Thread in Python

 

Thread is a collection of light-weight subprocess to execute the program, in the application, we will use Multithreading to implement multitasking.
using Multi-threading we can execute more than one process simultaneously in a single resource.
O/s is the best example of multi-threading because it can execute more than one program simultaneously.
When we want to create a game application then parallel execution is mandatory, which can be managed by the Multi-threading process.
Thread Life Cycle:-

Syntax of threading:-
import threading
class Classname(threading.Thread):
      functionality
      ........

import threading

import time

class ThreadExample(threading.Thread):

    def run(self):

        for i in range(1,10):

            print("Process is "+str(i))

            time.sleep(1)

t1 = ThreadExample()  #new state ,it will provide memory to store data

t1.start()  #start() is the predefine method which will convert thread process to runnable state to running state

Multithreading:-  If we start more then one Thread object simultaneous then it is called multithreading.

It is used to execute multiple programs set simultaneous.

 import threading

import time

class ThreadExample(threading.Thread):

    def run(self):

        for i in range(1,10):

            print("Process is "+str(i))

            time.sleep(1)

t1 = ThreadExample()  #new state ,it will provide memory to store data

t1.start()  #start() is the predefine method which will convert thread process to runnable state to running state

t2 = ThreadExample()

t2.start()

t3 = ThreadExample()

t3.start()      

Thread Process Synchronization:-

using this we can provide multi-threading execution is waiting for the state until the current thread process completed. when the process completed then join() will notify another thread and it will be executed .using the join()  method we can synchronize the thread process.

import threading

import time

class ThreadExample(threading.Thread):

    def run(self):

        for i in range(1,10):

            print("Process is "+str(i))

            time.sleep(1)

t1 = ThreadExample()  #new state ,it will provide memory to store data

t1.start()  #start() is the predefine method which will convert thread process to runnable state to running state

t1.join()

t2 = ThreadExample()

t2.start()

t2.join()

t3 = ThreadExample()

t3.start()

 Example of Thread?

import threading

import time

class Thread1(threading.Thread):

    def __init__(self):

        super(Thread1, self).__init__()

        self.num=int(input("enter number"))

    def run(self):

        for i in range(1,11):

            print(self.num*i)

            time.sleep(1)

class Thread2(Thread1):

    def __init__(self):

       super(Thread2, self).__init__()

    def run(self):

        self.s=''

        self.fact=1

        for i in range(self.num,0,-1):

            self.s = self.s + str(i) + "*"

            self.fact=self.fact*i

            time.sleep(1)

        print("result is "+self.s+" = "+str(self.fact))

t1 = Thread1()

t1.start()

t1.join()

t2 = Thread2()

t2.start()

How to implement Thread for procedural programming?

We can call the method under the thread object using target parameters.

import time

import threading

def fun():

           for i in range(1,10):

        print(i)

        time.sleep(1)

      t1 = threading.Thread(target=fun)

t1.start()

t1.join()        

t2 = threading.Thread(target=fun)

t2.start()

 Another Example of Thread to calculate table using class-based and method based program:-

Class based Program:-

import threading

import time

class Table(threading.Thread):

    def __init__(self,num):

        super().__init__()

        self.num = num

    def run(self):

        for i in range(1,11):

            print(str(self.num*i) + " ")

            time.sleep(1)

t = Table(5)

t.start()

t.join()

t1 = Table(9)

t1.start()

Method Based Program:-

import threading

import time

def table(num):

    for i in range(1,11):

            print(str(num*i) + " ")

            time.sleep(1)

t = threading.Thread(target=table(5))

t.start()

t1 = threading.Thread(target=table(9))

t1.start()

How to implement Thread Synchronization?

In multithreading when multiple threads are working simultaneously on a shared resource like a file(reading and writing data into a file), then to avoid concurrent modification error(multiple threads accessing the same resource leading to inconsistent data) some sort of locking mechanism is used wherein when one thread is accessing a resource it takes a lock on that resource and until it releases that lock no other thread can access the same resource.

Lock Object: Python Multithreading

In the threading module of Python, for efficient multithreading, a primitive lock is used. This lock helps us in the synchronization of two or more threads. Lock class perhaps provides the simplest synchronization primitive in Python.

The primitive lock can have two states: locked or unlocked and is initially created in an unlocked state when we initialize the Lock object. It has two basic methods, acquire() and release().

Following is the basic syntax for creating a Lock object:

import threading

threading.Lock()

Lock objects use two methods, they are:

acquire(blocking=True, timeout=-1) method

This method is used to acquire the lock. When it is invoked without arguments, it blocks until the lock is unlocked.

This method can take 2 optional arguments, they are:

blocking flag which if sent as False will not block the thread if the lock is acquired by some other thread already and will return False as result. If you provide the value for this blocking flag as True then the calling thread will be blocked if some other thread is holding the lock and once the lock is released then your thread will acquire the lock and return True.

the timeout argument is used to provide a positive floating-point value, which specifies the number of seconds for which the calling thread will be blocked if some other thread is holding the lock right now. The default value which is -1 means the thread will be blocked for an indefinite time if it cannot acquire the lock immediately.

release() method

It is used to release an acquired lock. If the lock is locked, this method will reset it to unlocked, and return. Also, this method can be called from any thread.

When this method is called, one out of the already waiting threads to acquire the lock is allowed to hold the lock.

Also, it throws a RuntimeError if it is invoked on an unlocked lock.

Time for an Example!

Below we have a simple python program in which we have a class SharedCounter which will act as the shared resource between our threads.

We have a task method from which we will call the increment() method. As more than one thread will be accessing the same counter and incrementing its value, there are chances of concurrent modification, which could lead to inconsistent value for the counter.

Example to thread synchronization:-

import threading

import time

from random import randint

class SharedCounter(object):

      def __init__(self, val = 0):

        self.lock = threading.Lock()

        self.counter = val

      def increment(self):

        print("Waiting\n")

        self.lock.acquire()

        try:

            print('Acquired', self.counter,"\n")

            self.counter = self.counter + 1

        finally:

            print('Released a lock, counter value: ', self.counter,"\n")

            self.lock.release()

def xyz(c):

    r = randint(1,5)

    for i in range(r):

      c.increment()

      print('Done')

sCounter = SharedCounter()

t1 = threading.Thread(target=xyz, args=(sCounter,))

t1.start()   

t2 = threading.Thread(target=xyz, args=(sCounter,))

t2.start()

#print('Waiting for worker threads')

#t1.join()

#t2.join()    

print('Counter:', sCounter.counter)

Thread Assignments:-

1)  Create DICE GAME?

2) CREATE Automated ATM System?