Remove obsolete DBus dispatch lock

In c2049f67e4, all DBus I/O was
moved into a service thread. The dispatch lock used to protect
DBus I/O in the threading setup before that commit. It is not
needed anymore.
No discernible difference in QtDBus benchmarks, roughly 500
bytes code size reduction on AMD64. The main point is to reduce
confusion from unnecessary code.

Change-Id: Idcbdd2b7e2b317cf6da0b5bfc5ec70afed1f1b48
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/dbus/qdbusconnection_p.h

@@ -59,7 +59,6 @@
 
 #include <QtCore/qatomic.h>
 #include <QtCore/qhash.h>
-#include <QtCore/qmutex.h>
 #include <QtCore/qobject.h>
 #include <QtCore/qpointer.h>
 #include <QtCore/qreadwritelock.h>
@@ -198,7 +197,6 @@ public:
     ~QDBusConnectionPrivate();
 
     void createBusService();
-    void setDispatchEnabled(bool enable);
     void setPeer(DBusConnection *connection, const QDBusErrorInternal &error);
     void setConnection(DBusConnection *connection, const QDBusErrorInternal &error);
     void setServer(QDBusServer *object, DBusServer *server, const QDBusErrorInternal &error);
@@ -275,6 +273,7 @@ protected:
 
 public slots:
     // public slots
+    void setDispatchEnabled(bool enable);
     void doDispatch();
     void socketRead(int);
     void socketWrite(int);
@@ -312,9 +311,6 @@ public:
         QDBusServer *serverObject;
     };
 
-    // the dispatch lock protects everything related to the DBusConnection or DBusServer
-    // including the timeouts and watches
-    QMutex dispatchLock;
     union {
         DBusConnection *connection;
         DBusServer *server;
@@ -390,7 +386,9 @@ public:
 public slots:
     void execute()
     {
-        con->setDispatchEnabled(true);
+        // This call cannot race with something disabling dispatch only because dispatch is
+        // never re-disabled from Qt code on an in-use connection once it has been enabled.
+        QMetaObject::invokeMethod(con, "setDispatchEnabled", Qt::QueuedConnection, Q_ARG(bool, true));
         if (!con->ref.deref())
             con->deleteLater();
         deleteLater();

src/dbus/qdbusintegrator.cpp

@@ -150,7 +150,6 @@ static dbus_bool_t qDBusAddTimeout(DBusTimeout *timeout, void *data)
     if (Q_UNLIKELY(!q_dbus_timeout_get_enabled(timeout)))
         return false;
 
-    QDBusDispatchLocker locker(AddTimeoutAction, d);
     Q_ASSERT(d->timeouts.key(timeout, 0) == 0);
 
     int timerId = d->startTimer(q_dbus_timeout_get_interval(timeout));
@@ -172,8 +171,6 @@ static void qDBusRemoveTimeout(DBusTimeout *timeout, void *data)
     QDBusConnectionPrivate *d = static_cast<QDBusConnectionPrivate *>(data);
     Q_ASSERT(QThread::currentThread() == d->thread());
 
-    QDBusDispatchLocker locker(RemoveTimeoutAction, d);
-
     QDBusConnectionPrivate::TimeoutHash::iterator it = d->timeouts.begin();
     while (it != d->timeouts.end()) {
         if (it.value() == timeout) {
@@ -210,7 +207,6 @@ static dbus_bool_t qDBusAddWatch(DBusWatch *watch, void *data)
 
     QDBusConnectionPrivate::Watcher watcher;
 
-    QDBusDispatchLocker locker(AddWatchAction, d);
     if (flags & DBUS_WATCH_READABLE) {
         //qDebug("addReadWatch %d", fd);
         watcher.watch = watch;
@@ -241,7 +237,6 @@ static void qDBusRemoveWatch(DBusWatch *watch, void *data)
     Q_ASSERT(QThread::currentThread() == d->thread());
     int fd = q_dbus_watch_get_unix_fd(watch);
 
-    QDBusDispatchLocker locker(RemoveWatchAction, d);
     QDBusConnectionPrivate::WatcherHash::iterator i = d->watchers.find(fd);
     while (i != d->watchers.end() && i.key() == fd) {
         if (i.value().watch == watch) {
@@ -263,8 +258,6 @@ static void qDBusToggleWatch(DBusWatch *watch, void *data)
     Q_ASSERT(QThread::currentThread() == d->thread());
     int fd = q_dbus_watch_get_unix_fd(watch);
 
-    QDBusDispatchLocker locker(ToggleWatchAction, d);
-
     QDBusConnectionPrivate::WatcherHash::iterator i = d->watchers.find(fd);
     while (i != d->watchers.end() && i.key() == fd) {
         if (i.value().watch == watch) {
@@ -766,7 +759,7 @@ static int findSlot(const QMetaObject *mo, const QByteArray &name, int flags,
  */
 void QDBusConnectionPrivate::setDispatchEnabled(bool enable)
 {
-    QDBusDispatchLocker locker(SetDispatchEnabledAction, this);
+    checkThread();
     dispatchEnabled = enable;
     if (enable)
         emit dispatchStatusChanged();
@@ -1024,7 +1017,7 @@ extern bool qDBusInitThreads();
 
