Qt 4.7 limit on number of signals?

[rghosh]

I've been trying to migrate an application from Qt 4.6.2 to 4.7.0, and had a problem in 4.7 where I can only successfully connect a certain number of signals.

I've written a simple test program in Python using the PySide bindings that demonstrates the problem. In the test program, on each timer timeout, a new signal is defined and connected to a callback, and all signals defined thus far are emitted. The source-code for this small test is in attached test.py and also listed at the bottom of this post.

Using Qt 4.6.2, this works as I expected, with the output in attached qt4.6.2output.txt

$ python test.py
0
0 1
0 1 2
0 1 2 3
0 1 2 3 4
0 1 2 3 4 5
0 1 2 3 4 5 6
0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7 8
0 1 2 3 4 5 6 7 8 9
0 1 2 3 4 5 6 7 8 9 10
0 1 2 3 4 5 6 7 8 9 10 11
0 1 2 3 4 5 6 7 8 9 10 11 12
0 1 2 3 4 5 6 7 8 9 10 11 12 13
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

$ python test.py
0
0 1
0 1 2
0 1 2 3
0 1 2 3 4
0 1 2 3 4 5
0 1 2 3 4 5 6
0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7 8
0 1 2 3 4 5 6 7 8 9
0 1 2 3 4 5 6 7 8 9 10
0 1 2 3 4 5 6 7 8 9 10 11
0 1 2 3 4 5 6 7 8 9 10 11 12
0 1 2 3 4 5 6 7 8 9 10 11 12 13
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

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But using Qt 4.7.0, the callback is not called for new signals after a limit has been reached: in the example the limit was 11. The output is in attached 4.7.0output.txt.

$ python test.py
0 
0 1 
0 1 2 
0 1 2 3 
0 1 2 3 4 
0 1 2 3 4 5 
0 1 2 3 4 5 6 
0 1 2 3 4 5 6 7 
0 1 2 3 4 5 6 7 8 
0 1 2 3 4 5 6 7 8 9 
0 1 2 3 4 5 6 7 8 9 10 
0 1 2 3 4 5 6 7 8 9 10 11 
0 1 2 3 4 5 6 7 8 9 10 11 
0 1 2 3 4 5 6 7 8 9 10 11 
0 1 2 3 4 5 6 7 8 9 10 11 
0 1 2 3 4 5 6 7 8 9 10 11 
0 1 2 3 4 5 6 7 8 9 10 11 
0 1 2 3 4 5 6 7 8 9 10 11 
0 1 2 3 4 5 6 7 8 9 10 11

$ python test.py
0 
0 1 
0 1 2 
0 1 2 3 
0 1 2 3 4 
0 1 2 3 4 5 
0 1 2 3 4 5 6 
0 1 2 3 4 5 6 7 
0 1 2 3 4 5 6 7 8 
0 1 2 3 4 5 6 7 8 9 
0 1 2 3 4 5 6 7 8 9 10 
0 1 2 3 4 5 6 7 8 9 10 11 
0 1 2 3 4 5 6 7 8 9 10 11 
0 1 2 3 4 5 6 7 8 9 10 11 
0 1 2 3 4 5 6 7 8 9 10 11 
0 1 2 3 4 5 6 7 8 9 10 11 
0 1 2 3 4 5 6 7 8 9 10 11 
0 1 2 3 4 5 6 7 8 9 10 11 
0 1 2 3 4 5 6 7 8 9 10 11

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The system with Qt 4.6.2 installed runs Ubuntu 10.04

$ cat /proc/version
Linux version 2.6.32-26-generic (buildd@rothera) (gcc version 4.4.3 (Ubuntu 4.4.3-4ubuntu5) ) #48-Ubuntu SMP Wed Nov 24 09:00:03 UTC 2010
$ apt-cache show libqtcore4
...
Version: 4:4.6.2-0ubuntu5.1

$ cat /proc/version
Linux version 2.6.32-26-generic (buildd@rothera) (gcc version 4.4.3 (Ubuntu 4.4.3-4ubuntu5) ) #48-Ubuntu SMP Wed Nov 24 09:00:03 UTC 2010
$ apt-cache show libqtcore4
...
Version: 4:4.6.2-0ubuntu5.1

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The system with Qt 4.7.0 installed runs Ubuntu 10.10

