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Fun with the ThreadPool #2: Find the bug
This bug caused a production system to grind to a screeching halt, under just the right amount of load. Took a while to figure out what was happening. I created a small test that shows what the problem is.
Here is a little description:
- The timer wakes a set of services that need to process input.
- To avoid re-entrancy issues, I used synchornized methods.
- Some services does non trivial amount of work.
class Program
{
static int count = 0;
static Timer timer;
static void Main(string[] args)
{
timer = new Timer(delegate
{
int temp = Interlocked.Increment(ref count);
ThreadPool.QueueUserWorkItem(DoLengthyWork, temp);
ThreadPool.QueueUserWorkItem(ReportStatus, temp);
},null,100,100);
Console.ReadKey();
}
[MethodImpl(MethodImplOptions.Synchronized)]
public static void DoLengthyWork(object counter)
{
//do stuff that may fail on re-entry
Thread.Sleep(1500);
Console.WriteLine("Finished lengthy work: {0}", counter);
}
public static void ReportStatus(object counter)
{
Console.WriteLine("Reporting status: {0}", counter);
}
}
For fun, this takes about a minute to fail...
What is the problem, and what is causing it?
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