Add a flag that ensure that a connection is made only one

It is often desirable, when doing connection, to ensure that the same
connection is only made once. This can be done with the
Qt::UniqueConnection 'flag'

Also documented the order the slot are called

Reviewed-by: Brad

5 files changed, 119 insertions, 19 deletions

diff --git a/doc/src/qnamespace.qdoc b/doc/src/qnamespace.qdoc
index fc4310b..069541f 100644
--- a/doc/src/qnamespace.qdoc
+++ b/doc/src/qnamespace.qdoc
@@ -528,6 +528,10 @@
                              Qt::DirectConnection; otherwise the
                              signal is queued, as with
                              Qt::QueuedConnection.
+    \value UniqueConnection  Same as AutoConnection, but there will be a check that the signal is
+                             not already connected to the same slot before connecting, otherwise,
+                             the connection will fail.
+                             \since 4.6
 
     With queued connections, the parameters must be of types that are known to
     Qt's meta-object system, because Qt needs to copy the arguments to store them
diff --git a/doc/src/signalsandslots.qdoc b/doc/src/signalsandslots.qdoc
index 5432bd4..29c8215 100644
--- a/doc/src/signalsandslots.qdoc
+++ b/doc/src/signalsandslots.qdoc
@@ -178,9 +178,13 @@
     looping in the case of cyclic connections (e.g., if
     \c{b.valueChanged()} were connected to \c{a.setValue()}).
 
-    A signal is emitted for every connection you make; if you
-    duplicate a connection, two signals will be emitted. You can
-    always break a connection using QObject::disconnect().
+    By default, for every connection you make, a signal is emitted;
+    two signals are emitted for duplicate connections. You can break
+    all of these connections with a single disconnect() call.
+    If you pass the Qt::UniqueConnection \a type, the connection will only
+    be made if it is not a duplicate. If there is already a duplicate
+    (exact same signal to the exact same slot on the same objects),
+    the connection will fail and connect will return false
 
     This example illustrates that objects can work together without needing to
     know any information about each other. To enable this, the objects only
@@ -218,8 +222,8 @@
     will continue immediately, and the slots will be executed later.
 
     If several slots are connected to one signal, the slots will be
-    executed one after the other, in an arbitrary order, when the signal
-    is emitted.
+    executed one after the other, in the order they have been connected,
+    when the signal is emitted.
 
     Signals are automatically generated by the \l moc and must not be
     implemented in the \c .cpp file. They can never have return types
diff --git a/src/corelib/global/qnamespace.h b/src/corelib/global/qnamespace.h
index 3367581..9e53d89 100644
--- a/src/corelib/global/qnamespace.h
+++ b/src/corelib/global/qnamespace.h
@@ -1327,7 +1327,8 @@ public:
         DirectConnection,
         QueuedConnection,
         AutoCompatConnection,
-        BlockingQueuedConnection
+        BlockingQueuedConnection,
+        UniqueConnection =  0x80
     };
 
     enum ShortcutContext {
diff --git a/src/corelib/kernel/qobject.cpp b/src/corelib/kernel/qobject.cpp
index 65d81f1..be622d9 100644
--- a/src/corelib/kernel/qobject.cpp
+++ b/src/corelib/kernel/qobject.cpp
@@ -301,7 +301,6 @@ void QObjectPrivate::addConnection(int signal, Connection *c)
 
     ConnectionList &connectionList = (*connectionLists)[signal];
     connectionList.append(c);
-
     cleanConnectionLists();
 }
 
@@ -2377,7 +2376,8 @@ int QObject::receivers(const char *signal) const
     can be connected to one slot.
 
     If a signal is connected to several slots, the slots are activated
-    in an arbitrary order when the signal is emitted.
+    in the same order as the order the connection was made, when the
+    signal is emitted.
 
     The function returns true if it successfully connects the signal
     to the slot. It will return false if it cannot create the
@@ -2385,9 +2385,13 @@ int QObject::receivers(const char *signal) const
     existence of either \a signal or \a method, or if their signatures
     aren't compatible.
 
