AsyncHelper.cs

public class AsyncHelper
{
    private volatile bool allDone = false;
    private volatile int doneCount = 0;
    private int actionsCount;
    private ICollection<Exception> exceptions = new List<Exception>();

    public bool ExecuteInParallel(params System.Action[] actions)
    {
        if (actions == null || actions.Length == 0) return false;
        
        actionsCount = actions.Length;

        foreach (var action in actions) {
            action.BeginInvoke(result => ProcessAsyncCallback(result, actionStatus), action);
        }

        while (alldone == false) {
            // do nothing or perhaps Thread.SpinWait();
        }
        // perhaps throw the exception(s) ?
        return exceptions.Count == 0;
    }

    private void ProcessAsyncCallback(IAsyncResult result, IDictionary<System.Action, bool> actionStatus)
    {
        var originatingAction = (System.Action)result.AsyncState;

        try {
            originatingAction.EndInvoke(result);
        }
        catch (Exception exception) {
            Trace.TraceError(exception.ToString());
            exceptions.Add(exception);
        }
        finally {
            if(Interlocked.Increment(ref doneCount) == actionsCount)
            {
                allDone = true;
            }
        }
    }
}