[SOLVED] using threads to eliminate a never ending loop

[ogopa]

Hi guys,
I have a program in Qt Creator which outputs a sine wave with the click of a pushButton. However, due to a never ending while loop in my pushButton function, the application freezes when I click the pushButton. So I am using threads for my function and ending the while loop by eliminating the thread with the click of another pushButton(pushButton2).
I build my code with no errors. however, when I run it, the pushButton does not generate a sine wave and I get the following message:
@QMetaObject::connectSlotsByName: No matching signal for on_write_loop(snd_pcm_t*,signed short*,snd_pcm_channel_area_t*)@

Any help would be greatly appreciated.

My code snippets are below:

wave.cpp:
@void wave::on_write_loop(snd_pcm_t *handles, signed short *samples , snd_pcm_channel_area_t *areas)
{
double freq = ui->frequency->text().toDouble();
double ampl = ui->amplitude->text().toDouble();
double phase = 0;
signed short ptr;
int err, cptr;
while (1) {
generate_sine(0, period_size, &phase, freq, ampl);
ptr = samples;
cptr = period_size;
while (cptr > 0) {
err = snd_pcm_writei(hspdif, ptr, cptr);
if (err == -EAGAIN)
continue;
if (err < 0) {
if (xrun_recovery(hspdif, err) < 0) {
printf("Write error: %s ", snd_strerror(err));
exit(EXIT_FAILURE);
}
break; / skip one period */
}
ptr += err * channels;
cptr -= err;
}
}

}

wave::wave(QWidget parent) :
QMainWindow(parent),
ui(new Ui::wave)
{
ui->setupUi(this);
//setup();
mThread = new MyThread(this);
connect(mThread, SIGNAL(write_loop(snd_pcm_t, signed short*, snd_pcm_channel_area_t*)), this, SLOT(on_write_loop(snd_pcm_t*, signed short*, snd_pcm_channel_area_t*)));
}

wave::~wave()
{
delete ui;

}

void wave::on_pushButton_clicked()
{

//Generate
mThread->start();

}

void wave::on_pushButton_2_clicked()
{
//Terminate
mThread->Stop = true;

}@

wave.h:
@#ifndef WAVE_H
#define WAVE_H
#include "ui_wave.h"
#include <alsa/asoundlib.h>
#include <QMainWindow>
#include <QObject>
#include "mythread.h"

namespace Ui {
class wave;
}

class wave : public QMainWindow
{
Q_OBJECT

public:
explicit wave(QWidget *parent = 0);
~wave();
MyThread *mThread;

private slots:
void on_pushButton_clicked();

void on_pushButton_2_clicked();

void setup();

private:
Ui::wave *ui;

public slots:
void on_write_loop(snd_pcm_t*, signed short*, snd_pcm_channel_area_t*);
;

#endif // WAVE_H@

MyThread.cpp:
@void MyThread::run()
{
QMutex mutex;
mutex.lock();
if (this->Stop)
mutex.unlock();

const char *device = "plughw:0,0";

snd_pcm_hw_params_alloca(&hwparams);
snd_pcm_sw_params_alloca(&swparams);

int err = snd_output_stdio_attach(&output, stdout, 0);
printf( "snd_output_stdio_attach err=%d\n", err);
err = snd_pcm_open(&hspdif, device, SND_PCM_STREAM_PLAYBACK, 0);
printf( "snd_pcm_open err=%d\n", err);
err = set_hwparams(hspdif, hwparams, SND_PCM_ACCESS_RW_INTERLEAVED);
printf( "set_hwparams err=%d\n", err);
err = set_swparams(hspdif, swparams);
printf( "set_swparams err=%d\n", err);

samples = new signed short [period_size * channels * snd_pcm_format_physical_width(format)];
printf( "samples array_size=%d\n", int( period_size * channels * snd_pcm_format_physical_width(format)) );

areas = new snd_pcm_channel_area_t [channels];
printf( "areas channels=%d\n", channels);
for (unsigned int chn = 0; chn < channels; chn++) {
        areas[chn].addr = samples;
        areas[chn].first = chn * snd_pcm_format_physical_width(format);
        areas[chn].step = channels * snd_pcm_format_physical_width(format);
}
emit write_loop(hspdif, samples, areas);

}@

MyThread.h:
@#ifndef MYTHREAD_H
#define MYTHREAD_H
#include <alsa/asoundlib.h>
#include <QThread>

class MyThread : public QThread
{
Q_OBJECT
public:
explicit MyThread(QObject *parent = 0);
void run();
bool Stop;

signals:
void write_loop(snd_pcm_t*, signed short*, snd_pcm_channel_area_t*);

public slots:
};

#endif // MYTHREAD_H@

[loladiro]

Your on_write_loop is still in your mainWindow object and will be executed in the default thread.
Also, it is recommended not to subclass QThread, but to create a class for handling your logic and then calling moveToThread on that.

[dangelog]

Unless you plan not to use the connectSlotsByName feature, don't name your slots on_Foo_Bar (which will look for a children named Foo and connect that slot to Foo's Bar signal. It's very likely that you don't have a children named "write" with a signal named "loop"). And setupUi() WILL call connectSlotsByName.

http://doc.qt.nokia.com/4.7/qmetaobject.html#connectSlotsByName

[ogopa]

[quote author="peppe" date="1313161135"]Unless you plan not to use the connectSlotsByName feature, don't name your slots on_Foo_Bar (which will look for a children named Foo and connect that slot to Foo's Bar signal. It's very likely that you don't have a children named "write" with a signal named "loop"). And setupUi() WILL call connectSlotsByName.

http://doc.qt.nokia.com/4.7/qmetaobject.html#connectSlotsByName[/quote]

Ahh, yes, I see what you mean. I have corrected that. Thank you. However, I have a new problem now. My application terminates the moment I click the pushButton.. I get the message:
The program has unexpectedly finished.

[goetz]

If you run it in a debugger, you'll see the line of code where it bailed out.

[ogopa]

got it working. Thanks for all the help.

[mlong]

Be sure and mark the topic [Solved]! Thanks!

[ogopa]

I am sure. Thanks

[ogopa]

Here is the solution:

mythread.h:
@#ifndef MYTHREAD_H
#define MYTHREAD_H
#include <QThread>

class MyThread : public QThread
{
Q_OBJECT
protected:
void run();
public:
explicit MyThread(QObject *parent = 0);
};
#endif // MYTHREAD_H
@

mythread.cpp:
@#include "wave.h"
#include "mythread.h"

MyThread::MyThread(QObject *parent) :
QThread(parent)
{
}
void MyThread::run()
{
onWriteLoop();
}@
wave.cpp:
@wave::wave(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::wave)
{
ui->setupUi(this);
setup();

thread = new MyThread();

}

wave::~wave()
{
delete ui;
delete thread;
}

void wave::on_pushButton_clicked()
{
//Generate
freq = ui->frequency->text().toDouble();
ampl = ui->amplitude->text().toDouble();
thread->start();
ui->pushButton->setEnabled(false);
ui->pushButton->setStyleSheet("background-color: gray");
ui->pushButton_2->setStyleSheet("background-color: rgb(255, 192, 192);"
"color: red;");
ui->pushButton_2->setEnabled(true);
}

void wave::on_pushButton_2_clicked()
{
//Terminate
thread->terminate();
ui->pushButton_2->setEnabled(false);
ui->pushButton_2->setStyleSheet("background-color: gray");
ui->pushButton->setStyleSheet("background-color: rgb(192, 255, 208);"
"color: green;");
ui->pushButton->setEnabled(true);

}@