How to receive from two UDP clients concurrently using multi-threaded UDP server in python? - udp

Question

I am trying to implement UDP concurrent server (multi-threaded) which can accept new client and communicate with old client simultaneously. I have a main python program (called server) which creates a thread for every new accepted client and then loops back and wait for request from new client. The created thread deals with the respective client regarding upload, download and other tasks. The problem arises when two socket.recvfrom(1024) functions are called simultaneously, one in the main thread (where new clients are being accepted) and the other in the previously created thread where a function tries to receives data from the corresponding client. So, an UPD packet sent from a client, ends up in unexpected location as the function socket.recvfrom(1024) are running concurrently in two threads.
In my case, when a client which is already connected, tries to send data to the server for a function, the data which is supposed to be received by the corresponding thread of the server, is being received by the main program (main thread) which is supposed to receive new client request. So, the client get stuck there.
My code for the main program (main thread) and the function (which runs as a separate thread) is given below:
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.bind((UDP_IP, PORT))
def ClientHandler(addr):
while True:
str = "Select an option from below:\n 1. Upload\n 2. Download"
sock.sendto(str.encode(), addr)
data, addr = sock.recvfrom(1024) #receiver 2 running in parallel thread
if(data.decode()=="Upload" or data.decode()=="upload"):
ReceiveFile() #receive a file from the client
elif(data.decode()=="Download" or data.decode()=="download"):
SendFile() #send a file to the client
while True:
print("\nListening...\n")
data, addr = sock.recvfrom(1024) #receiver 1 running in main thread
if(data.decode()=="Hello"): #Using the Hello keyword to detect new client
print("Connected to a New Client " + str(addr))
t1=threading.Thread(target=ClientHandler, args=(addr,))
t1.start()