-    For every connection you make, a signal is emitted; two signals are emitted
-    for duplicate connections. You can break all of these connections with a
-    single disconnect() call.
+    By default, a signal is emitted for every connection you make;
+    two signals are emitted for duplicate connections. You can break
+    all of these connections with a single disconnect() call.
+    If you pass the Qt::UniqueConnection \a type, the connection will only
+    be made if it is not a duplicate. If there is already a duplicate
+    (exact same signal to the exact same slot on the same objects),
+    the connection will fail and connect will return false
 
     The optional \a type parameter describes the type of connection
     to establish. In particular, it determines whether a particular
@@ -2520,7 +2524,8 @@ bool QObject::connect(const QObject *sender, const char *signal,
         }
     }
 #endif
-    QMetaObject::connect(sender, signal_index, receiver, method_index, type, types);
+    if (!QMetaObject::connect(sender, signal_index, receiver, method_index, type, types))
+        return false;
     const_cast<QObject*>(sender)->connectNotify(signal - 1);
     return true;
 }
@@ -2771,6 +2776,22 @@ bool QMetaObject::connect(const QObject *sender, int signal_index,
     QObject *s = const_cast<QObject *>(sender);
     QObject *r = const_cast<QObject *>(receiver);
 
+    QOrderedMutexLocker locker(signalSlotLock(sender),
+                               signalSlotLock(receiver));
+
+    if (type & Qt::UniqueConnection) {
+        QObjectConnectionListVector *connectionLists = s->d_func()->connectionLists;
+        if (connectionLists && connectionLists->count() > signal_index) {
+            QObjectPrivate::ConnectionList &connectionList = (*connectionLists)[signal_index];
+            for (int i = 0; i < connectionList.count(); ++i) {
+                QObjectPrivate::Connection *c2 = connectionList.at(i);
+                if (c2->receiver == receiver && c2->method == method_index)
+                    return false;
+            }
+        }
+        type &= Qt::UniqueConnection - 1;
+    }
+
     QObjectPrivate::Connection *c = new QObjectPrivate::Connection;
     c->sender = s;
     c->receiver = r;
@@ -2778,9 +2799,6 @@ bool QMetaObject::connect(const QObject *sender, int signal_index,
     c->connectionType = type;
     c->argumentTypes = types;
 
-    QOrderedMutexLocker locker(signalSlotLock(sender),
-                               signalSlotLock(receiver));
-
     s->d_func()->addConnection(signal_index, c);
     r->d_func()->senders.append(c);
 
diff --git a/tests/auto/qobject/tst_qobject.cpp b/tests/auto/qobject/tst_qobject.cpp
index fb46073..399d021 100644
--- a/tests/auto/qobject/tst_qobject.cpp
+++ b/tests/auto/qobject/tst_qobject.cpp
@@ -116,6 +116,7 @@ private slots:
     void dumpObjectInfo();
     void connectToSender();
     void qobjectConstCast();
+    void uniqConnection();
 protected:
 };
 
@@ -204,12 +205,20 @@ public:
 	sequence_slot3 = 0;
 	sequence_slot2 = 0;
 	sequence_slot1 = 0;
+        count_slot1 = 0;
+        count_slot2 = 0;
+        count_slot3 = 0;
+        count_slot4 = 0;
     }
 
     int sequence_slot1;
     int sequence_slot2;
     int sequence_slot3;
     int sequence_slot4;
+    int count_slot1;
+    int count_slot2;
+    int count_slot3;
+    int count_slot4;
 
     bool called(int slot) {
         switch (slot) {
@@ -224,10 +233,10 @@ public:
     static int sequence;
 
 public slots:
-    void slot1() { sequence_slot1 = ++sequence; }
-    void slot2() { sequence_slot2 = ++sequence; }
-    void slot3() { sequence_slot3 = ++sequence; }
-    void slot4() { sequence_slot4 = ++sequence; }
+    void slot1() { sequence_slot1 = ++sequence; count_slot1++; }
+    void slot2() { sequence_slot2 = ++sequence; count_slot2++; }
+    void slot3() { sequence_slot3 = ++sequence; count_slot3++; }
+    void slot4() { sequence_slot4 = ++sequence; count_slot4++; }
 
