Question

I have an infinite loop in a separate thread operating on a List of strings. I want to be able to add strings to this list while the thread is runnning. I have a feeling the code I am writing is ‘wrong’. In the infinite loop I am iterating through each string in the list and performing operations on it, so it seems like I can’t just add a string to this list from my main thread, as I will be interfering with a variable that is concurrently being accessed by another thread. Here’s what my code looks like –

class StringTest
{
public List<string> ListOfStrings = new List<string>();
public Task MainLoopTask;
bool IsRunning = false;

public void AddToList(string myString)
{
    ListOfStrings.Add(myString); // Adding a string to the list

    if (!IsRunning)
    {
        IsRunning = true;
        MainLoopTask = Task.Factory.StartNew(MainLoop);
    }
}

public void MainLoop()
{
    while (true)
    {
        foreach(string s in ListOfStrings) // Operating on the list in a separate thread
        {
            ...
            ...
            ...
        }
}

}

Is this bad code or is it ok? If it’s is bad, what can I do to fix it?

Answer 1

That is not safe, and will eventually fail spectacularly in production.

Instead, you should use a thread-safe collection; probably a concurrent queue.