What is a Thread?

A thread is an active flow of control that can be activated in parallel with other threads within the same process.
Each thread can execute a set of instructions independently and in parallel with other processes or threads.
They share space addressing and then the data structures.
A thread is sometimes called a lightweight process.
The implementation of a thread is less onerous than that of a real process.
However, unlike process, multiple threads may share many resources.

Processes V/S Threads

A process can consist of multiple parallel threads.
The creation and management of a thread by the operating system is less expensive in terms of CPU’s resources than the creation and management of a process.
Threads are used for small tasks, whereas processes are used for more heavyweight tasks.
The threads of the same process share the address space and other resources, while processes are independent of each other.

Threads and Python

Thread-based parallelism is the standard way of writing parallel programs
The python interpreter is not fully thread-safe
In order to support multithreaded Python programs, a global lock called the Global Interpreter Lock (GIL) is used.
Only one thread can execute the python code at the same time.
Python automatically switches to next thread after a short period of time.
If multiple threads attempt to access the same data object, it may end up in an inconsistent state.

from threading import Thread

from time import sleep


# To create a thread in Python, you'll want to make your class work as a thread.
# For this, you should subclass your call from the Thread class

class CookBook(Thread):

    def __init__(self):
        Thread.__init__(self)
        self.message = "Hello parallel code!"

    # this method prints only the message
    def print_message(self):
        print(self.message)

    # the run method prints ten times the message
    def run(self):
        print("Thread firing up")
        x = 0
        while x < 10:
            self.print_message()
            sleep(2)
            x += 1
        print("Thread Ended\n")


# start the main process
print("Process started")

hello_py = CookBook()

hello_py.start()

print("Process Ended")