 };
 
@@ -2783,5 +2792,69 @@ void tst_QObject::qobjectConstCast()
     QVERIFY(qobject_cast<const FooObject *>(cptr));
 }
 
+void tst_QObject::uniqConnection()
+{
+    SenderObject *s = new SenderObject;
+    ReceiverObject *r1 = new ReceiverObject;
+    ReceiverObject *r2 = new ReceiverObject;
+    r1->reset();
+    r2->reset();
+    ReceiverObject::sequence = 0;
+
+    QVERIFY( connect( s, SIGNAL( signal1() ), r1, SLOT( slot1() ) , Qt::UniqueConnection) );
+    QVERIFY( connect( s, SIGNAL( signal1() ), r2, SLOT( slot1() ) , Qt::UniqueConnection) );
+    QVERIFY( connect( s, SIGNAL( signal1() ), r1, SLOT( slot3() ) , Qt::UniqueConnection) );
+    QVERIFY( connect( s, SIGNAL( signal3() ), r1, SLOT( slot3() ) , Qt::UniqueConnection) );
+
+    s->emitSignal1();
+    s->emitSignal2();
+    s->emitSignal3();
+    s->emitSignal4();
+
+    QCOMPARE( r1->count_slot1, 1 );
+    QCOMPARE( r1->count_slot2, 0 );
+    QCOMPARE( r1->count_slot3, 2 );
+    QCOMPARE( r1->count_slot4, 0 );
+    QCOMPARE( r2->count_slot1, 1 );
+    QCOMPARE( r2->count_slot2, 0 );
+    QCOMPARE( r2->count_slot3, 0 );
+    QCOMPARE( r2->count_slot4, 0 );
+    QCOMPARE( r1->sequence_slot1, 1 );
+    QCOMPARE( r2->sequence_slot1, 2 );
+    QCOMPARE( r1->sequence_slot3, 4 );
+
+    r1->reset();
+    r2->reset();
+    ReceiverObject::sequence = 0;
+
+    QVERIFY( connect( s, SIGNAL( signal4() ), r1, SLOT( slot4() ) , Qt::UniqueConnection) );
+    QVERIFY( connect( s, SIGNAL( signal4() ), r2, SLOT( slot4() ) , Qt::UniqueConnection) );
+    QVERIFY(!connect( s, SIGNAL( signal4() ), r2, SLOT( slot4() ) , Qt::UniqueConnection) );
+    QVERIFY( connect( s, SIGNAL( signal1() ), r2, SLOT( slot4() ) , Qt::UniqueConnection) );
+    QVERIFY(!connect( s, SIGNAL( signal4() ), r1, SLOT( slot4() ) , Qt::UniqueConnection) );
+
+    s->emitSignal4();
+    QCOMPARE( r1->count_slot4, 1 );
+    QCOMPARE( r2->count_slot4, 1 );
+    QCOMPARE( r1->sequence_slot4, 1 );
+    QCOMPARE( r2->sequence_slot4, 2 );
+
+    r1->reset();
+    r2->reset();
+    ReceiverObject::sequence = 0;
+
+    connect( s, SIGNAL( signal4() ), r1, SLOT( slot4() ) );
+
+    s->emitSignal4();
+    QCOMPARE( r1->count_slot4, 2 );
+    QCOMPARE( r2->count_slot4, 1 );
+    QCOMPARE( r1->sequence_slot4, 3 );
+    QCOMPARE( r2->sequence_slot4, 2 );
+
+    delete s;
+    delete r1;
+    delete r2;
+}
+
 QTEST_MAIN(tst_QObject)
 #include "tst_qobject.moc"