m = NULL;
+
+        assert_se(sd_bus_open_system(&bus) >= 0);
+
+        assert_se(sd_bus_message_new_signal(bus, "/an/object/path", "an.interface.name", "Name", &m) >= 0);
+
+        printf("after message_new_signal: refcount %u\n", REFCNT_GET(bus->n_ref));
+
+        sd_bus_unref(bus);
+        printf("after bus_unref: refcount %u\n", m->n_ref);
+}
+
+int main(int argc, char **argv) {
+        log_parse_environment();
+        log_open();
+
+        test_bus_new();
+        test_bus_open();
+        test_bus_new_method_call();
+        test_bus_new_signal();
+}