Need

Prevention of race conditions in the system

Context

Description

import 'dart:async';
import 'package:shelf/shelf.dart' as shelf;
import 'package:shelf/shelf_io.dart' as io;

shelf.Response handleRequest(shelf.Request request) {
  var path = request.url.path;
  if (path == 'start') {
  } else if (path == 'end') {...

In the above code snippet, we have a server application that uses the Shelf framework. This application has two endpoints: `/start` and `/end`. When a request is received at the `/start` endpoint, it initiates a process (simulated by a delay of 2 seconds), and when a request is received at the `/end` endpoint, it ends the process (also simulated by a delay of 2 seconds). The vulnerability lies in the fact that these two processes are independent and don't check the state of each other. This leads to a race condition where if the `/end` request arrives before the `/start` request has completed, the system will try to end a process that hasn't started yet, leading to unexpected behavior. For example, if two requests are made almost simultaneously, one to `/start` and one to `/end`, there's no guarantee that the start process will complete before the end process begins. If the end process tries to end a process that hasn't started, it could lead to errors or unexpected behavior. This is a classic example of a race condition, where the order and timing of events can affect the system's behavior. In this case, the system assumes that the `/start` request will always complete before the `/end` request is received, which may not always be the case.

import 'dart:async';
import 'package:shelf/shelf.dart' as shelf;
import 'package:shelf/shelf_io.dart' as io;

bool isProcessRunning = false;

shelf.Response handleRequest(shelf.Request request) {
  if (path == 'start') {...

The code above introduces a locking mechanism to prevent race conditions. A boolean flag `isProcessRunning` is used to track whether a process is currently running. In the `handleRequest` function, before starting a process with `startProcess`, it checks if a process is already running by checking the `isProcessRunning` flag. If a process is running, it will not start another one, preventing multiple processes from running concurrently. Similarly, before ending a process with `endProcess`, it checks if a process is currently running. If no process is running, it will not attempt to end a process, ensuring that the `endProcess` function can only be called after the `startProcess` function has completed. In the `startProcess` function, the `isProcessRunning` flag is set to true at the beginning, indicating that a process is running. In the `endProcess` function, the `isProcessRunning` flag is set to false at the end, indicating that no process is running. This solution ensures that the `startProcess` and `endProcess` functions are not executed concurrently, preventing race conditions. If the order of requests is important, consider using a queue to manage the order of function calls.

References