QtSerialPort and memory usage

codeaway

Hi,

I have this following code reading the serial port on Windows.

As the application keeps reading the serial port byte after byte,
I do see that the memory usage keeps on going up. But if I do
comment out the read(), the memory usage is stable and constant.

Is it something that I am missing or doing incorrectly ?

Thanks,

#include <QtSerialPort/QSerialPort>
#include <QCoreApplication>
#include <QDebug>

int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
QSerialPort port;
char dt;

port.setPortName("COM13");
if (!port.open(QIODevice::ReadWrite)) {
	qDebug() << "Open" << port.portName() << "failed";
	return -1;
}
qDebug() << port.portName() << "Open";
port.setBaudRate(QSerialPort::Baud9600);	// Baud rate
port.setDataBits(QSerialPort::Data8);		// Data bits
port.setParity(QSerialPort::NoParity);		// Parity
port.setStopBits(QSerialPort::OneStop);		// Stop bits
port.setFlowControl(QSerialPort::NoFlowControl);// Flow control

port.setReadBufferSize(1);
while (1) {
	if (port.waitForReadyRead(10)) {
		port.read(&dt, 1);
	}
}
return a.exec();

}

mrjj

+1 for running able code.
Win 7, 64. mingw. Qt 5.5
memory seems stable.
how long to watch ?

codeaway

@mrjj

I am running
Win 7 SP1 32bit Version 6.1.7601
QT 5.5.0,
QT creator: 3.4.2 revision b57ac109a2
MinGW 2013072200

The memory usage, seen as with Task Manager
is as follows:

starts at about : ~2.4M
@ about 10Sec : ~32M
@ 60Sec : ~64M
@ 120Sec : ~96M
@ about 300Sec : ~227M

I dont know, just a thought, as though each read() is not
freeing up read memory within the library. Is that possible situation ?
But then, lot of other people should also be facing the same situation,
but I guess that isnt the scenario.

Thanks

mrjj

@codeaway
Well bugs are always possible.
Also tried at work. After 25 sec, still have same Memory.
So I cannot reproduce it easy.
Is it a real comport or a virtual one ?
both tested here are virtual.
(com1.)
I wonder if it could be your driver .
can you reproduce it on other system ?
update:
tried on system with real comport. still stable mem.
sorry.

codeaway

@mrjj

I am using a BAFO USB to serial converter
as seen here:
http://www.dx.com/p/bafo-usb-to-rs232-converter-5947#.VhTCIuyqpHw

Trying to eliminate some unknown possible situations:
Assuming for a moment that there is a hardware bug with the
USB to serial converter hardware/driver

The same serial hardware is connected to the same converter and is read
with Terra Term (Version 4.76)

It's memory usage (Private Working set) remains stable at 8,668K reading
the same data. I just wonder why it is showing stable memory usage.

http://postimg.org/image/a2qb10ev1/

I wondered, how the other QtSerialExamples behaved;
Tried with the simple terminal example
D:\Qt\Qt5.5.0\5.5\Src\qtserialport\examples\serialport\terminal\release>

Even terminal shows a memory usage increment, much like the code snippet
that's under scrutiny. I wonder, how Terra Term is able to cope with a
consistent memory usage

Updated the original code to print out the memory usage.
Updated code output screencap shows the usage memory
incrementing:
http://postimg.org/image/cfofnghnl/

For sake of completeness, including the updated code in here

#include <windows.h>
#include "psapi.h"

