recv 命令在线程和服务器崩溃时无法正常工作

Question

I set up a TCP server with the Python socket library that multiple devices can be connected to. Since I use threading here, I regularly accept new incoming connections and try to recruit messages in the list. My question is that usually recv threading gets stuck somewhere. Sometimes the server, which is running smoothly, sometimes hangs on the first day. Showing Incoming Connections but not receiving messages. c in clients, so when I print each threaded connection before get in recv command

Now on <socket.socket fd=8, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=0, laddr=('172.31.15.96', 9680), raddr=('24.133.144.150', 56446)>
Now on <socket.socket fd=8, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=0, laddr=('172.31.15.96', 9680), raddr=('24.133.144.150', 56446)>
Now on <socket.socket fd=8, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=0, laddr=('172.31.15.96', 9680), raddr=('24.133.144.150', 56446)>
Now on <socket.socket fd=8, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=0, laddr=('172.31.15.96', 9680), raddr=('24.133.144.150', 56446)>
Now on <socket.socket fd=8, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=0, laddr=('172.31.15.96', 9680), raddr=('24.133.144.150', 56446)>
Now on <socket.socket fd=8, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=0, laddr=('172.31.15.96', 9680), raddr=('24.133.144.150', 56446)>
Now on <socket.socket fd=8, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=0, laddr=('172.31.15.96', 9680), raddr=('24.133.144.150', 56446)>
Now on <socket.socket fd=9, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=0, laddr=('172.31.15.96', 9680), raddr=('24.133.144.150', 56456)>

In the loop, it continued to show the same port (probably more than thousand times) until it sent a new message from the phone. I am showing the problematic part because the code I wrote is about 500 lines after recv.

import socket
import threading

host = '172.31.15.96'
port = 9680   

try:
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    print("socket created")
    s.bind((host, port))
    print("socket connected {} port".format(port))
    s.listen(250)
    print("socket listening")
    db.logHere.insert_one({"socket log": {"socket created and port opened": port, "Time": time()}})

except socket.error as msg:
    print("Error:", msg)
    db.logHere.insert_one(
        {"Socket Log": {"Error happened": msg, "Time": time()}})

clients = [] # this is list for connected client

def accept():
    while True:
        global clients
        client, addr = s.accept()
        print('Connection from:', addr)
        db.logHere.insert_one({"Connection Log": {"Connection ip from": str(addr[0])+":"+str(addr[1]), "Connection time": time()}, "Time": time()})
        clients.append(client)

def new_message():
    while True:
        for c in clients:
            print("Now on", c) # I just try to use this print if new message thread work or stopped
            try:
                message = c.recv(2048)
                if message:
                    #there is my split or sendall commands. I put if messages inside try advice from : Marquis of Lorne*
            except socket.error as err:
                print("socket error", err)
                c.close()

threading.Thread(target=accept).start()
threading.Thread(target=new_message).start()

What should I do in order to solve this problem and to be able to operate properly with every incoming connection, that is, to maintain a healthy server? I think my main problem is i cannot delete disconnected client frim that clients list. try except is not enough for that. How can i understand one of client disconnected?

**I apologize for my incomplete and incorrect language usage. My native language is not English.

Answer 1

Here is a minimal fix to your code using select to only read on client sockets having available data and removing closed sockets from the list:

...
def new_message():
    while True:
        # don't try to wait on a empty list...
        if len(clients) == 0:
            sleep(5)
        else:
            ready, _, _ = select.select(clients, [], [])
            # only loop on sockets having available data to read
            for c in ready:
                print("Now on", c) # I just try to use this print if new message thread work or stopped
                try:
                    message = c.recv(2048)
                    if message:
                        #there is my split or sendall commands. I put if messages inside try advice from : Marquis of Lorne*
                        print(message.decode())
                    else:
                        clients.remove(c)
                except socket.error as err:
                    ...

But in fact, you could include the listening socket on the select list, and fully discard one thread:

...
clients = [s] # this is list for connected client AND the listening socket

##def accept():
##    while True:
##        global clients
##        client, addr = s.accept()
##        print('Connection from:', addr)
##        db.logHere.insert_one({"Connection Log": {"Connection ip from": str(addr[0])+":"+str(addr[1]), "Connection time": time()}, "Time": time()})
##        clients.append(client)

def new_message():
    while True:
        ready, _, _ = select.select(clients, [], [])
        for c in ready:                    # loop over ready sockets
            if c == s:                     # special processing for listening one
                try:
                    client, addr = s.accept()
                except socket.error:       # exit if the listening socket is closed
                    for x in clients:
                        x.close()
                    return 
                print('Connection from:', addr)
                db.logHere.insert_one({"Connection Log": {"Connection ip from": str(addr[0])+":"+str(addr[1]), "Connection time": time()}, "Time": time()})
                clients.append(client)
            else:
                print("Now on", c) # I just try to use this print if new message thread work or stopped
                try:
                    message = c.recv(2048)
                    if message:
                        #there is my split or sendall commands. I put if messages inside try advice from : Marquis of Lorne*
                        print(message.decode())
                    else:
                        clients.remove(c)
                except socket.error as err:
                    print("socket error", err)
                    c.close()

##threading.Thread(target=accept).start()
threading.Thread(target=new_message).start()