Qthread n QTimer Problem

[quickNitin]

hi
i am trying to print a no. o points on canvas. These points are read from a fifo through a clas MyThread.

class MyThread: public QThread
{
Q_OBJECT
public:
	MyThread(QObject *parent=0);
	~MyThread();
	double x;
	double y;
 
protected:
	void run();
signals:
	void dataAvailable();
public slots:
	void startThread();
 
};
 
#endif

class MyThread: public QThread
{
Q_OBJECT
public:
	MyThread(QObject *parent=0);
	~MyThread();
	double x;
	double y;

protected:
	void run();
signals:
	void dataAvailable();
public slots:
	void startThread();

};

#endif

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amd its implementation is as

#ifndef MYTHREAD_cpp
#define MYTHREAD_cpp
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include "MyThread.h"
#include <iostream.h>
 
 
MyThread::MyThread(QObject *parent) :QThread(parent)
{
 
}
 
MyThread::~MyThread()
{
}
 
void MyThread::run()
{
	int fd0;
 
 
	fd0 = open("/home/prince/mydev01",O_RDWR);
	if(fd0== -1)
		cout<<"\n------------------- No fifo found///////---------------------\n\n";
	else
		cout<<" Fifo founf \n";
 
	read(fd0,&x,sizeof(int));
	read(fd0,&y,sizeof(int));
	printf("\nReceived  x = %d  & y = %d from RTCore\n",
		x,y);
	close(fd0);
	emit dataAvailable();
}
void MyThread::startThread()
{
	start(LowPriority);  
}
 
 
#endif

#ifndef MYTHREAD_cpp
#define MYTHREAD_cpp
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include "MyThread.h"
#include <iostream.h>


MyThread::MyThread(QObject *parent) :QThread(parent)
{
	  
}

MyThread::~MyThread()
{
}

void MyThread::run()
{
	int fd0;
	

	fd0 = open("/home/prince/mydev01",O_RDWR);
	if(fd0== -1)
		cout<<"\n------------------- No fifo found///////---------------------\n\n";
	else
		cout<<" Fifo founf \n";
		
	read(fd0,&x,sizeof(int));
	read(fd0,&y,sizeof(int));
	printf("\nReceived  x = %d  & y = %d from RTCore\n",
		x,y);
	close(fd0);
	emit dataAvailable();
}
void MyThread::startThread()
{
	start(LowPriority);  
}


#endif

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I need to refresh view every second. So a Timer generates a signal everysecond to run some code to claa slot MyThread::startThread(). Control reaches and it also goes to run(). But either it donot enters run() ( i checked it with gdb breakpoint method) or before reads it again comes to MyThread::startThread().
I couldn't figure out the cause

[jacek]

I would do it like this:

void MyThread::run()
{
	int fd0 = open("/home/prince/mydev01",O_RDWR);
	...
	while( ! _end ) {
		read(fd0,&x,sizeof(int));
		...
		_semaphore.acquire();
	}
	close(fd0);	
}
 
void MyThread::startThread()
{
	if( isRunning() ) {
		_semaphore.release();
	}
	else {
		start( LowPriority );
	}
}
 
void MyThread::stopThread()
{
	_end = true;
	_semaphore.release();
}

void MyThread::run()
{
	int fd0 = open("/home/prince/mydev01",O_RDWR);
	...
	while( ! _end ) {
		read(fd0,&x,sizeof(int));
		...
		_semaphore.acquire();
	}
	close(fd0);	
}

void MyThread::startThread()
{
	if( isRunning() ) {
		_semaphore.release();
	}
	else {
		start( LowPriority );
	}
}

void MyThread::stopThread()
{
	_end = true;
	_semaphore.release();
}

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[quickNitin]

thanks jacek! i am trying this code. My purpose is while reading from fifo gui shouldn't be blocked and it keep o updating as well. That ws the reason i was reading elements from fifo one at a time. Will not this code will block event loop.

[jacek]

thanks jacek! i am trying this code. My purpose is while reading from fifo gui shouldn't be blocked and it keep o updating as well. [...] Will not this code will block event loop.

It won't block the event loop, because it will happen in a different thread.

That ws the reason i was reading elements from fifo one at a time.

In that case maybe you don't need that timer at all? Maybe a QThread::sleep() will be enough? How often that device will produce data?

[quickNitin]

an algo will write points to fifo. Appx every second

[wysota]

If the thread only reads data, maybe it's enough to do a blocking (temporary) read in the other thread without any need for other sync mechanisms. "waitForReadyRead" may be helpfull here.