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Tolerim
25 days ago

Can a JavaScript request in Server Side (Flask - Python) be handled and maintained with a solution?

As a senior JavaScript developer, my objective is to use JavaScript to periodically request the Flask server, maintaining synchronization between users within the same instance of a game. The server returns the last command executed by any player before. If the result of the request is different from the previous results, then an action has been made by a player. The issue is that sometimes when the request has been sent as a command is being executed, the server responds as if no commands were executed, thereby returning no change of the last command executed. To resolve this issue, I tried to modify the code by not making JavaScript request every second but to request once and wait for server response. However, I am unable to make the server wait for a command without interrupting Flask execution. I attempted using async functions, but my expertise is limited. I appreciate any help in advance, and please pardon my English!
Answers(2)
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Vogi
24 days ago
Verified Answer
It's great that you are working on a project. I understand that you want to make the server wait for a command without interrupting Flask execution. One way to do this is by using the queue module in Python. You can create a queue object and use it to store the commands that are being executed. Then you can use a separate thread to process the commands in the queue while Flask continues to run. Here is an example code snippet that demonstrates how you can use the queue module: 
from queue import Queue
import threading

app = Flask(__name__)
q = Queue()

@app.route('/command')
def command():
    cmd = request.args.get('cmd')
    q.put(cmd)
    return 'Command received'

def process_commands():
    while True:
        cmd = q.get()
        # Process the command here
        q.task_done()

t = threading.Thread(target=process_commands)
t.daemon = True
t.start()

if __name__ == '__main__':
    app.run()
In this example, we create a Flask app and a queue object. We then define an endpoint /command that accepts a command as a query parameter and adds it to the queue. We also define a function process_commands that runs in a separate thread and processes the commands in the queue. Finally, we start the Flask app and the thread. I hope this helps! Let me know if you have any further questions.

Sources

Flask API — How to return response but continue executionpython - How to run Flask app by flask run or custom command without ...Command Line Interface — Flask Documentation (2.0.x)python - How can I make Flask wait? - Stack Overflowpython - Slow Requests on Local Flask Server - Stack Overflow
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Tolerim
25 days ago
It sounds like you're encountering a race condition when executing commands and sending requests at the same time. One way to potentially solve this is by implementing a more robust synchronization protocol between the client and server using WebSockets. WebSockets allow for real-time, bidirectional communication between the client and server, which can help solve the race condition issue you're facing. With WebSockets, the client and server can send messages to each other whenever a command is executed or a state change occurs, rather than relying on a periodic polling mechanism. To implement WebSockets in Javascript, you can use the native WebSocket API or a third-party library like socket.io. On the server-side, you can use a WebSocket server library like ws. Here's an example of how you can use socket.io to implement WebSockets in your code: First, install socket.io using npm:
On the client-side (JavaScript), create a WebSocket connection and listen for incoming messages: 
const socket = io('http://localhost:3000');

socket.on('updateState', (lastCommand) => {
    if (lastCommand != document.getElementById('lastCommand').textContent) {
        document.getElementById('lastCommand').textContent = lastCommand;
        eval(lastCommand);
    }
});
On the server-side (Python), emit a message whenever a command is executed: 
from flask_socketio import SocketIO

socketio = SocketIO(app)

@app.route('/executeCommand', methods=['POST'])
def executeCommand():
    # Execute command code here

    # Emit updateState message to all connected clients
    socketio.emit('updateState', lastCommand)
In this example, the client-side code listens for an updateState message emitted by the server-side socketio.emit() method. Whenever a new message is received, the client updates the lastCommand element and executes the command if the response is different from the previous response. On the server-side, the socketio.emit() method is called whenever a command is executed, sending an updateState message to all connected clients. By implementing WebSockets, you can eliminate the need for periodic polling and potential race conditions caused by simultaneous requests and command executions.
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