Multithreading Concepts
Multithreading is the core concept of nearly all modern programming languages especially python because of its simplistic implementation of threads.
A thread is a sub-program within a program that can be executed independently of other section of the code. A thread executes in the same context sharing program’s runnable resources like memory.
When in a single process, we are executing multiple threads simultaneously, it is called multithreading.
Python Multithreading Modules for a thread implementation
To implements threads in programs, python provides two modules −
- thread (for python 2.x) or _thread(for python 3.x) module
- threading module
Where the thread module creates a thread as a function whereas the threading module provides an object-oriented approach to create a thread.
Syntax
_thread.start_new_thread(func, args[, kwargs])
Above starts a new thread and returns its identifier. The first argument is a function func which the thread executes with the second argument containing a tuple with a positional list of arguments. The optional kwargs argument specifies a dictionary of keyword arguments. When the function returns, the thread silently exists.
In this, we see a basic example of a client-server application. Where clients basically open a socket connection and send queries to the server. The server responds back.
On running with no argument, this program starts with a TCP socket server that listens for connections to 127.0.0.1 on port 8000.
client_thread1.py
import socket
import sys
def main():
soc = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
host = "127.0.0.1"
port = 8000
try:
soc.connect((host, port))
except:
print("Connection Error")
sys.exit()
print("Please enter 'quit' to exit")
message = input(" -> ")
while message != 'quit':
soc.sendall(message.encode("utf8"))
if soc.recv(5120).decode("utf8") == "-":
pass # null operation
message = input(" -> ")
soc.send(b'--quit--')
if __name__ == "__main__":
main()Whereas the server program is,
server_thread1.py
import socket
import sys
import traceback
from threading import Thread
def main():
start_server()
def start_server():
host = "127.0.0.1"
port = 8000 # arbitrary non-privileged port
soc = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
soc.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
print("Socket created")
try:
soc.bind((host, port))
except:
print("Bind failed. Error : " + str(sys.exc_info()))
sys.exit()
soc.listen(6) # queue up to 6 requests
print("Socket now listening")
# infinite loop- do not reset for every requests
while True:
connection, address = soc.accept()
ip, port = str(address[0]), str(address[1])
print("Connected with " + ip + ":" + port)
try:
Thread(target=client_thread, args=(connection, ip, port)).start()
except:
print("Thread did not start.")
traceback.print_exc()
soc.close()
def clientThread(connection, ip, port, max_buffer_size = 5120):
is_active = True
while is_active:
client_input = receive_input(connection, max_buffer_size)
if "--QUIT--" in client_input:
print("Client is requesting to quit")
connection.close()
print("Connection " + ip + ":" + port + " closed")
is_active = False
else:
print("Processed result: {}".format(client_input))
connection.sendall("-".encode("utf8"))
def receive_input(connection, max_buffer_size):
client_input = connection.recv(max_buffer_size)
client_input_size = sys.getsizeof(client_input)
if client_input_size > max_buffer_size:
print("The input size is greater than expected {}".format(client_input_size))
decoded_input = client_input.decode("utf8").rstrip()
result = process_input(decoded_input)
return result
def process_input(input_str):
print("Processing the input received from client")
return "Hello " + str(input_str).upper()
if __name__ == "__main__":
main()On running above script, run the server_thread1.py in the terminal as,
python server_thread1.py Socket created Socket now listening
We will watch the server window and understand the flow. Now open multiple clients terminal, run client thread
python client_thread1.py Enter 'quit' to exit -> Zack ->
In another terminal, run another client program & watch server terminal window too,
python client_thread1.py Enter 'quit' to exit -> Python -> quit
Another terminal, run client thread,
python client_thread1.py Enter 'quit' to exit -> world! -> Anothny ->
And we can see our server window will display output something like,
Socket created Socket now listening Connected with 127.0.0.1:50275 Processing the input received from client Processed result: Hello ZACK Connected with 127.0.0.1:50282 Processing the input received from client Processed result: Hello PYTHON Processing the input received from client Client is requesting to quit Connection 127.0.0.1:50282 closed Connected with 127.0.0.1:50285 Processing the input received from client Processed result: Hello WORLD! Processing the input received from client Processed result: Hello ANOTHNY
So threads provide one of the most common technique to handle multiple socket connection and clients.