ZEXI JIN

1. Multi-threading states
2. Java thread init methods
3. Examples of Thread and Runnable

Multi-threading states

1. new: 新建状态，保持这个状态直到程序start()
2. ready: 调用了start()，就绪状态的线程处于就绪队列中，要等待JVM里线程调度器的调度
3. running: 获取了CPU资源，执行run()里面的指令
4. suspend: 失去所占用资源之后，该线程就从运行状态进入阻塞状态。在睡眠时间已到或获得设备资源后可以重新进入就绪状态。可以分为三种
   • 等待阻塞: wait()
   • 同步阻塞: 线程在获取synchronized同步锁失败后
   • 其他阻塞: 其他阻塞：通过调用线程的sleep()或join()发出了I/O请求时，线程就会进入到阻塞状态
5. dead: 一个运行状态的线程完成任务或者其他终止条件发生时，该线程就切换到终止状态

Java thread init methods

Java 提供了三种创建线程的方法

• 通过实现Runnable接口
• 通过继承Thread类本身
• 通过Callable和Future创建线程

Java thread example

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// class extending Thread
import java.util.*;
// new class
class MyThread extends Thread {
    private int ticket = 10;
    private String name;
    private Random rand = new Random();
    // constructors
    public MyThread(String name) {
        this.name = name;
        System.out.println(this.name + " starts with " + this.ticket + ".");
    }
    // Override the run function to implement functionality
    @Override
    public void run() {
        for (int i = 0; i < 500; i++) {
            if (this.ticket > 0) {
                // create a random number between two sales
                int nxt = rand.nextInt(20) * 10;
                this.ticket--;
                System.out.println(this.name + " sold a ticket, now has " + this.ticket + " tickets.");
                try {
                    Thread.sleep(nxt);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
        System.out.println("Now, " + this.name + " has ended.");
    }
}
// method to run the class above
public class ThreadDemo {
    public static void main(String[] args) {
        System.out.println("start");
        MyThread mt1 = new MyThread("Counter 1");
        MyThread mt2 = new MyThread("Counter 2");
        MyThread mt3 = new MyThread("Counter 3");
        mt1.start();
        mt2.start();
        mt3.start();
    }
}

Runnable Example

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import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import java.util.Random;
// now using Runnable interface instead of extending a class
public class MyRunnable implements Runnable{
    private int ticket = 30;
    private Random rand = new Random();
    private Lock lock = new ReentrantLock();
    public MyRunnable() {
        System.out.println("This class starts with " + this.ticket + " tickets.");
    }
    // overriding the run method just as before
    @Override
    public void run() {
        while (this.ticket > 0) {
            // tryLock() checks if the lock is available, takes the lock and return true if yes, else return false
            if (lock.tryLock()){
                try {
                    // command to execute with the lock
                    System.out.println(Thread.currentThread().getName() + " acquired lock.");
                    this.ticket--;
                    System.out.println(Thread.currentThread().getName() + " sold a ticket, now has " + this.ticket + " tickets.");
                } catch (Exception e) {
                    System.err.println(e);
                } finally {
                    // releasing the lock
                    System.out.println(Thread.currentThread().getName() + " released lock.");
                    lock.unlock();
                }
                // wait for a random length after selling a ticket
                int nxt = rand.nextInt(20) * 10;
                try {
                    Thread.sleep(nxt);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            } 
            // if lock is not available, wait
            else {
                try {
                    Thread.sleep(10);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
        System.out.println("Now, " + Thread.currentThread().getName() + " has ended.");
    }
}

Django directory levels

1. manage.py: we use this to communicate with Django server
2. project directory:
   1. __init__.py: tells Django to use directory as a python package
   2. settings.py: Django configuration file
   3. urls.py: url schema
   4. wsgi.py: project and wsgi integration web server

Database (MySQL) config

• dependencies used:
  mysql 5.7.24 h56848d4_0
  mysql-connector-c 6.1.11 hccea1a4_0
  mysql-connector-python 8.0.17 py27h3febbb0_0 anaconda
  mysql-python 1.2.5 py27h1de35cc_0 anaconda
  pymysql 0.9.3 py27_0
• __init__.py:, add the following code:

  1 2	import pymysql pymysql.install_as_MySQLdb()

• in settings.py: add database configurations to connect to the database

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  DATABASES = { 'default': { 'ENGINE': 'django.db.backends.mysql', 'NAME': # server name 'USER': # user name 'PASSWORD': # password 'HOST': 'localhost', 'PORT': '3306', } }

Init new application

• init new application:

  1	python manage.py startapp <myApp>

• codes above creates:
  • admin.py: website config
  • models.py: model
  • views.py: view
• In setting, add to INSTALLED_APP:

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  INSTALLED_APPS = [ 'django.contrib.admin', 'django.contrib.auth', 'django.contrib.contenttypes', 'django.contrib.sessions', 'django.contrib.messages', 'django.contrib.staticfiles', 'myApp' ]

models.py file

• the following is an example of models.py

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  # -*- coding: utf-8 -*- from __future__ import unicode_literals from django.db import models # Create your models here. class Grades(models.Model): gname = models.CharField(max_length=20) gdate = models.DateTimeField() ggirlnum = models.IntegerField() gboynum = models.IntegerField() isDelete = models.BooleanField(default=False) def __str__(self): return "%s-%d-%d"%(self.gname, self.gboynum, self.ggrilnum) class Students(models.Model): sname = models.CharField(max_length=20) sgender = models.BooleanField(default=True) sage = models.IntegerField() scontend = models.CharField(max_length=20) isDelete = models.BooleanField(default=False) sgrade = models.ForeignKey("Grades") def __str__(self): return "%s-%d-%s"%(self.sname, self.sage, self.scontend)

• make migration and execute migration file: will create database according to models.py

  1 2	python manage.py makemigrations # create migration file python manage.py migrate # execute migration file

To add new entries with manage.py shell commands

1. enter shell:

   1	python manage.py shell

2. import packages in shell:

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   from myApp.models import Grades, Students from django.utils import timezone from datetime import *

3. add new entry to db:

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   grade1 = Grades() grade1.gname = "something" grade1.gdate = datetime(year=,month=,day=) grade1.ggirlnum = 70 grade1.gboynum = 35 grade1.save()

4. some other command:

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   Grades.objects.all() # get all data entries in Grades g = Grades.objects.get(pk=1) # get the 1st object in Grades g.gboynum = 45 g.save() # alternate existing data d.delete() # delete, including the one in db stu1 = g.students_set.create(sname=...) # add new student with one line

To run server

• execute:

  1	python manage.py runserver ip:port

• Admin:
  • publish content
  • add/modify/delete content
  • add “‘django.contrib.admin’” in INSTALLED_APPS
  • exists by defualt
  • add “/admin” and log in
  • change language or timezone based on preference

(to be continued…)