CODEWITHSUNDEEP
c#multithreading
wow
wow

Reputation: 3899

NullReferenceException on ConcurrentBag.Add with threads

I was originally using a List for this but I changed to a ConcurrentBag after seeing that Lists where not "thread-safe".

The following is my code so far. When it runs, it will not add to the ConcurrentBag, I get a NullReferenceException - "Object reference not set to an instance of an object." and I am not sure what the problem is as I do not have much experience with threads.

static ConcurrentBag<String> urls;

// ...

static void buildThreads()
{
    for (int i = 0; i < threads; i++)
    {
        Thread thread = new Thread(buildTokens);
        thread.Start();
    }
}

static void buildTokens()
{
    while (true)
    {
        if (numSockets < tokens)
        {
            getUrl();

            numSockets++;
            Console.WriteLine(numSockets + "/" + tokens);
        }
    }
}

static void getUrl()
{
    urls.Add("test");
}

I would appreciate any help. Thanks.

Upvotes: 0

Views: 810

Answers (3)

Sudhakar Tillapudi
Sudhakar Tillapudi

Reputation: 26209

Problem : Your ConcurrentBag variable urls is null as you have not initialised it properly.

Solution: You need to initialise your ConcurrentBag variable urls properly using new keyword.

Replace This:

static ConcurrentBag<String> urls;

With This:

static ConcurrentBag<String> urls = new ConcurrentBag<String>();

Upvotes: 1

juanvilla
juanvilla

Reputation: 196

You have to "new" your concurrent bag (create an instance):

static ConcurrentBag<String> urls = new ConcurrentBag<String>()

If you are using Visual Studio to build and debug your code you should be able to place a break point on the line where you add to the bag and notice the value of the variable is "null"

Upvotes: 2

Yair Nevet
Yair Nevet

Reputation: 13003

Perform this instantiating before accessing this object, it's contains a null reference right now:

static ConcurrentBag<string> urls = new ConcurrentBag<string>();

Upvotes: 2

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