$ cat /proc/version
Linux version 2.6.35-24-virtual (buildd@vernadsky) (gcc version 4.4.5 (Ubuntu/Linaro 4.4.4-14ubuntu5) ) #42-Ubuntu SMP Thu Dec 2 05:01:52 UTC 2010
$ apt-cache show libqtcore4
...
Version: 4:4.7.0-0ubuntu4

$ cat /proc/version
Linux version 2.6.35-24-virtual (buildd@vernadsky) (gcc version 4.4.5 (Ubuntu/Linaro 4.4.4-14ubuntu5) ) #42-Ubuntu SMP Thu Dec 2 05:01:52 UTC 2010
$ apt-cache show libqtcore4
...
Version: 4:4.7.0-0ubuntu4

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Here is the source code for the example:

import sys
from PySide import QtCore, QtGui
 
class Window(QtGui.QMainWindow):
 
    def __init__(self):
        super(Window, self).__init__()
        self.timer = QtCore.QTimer(self)
        self.timer.timeout.connect(self.onTimeout)
        self.n = 0
 
        self.timer.start(1000)
 
    @QtCore.Slot()
    def onTimeout(self):
 
        exec("Window.sig%d = QtCore.Signal(object, object)" % self.n)
        eval("self.sig%d" % self.n).connect(self.onSignalN)
 
        for i in xrange(self.n+1):
            eval("self.sig%d[object, object]" % i).emit( i,self )
 
        self.n += 1
        print ""
 
    @QtCore.Slot(object, object)
    def onSignalN(self, o1, o2):
        print o1,
 
app = QtGui.QApplication(sys.argv)
 
win = Window()
 
win.resize(320, 240)
win.setWindowTitle("Hello, World!")
win.show()
 
sys.exit(app.exec_())

import sys
from PySide import QtCore, QtGui

class Window(QtGui.QMainWindow):

    def __init__(self):
        super(Window, self).__init__()
        self.timer = QtCore.QTimer(self)
        self.timer.timeout.connect(self.onTimeout)
        self.n = 0

        self.timer.start(1000)

    @QtCore.Slot()
    def onTimeout(self):

        exec("Window.sig%d = QtCore.Signal(object, object)" % self.n)
        eval("self.sig%d" % self.n).connect(self.onSignalN)

        for i in xrange(self.n+1):
            eval("self.sig%d[object, object]" % i).emit( i,self )

        self.n += 1
        print ""

    @QtCore.Slot(object, object)
    def onSignalN(self, o1, o2):
        print o1,

app = QtGui.QApplication(sys.argv)

win = Window()

win.resize(320, 240)
win.setWindowTitle("Hello, World!")
win.show()

sys.exit(app.exec_())

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Ranen

[wysota]

If such a limitation exists, it is implied by PySide and not Qt. This code works properly in Qt 4.7:

#include <QtCore>
 
class Object : public QObject {
  Q_OBJECT
public:
  Object() {}
signals:
  void sig1();
  void sig2();
  void sig3();
  void sig4();
  void sig5();
  void sig6();
  void sig7();
  void sig8();
  void sig9();
  void sig10();
  void sig11();
  void sig12();
  void sig13();
  void sig14();
  void sig15();
  void sig16();
  void sig17();
  void sig18();
  void sig19();
  void sig20();
private slots:
  void onsig1() { qDebug() << Q_FUNC_INFO; }
  void onsig2() { qDebug() << Q_FUNC_INFO; }
  void onsig3() { qDebug() << Q_FUNC_INFO; }
  void onsig4() { qDebug() << Q_FUNC_INFO; }
  void onsig5() { qDebug() << Q_FUNC_INFO; }
  void onsig6() { qDebug() << Q_FUNC_INFO; }
  void onsig7() { qDebug() << Q_FUNC_INFO; }
  void onsig8() { qDebug() << Q_FUNC_INFO; }
  void onsig9() { qDebug() << Q_FUNC_INFO; }
  void onsig10() { qDebug() << Q_FUNC_INFO; }
  void onsig11() { qDebug() << Q_FUNC_INFO; }
  void onsig12() { qDebug() << Q_FUNC_INFO; }
  void onsig13() { qDebug() << Q_FUNC_INFO; }
  void onsig14() { qDebug() << Q_FUNC_INFO; }
  void onsig15() { qDebug() << Q_FUNC_INFO; }
  void onsig16() { qDebug() << Q_FUNC_INFO; }
  void onsig17() { qDebug() << Q_FUNC_INFO; }
  void onsig18() { qDebug() << Q_FUNC_INFO; }
  void onsig19() { qDebug() << Q_FUNC_INFO; }
  void onsig20() { qDebug() << Q_FUNC_INFO; }
private:
  friend int main(int, char**);
};
 
