Provides a base class for NCron jobs which are not allowed to be executed in parallel.

SynchronizedCronJob.cs

namespace NCron
{
    public abstract class SynchronizedCronJob<TJob> : CronJob where TJob : SynchronizedCronJob<TJob>
    {
        private static readonly object SyncRoot = new object();
        private static bool IsRunning = false;

        public override void Execute()
        {
            var runNow = false;

            lock (SyncRoot)
            {
                if (!IsRunning)
                {
                    IsRunning = true;
                    runNow = true;
                }
            }

            if (runNow)
            {
                try
                {
                    ExecuteSynchronized();
                }
                finally
                {
                    IsRunning = false;
                }
            }
            else
            {
                Log.Warn(() => string.Format("Job of type {0} is already running.", typeof(TJob).Name));
            }
        }

        /// <summary>
        /// This method is invoked whenever the job is due for execution, after job initialization.
        /// </summary>
        public abstract void ExecuteSynchronized();
    }
}

Shouldn't line 14 be if(!IsRunning)?