#include <QtSerialPort/QSerialPort>
#include <QCoreApplication>
#include <QDebug>
#include <QDateTime>

int main(int argc, char *argv[])
{
PROCESS_MEMORY_COUNTERS_EX pmc;
QCoreApplication a(argc, argv);
QSerialPort port;
char dt;

port.setPortName("COM13");
if (!port.open(QIODevice::ReadWrite)) {
	qDebug() << "Open" << port.portName() << "failed";
	return -1;
}

qDebug() << port.portName()
	 << "Open @" << QDateTime::currentMSecsSinceEpoch();

port.setBaudRate(QSerialPort::Baud9600);	// Baud rate
port.setDataBits(QSerialPort::Data8);		// Data bits
port.setParity(QSerialPort::NoParity);		// Parity
port.setStopBits(QSerialPort::OneStop);		// Stop bits
port.setFlowControl(QSerialPort::NoFlowControl);// Flow control

port.setReadBufferSize(1);
while (1) {
	if (port.waitForReadyRead(10)) {
		port.read(&dt, 1);
		GetProcessMemoryInfo(GetCurrentProcess(),
				    (PROCESS_MEMORY_COUNTERS*)&pmc,
				     sizeof(pmc));

		qDebug() << "Read @" << QTime::currentTime()
			 << "Used:" << pmc.PrivateUsage;
	}
}
return a.exec();

}

mrjj

Hmm if tera works with same usb serial then it cant be the driver.
Im also using serial over usb.

Tried to run updated code. just to ebe sure.
get link error
undefined reference to `GetProcessMemoryInfo@12'

What should i put in .pro to run ?
something with -lpsapi.
Mostly on linux so not sure with syntax

codeaway

@mrjj

Yes.

Sorry, missed the .pro file. inlined it

#-------------------------------------------------

Project created by QtCreator 2015-10-06T21:35:43

#-------------------------------------------------

win32:LIBS += -lpsapi

QT += core serialport

QT -= gui

TARGET = Serial
CONFIG += console
CONFIG -= app_bundle

TEMPLATE = app

SOURCES += main.cpp

mrjj

works.
Still stable.
Do you have input on the serial ?
I will connect something that sends data. just to check.
How do you make it open console also ?
Here its just a process.
Update:
ignore last question. just saw its QDebug
Also, with input , I do see mem raising.
Testing more

mrjj

ok,
slowly from 12k to 17k. over time when it has input.
Also the pmc changes.
So yes. I see the same.
Will leave it running for some time to check if it stops.

codeaway

@mrjj

Yes, I do have a microcontroller reading values and outputting to serial port
continuously.

Actually, the application I created is a console application. The info is output
with QDebug additionally.

Nevertheless, you can choose to output with console without QDebug too.

CONFIG += console

in the .pro file

Create a output stream in the actual code

QTextStream out(stdout);

and output whatever required

out << "Something" << endl;

mrjj

@codeaway
Ok i killed it at 25K.
Since we just reading a char, it cant be in the us that leaks.

I must agree it seems odd.

kuzulis

Can you please test same with the virtual com0com: http://sourceforge.net/projects/com0com/
A signed driver for x64: https://code.google.com/p/powersdr-iq/downloads/detail?name=setup_com0com_W7_x64_signed.exe&can=2&q=

codeaway

@kuzulis

I downloaded the x86 build, as I am running a 32 bit OS.
How should I configure com0com ?

mrjj

@kuzulis
just as a virtual port or as a loop ?

kuzulis

How should I configure com0com ?

Just create a pair with the "use port class" and "eneble buffer overrun" (via setupg.exe ui)

just as a virtual port or as a loop ?

as a two virtual ports. . e.g. COM1 as receiver for qserialport and COM2 as sender for other software (e.g. I have used Termite app to send).

UPD:

Yes, I too can reproduce this memory leak..

codeaway

@kuzulis

Yeah, reproduced it with com0com and termite.
Attached link to screencap

http://postimg.org/image/mku4ege29/

After a detailed analysis, it looks as though all QtSerialPort examples
also face this issue.

mrjj

@codeaway
Yep got ever increasing mem use also with com0com.
If time permits I try the examples too.

kuzulis

Probably it is a bug of QWinOverlappedIoNotifier : https://bugreports.qt.io/browse/QTBUG-48653
Let's wait for more info about..