Saturday, May 26, 2012

[Qt] memory management and implicit sharing

There are some points that we have to know when we program using Qt:

  • The ownership of all child QObjects is transferred to the parent.
    • Automatic deletion by the parent
    • Allocated from the heap (using new)
    • manual deletion is not necessary but it won't cause any problems.
  • All QObjects without a parent must be deleted manually.
  • Pay attention to ownership and responsibilities. Qt does not provide a garbage collection.
Only if you have Classes with QObjects, then child items will be deleted if the parent is deleted:

QObject *parent = new QObject; 
QWidget *child1 = new QWidget(parent); QPushButton *child2 = new QPushButton(parent); delete parent; // child1 and child2 will be deleted automatically!

 



Implicit sharing (IS)
The following example is about how implicit sharing works when test() returns QList object (on stack). This memory address of "a" is shared to "result" and "a" is not destroyed when method:test() is out of scope.
#include "mainwindow.h" #include "ui_mainwindow.h" #include <QList> #include <QtGui> QList<QString> MainWindow::test() { QList<QString> a; // on stack QList<QString> b = QList<QString>(); // on stack QList<QString> *c = new QList<QString>(); // on heap for (int i = 0; i < 10; i++) { /* if we append a reference of QString, it will consume the memory of the QList Object based on the size of string */ a.append("a_helo:"); a.append(QString::number(i)); b.append("b_helo:"); b.append(QString::number(i)); c->append("c_helo:"); c->append(QString::number(i)); } qDebug() << a << " addres:" << &a; qDebug() << b << " addres:" << &b; qDebug() << *c << " addres:" << c; //delete &b; // we cannot manually free the memory of b or c on stack delete c; // OK return a; // Implicit Sharing } MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWindow) { ui->setupUi(this); /* The memory address of result is same with a object in test() because of implicit sharing */ QList<QString> result = test(); QList<QString> result2; qDebug() << result << " addres:" << &result; qDebug() << result2 << " addres:" << &result2; } MainWindow::~MainWindow() { delete ui; }

Monday, May 14, 2012

[Explanation][Trema] The message mechanism in flow_manager app

I give 2 pictures to illustrate the message mechanism in flow_manager app.

1. Request/Reply message using send_request_message() and send_reply_message()


2. (Received) Message using send_message()

Wednesday, May 9, 2012

[Open vSwitch] Simply test ovs-ofctl command on GNS3 simulation network


This article is to test ovs-ofctl command on GNS3 simulation network. PC1 and PC2 are  virtual machine on Qemu. U_OVS is emulated with Open vSwitch and an OpenFlow Controller is also on it. Please see the following picture:

1. For how to build the following GNS3 environment, please refer to the URL:
http://brezular.wordpress.com/2011/06/25/part2-openvswich-vlans-trunks-l3-vlan-interface-intervlan-routing-configuration-and-testing/
2. Run > sudo ovs-ofctl show br0

OFPT_FEATURES_REPLY (xid=0x1): ver:0x1, dpid:000008002725cd53
n_tables:1, n_buffers:256
features: capabilities:0x87, actions:0xfff
 1(eth1): addr:08:00:27:95:ef:0b
     config:     0
     state:      LINK_DOWN
     current:    COPPER AUTO_NEG
     advertised: 10MB-HD 10MB-FD 100MB-HD 100MB-FD 1GB-FD COPPER AUTO_NEG
     supported:  10MB-HD 10MB-FD 100MB-HD 100MB-FD 1GB-FD COPPER AUTO_NEG
 2(eth3): addr:08:00:27:25:cd:53
     config:     0
     state:      0
     current:    1GB-FD COPPER AUTO_NEG
     advertised: 10MB-HD 10MB-FD 100MB-HD 100MB-FD 1GB-FD COPPER AUTO_NEG
     supported:  10MB-HD 10MB-FD 100MB-HD 100MB-FD 1GB-FD COPPER AUTO_NEG
 3(eth2): addr:08:00:27:c3:5f:90
     config:     0
     state:      0
     current:    1GB-FD COPPER AUTO_NEG
     advertised: 10MB-HD 10MB-FD 100MB-HD 100MB-FD 1GB-FD COPPER AUTO_NEG
     supported:  10MB-HD 10MB-FD 100MB-HD 100MB-FD 1GB-FD COPPER AUTO_NEG
 LOCAL(br0): addr:08:00:27:25:cd:53
     config:     PORT_DOWN
     state:      LINK_DOWN
OFPT_GET_CONFIG_REPLY (xid=0x3): frags=normal miss_send_len=0

3. After PC1 and PC2 ping each other, run > sudo ovs-ofctl dump-flows br0
NXST_FLOW reply (xid=0x4):
 cookie=0x0, duration=17.125s, table=0, n_packets=14, n_bytes=1372, idle_timeout=5,priority=65535,icmp,in_port=2,vlan_tci=0x0000,dl_src=00:aa:00:3c:24:00,dl_dst=00:aa:00:4d:1d:00,nw_src=192.168.1.2,nw_dst=192.168.1.1,nw_tos=0,icmp_type=8,icmp_code=0 actions=output:3
 cookie=0x0, duration=18.13s, table=0, n_packets=15, n_bytes=1470, idle_timeout=5,priority=65535,icmp,in_port=3,vlan_tci=0x0000,dl_src=00:aa:00:4d:1d:00,dl_dst=00:aa:00:3c:24:00,nw_src=192.168.1.1,nw_dst=192.168.1.2,nw_tos=0,icmp_type=0,icmp_code=0 actions=output:2


p.s:
the script of PC1 configuration
Login is tc without password set.
Assign IP address 192.168.1.1/24 to eth0 and make it persistent after next reboot of Microcore
sudo hostname PC1
sudo ifconfig eth0 192.168.1.1 netmask 255.255.255.0
echo "hostname PC1" >> /opt/bootlocal.sh
echo "ifconfig eth0 192.168.1.1 netmask 255.255.255.0" >> /opt/bootlocal.sh
/usr/bin/filetool.sh -b

Sunday, May 6, 2012

[Explanation][Trema] The Register Event in Routing Switch App

If we want to understand how Routing Switch App works in Trema, we have to know the event register first. Here is a simple explanation about the register event in Routing Switch App, which is related Topology Ap.

Tuesday, May 1, 2012

[How to] Find a key word or Replace it with other string on Linux

Please refer to these examples:

Find the key word "ProcessType=6" in text files under current path (included sub folder)
> find ./ -name "*.txt" -exec grep -n -H "ProcessType=6" {} \;

Replace the key word "python2.4" with "python2.6" in python files under /opt/stack (included sub folder)
> find /opt/stack -name "*.py" -exec sed -i 's/python2.4/python2.6/' '{}' \;

Based on the script above, you will be able to find or replace a key word quickly and efficiently.