#include "main.moc"
 
int main(int argc, char **argv){
  Object o;
  for(int i=1;i<=20;++i){
    QObject::connect(&o, qPrintable(QString("2sig%1()").arg(i)), &o, qPrintable(QString("1onsig%1()").arg(i)));
  }
  emit o.sig1();
  emit o.sig2();
  emit o.sig3();
  emit o.sig4();
  emit o.sig5();  
  emit o.sig6();  
  emit o.sig7();  
  emit o.sig8();
  emit o.sig9();
  emit o.sig10();
  emit o.sig11();
  emit o.sig12();
  emit o.sig13();
  emit o.sig14();
  emit o.sig15();
  emit o.sig16();
  emit o.sig17();
  emit o.sig18();
  emit o.sig19();
  emit o.sig20();  
  return 0;
}

#include <QtCore>

class Object : public QObject {
  Q_OBJECT
public:
  Object() {}
signals:
  void sig1();
  void sig2();
  void sig3();
  void sig4();
  void sig5();
  void sig6();
  void sig7();
  void sig8();
  void sig9();
  void sig10();
  void sig11();
  void sig12();
  void sig13();
  void sig14();
  void sig15();
  void sig16();
  void sig17();
  void sig18();
  void sig19();
  void sig20();
private slots:
  void onsig1() { qDebug() << Q_FUNC_INFO; }
  void onsig2() { qDebug() << Q_FUNC_INFO; }
  void onsig3() { qDebug() << Q_FUNC_INFO; }
  void onsig4() { qDebug() << Q_FUNC_INFO; }
  void onsig5() { qDebug() << Q_FUNC_INFO; }
  void onsig6() { qDebug() << Q_FUNC_INFO; }
  void onsig7() { qDebug() << Q_FUNC_INFO; }
  void onsig8() { qDebug() << Q_FUNC_INFO; }
  void onsig9() { qDebug() << Q_FUNC_INFO; }
  void onsig10() { qDebug() << Q_FUNC_INFO; }
  void onsig11() { qDebug() << Q_FUNC_INFO; }
  void onsig12() { qDebug() << Q_FUNC_INFO; }
  void onsig13() { qDebug() << Q_FUNC_INFO; }
  void onsig14() { qDebug() << Q_FUNC_INFO; }
  void onsig15() { qDebug() << Q_FUNC_INFO; }
  void onsig16() { qDebug() << Q_FUNC_INFO; }
  void onsig17() { qDebug() << Q_FUNC_INFO; }
  void onsig18() { qDebug() << Q_FUNC_INFO; }
  void onsig19() { qDebug() << Q_FUNC_INFO; }
  void onsig20() { qDebug() << Q_FUNC_INFO; }
private:
  friend int main(int, char**);
};

#include "main.moc"

int main(int argc, char **argv){
  Object o;
  for(int i=1;i<=20;++i){
    QObject::connect(&o, qPrintable(QString("2sig%1()").arg(i)), &o, qPrintable(QString("1onsig%1()").arg(i)));
  }
  emit o.sig1();
  emit o.sig2();
  emit o.sig3();
  emit o.sig4();
  emit o.sig5();  
  emit o.sig6();  
  emit o.sig7();  
  emit o.sig8();
  emit o.sig9();
  emit o.sig10();
  emit o.sig11();
  emit o.sig12();
  emit o.sig13();
  emit o.sig14();
  emit o.sig15();
  emit o.sig16();
  emit o.sig17();
  emit o.sig18();
  emit o.sig19();
  emit o.sig20();  
  return 0;
}

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witht the result of:

void Object::onsig1()
void Object::onsig2()
void Object::onsig3()
void Object::onsig4()
void Object::onsig5()
void Object::onsig6()
void Object::onsig7()
void Object::onsig8()
void Object::onsig9()
void Object::onsig10()
void Object::onsig11()
void Object::onsig12()
void Object::onsig13()
void Object::onsig14()
void Object::onsig15()
void Object::onsig16()
void Object::onsig17()
void Object::onsig18()
void Object::onsig19()
void Object::onsig20()

[rghosh]

Thank you. I have forwarded my question to the pyside mailing list. (The alternative python bindings, PyQt, didn't have this problem)