When is thread safety an issue?

Question

Thread safety is not so much important when you instance classes and use their methods to start the thread correcT?

Answer 1

If multiple threads are accessing the same object instance, then you need to add locking to ensure thread safety:

// make sure that this is defined *outside* the method
// so that all threads lock on the same instance
private readonly object _lock = new object();

...

// add a lock inside your event handler
proc.OutputDataReceived += (object sendingProcess, DataReceivedEventArgs e) =>
{
    if (e.Data != null)
    {
        lock (_lock)
           info.additional += e.Data;
    }
};

As a side note, if you are using .NET 4, you might want to check the ConcurrentQueue class. It's a thread safe implementation of a FIFO buffer, which can be useful if multiple threads need to enqueue their items simultaneously:

private ConcurrentQueue<SomeInfo> _queue = new ConcurrentQueue<SomeInfo>();

...

proc.OutputDataReceived += (object sendingProcess, DataReceivedEventArgs e) =>
{
    if (e.Data != null)
    {
        // no need to lock
        _queue.Enqueue(e.Data);
    }
};

To dequeue items in a separate thread, you would use:

SomeData data = null;
while (_queue.TryDequeue(out data))
{
    // do something with data
}