 QDBusConnectionPrivate::QDBusConnectionPrivate(QObject *p)
     : QObject(p), ref(1), capabilities(0), mode(InvalidMode), busService(0),
-      dispatchLock(QMutex::Recursive), connection(0),
+      connection(0),
       rootNode(QString(QLatin1Char('/'))),
       anonymousAuthenticationAllowed(false),
       dispatchEnabled(true)
@@ -1176,7 +1169,6 @@ bool QDBusConnectionPrivate::handleError(const QDBusErrorInternal &error)
 void QDBusConnectionPrivate::timerEvent(QTimerEvent *e)
 {
     {
-        QDBusDispatchLocker locker(TimerEventAction, this);
         DBusTimeout *timeout = timeouts.value(e->timerId(), 0);
         if (timeout)
             q_dbus_timeout_handle(timeout);
@@ -1187,7 +1179,6 @@ void QDBusConnectionPrivate::timerEvent(QTimerEvent *e)
 
 void QDBusConnectionPrivate::doDispatch()
 {
-    QDBusDispatchLocker locker(DoDispatchAction, this);
     if (mode == ClientMode || mode == PeerMode) {
         while (q_dbus_connection_dispatch(connection) == DBUS_DISPATCH_DATA_REMAINS) ;
         if (dispatchEnabled && !pendingMessages.isEmpty()) {
@@ -1205,7 +1196,6 @@ void QDBusConnectionPrivate::doDispatch()
 
 void QDBusConnectionPrivate::socketRead(int fd)
 {
-    QDBusDispatchLocker locker(SocketReadAction, this);
     WatcherHash::ConstIterator it = watchers.constFind(fd);
     while (it != watchers.constEnd() && it.key() == fd) {
         if (it->watch && it->read && it->read->isEnabled()) {
@@ -1220,7 +1210,6 @@ void QDBusConnectionPrivate::socketRead(int fd)
 
 void QDBusConnectionPrivate::socketWrite(int fd)
 {
-    QDBusDispatchLocker locker(SocketWriteAction, this);
     WatcherHash::ConstIterator it = watchers.constFind(fd);
     while (it != watchers.constEnd() && it.key() == fd) {
         if (it->watch && it->write && it->write->isEnabled()) {
@@ -1283,10 +1272,7 @@ void QDBusConnectionPrivate::relaySignal(QObject *obj, const QMetaObject *mo, in
     //qDBusDebug() << "Emitting signal" << message;
     //qDBusDebug() << "for paths:";
     q_dbus_message_set_no_reply(msg, true); // the reply would not be delivered to anything
-    {
-        QDBusDispatchLocker locker(HuntAndEmitAction, this);
-        huntAndEmit(connection, msg, obj, rootNode, isScriptable, isAdaptor);
-    }
+    huntAndEmit(connection, msg, obj, rootNode, isScriptable, isAdaptor);
     q_dbus_message_unref(msg);
 }
 
@@ -2164,7 +2150,6 @@ void QDBusConnectionPrivate::sendInternal(QDBusPendingCallPrivate *pcall, void *
     Q_ASSERT(isNoReply == !!q_dbus_message_get_no_reply(msg));
 
     checkThread();
-    QDBusDispatchLocker locker(SendMessageAction, this);
 
     if (isNoReply && q_dbus_connection_send(connection, msg, nullptr)) {
         // success

src/dbus/qdbusthreaddebug_p.h

@@ -95,17 +95,6 @@ enum ThreadAction {
     PendingCallBlockAction = 28,
     SendMessageAction = 29,
     HuntAndEmitAction = 30,
-
-    AddTimeoutAction = 50,
-    RealAddTimeoutAction = 51,
-    RemoveTimeoutAction = 52,
-    KillTimerAction = 58,
-    TimerEventAction = 59,
-    AddWatchAction = 60,
-    RemoveWatchAction = 61,
-    ToggleWatchAction = 62,
-    SocketReadAction = 63,
-    SocketWriteAction = 64
 };
 
 struct QDBusLockerBase
@@ -176,35 +165,6 @@ struct QDBusWriteLocker: QDBusLockerBase
     }
 };
 
-struct QDBusMutexLocker: QDBusLockerBase
-{
-    QDBusConnectionPrivate *self;
-    QMutex *mutex;
-    ThreadAction action;
-    inline QDBusMutexLocker(ThreadAction a, QDBusConnectionPrivate *s,
-                            QMutex *m)
-        : self(s), mutex(m), action(a)
-    {
-        reportThreadAction(action, BeforeLock, self);
-        mutex->lock();
-        reportThreadAction(action, AfterLock, self);
-    }
-
-    inline ~QDBusMutexLocker()
-    {
-        reportThreadAction(action, BeforeUnlock, self);
-        mutex->unlock();
-        reportThreadAction(action, AfterUnlock, self);
-    }
-};
-
-struct QDBusDispatchLocker: QDBusMutexLocker
-{
-    inline QDBusDispatchLocker(ThreadAction a, QDBusConnectionPrivate *s)
-        : QDBusMutexLocker(a, s, &s->dispatchLock)
-    { }
-};
-
 #if QDBUS_THREAD_DEBUG
 # define SEM_ACQUIRE(action, sem)                                       \
     do {                                                                \